Fixed Network PlanningIn GSM Networks
V-1.1
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Course InformationCourse Information
n Course Title – Fixed Network Planning (GSM Version)
n Duration – 5 Days
n Target Audience– GSM Network Engineers
n Pre-requisite– Familiarity with
– Basic Math and Probability, – Basic GSM Parameters and – RF Network Planning
n Instructor: Dr. Kamran Etemad
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Introduction & Background CheckIntroduction & Background CheckIntroduction & Background Check
n Introductionn Backgroundsn Concerns& Interests
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Scope of the CourseScope of the CourseScope of the Course
Call Flows and Signaling Protocols
GSM ProtocolChannelization,Network Elements
(Review)
Configuration & Planing
Network DimensioningTraffic Theory
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OutlineOutlineOutline
n Chapter 1:– Introduction, GSM Protocol, Network Elements and
RF Planning
n Chapter 2:– Call Flows and Signaling Network and Protocols
n Chapter 3:– Fundamentals of Traffic Models and Erlang
Calculations
n Chapter 4: – Network Dimensioning
n Chapter 5: – Network Configuration & System Expansion
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Chapter 1.Chapter 1.Chapter 1.
n Introduction, Course Overview and Objectivesn Review of GSM Protocol
– Spectrum and Physical Channels– Frame and Time Slot Structure– Logical Channels– GSM Coding and Modulations
n Network Elements and Architecture– BSS– NSS– OAM
n Fixed Network Connectionsn Overview of RF network Planningn Section Summary and Discussions
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Introduction: GSM HistoryIntroduction: GSM HistoryIntroduction: GSM History
n Global System for Mobile (GSM) is a second generation cellular system standard that was developed to solve the fragmentation problems of the first cellular systems in Europe.
n GSM is the world's first cellular system to specify digital modulation and network level architectures and services. Before GSM, European countries used different cellular standards throughout the continent, and it was not possible for a customer to use a single subscriber unit throughout Europe.
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GSM in the WorldGSM in the WorldGSM in the World
n GSM was originally developed to serve as the pan-European cellular service and promised a wide range of network services through the use of ISDN.
n GSM's success has exceeded the expectations of virtually everyone, and it is now the world's most popular standard for new cellular radio and personal communications equipment throughout the world.
n It is predicted that by the year 2000, there will be between 20 and 150 million GSM subscribers worldwide.
n Recently, GSM has changed its name to the Global System for Mobile Communications for marketing reasons. The setting of standards for GSM is currently under the aegis of the European Technical Standards Institute (ETSI).
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Some of GSM System FeaturesSome of GSM System FeaturesSome of GSM System Features
n Some of the important features of GSM:– Good subjective speech quality– Message Security – Maximum flexibility to provide services that are
compatible with ISDN.– High data rate transfer, short bursts, slow frequency
hopping, – Open-network architecture.– Use of the SIM (Subscriber Identity module)– Support international roaming.– Low terminal and Service Costs.
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GSM ServicesGSM ServicesGSM Services
n Services are defined as anything the end user explicitly sees as worth paying for.
n Services are classified into three groups: – Tele-services, – Bearer Services– Supplementary Services.
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Tele-ServicesTeleTele--ServicesServices
n Speech Services– Telephony (+Voice Mail)– Emergency Calls
n Data Services– FAX group 3, alternate speech then fax– FAX group 3 automatic
n Short Message Service (SMS)– SMS is similar to the paging service, but much more
comprehensive, allowing bi-directional messages, store-and-forward delivery, and acknowledgment of a successful delivery.
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Additional Data ServicesAdditional Data ServicesAdditional Data Services
n 14.4 Circuit Switched– requires new channel coding– standardization– New Abis data framing
n High Speed Circuit Switched Data (HSCSD)n General Packet Radio Service (GPRS)
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SMSSMSSMS
n Part of Tele-services described by GSM provides a mean for the Mobile Subscriber to send and receive short messages (<160 characters) via the Mobile unit.
n These services are– SMS point to point services
» SMS Mobile Originating SMS-MO/PP» SMS Mobile Terminating SMS-MT/PP
– SMS Cell Broadcast SMS-CB
n These services are provided by the Short Message Service Center (SM-SC).
888888888888
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Supplementary servicesSupplementary servicesSupplementary services
n These services are provided by the MSC/VLR but managed by the HLR – Call Forwarding Unconditional (CFU)– Call Forwarding Busy (CFB)– Barring of Outgoing call – Barring of incoming call– Call Waiting– Conference call– Call Transfer
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Bearer ServicesBearer ServicesBearer Services
n PAD , Asynchronous access to PAD– 300 bps
n Packet Data, Synchronous access to PSPDN– 2.4,4.8 9.6 bps
n Alternate Speech/Datan Unrestricted Digital Information (UDI)n Asynchronous 300,1.2,2.4,4.8,9.6 bpsn Synchronous 1.2,2.4,4.8,9.6 bps
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GSM Spectrum AllocationGSM Spectrum AllocationGSM Spectrum Allocation
890MHz
915MHz
124 frequencies
935MHz
960MHz
124 frequencies
50 frequencies
50 frequencies
880MHz
925MHz
Forward Link Spectrum
Reverse Link Spectrum
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Absolute Radio Frequency Channel Absolute Radio Frequency Channel Absolute Radio Frequency Channel
(890+n x 0.2)MHz (935+n x 0.2) MHz
MS TX BTS TX
200 kHz 200 kHz
45 MHz
MS Transmit Frequency (MHz) = 890.0 + [(ARFCN)x(.2)]
BTS Transmit Frequency (MHz) = 935.0 + [(ARFCN)x(.2)]
ARFCN = Absolute Radio Frequency Channel Number
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Physical vs. Logical ChannelsPhysical vs. Logical ChannelsPhysical vs. Logical Channels
T0 T1 T2 T3 T4 T5 T6 T7
F1F2
F3F4
F5RF Channels
Time Slots
n The combination of a TS number and an ARFCN constitutes a physical channel for both the forward and reverse link.
n Channelization is accomplished by the notion of virtual circuits or logical Channels.
n Each physical channel in a GSM system can be mapped into different logical channels at different times.
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FDMA-TDMAFDMAFDMA--TDMATDMA
T0 T1 T3T2 T4 T5 T6 T7
200KHz
T0 T1 T3T2 T4 T5 T6 T7
Frequency
Time4.615msec Frame
Time Slot:156.25bits576.92µµs
RF Channels
n The frame duration is 4.645 ms divided among eight time slots. n Each of these timeslots is a physical channel occupied by an
individual user. Each timeslot, or physical channel, carries control and traffic data in a burst form.
n The time duration of an individual channel is 3/5200 sec(=0.577 ms).
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Staggering TDMA FramesStaggering TDMA FramesStaggering TDMA Frames
n At the BTS, TDMA frames on all radio frequency channels, in the downlink as well as on the uplink, are aligned.
n However, the start of an uplink TDMA frame is delayed with respect to downlink by a fixed period of three timeslots.
n Staggering TDMA frames allows the same time slot number (TN) to he used in both the down and uplinks while avoiding the requirement for mobile to transmit and receive simultaneously.
n The TN within a frame is numbered from 0 to 7, and each TN can he referenced by a unique TN.
T0 T1 T3T2 T4 T5 T6 T7
T0 T1 T3T2 T4 T5 T6 T7
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GSM Burst TypesGSM Burst TypesGSM Burst Types
10 2 3 4 5 6 7
1 TDMA frame =8 time slots (4.615 msec)
Each TDMA time slot may carry one of five possible bursts. – Normal Burst– Frequency Correction Burst– Synchronization Burst– Random Access Burst– Dummy Burst
n Each user transmits a burst of data during the time slot assigned to it.
n These data bursts may have one of five specific formats used for various control and traffic bursts.
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Chapter 1.Chapter 1.Chapter 1.
n Introduction, Course Overview and Objectivesn Review of GSM Protocol
– Spectrum and Physical Channels– Frame and Time Slot Structure– Logical Channels– GSM Coding and Modulations
n Network Elements and Architecture– BSS– NSS– OAM
n Fixed Network Connectionsn Overview of RF network Planningn Section Summary and Discussions
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Logical ChannelsLogical ChannelsLogical Channels
n In a GSM system no RF carrier and no slot is dedicated a priori to an exclusive logical use.
n Channelization is accomplished by the data communications notion of virtual circuits or logical channels.
n According to the functions performed the channels are divided into two Logical Channels.– Traffic Channels (TCH) – Control Channels (CCH)
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GSM Traffic ChannelsGSM Traffic ChannelsGSM Traffic Channels
n There are two types of TCHs that are differentiated by their traffic rates and are defined as follows.
n Full Rate– Full-Rate Speech Channel(TCH/FS)– Full-Rate Data Channel
» 9.6kbps (TCH/F9.6)» 4.8kbps (TCH/F4.8)» 2.4kbps (TCH/F2.4)
n Half Rate – Half-Rate Speech Channel(TCH/HS)– Half-Rate Data Channel
» 4.8kbps (TCH/H4.8)» 2.4kbps (TCH/H2.4)
Traffic Channels
2 half-rate channel users would share the same time slot, but would alternately transmit during every other frame.
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GSM Control ChannelsGSM Control ChannelsGSM Control Channels
n Broadcast CHannel (BCH)» Broadcast Control CHannel (BCCH)» Frequency Correction CHannel(FCCH)» Synchronization CHannel(SCH)
n Common Control CHannel (CCCH)» Paging CHannel(PCH)» Random Access CHannel(RACH)» Access Grant CHannel(AGCH)
n Dedicated Control CHannel (DCCH)» Stand-alone Dedicated Control Channel(SDCCH)» Slow Associated Control CHannel(SACCH)» Fast Associated Control CHannel(FACCH)
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Broadcast Control CHannelBroadcast ControlBroadcast Control CHannelCHannel
n The BCCH carrier broadcasts continuously for the MS to measure and average the signal strengths from a site, to identify the BTS with the best serving potential.
n At any base station, only one RF channel or carrier transmits the BCCH data: this RF channel is called the BCH carrier.
n The BTS will never reduce the power transmitting the BCH carrier because the MS’s need to measure the signal strengths from this frequency broadcasting at its maximum power or highest potential.
n The BTS must fill every timeslot on the BCCH carrier with a burst and if it has no “real” data to send to the MSs, the BTS will send a
dummy burst.
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FCCH and SCHFCCH and SCHFCCH and SCH
n Frequency Correction Channel: – This logical channel is used for initial carrier
acquisition or synchronization of the base station for the mobile unit
n Synchronization Channel: – The Frequency correction channel helps the mobile
unit to get an estimate of the carrier frequency. For further tuning, and proper frame synchronization, the SCH is used.
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Common Control CHannelCommon ControlCommon Control CHannelCHannel
n CCCHs are the most commonly used control channels and are used to page specific subscribers, assign signaling channels to specific users, and receive mobile requests for service.
n Common Control Channel: The CCCH logical channel consists of:– Random Access Channel (RACH) in the Reverse direction.
» The RACH is a reverse link channel used by MS to acknowledge a page from the PCH, and is also used by mobiles to originate a call.
– Paging Channel (PCH) or the Access Grant Channel (ACGH) in the Forward direction.
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Dedicated Control CHannelsDedicated ControlDedicated Control CHannelsCHannels
n Dedicated Control CHannel (DCCH)– Stand-alone Dedicated Control Channel(SDCCH)– Slow Associated Control CHannel(SACCH)– Fast Associated Control CHannel(FACCH)
n Like traffic channels – they are bi-directional and – have the same format and function on both the
forward and reverse links. – may exist in any time slot and on any ARFCN
except TS0 of the BCH ARFCN.
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Stand Alone Dedicated CCHStand Alone Dedicated CCHStand Alone Dedicated CCH
n SDCCH carries signaling data following the connection of the mobile with the base station, and just before a TCH assignment is issued by the base station.
n The SDCCH ensures that the mobile station and the base station remain connected while the base station and MSC verify the subscriber unit and allocate resources for the mobile.
n SDCCHs may be assigned their own physical channel or may occupy TS0 of the BCH if there is low demand for BCH or CCCH traffic.
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Slow Associated CCHSlow Associated CCHSlow Associated CCH
n SACCH is always associated with a traffic channel or a SDCCH and maps onto the same physical channel.
n On the forward link, the SACCH is used to send slow but regularly changing control information to each mobile on that ARFCN, such as – power control instructions – specific timing advance instructions
n The reverse SACCH carries information about the received signal strength and quality of the TCH, as well as BCH measurement results from neighboring cells.
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Fast Associated CCHFast Associated CCHFast Associated CCH
n FACCH carries urgent messages, and contains essentially the same type of information as the SDCCH.
n A FACCH is assigned whenever a SDCCH has not been dedicated for a particular user and there is an urgent message (such as a handoff request).
n The FACCH gains access to a time slot by stealing frames from the traffic channel to which it is assigned.
n This is done by setting two special bits, called stealing bits, in a TCH forward channel burst. If the stealing bits are set, the time slot is known to contain FACCH data, not a TCH, for that frame.
Speech Frames Speech FramesFACCH Frames
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Signaling Outside a Call (TCH/8)Signaling Outside a Call (TCH/8)Signaling Outside a Call (TCH/8)
n In order to increase system efficiency when it comes to signaling transactions, an additional type of channel has been introduced. Its rate is very low and only has specified usage for signaling and short message transmission.
n This channel is referred as TCH/8. If a TCH/H is considered as half a TCH/F, then this is one-eighth of a TCH/F.
n A TCH/8 message is sent over one time slot for every other 8 frames.
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Cell Broadcast ChannelCell Broadcast ChannelCell Broadcast Channel
n Cell Broadcast Short message requires the means to transmit around one 80 octet message every two seconds from the network toward the mobile stations in idle mode.
n This corresponds to half the capacity of a downlink TCH/8. In each cell where this service is supported. a special channel a CBCH (Cell Broadcast Channel ) is used (or broadcasting messages.
n A CBCH is derived from a TCH/8. Some special constraints exist for the design of this channel. because of the requirement that it can be listened to in parallel with the BCCH information and the paging messages
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Higher Order FrameHigher Order FrameHigher Order Frame
n Higher order frames called multiframe, consist of 26 frames and have a duration of 120 ms (26 x 4.615 ms).
n This multiframe consists (of 26 TDMA) frames and carries a traffic channel TCH SACCH and FACCH. Similarly, a 51 -frame multi frame has a duration of 235.363 ms (51 x 4.615 ms).
n One superframe consists of 51 traffic multiframes or 26 controlmultiframes and consists of 51 x 26 TDMA frames with a total duration of 6.12 sec (51 x 120 ms).
n A 26 TDMA frame multiframe supports traffic and associated control channels, and a 51 TDMA frame multiframe supports Broadcast Control (BCC) and Stand Alone Dedicated Control Channels.
n The highest order frame is called a hyperframe and consists of
2,048 superframes, or 2,715,648 frames (2048 x 51 x 26).
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Frame Structure HierarchyFrame Structure HierarchyFrame Structure Hierarchy
1 superframe = 51 multiframes (6.12 sec)
0 1 2 50 0 1 2 25
1 hyperframe = 2048 superframe = 2,715,648 frames (3hr, 28 min, 53 sec, 760 msec)
OR
1 superframe = 26 multiframes (6.12 sec)
0 1 2 500 1 2 25
1 51-frame multiframes (235.4 msec)1 26-frame multiframes (120 msec)
10 2 3 4 5 6 7
1 TDMA frame = 8 time slots (4.615 msec)
10 2 2047. . . . . . . . .
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Structure of Control MultiframesStructure of ControlStructure of Control MultiframesMultiframes
0 1 2 3 4 5 6 7 8 9 ................................................................ 50
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... R
235 ms = 51 FRAMES
Uplink Direction --- All Frames/Slots Belong to the Rach
F S B B B B C C C C F S C C C C C C C C F S C ... ... ..I
235 ms = 51 FRAMES
Down Link Direction Frame/Slot Usage Is As Shown
R R R R R R R R
0 1 2 3 4 5 6 7 8 9 ................................................................ 50
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Inter-BTS SynchronizationInterInter--BTS SynchronizationBTS Synchronization
n Intercell-Synchronization impacts the quality of service in the area of handover performances.
n This notion of Synchronization includes also the de-synchronization of the cells as we will see that full synchronization can be very detrimental to some aspects of system performance.
n Best performance is obtained when time bases in neighbor cells are synchronized so that burst emissions are synchronous, but de-synchronized so that in particular multiframes are not synchronous.
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Inter-BTS SynchronizationInterInter--BTS SynchronizationBTS Synchronization
n Synchronization between cells, if limited to bursts. can also be useful for pre-synchronization. It improves the search time for neighbor cells, though not in an obvious way.
n In fact all-clock phasing is the worst possible case for pre-synchronization performance.
n The best scheme for pre-synchronization is when cell clocks are organized to minimize the probability of simultaneity between FCCH. SCH or BCCH bursts in two adjacent cells.. This kind of "offset" synchronization is of course more complex to implement than an all-clock phasing synchronization.
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GSM Physical ChannelsGSM Physical ChannelsGSM Physical Channels
GSM DCS-1800 PCS-1900Mobile Frequency (MHz) Rx: 935-960
Tx: 890-915Rx: 1805-1880Tx: 1710-1785
Rx: 1930-1990Tx: 1850-1910
Total Spectrum (MHz) 2 x 25 2 x 75 2 x 60Number of Carriers 124
8 ch./carrier372
8 ch./carrier300
8 ch./carrierPeak Power (mobile) .8-20 W .25-1 W .25-1 WMean Power (mobile) .1-2.5 W .03-0.25 W .03-0.25 W
n The most important difference between the DCS and GSM system is the frequency of operation and number of voice channels.
n DCS is restricted and optimized to two hand portable mobile power classes of the 1 Watt and .25 Watt peak power where as GSM mobile power is much higher..
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GSM Physical Layer ParametersGSM Physical Layer ParametersGSM Physical Layer Parameters
GSM/DCSMultiple Access Method TDMA/FDMDuplex Method FDDCarrier Spacing 200 khzModulation GMSKModulation Rate 271 kbpsSpeech Codec RPE-LTPData Rateafter Channel Coding
22.8 kbps
Data Rateafter Speech Coding
13 kps
Total Channel Bit Rate 270.833kbs
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Review of FunctionalitiesReview of Functionalities
Insecure, Unreliable DigitalFading Channel
Insecure, Unreliable DigitalMemoryless Channel
Information Destination
Source Decoder
Source Decoder
Channel DecoderChannel Decoder
DemodulatorDemodulator
Insecure Analog Fading Channel
DeinterleaverDeinterleaver
Secure, Reliable, DigitalMemoryless Channel
DecryptionDecryption
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GSM Speech Coding GSM Speech Coding GSM Speech Coding
n The GSM speech coder is based on the Residually Excited Linear Predictive Coder (RELP)
n The coder provides 260 bits for each 20 ms blocks of speech, which yields a bit rate of 13 kbps.
n GSM voice coder uses– Voice Activity Detector (VAD)– Discontinuous Transmission (DTX)– Comforting Noise Subsystem (CNS)
n Provisions for incorporating half-rate coders are included in the specifications.
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CELP based VocodersCELP basedCELP based VocodersVocoders
LPC filter Coef.
Pitch Parameters (Gain and Lag)
Excitation Parameters (Index and Gain)
Speech Synthesis Vocal Tract
Filter
Excitation
Pitch
Try to imitate Vocal Cords
Tries to imitate Vocal Tract
SynthesizedSpeech
MUX
Speech Analysis
ChannelCoder
Code Excited Linear Predictive (CELP) Coder
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Channel CodingChannel CodingChannel Coding
Speech Coder
CRC
ConvolutionalEncoder++Traffic
Blocks
Channel Encoder
Interleaver
Traffic Frames
Tail Bits
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Selective Channel CodingSelective Channel CodingSelective Channel Coding
n Not all 260 bits at the output of speech coder have the same importance as far as voice quality is concerned, In the order of their significance:
n Class 1a: 50 bits – protected with 3 CRC bits– If in error, entire block is ignored and interpolation is used
n Class 1b: 132 bits– (Class 1a+ CRC) + Class 1b + 4 tail bits are encoded,– using a convolutional encoder of rate 1/2 & constraint length 5– The result is 378 bit
n Class 2: Remaining: 78 bits– are transmitted with no protection
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Summary of Channel CodingSummary of Channel CodingSummary of Channel Coding
Class 1a50 bits
Class 1b 132 bits
Class 2 78 bits
Class 1a50 bits
CRC3 bits
Class 1b 132 bits
Class 2 78 bits
4Tail bits
378 Channel Encoded Bits
1/2 Rate Convolutional Encoder
NoCoding
260 Voice bits/20msec
456bits
456=57*8 Channel bits/20msec=28.8kbps
Interleaving with degree 8
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Diagonal Block InterleavingDiagonal Block InterleavingDiagonal Block Interleaving
n Interleaving is used to randomize bursty errors due to fading effects.
n If a burst is lost due to interference or fading, channel coding ensures that enough bits will still be received correctly to allow the error correction to work.
A1 B3 A2 B4 A3 B5 A4 B6 A5 B7 A6 B8 A7 B1 A8
i i+1 i+2 i+3 i+4 i+5 i+6 i+7
Frame Number
A1 A2 A3 A4 A5 A6 A7 A8
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CipheringCipheringCiphering
n Ciphering modifies the contents of the eight interleaved blocks through the use of encryption techniques known only to the particular mobile station and base station.
n Security is further enhanced by the fact that the encryption algorithm is changed from call to call.
n Two types of ciphering algorithms, called A3 and A5, are used in GSM to prevent unauthorized network access and privacy for the radio transmission respectively.
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Coding for Control ChannelsCoding for Control ChannelsCoding for Control Channels
n GSM control channel messages are defined to be 184 bits long.
n These bits are encoded using a shortened binary cyclic fire code, followed by a half-rateconvolutional coder.
n The resulting 456 encoded bits are interleaved onto eight consecutive frames in the same manner as TCH speech data.
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ModulationModulationModulation
n The modulation scheme used by GSM is 0.3 GMSK n GMSK is a special type of digital FM modulation. n The channel data rate of GSM is , 270.833 kbps, n The MSK modulated signal is passed through a
Gaussian filter to smooth the rapid frequency transitions which would otherwise spread energy into adjacent channels.
0100 1101.....
Mapping bit streams to waveforms
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Slow Frequency HoppingSlow Frequency HoppingSlow Frequency Hopping
n Under normal conditions, each data burst is sent over the same time slot of a specific RF carrier.
n But – under sever fading conditions in a cell a low frequency
hopping may be implemented to combat the multipath or interference effects.
– Frequency hopping is carried out on a frame-by-frame basis.– Frequency hopping is completely specified by the service
provider.
F1 F2 F3 F4 F5 F6 F7 F8
T=1 T=2 T=3
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Chapter 1.Chapter 1.Chapter 1.
n Introduction, Course Overview and Objectivesn Review of GSM Protocol
– Spectrum and Physical Channels– Frame and Time Slot Structure– Logical Channels– GSM Coding and Modulations
n Network Elements and Architecture– BSS– NSS– OAM
n Fixed Network Connectionsn Overview of RF network Planningn Section Summary and Discussions
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System ArchitectureSystem ArchitectureSystem Architecture
n A GSM system is basically designed as a combination of three major subsystems:– the Network Switching SubSystem (NSS) or (SSS)– the Radio Subsystem (RSS), or Base Station Subsystem (BSS) – the Operation Support Subsystem (OSS).
n The Mobile Station (MS) is usually considered to be part of the RSS.
Base Station Subsystem
Network SwitchingSubsystem
PublicNetworks
Operation Support Subsystem
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Network ArchitectureNetwork ArchitectureNetwork Architecture
BTS
BTS
BTS
BSC
BTS
BTS
BTS
BSC
ISDN
PSTN
DataNetworks
MS
MS
Base Station Subsystem
Network SwitchingSubsystem
PublicNetworks
AUCHLR VLR
MSC
IWFEIR EC
OMC
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The Radio subsystemThe Radio subsystemThe Radio subsystem
n The radio subsystem includes the equipment and functions related to the management of the connections on the radio path, including the management of handovers. It mainly consists of a BSC, BTS, and the MS.
n The GSM system is realized as a network of radio cells. Each cell has a BTS with several transceivers. A group of BTSs are controlled by one BSC.
n BSC and BTS together are known as a BSS, which is viewed by the MSC through a single interface as being the entity responsible for communication with MSs in a certain area.
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Network SubsystemNetwork SubsystemNetwork Subsystem
n The network subsystem includes the equipment and functions related to end-to-end calls, management of subscribers, mobility, and interface with the fixed PSTN.
n The network and the switching subsystem together include the main switching functions of GSM as well as the databases needed for subscriber data and mobility management
n In particular, the switching subsystem consists of – Mobile Switch Center (MSC),– Visitor Location Register (VLR), – Home Location Register (HLR), – Authentication Center (AUC), and – Equipment Identity Register (EIR)– Echo Canceller (EC)– InterWorking Function (IWF)– ......
AUCHLR VLR
MSC
Network SwitchingSubsystem
IWFEIR EC
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Operation Support SubsystemOperation Support SubsystemOperation Support Subsystem
n The Operational and Maintenance Center (OMC) subsystem includes the operation and maintenance of GSM equipment and supports the operator network interface.
n It is connected to all equipment in the switching system and to the BSC.
n OMC performs GSM's administrative functions (for example, billing) within a country.
n One of the OMC's most important functions is the maintenance of the country's HLR.
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GSM Hierarchical Network StructureGSM Hierarchical Network StructureGSM Hierarchical Network Structure
n In the GSM system, the network is divided into the following partitioned areas.– GSM service area;– PLMN service area;– MSC service area;– Location area (LA);– Cells GSM Service Area
PLMN LAMSCService Area
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GSM Service Area & PLMNGSM Service Area & PLMNGSM Service Area & PLMN
n The GSM service area is the total area served by the combination of all member-countries where a mobile can be serviced.
n The next level is the PLMN service area. There can be several within a country, based on its size. – The links between a GSM/ PLMN network and other PSTN,
ISDN, or PLMN networks will be on the level of international or national transit exchanges.
– All incoming calls for a GSM/PLMN network will be routed to a Gateway MSC.
– Call connections between PLMNs, or to fixed networks, must be routed through certain designated MSCs called a gateway MSC.
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MSC Service Area & Location AreaMSC Service Area & Location AreaMSC Service Area & Location Area
n In one PLMN there can be several MSC/VLR service areas. – MSC/VLR is a sole controller of calls within its jurisdiction.
The mobile location can be uniquely identified since the MS is registered in a VLR, which is generally associated with an MSC.
– There are several LAs within one MSC/VLR combination. – A LA is a part of the MSC/VLR service area in which a MS
may move freely without updating location information to the MSC/VLR exchange that controls the LA.
n Lastly, a LA is divided into many cells. – A cell is an identity served by one BTS. The MS distinguishes
between cells using the Base Station Identification Code (BSIC) that the cell site broadcasts over the air
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MS FunctionsMS FunctionsMS Functions
n A list of relevant MS functions includes – Voice and data transmission;– Frequency and time synchronization;– Monitoring of power and signal quality of the
surrounding cells for optimum handover;– Provision of location updates;– Equalization of multipath distortions;– Display of short messages up to 160 characters long;– Timing advance.
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MS IdentificationMS IdentificationMS Identification
n GSM uses a number of descriptors to identify subscribers, equipment, and fixed stations/areas. Many are temporary and used to maintain the confidentiality of fixed identities. An understanding of these descriptors is essential when considering GSM exploitation.– International Mobile station Equipment Identity (IMEI)– Mobile Subscriber ISDN Number (MSISDN)– International Mobile Subscriber Identity (IMSI) – Temporary Mobile Subscriber Identity (TMSI)
n In general, identities are used in the interfaces between the MSC and the MS, while numbers are used in the fixed part of the network, such as, for routing.
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SIM CardSIM CardSIM Card
n By making a distinction between the subscriber identity and the mobile equipment identity, a GSM PLMN can route calls and perform billing based on the identity of the subscriber rather than the mobile unit being used.
n This can be done using a removable Subscriber Identity Module (SIM).
n The smart card SIM is portable between Mobile Equipment (ME) units.
S I
M
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SIM (cont.)SIM (cont.)SIM (cont.)
n The contents of the SIM card are as follows.– Removable plastic card or the SIM module;– Unique mobile subscriber ID through IMSI and ISDN
numbers;– PIN;– Authentication key Ki and A3, AS, and A8 algorithms.
n The SIM is a removable SC, the size of a credit card, and contains an integrated circuit chip with a microprocessor, random access memory (RAM), and read-only memory (ROM).
n A smart card (SC) is one possible implementation of a SIM; the other implementation can be the module mounted on the mobile equipment.
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IMEIIMEIIMEI
n The IMEI is the unique identity of the equipment used by a subscriber by each PLMN and is used to determine – authorized (white), – unauthorized (black), and – malfunctioning (gray) GSM hardware.
n In conjunction with the IMSI, it is used to ensure that only authorized users are granted access to the system.
n An IMEI is never sent in cipher mode by a MS
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IMSIIMSIIMSI
n International Mobile Subscriber Identityn An IMSI is assigned to each authorized GSM
user. It consists of a– a mobile country code (MCC),– a mobile network code (MNC), and – a PLMN unique mobile subscriber identification
number (MSIN).
n The IMSI is not hardware-specific. Instead, it is maintained on a SC by an authorized subscriber and is the only absolute identity that a subscriber has within the GSM system. The IMSI shall not exceed 15 digits.
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TMSITMSITMSI
n TMSI is a temporary identification number that is assigned by the serving MSC/VLR combination.
n It is assigned only after successful subscriber authentication. Since the TMSI has only local significance (that is, within the VLR and the area controlled by the VLR), the structure of this can be chosen by each administration in order to meet local needs.
n The TMSI is mainly used for security reasons to avoid broadcasting the IMSI over the RF air interface, thereby making it harder for eavesdroppers.
n The TMSI is supposed to be changed on a per-call basis as recommended by GSM specific actions.
69
MS-ISDNMSMS--ISDNISDN
n Mobile Station ISDN Number: The MS international number must be dialed after the international prefix in order to obtain a mobile subscriber in another country.
n The MSISDN number is composed of – the country code (CC) followed by – the National Significant Number (N(S)N), which shall not
exceed 15 digits.
n The Mobile Station Roaming Number (MSRN): is allocated on a temporary basis when the MS roams into another numbering area. The MSRN number is used by the HLR for rerouting calls to the MS.
70
Base Station SystemBase Station SystemBase Station System
n The BSS is a set of BS equipment (such as transceivers and controllers) that is in view by the MSC through a single A interface as being the entity responsible for communicating with MSs in a certain area.
n The function split is basically between a transmission equipment, the BTS, and a managing equipment at the BSC.– A BTS comprises radio transmission and reception devices, up
to and including the antennas, and also all the signal processing specific to the radio interface.
– A BSC is a network component in the PLMN that functions for control of one or more BTS. It is a functional entity that handles common control functions within a BTS.
n The interface between the BSC and a remote BTS is a standard interface termed the A-bis. BTSBSC
71
Base Transceiver SubsystemBase Transceiver SubsystemBase Transceiver Subsystem
Abis
BTS
TRXn
TRXn-1
TRX2
TRX1
BCFBSC
Um
n A BTS is a network component that serves one cell and is controlled by a BSC.
n BTS is typically able to handle three to five radio carriers, carrying between 24 and 40 simultaneous communications.
72
BTS FunctionsBTS FunctionsBTS Functions
n A list of functions performed by BTS is as follows.– BTS Encodes, encrypts, multiplexes, modulates and feeds the
RF signals to the antenna;– Transcoding and rate adaptation;– Time and frequency synchronization signals transmitted from
BTS;– Voice communication through full rate or half rate (future
date) speech channel;– Received signal from mobile is decoded, decrypted and
equalized before demodulation;– Frequency hopping controlled such that no two MSs in the
same BSC area are hopped together;– Random access detection;– Timing advance;– Uplink radio channel measurements. BTS
73
Transcoder/Rate Adapter UnitTranscoderTranscoder/Rate Adapter Unit/Rate Adapter Unit
n The Transcoder/Rate Adapter Unit (TRAU) is the equipment in which coding and decoding is carried out as well as the rate adaptation in case of data.
n The transcoder takes 13-Kbps speech or 3.6/6/12-Kbps data and multiplexes four of them to convert into standard 64-Kbps data. – First, the 13 Kbps or the data at 3.6/6/12 Kbps are brought up to the
level of 16 Kbps by inserting additional synchronizing data to make up the difference between a 13-Kbps speech or lower rate data, and then four of them are combined in the transcoder to provide 64 Kbps.
– Then, up to 30 such 64-Kbps channels are multiplexed onto a 2.048Mbps if a CEPT1 channel is provided on the A-bis interface.
TRAU4 x CodedSpeech Channels
64 Kbps
74
TRAU (cont.)TRAU (cont.)TRAU (cont.)
n Depending on the relative costs of a transmission plant for a particular cellular operator, there may be some benefit, for larger cells and certain network topologies, in having the transcoders either at the BTS, BSC, or MSC location. – If the transcoder is located at MSC, they are still considered
functionally a part of the BSS. This approach allows for the maximum of flexibility and innovation in optimizing the transmission between MSC and BTS.
– If the transcoder/rate adapter is placed outside the BTS (part of BSC or MSC), the A-bis interface can only operate on a 16-Kbps channel within the BSS. Four traffic channels can then be multiplexed on one 64-Kbps circuit. Thus, the TRAU output data
rate is 64 Kbps.
75
BTS TRAU BSC MSC To Fixed Networks
To MS
BTS MSC To Fixed Networks
To MS BSC TRAU
BTS MSC To Fixed Networks
To MS BSC TRAU
AInterface
A-bisInterface
RF AirInterface
13 kbps encoded voice / 12 kbps data
16 kbps transmission
64 kbps transmission
Physical site
TRAU LocationTRAU LocationTRAU Location
76
Base Station Controller Base Station Controller Base Station Controller
n The BSC is connected to the MSC on one side and to the BTSs on the other.
n The BSC performs the Radio Resource (RR) management for the cells under its control.
BTS BSC
BTS
MSC
77
BSC FunctionsBSC FunctionsBSC Functions
n The functions of BSC are as follows.– RR management for BTSs under its control;– Intercell handover;– Reallocation of frequencies among BTSs;– Power management of BTSs;– Time and frequency synchronization signals to BTSs;– Time delay measurement of the received signals from MSs
with respect to BTS clock;– Controls frequency hopping;– Performs traffic concentration to reduce the number of lines
from BSC to MSC and BTSs;– Provides interface to the Operations and Management for BSS.
78
BTS-BSC ConnectionsBTSBTS--BSC ConnectionsBSC Connections
TRX
BCF
TRXTRXTRXTRX
TRX
TRXTRXTRX
BCF
TRXTRXTRX
BCF
TRX
TRX
BCF
BBSSCC
Abis
Abis
Abis
Abis
BTS1
BTS2
BTS3
BTS4
79
Chapter 1.Chapter 1.Chapter 1.
n Introduction, Course Overview and Objectivesn Review of GSM Protocol
– Spectrum and Physical Channels– Frame and Time Slot Structure– Logical Channels– GSM Coding and Modulations
n Network Elements and Architecture– BSS– NSS– OAM
n Fixed Network Connectionsn Overview of RF network Planningn Section Summary and Discussions
80
Mobile Switch Center (MSC)Mobile Switch Center (MSC)Mobile Switch Center (MSC)
n The main role of the MSC is to manage the communications between the GSM users and other telecommunications network users. The basic switching function is performed by the MSC, whose main function is to coordinate setting up calls to and from GSM users.
n The MSC has interfaces with the BSS on one side (through which MSC VLR is in contact with GSM users) and the external networks on the other (ISDN/PSTN/PSPDN)
n An MSC is generally connected to several BSSs, which provide radio coverage to the MSC area.
n MSC is also connected to other GSM PLMN entities such as other MSCs and HLR through a fixed network.
AUCHLR VLR
MSC
IWFEIR EC
81
MSC (cont.)MSC (cont.)MSC (cont.)
n The MSC provides the interface between the fixed and mobile networks. The MSC is the telephone switching office for mobile-originated or terminated traffic.
n The MSC controls the call setup and routing procedures in a manner similar to the functions of a land network end office.
n The MSC provides – call setup, – routing, and– handover between BSCs in its own area and
to/from other MSC; – an interface to the fixed PSTN;
– and other functions such as billing.
AUCHLR VLR
MSC
IWFEIR EC
82
MSC FunctionsMSC FunctionsMSC Functions
n Some of functions performed by MSC – Paging;– Coordination of call set up from all MSs in its jurisdiction;– Dynamic allocation of resources;– Handover management;– Reallocation of frequencies to BTSs in its area to meet heavy demands;
n Specifically, the call-handling function of paging is controlled by MSC. MSC coordinates the set up of calls to and from all GSM subscribers operating in its area.
n The dynamic allocation of access resources is done in coordination with the BSS. More specifically, the MSC decides when and which types of channels should be assigned to which MS. The channel identity and related radio parameters are the responsibility of the BSS.
83
MSC Functions (cont.)MSC Functions (cont.)MSC Functions (cont.)
n Some of other functions performed by MSC– Location registration;– Billing for all subscribers based in its area;– Encryption;– Signaling exchange between different interfaces;– Synchronization with BSSs;– One MSC may interface several BSSs– Some other network elements are:
84
Visitor Location Register Visitor Location Register Visitor Location Register
n The VLR Constitutes the database that supports the MSC in the storage and retrieval of the data of subscribers present in its area.
n The VLR supports a mobile paging and tracking subsystem in the local area where the mobile is presently roaming.
n A VLR may be in charge of one or several MSCLAs.
85
VLR and Location UpdatingVLR and Location UpdatingVLR and Location Updating
LAILAI-2
MSC2VLR2
HLR
1
3 2
54
6MSC1VLR1
Delete This MS From Database
Delete This MS to Database
n When a mobile subscriber roams from one LA to another, their current location is automatically updated in their VLR.
n If the old and new LAs are under the control of two different VLRs, the entry on the old VLR is deleted and an entry is created in the new VLR by copying the basic data from the HLR.
n The subscriber's current VLR address, stored at the HLR, is alsoupdated. This provides the information necessary to complete calls to roaming mobiles.
86
Location UpdateLocation UpdateLocation Update
n MS must request a location update when an optional timer expires. This periodic updating increases the accuracy of the data in the VLR.
n The BTS broadcasts the timer on the BCCH to tell the MS how often to update locations within a LAI.
n The MS must go from the idle mode to the dedicated mode and back to the idle mode to complete a location update.
n SDCCH is the channel that the MS and BTS use for a location update.
n The MS does not update locations during a call.
87
Data in VLRData in VLRData in VLR
n Data stored in VLR are as follows.– IMSI– MSISDN– MSRN– TMSI– The LA where the MS has been registered – Supplementary service parameters– MS category– Authentication key, query and response obtained
from AUC– ID of the current MSC
88
VLR FunctionsVLR FunctionsVLR Functions
n VLR– Works with the HLR and AUC on
authentication;– Relays cipher key from HLR to BSS for
encryption/decryption;– Controls allocation of new TMSI numbers; a
subscriber's TMSI number can be periodically changed to secure a subscriber's identity;
– Supports paging;– Tracks state of all MSs in its area.
89
Home Location RegisterHome Location RegisterHome Location Register
n The HLR is the reference database that permanently stores data related to a given set of subscribers.
n Various identification numbers and addresses as well as authentication parameters, services subscribed, and special routing information are stored.
n Current subscriber status, including a subscriber's temporary roaming number and associated VLR if the mobile is roaming, are maintained.
n Location registration is performed by HLR.
90
HLR FunctionsHLR FunctionsHLR Functions
n The HLR provides data needed to route calls to all MS-SIMs home based in its MSC area, even when they are roaming out of area orin other GSM networks.
n The HLR provides the current location data needed to support searching for and paging the MS-SIM for incoming calls, wherever the MS-SIM may be.
n The HLR is responsible for storage and provision of SIM authentication and encryption parameters needed by the MSC where the MS-SIM is operating. It obtains these parameters from the AUC.
n The HLR maintains records of which supplementary services each user has subscribed to and provides permission control in granting access to these services.
n Both the HLR and the VLR can be implemented in the same equipment in an MSC (collocated).
n A PLMN may contain one or several HLRs.
91
HLR DataHLR DataHLR Data
n Based on described functions, different types of data are stored in HLR. – Some data are permanent; that is, they are modified
only for administrative reasons, – while others are temporary and modified
automatically by other network entities depending on the movements and actions performed by the subscriber.
– Some data are mandatory, other data are optional.
92
HLR Data (Permanent)HLR Data (Permanent)HLR Data (Permanent)
n IMSI: It identifies unambiguously the MS in the whole GSM system;
n International MS ISDN number: It is the directory number of the mobile station;
n MS category specifies whether a MS is a pay phone or not;n Roaming restriction (allowed or not);n Closed user group (CUG) membership data;n Supplementary services related parameters: Forwarded-to
number, registration status, no reply condition timer, call barring password, activation status, supplementary services check flag;
n Authentication key, which is used in the security procedure and especially to authenticate the declared identity of a MS.
93
HLR Data (Temporary)HLR Data (Temporary)HLR Data (Temporary)
n The temporary data consists of the following.– LMSI (Local MS identity);– RAND/SRES and Kc; data related to authentication and
ciphering;– MSRN;– VLR address, which identifies the VLR currently handling the
MS;– MSC address, which identifies the MSC area where the MS is
registered;– Roaming restriction;– Messages waiting data (used for SMS);
n Temporary data changes from call to call. The HLR interacts with MSCs mainly for the procedures of interrogation for routing calls to a MS and to transfer charging information after call termination.
94
Authentication CenterAuthentication CenterAuthentication Center
n Authentication information and ciphering keys are stored in a database within the AUC, which protects the user information against unwanted disclosure and access.
n The HLR is also responsible for the "authentication" of the subscriber each time he makes or receives a call.
n The AUC, which actually performs this function, is a separate GSM entity that will often be physically included with the HLR. Being separate, it will use separate processing equipment for the AUC database functions.
95
Authentication ConceptAuthentication ConceptAuthentication Concept
AuthenticationAlgorithm
AuthenticationAlgorithm
At Serving SystemAt Serving System
Matched ?
Yes
No
Random Number
SharedSecret Data
SharedSecret Data
AIR
Int
erfa
ce
Access Granted.Access Denied
Authentication Response
At Mobile UnitAt Mobile Unit
96
Authentication ProcessAuthentication ProcessAuthentication Process
n A PIN number is used to activate the MS.n MS sends its IMSIn The network sends back a randomly generated number
(RAND).n MS computes the Signed Response (SRES) using an
authentication algorithm (A3), the Key which is like a shared secret data, and RAND.
n MS send the SRES to the networkn The network computes SRES independently and
compare is with the received SRES from mobile.n A match indicates an authorized user whereas a
mismatch results in failed authentication and no service.
97
Key ExchangeKey ExchangeKey Exchange
n In the authentication procedure, the key is never transmitted to the mobile over the air path, only a random number is sent.
n In order to gain access to the system, the mobile must provide the correct Signed Response (SRES) in answer to a random number (RAND) generated by AUC.
n Also, K1 and the cipher key Kc are never transmitted across the air interface between the BTS and the MS. Only the random challenge and the calculated response are transmitted. Thus, the value of Ki andKc are kept secure.
n The cipher key, on the other hand, is transmitted on the SS7 link between the home HLR/AUC and the visited MSC, which is a point of potential vulnerability.
n On the other hand, the random number and cipher key is supposedto change with each phone call, so finding them on one call will not benefit using them on the next call.
98
Equipment Identity RegisterEquipment Identity RegisterEquipment Identity Register
n EIR is a database that stores the IMEI numbers for all registered ME units.
n EIR database stores the ME identification and has nothing to do with the subscriber who is receiving or originating a call.
n There are three classes of ME that are stored in the database, and each group has different characteristics.
– White List: contains those IMEIs that are known to have been assigned to valid MSs.
– Black List: contains IMEIs of mobiles that have been reported stolen.
– Gray List: contains IMEIs of mobiles that have problems (for example, faulty software, wrong make of the equipment). This list contains all MEs with faults not important enough for barring.
99
Interworking Function (IWF)InterworkingInterworking Function (IWF)Function (IWF)
n A GSM system provides a wide range of data services to its subscribers and interfaces with the various forms of public and private data networks currently available.
n It is the job of the IWF to provide this interfacing capability.
n Networks to which IWF presently provides interface are as follows.– PSTN;– ISDN;– Circuit-switched public data networks (CSPDN);– Packet-switched public data networks (PSPDN).
100
BSS ECMSCPSTN
4w to 2w
Hybrid bridge
MS Landtelephone
PLMN4 wire circuit
Echo Canceller (EC)Echo Canceller (EC)Echo Canceller (EC)
n The EC is used on the PSTN side of the MSC for all voice circuits. n The EC is required at the MSC PSTN interface to reduce the effect
of GSM delay when the mobile is connected to the PSTN circuit.
101
Echo Canceller (Cont.)Echo Canceller (Cont.)Echo Canceller (Cont.)
n Normally this delay would not be an annoying factor to the mobile, except when communicating to PSTN as it requires a two-wire to four-wire hybrid transformer in the circuit.
n Due to the presence of this hybrid, some of the energy at its four-wire receive side from the mobile is coupled to the four-wire transmit side and thus retransmitted to the mobile. This causes the echo
n The resulted echo does not affect the land subscriber but is an annoying factor to the mobile. The standard EC cancels about 70 ms of delay.
102
Some Other Network ElementsSome Other Network ElementsSome Other Network Elements
n Gateway MSC is the anchor MSC which has direct signaling interaction with PSTN.– It is the gateway of the GSM network to/from outside network.
n Message Center (MC): or Voice Mail Services (VMS), which handles voice mail messaging and stores/forwards voice mails.
n Billing Center (BC): Keep track of charges for all mobile in the network.
MSC
MSC
GMSCPSTN
103
Chapter 1.Chapter 1.Chapter 1.
n Introduction, Course Overview and Objectivesn Review of GSM Protocol
– Spectrum and Physical Channels– Frame and Time Slot Structure– Logical Channels– GSM Coding and Modulations
n Network Elements and Architecture– BSS– NSS– OAM
n Fixed Network Connectionsn Overview of RF network Planningn Section Summary and Discussions
104
Operations & Maintenance CenterOperations & Maintenance CenterOperations & Maintenance Center
n The main purpose of the OMC is to perform all operations and maintenance functions on elements of the GSM PLMN system.
n The OMC uses a separate Telecommunications Management Network (TMN) to communicate with the various components of the GSM system. In general, it is done through leased lines on the PSTN or other fixed networks.
n The OMC message and data transfers can either be carried by SS7 or X.25 protocols.
105
Intra-Network OMC ConnectionsIntraIntra--Network OMC ConnectionsNetwork OMC Connections
BTS BSC
ISDN
PSTN
DataNetworks
MS
Base Station Subsystem
Network SwitchingSubsystem
PublicNetworks
AUCHLR
VLR
MSC
IWFEIR EC
OMC
X.25
106
OMC FunctionsOMC FunctionsOMC Functions
n Maintenance functions cover both technical and administrative actions to maintain and correct the system operation, or to restore normal operations after a breakdown, in the shortest possible time.
n the following network functions are performed.– Supports for maintenance;– X.25 interface;– Alarm handling;– Fault management;– Performance management;– Software version and configuration control;– Network status;– Traffic collection from network.
107
OMC (cont.)OMC (cont.)OMC (cont.)
n A mobile call trace facility can also be invoked. n The performance management functions include
collecting traffic statistics from the GSM network entities and archiving them in disk files or displaying them for analysis.
n Because a potential to collect large amounts of data exists, maintenance personnel can select which of the detailed statistics to be collected based on personal interests and past experience.
n The OMC provides system change control for the software revisions and configuration data bases in the network entities.
n Software loads can be downloaded from the OMC to other network entities or uploaded to the OMC.
108
Network Management CenterNetwork Management CenterNetwork Management Center
n The salient characteristics and features of the NMC are as follows.– Single NMC per network;– Provides traffic management for the whole network;– Monitors high-level alarms such as failed or
overloaded nodes;– Performs responsibilities of an OMC when it is not
staffed;– Provides network planners with essential data for
network performance.
n The NMC is generally connected to the PLMN subsystems through leased lines via PSTN.
109
OMC vs. MNC OMC vs. MNC OMC vs. MNC
n OMC is a regionalized management center,
n OMC is used for monitoring and controlling the daily activities of the system operations,
n OMC is used by network operators
n while NMC is the global management center.
n while NMC is for the long-term planning.
n while NMC is used by network managers and network planners.
110
Chapter 1.Chapter 1.Chapter 1.
n Introduction, Course Overview and Objectivesn Review of GSM Protocol
– Spectrum and Physical Channels– Frame and Time Slot Structure– Logical Channels– GSM Coding and Modulations
n Network Elements and Architecture– BSS– NSS– OAM
n Fixed Network Connectionsn Overview of RF network Planningn Section Summary and Discussions
111
GSM InterfacesGSM InterfacesGSM Interfaces
n There are three dominant interfaces, namely, an interface between MSC and the Base Station Controller (BSC), an A-bis interface between BSC and the Base Transceiver Station (BTS), and an Urn interface between the BTS and MS.
BTS
BTS
BTS
BSC PSTNMSC
MS
GSM UmRadio
Air Interface
AbisInterface
A Interface
SS7
112
Abis InterfaceAbisAbis InterfaceInterface
n All the data, both signaling and user data, move between the base station (the BTS part) and the BSC on the Abisinterface.
n The Abis is implemented when the BTS and BSC are located at different sites. If both are positioned at the same location, even in the same cabinet or rack, different solutions are possible, depending on the manufacturer.
n Due to its late and initially fragmented standardization, the Abis interface appeared in a variety of different interpretations and implementations. This led to incompatibilities among network components from different manufacturers. So, if network operators decided to buy a BSC from one supplier, they had little choice but to buy BTSs from the same supplier
113
BTS-BSC ConnectionsBTSBTS--BSC ConnectionsBSC Connections
TRX
BCF
TRXTRXTRXTRX
TRX
TRXTRXTRX
BCF
TRXTRXTRX
BCF
TRX
TRX
BCF
BBSSCC
Abis
Abis
Abis
Abis
BTS1
BTS2
BTS3
BTS4
114
Digital Transmission LinksDigital Transmission Links
n Hierarchy Digital Transmission adopted by CEPT are– E0 64Kbps 1VC– E1 2.048Mbps 30E0– E2 8.4Mbps 4 E1– E3 34.3Mbps 16E1– E4 139.2Mbs 64E1– E5 565.1Mbps 256E1
115
Abis Interface, Time SlotsAbisAbis Interface, Time SlotsInterface, Time Slots
n In a manner similar to the air interface, the Abisinterface also uses a layered structure, Layers 1, 2, and 3. Though the three layers in the Abis have identical functions to those on the Um interface, their details are somewhat different.
n Layer 1 on the Abis is also the physical layer on which we find the digital data (speech and signaling) moving between the base station and the BSC at a rate of 2,048 kbps.
n It makes use of a TDMA structure using 32 time slots, each at a rate of 64 kbps.
116
E1 or PCM30 LinkE1 or PCM30 LinkE1 or PCM30 Link
n Due to its structure and speech coding, the 2-Mbps link is also referred to as a PCM3O link.
– PCM stands for the type of modulation used on Layer 1, pulse code modulation,
– and the number 30 indicates that out of the 32 time slots 30 areused for user data communication between the base station and its controller.
– The other two time slots, indicated by the shaded squares in Figure are dedicated to synchronization tasks (on TS 0) and the signaling required between the base station and the BSC simply to maintain Layer 2 of the Abis link (on TS 16).
TS0 TS1 TS15 TS16 TS17 TS30 TS31..... .....
117
TS mapping between Abis and UmTS mapping betweenTS mapping between AbisAbis and Umand Um
S T T T T T T T T
TS 0
TS 1
TS 2
TS 3
TS 4
TS 5
TS 6
TS 7
16 kbps Subslots
TRX
Abis
Um
118
Subslots in PCM30SubslotsSubslots in PCM30in PCM30
n In addition to the allocation of time slots on the 2-Mbps frame, the specifications allow a further variation.
n A 64-kbps channel may be subdivided into foursubslots of 16 kbps each.
n Such a subslot is not only addressed by its time slot number (in the Abis sense), but also by itssubslot number. The subslot may be used for signaling purposes or traffic channel assignments.
TS0 TS1 TS15 TS16 TS17 TS30 TS31..... .....
T1
T1
T1
T1
119
The A interfaceThe A interface
n The A interface is the interface signaling protocol between BSC and MSC.
n The A interface defines the messages between the BSC and the MSC, and messages to/from MS.
n Uses 64Kbps E0 channelsn Uses the SS7 lower layer protocol stack for carriage
protocol (MTP and SCCP, to be discussed later)n Two message sets are defined for this purpose
– DTAP (Direct Transfer Application Part)– BSSMAP (BSS Management Part)– These protocols will be described later
120
Chapter 1.Chapter 1.Chapter 1.
n Introduction, Course Overview and Objectivesn Review of GSM Protocol
– Spectrum and Physical Channels– Frame and Time Slot Structure– Logical Channels– GSM Coding and Modulations
n Network Elements and Architecture– BSS– NSS– OAM
n Fixed Network Connectionsn Overview of RF network Planningn Section Summary and Discussions
121
Network PlanningNetwork PlanningNetwork Planning
n The problem of planning a wireless network can be formalized as follows: Given – the subscribers’ density and their statistical behavior, – terrain and propagation environment characteristics– and available bandwidthas input data, – minimize the cost of radio and network infrastructure with respect
to radio coverage and cell layout, channel reuse and frequency plan,
– subject to quality of service constraints.
n This problem is quite complex and is typically addressed
through decomposition.
122
Design ConsiderationsDesign ConsiderationsDesign Considerations
n Implementation Issues– Cost and Time to Market– Resources– Expansion Provisions
n Performance Issues– Coverage– Grade of Service– Quality of Service
123
Coverge IssuesCovergeCoverge IssuesIssues
n RF Channel Characterizationn Receiver Sensitivity n Coverage Design Parametersn Coverage Simulations and Performance
analysisn Field Verificationn Handoff Provisioning
124
Traffic and Capacity IssuesTraffic and Capacity IssuesTraffic and Capacity Issues
n Subscriber Forecast, – Expected Service Penetration– Subscriber Distribution Maps
n Traffic Modeling,– Traffic Types– Access Pattern – Average Load per Call– Grade of Service
n Air Interface Capacityn Hardware Limitationsn Backhaul and Fixed Network Impact
125
Quality of Service IssuesQuality of Service IssuesQuality of Service Issues
n Inter-cell and Intracell interference Issues in – TDMA Networks– CDMA Networks
n Interference Management– Interference Avoidance Techniques– Channel Assignment
» FCA» DCA
– Interference Cancellation Techniques– Interference Averaging Techniques
126
Design ProcessDesign ProcessDesign Process
n Network Planning is typically addressed through decomposition.
n The main steps characterizing the mobile network planning procedure include – traffic and mobility model, – radio coverage and cell dimensioning,– frequency plan, – distribution, switching, and signaling and database
network planning. – As the planning phases are strictly dependent on each
other, an iterative approach is typically used.
127
RF Design PreparationRF Design PreparationRF Design Preparation
n RF design Starts with some preparation,n Selecting the vendorn Setting Design Objectives and Standardsn Setting up required databases
– Terrain, Morphology, Road Maps, Demographics, Client Preferred site locations,
n Antenna’s and Hardware related specificationsn Estimating required Resources
– RF engineers (man-hours)– Measurement Tools
– Software Tools
128
Predesign MeasurementsPredesignPredesign MeasurementsMeasurements
n Measurement tools should be used to characterize the propagation environment in various areas within the market.
n Fine tune the parameters of the propagation model used by the software tool; e.g. Correction Factors, path Loss Slope ...
n Optional ( if time and money restrictions permit)– Penetration Losses (In-building, In-car,..) – Fading and Delay spread statistics.
129
Paper Design (LBA)Paper Design (LBA)Paper Design (LBA)
n Link Budget Analysis (LBA) is a spread-sheet type analysis of losses and gains in the forward and reverse radio paths.– LBA has the following objectives:– Estimating Maximum allowable path loss– Balancing forward and reverse link foot prints– Defining coverage thresholds for various coverage classes– determining typical transceiver parameters
n LBA also provides us with estimates of cell radius and cell count, which together can define a first cut cell layout.
130
Maximum RF Path LossMaximum RF Path LossMaximum RF Path Loss
RXBSSensitivity
RXMSSensitivity
Path Loss Down Link
Path Loss Up Link
PABS
PAMS
131
LBA InputsLBA InputsLBA Inputs
n Base and Mobile Receiver Sensitivity Parameters– Minimum Acceptable Signal to Noise Ratio – Environmental/Thermal Noise Assumption– Receiver Noise Figure
n Antenna Gain at Base and Mobile Station
n Hardware Losses (Cable, Connectors, Combiner,....)
n Target Coverage Reliabilityn Propagation Characteristics of the
Channeln Receiving Environment
LBA
132
LBA OutputsLBA OutputsLBA Outputs
n Coverage Design Thresholds– In-Building– In-Car– On-Street
n Base Station ERPn Maximum Allowable Path
Lossn Cell Size Estimaten Cell Count Estimate
LBA
133
Cell Size/Count EstimationCell Size/Count EstimationCell Size/Count Estimation
n Objective:– To determine the size and number of cells required to
provide coverage for a given area.
n Required Input:– Maximum Allowable Path Loss (MAPL)– Propagation Loss Model– Market Boundaries
134
Cell Size/Count Estimation Cell Size/Count Estimation Cell Size/Count Estimation
Link Budget Analysis
Max Allowable Path Loss
Cell Radius Estimate
Cell Count Estimate
Path Loss Model
Field Tests
Market Boundaries
135
n Using Hata’s Empirical Formula
Cell Size EstimatationCell SizeCell Size EstimatationEstimatation
Solve it backward to Cell radius estimate based on Hata’sformula:
PL f h
h R a hc b
b m
= + − +
− −
69 55 2616 13 82
44 9 6 5510 10
10 10
. . log . log
( . . log ) log ( )
log. . log . log ( )
. . log1010 10
10
69 55 2616 13 82
44 9 6 55R
MAPL f h a hh
c b m
b
==−− −− ++ ++
−−
136
Cell Count EstimationCell Count EstimationCell Count Estimation
137
Simulations & ImplementationSimulations & ImplementationSimulations & Implementation
n Initial Design consists of the following major steps,
n Site Selection consideringn Capacity Analysisn Interference avoidance
through careful frequency planning
n These steps usually involve iterations.– Any change in site configuration
to alleviate a capacity or interference problem may violate coverage rules and objectives.
Coverage AnalysisCoverage Analysis
Capacity AnalysisCapacity Analysis
Interference AnalysisInterference Analysis&&
Frequency PlanningFrequency Planning
ImplementationImplementation
OptimizationOptimization
138
Radio Coverage DesignRadio Coverage DesignRadio Coverage Design
n For radio coverage and cell dimensioning, the previous traffic data are considered together with the propagation issues.
n The main factors affecting the electromagnetic coverage forecast are: – Terrain configuration,– Mobility and Fading effects. – Land use, vegetation, and urbanization density– Penetration losses associated with receiving
environments, buildings and vehicles.
139
Traffic AnalysisTraffic AnalysisTraffic Analysis
n As for the traffic modeling,n the PCS service area must be characterized based on
subscribers' density and distribution. n Geographical maps or territorial databases are utilized
to identify the main roads, inhabitant densities, and business areas. Urban and geographical analysis can be integrated, when necessary, with data relevant to the fixed telecommunication users distribution.
n In this step also mobility attributes are modeled, since they affect significantly signaling network and distributed data base dimensioning.
140
Joint Radio & Traffic Design Joint Radio & Traffic Design Joint Radio & Traffic Design
n In principle radio coverage and traffic distribution are to be considered jointly.
n However, due to the inherent task complexity, the procedure calculates – first of all a suitable radio coverage for the service area, – Then it verifies if that coverage can fulfill the cell capacity
requirements deriving from the traffic forecasting.
n These two very strictly dependent steps are iterated until a satisfactory solution is derived.
n The factors conditioning the resulting cell layout come from either propagation or traffic constraints, depending on the most critical conditions.
141
Frequency Planning & FCAFrequency Planning & FCAFrequency Planning & FCA
n Once the cell layout and the cell dimensioning (in terms of channels) are identified, a frequency plan is to be evaluated by keeping the relevant quality of service above an assigned threshold.
n A formal description of the frequency planning task in a Fixed Channel Assisgnment (FCA) system follows:– minimize the overall bandwidth (union of used frequencies Fi ) – subject to (C/I)i > (C/I)0 for all i’s. Fi is the set of frequencies
assigned to cell i and (C/I)0 represents the minimum allowed carrier to interference threshold (the quality of service measure).
142142
Channel AssignmentChannel AssignmentChannel Assignment
n Channel assignment is the problem of – allocating enough channels or frequencies to each
base station to meet its capacity needed, subject to– maintaining a minimum C/I for all points within
the service area.
n The channel assignment can be– Fixed – Semi_fixed– Dynamic
143143
Fixed Assignment Fixed Assignment Fixed Assignment
n In fixed assignment, channels are permanently allocated to each cell to meet a pre-determined GOS.
n Fixed assignment can be based on:– Uniform reuse pattern if traffic is uniformly distributed
among cells.– Non-uniform based on estimated traffic in each cells coverage
area.
n Frequency planning is a search for the assignment that causes minimum intercell co-channel and adjacent channel interference.
Question:What is Semi-Fix Channel Assignment?
144144
Dynamic Channel AssignmentDynamic Channel AssignmentDynamic Channel Assignment
n In DCA the allocation of channels is changed adaptively according to the dynamics of the call traffic.
n DCA relies on periodic uplink and/or down link measurements of multiple channels to find the one which causes least amount of interference.
n DCA maximizes the bandwidth utilization by effectively – maximizing the number of channel reuses and– minimizing the number of idle channels
n DCA algorithms may be centralized or distributed.
145
Implementation & OptimizationImplementation & OptimizationImplementation & Optimization
n Once all the coverage, capacity and interference objectives are met site acquisition and candidate site evaluation starts.
n For time and cost considerations, in some design projects client prefers to perform an extensive initial site acquisition and evaluations.
n System implementation and optimization requires both drive tests and simulations.
n At this phase iterations on coverage, capacity and interference analysis and frequency plan, similar to previous phase, is performed but now based on real and feasible sites.
146
Chapter 1: Review and DiscussionsChapter 1: Review and DiscussionsChapter 1: Review and Discussions
Introduction &Review of GSM ChannelizationNetwork Elements &RF Planning
147
GSM Signaling ProtocolsGSM Signaling ProtocolsGSM Signaling Protocols
MTP1
MTP2
MTP3
SCCP
Radio
LAP-Dm
CEPT0
LAP-D
MTP1
MTP2
MTP3
SCCP
MTP1
MTP2
MTP3
SCCP
MTP1
MTP2
MTP3
SCCP
MTP1
MTP3
MAP/C
BSSMAP
MTP3
MAP/EMAP/G
TUPISUP
MAP/D
MS BTS BSC Relay MSC/VLR
Anchor MSC/VLR
HLR/AuC
RSM
GMSCSMS Gateway
RIL3-RR
RIL3-MM
PSTN/ISDN
RIL3-CC
PhysicalData Link
Network
TransportSessionPresentation
Ap
pli
cati
on
CCMMRR
OSI Layers Um
InterfaceA-bis
InterfaceA
InterfaceB
InterfaceC,D
Interface
148
Functional PlanesFunctional PlanesFunctional Planes
n In the telecommunications domain. a powerful method to obtain a functional grouping is to use the Open System Interconnection model. Functions are grouped in functional planes, represented as stacked one upon the other.
n The lowest plane, devoted to the physical transmission of information between distant entities, relies on physical hardware media.
n whereas the highest one represents the view of external users. Each plane (or layer) provides services to the next layer up, these services being themselves enhancements of the services provided by the next layer below.
OAMCM
MM
RR
Transmission
OperatorUser
149
TransmissionTransmissionTransmission
n At the bottom lies the basis of any telecommunications system, i.e. the transmission plane. It provides transmission means for the communication needs of the users as well as for information transfer between the co-operating machines.
n Transmission layer includes both physical and link layer functionalities.
n Transmission is a domain for very short time scale events. from microseconds (e.g.. bit modulation) to seconds (for message transmission).
OAMCM
MM
RR
Transmission
OperatorUser
150
Transmission (cont.)Transmission (cont.)Transmission (cont.)
n Some of the GSM machines are concerned with transmission only. – An obvious example is the transcoder and rate adapter unit
(TRAU). which is only concerned in adapting speech or data representations.
– But most other transit exchange machines also play a more or less complex role in transmission. The mobile station obviously does so, and so does the BSC. the MSC and theinterworking function (IWF) which may all be along the transmission path between two users.
– Conversely. some of the machines have no relation to transmission except for the minimum needs concerning signaling with the other machines. These include the data bases (HLR. VLR. EIR and the OSS in general.
151
Radio Resource ManagementRadio Resource ManagementRadio Resource Management
n The next plane up is concerned with the management or transmission resources. The RR layer provides stable links between the mobile stations and the MSCs coping in particular with the movements of the users during the call (handovers).
n In telecommunications networks, these functions are usually grouped with the communication management functions, because fixed circuit management represents a small portion thereof. However, in the case of a cellular system such as GSM. the management of transmissionresources on the radio path is a complex issue and it warrants its own functional plane.
n From a temporal point of view this plane and the two next ones deal with events on the scale of the call; that is to say from seconds to minutes.
OAMCM
MM
RR
Transmission
Operator User
152
Mobility ManagementMobility ManagementMobility Management
n Next comes a small functional plane. which has not been grouped with communication management because of its strong GSM specificity.
n This Mobility Management layer or MM layer.is in charge of managing subscriber data bases and in particular the subscriber location data.
n An additional task of the MM layer is the management of confidentiality aspects such as authentication.
n The SIM, HLR and AuC are examples of machines mostly involved in MM activities.
n The MM layer adds to the transmission functions provided by the lower layers the means to track mobile users when not engaged communication. and the security related functions.
OAMCM
MM
RR
Transmission
Operator User
153
Communication ManagementCommunication ManagementCommunication Management
n Communication Management (CM)» The next plane is much less specific to GSM. It makes use of the
stable basis provided by the RR and MM layers to provide telecommunications services to the users.
» CM layer consists of several independent components, depending on the type of service.
» The NSS, mainly the MSC, has a strong involvement in the CM layer.
n The variety of the Communication Management functions makes it easier to describe as three sub-domains.
» Call Control (CC)» Supplementary Services Management (SS)» Short Message Services (SMS)
OAMCM
MM
RR
Transmission
Operator User
154
CM---CCCMCM------CCCC
n The MSC/VLRs, GMSCs, IWFs and HLRs through basic call management functions are able to manage most of the circuit oriented services provided to GSM users including speech and circuit data. This functional core represents a sub-part of the CM layer and is called Call Control (CC) in the specifications.
n An important aspect of communication management beside establishing, maintaining, and releasing calls is the routing function i.e. the choice of transmission segments linking distant users and their concatenation through switching entities.
n GSM mostly relies on external networks to perform this task, interfacing these networks through MSCs andGMSCs.
155
CM---SS MangementCMCM------SSSS MangementMangement
n Users in GSM have some control on the way their calls are handled by the network.
n This capability is described as supplementary services, each one of them corresponding to some specific variation of the way the basic service is rendered to the user.
n The entities involved in SS management are very few: the mobile station and HLR are the only entities involved
156
CM---SMSCMCM------SMSSMS
n The last aspect of the CM layer is related to the point-to-point short message services (SMS-PP).
n For the purpose of these services GSM is in contact with a Short Message Service Center (SM-SC).
n A service center may be connected to several GSM networks. In each of these one or several functional entities are in charge of interfacing the SM-SC. They are basically gateway functions.
157
OAMOAMOAM
n Operation, Administration and Maintenance (OAM)– The OAM plane includes the functions which enable
the operator to monitor and control the system. » In one direction, it mediates the observation flow from
machines to the operator. » In the other direction, it enables the operator to modify the
configuration of machines and functions ..\s a functional plane, it hovers over all the others. whilst not using the services provided by the other planes except the basic transmission functions for the exchanges between the concerned machines.
OAMCM
MM
RR
Transmission
Operator User
158
Who is involved in OAM PlaneWho is involved in OAM PlaneWho is involved in OAM Plane
n The kinship between the OAM plane and the OSS is obvious. The OSS is an integral part (if the OAM plane. but all the machines in the BSS and the NSS also contribute to the Operation and Maintenance functions.
n There are a variety of small tasks incumbent on these machines: they are often those of the smallest time scale and scope.
n For instance :– the raw information which forms the basis for the observation of
the system behavior is clearly issued inside the traffic handling machines themselves. The data are then transferred to OSS machines.
159
Signaling typesSignaling typesSignaling types
In-Band
Out-of-Band: Associated
Out-of-Band: Disassociated
Out-of-Band: Quasi-Associated
Voice Channels
Signaling Channel
(Trunk Group)
Quasi-Associated
STP
Associated
Associated
160
Network Signaling TypesNetwork Signaling TypesNetwork Signaling Types
n In-Band– Network signaling and speech share the same physical channel
(e.g., trunk circuit).– Limited by long setup times and minimal data transfer (e.g.,
dialed digits, ANI, CIC).– End-to-end setup of voice circuit necessary before determining if
destination party is reachable.
n Out-of-Band: Associated– Network signaling and speech are on separate physical channels.– Signaling, between switching offices, follows the same path as
the voice channels.– Benefits include shorter setup times and the ability to transfer
more data, quickly.– Not necessary to setup voice facilities, only to findout that end
party is unreachable
161
Network Signaling Types (cont.)Network Signaling Types (cont.)Network Signaling Types (cont.)
n Out-of-Band: Quasi-associated– Network signaling and speech are on separate physical
channels.– Signaling may, but does not have to, follow the same path as
the voice channels it supports.– Unlike non-associated, the path taken by quasi-associated
messages is fixed.
n Out-of-Band: Disassociated– Network signaling and speech are on separate physical
channels.– Signaling and voice channels are on two, completely separate
networks.– All the Out-of-Band benefits, plus additional benefits with an
independent data network.
162
Chapter 2Chapter 2Chapter 2
n Overview of protocols and interfaces– Functional Planes– Basic Signaling Concepts and OSI (review)
n GSM Interfaces and Protocols– LAP-D and LAP-Dm– X.25 Signaling– SS7 Signaling Network
n MAPn Recap of GSM Protocols and Interfacesn GSM Call Flows and Short Message Subsystemn Summary and Discussions
163
OSI LayersOSI LayersOSI Layers
1 -
2 -
3 -
Physical
Network
Link
Physical
Network
Link
Transport
Presentation
Session
Application
4 -
5 -
6 -
7 -
Physical
Network
Link
Transport
Presentation
Session
Application
End UserEnd User Packet Switch
Open Systems Interconnection (OSI) Reference Model for Data CommunicationsCreated in the late 1970’s by the International Standards Organization (ISO)
End to End Layers
ChainedLayers
164
Headers and LayersHeaders and LayersHeaders and Layers
DataData
Prot
ocol
Con
trol
inf
orm
atio
n(PC
I)
Physical
Network
Link
Transport
Presentation
Session
Application
Physical
Network
Link
Transport
Presentation
Session
Application
165
Layer 1 & 2Layer 1 & 2Layer 1 & 2
n Layer 1 - Physical– Defines the mechanical and electrical aspects of the
transmission medium - evervthing needed to transfer bits between two adjacent devices.
n Layer 2 - Link– Specifies the protocol that will provide for error-free
transmission of messages between adjacent nodes. It is a point-to-point protocol
– Takes the Layer 3 user info and encases it with a header and/or trailer before sending it to the Layer 1 protocol (and vice-versa).
166
Layer 3Layer 3Layer 3
n Layer 3 - Network– Specifies the protocol that will (1) address
messages and (2) route them from end-to-end across any number of subnetworks.
– Takes the Layer 4 user info and appends its own Protocol Control Information (PCI) before sending it to Layer 2 (and vice-versa).
167
Layer 4Layer 4Layer 4
n Layer 4 - Transport– Specifies the protocol that will provide end-
to-end control of the communications. Provides end-to-end error recovery and flow control.
– The size and complexity' of the layer 4protocol depends on the reliability of layer 3protocol to sequentially deliver messages error-free.
168
Layers 5, 6 & 7Layers 5, 6 & 7Layers 5, 6 & 7
n Layer 5 - Session– Specifies the protocol that will provide process-to-
process control of the communications.– Establishes, manages. and terminates connections
(sessions) between applications.
n Layer 6: Presentation– Performs a transformation on data so that a
standardized application interface (video screen. Printer. etc.) can be provided.
n Layer 7 - Application– Provides services to the network users.
169
Chapter 2Chapter 2Chapter 2
n Overview of protocols and interfaces– Functional Planes– Basic Signaling Concepts and OSI (review)
n GSM Interfaces and Protocols– LAP-D and LAP-Dm– X.25 Signaling– SS7 Signaling Network
n MAPn GSM Call Flows and Short Message Subsystemn Recap of GSM Protocols and Interfacesn Summary and Discussions
170
GSM Signaling ProtocolsGSM Signaling ProtocolsGSM Signaling Protocols
MTP1
MTP2
MTP3
SCCP
Radio
LAP-Dm
CEPT0
LAP-D
MTP1
MTP2
MTP3
SCCP
MTP1
MTP2
MTP3
SCCP
MTP1
MTP2
MTP3
SCCP
MTP1
MTP3
MAP/C
BSSMAP
MTP3
MAP/EMAP/G
TUPISUP
MAP/D
MS BTS BSC Relay MSC/VLR
Anchor MSC/VLR
HLR/AuC
RSM
GMSCSMS Gateway
RIL3-RR
RIL3-MM
PSTN/ISDN
RIL3-CC
PhysicalData Link
Network
TransportSessionPresentation
Ap
pli
cati
on
CCMMRR
OSI Layers Um
InterfaceA-bis
InterfaceA
InterfaceB
InterfaceC,D
Interface
171
LAPD (Link Access Protocol D)LAPD (Link Access Protocol D)LAPD (Link Access Protocol D)
n Is the interface protocol between the BTS and BSC Abislink layer
n Is a link layer protocol for a point-to-multi-point connection
n Is the ISDN link layer protocol defined by Q.921 standard.n Each frame contain an address identifying the source and
destinationn Is the HDLC based protocol and has the same frame
structure as HDLCn Provides the same benefits as HDLC based protocols
(ensures error free transmission)n Provides reliability, efficiency and hierarchical
independence.
172
LAPD Frame FormatLAPD Frame FormatLAPD Frame Format
n Flag: The bit sequence 01111110 constitute a frame boundary. n Adjacent frames can be separated by single flags.n Address: contains the Service Access Point identifier(SAPI) rangen from 0-63 and Terminal Endpoint Identifier(TEI) range from 0-127.n Control: Indicates the frame types and frame sequence.n Information: Data(only present in I and FRMR frames)n FCS: The frame check sequence detects corruption due to random n or burst line errors. FCS insertion and control is performed n traditionally by the hardware. The FCS is a polynomial of the form
FLAG ADDRESS CONTROL INFORMATION FCS FLAG
8 bits 8 bits 8 bits 8 bitsN bits (260 bytes) 16 bits
173
LAPDm Frame FormatLAPDmLAPDm Frame FormatFrame Format
n It is the protocol that used by the Um interface between the MS and BTS.
n It is similar to LAPD protocol but with different frame format.
n LAPDm frame format
ADDRESS CONTROL INFORMATION
8 bits 8 bits 21 to 23 bytes
174
LAPD and LAPDm differencesLAPD andLAPD and LAPDmLAPDm differencesdifferences
n A few differences in each functional area are:– Segmentation and Re-assembly function
» LAPDm frame length are 21(TCH) to 23(SACCH) octet, it may be too short for a complete message
» LAPD frame size is 264 octets no need for segmentation
– Error detection and correction» No flags are between LAPDm frames. A length indicator
and a filler value (00101011 or 11111111) is included byLAPDm
» No CRC checksum in LAPDm (The radio insures error free transmission)
» Sequencing of Modulo 8 used by LAPDm, LAPD uses 128
175
LAPD/LAPDm Differences (cont.)LAPD/LAPD/LAPDmLAPDm Differences (cont.)Differences (cont.)
» Window size of 1 (send and wait) is used by LAPDm, LAPD uses variable window size of 1 - 8.
» The LAPDm link initialization can contain data (SABM, UA, piggy backed data) but LAPD does not allow piggy back on initialization frames.
» Multiplexing» LAPDm is address field only contains SAPI.» SAPI 0 for signaling and SAPI 3 for SMS on LAPDm» SAPI 62 operation and maintenance, SAPI 63 Layer 2
management
– Flow Control» RNR and REJ frames are not supported on LAPDm No
stop-go procedure
176
X.25X.25X.25
n ITU(formerly CCITT) Recommendation that defines the interface between the user (DTE) and the Network (DCE) for user data packets.– Based on the OSI layered protocol defined by ITU
(CCITT x series) and ISO.– Protocols are defined for physical(layer 1),
link(layer 2) and network(layer 3).– Provides error free link, flow control and routing
capability. Most reliable data transfer method.n Frames based on High level Data link Control(HDLC)n The GSM OMC interface to NSS elements uses X.25
protocol.
177
X.25X.25X.25
DTE DCE DTE
1 -
2 -
3 -
Physical
Network
Link
Physical
Network
Link
Physical
Network
Link
n The Layer 1 protocol deals with the electrical, mechanical, procedural, and functional interface between the subscriber (DTE), and the base station (DCE).
n The Layer 2 protocol defines the data link on the common air-interface between the sub-scriber and the base station.
n Layer :3 provides connection between the base station and the MSC, and is called the packet layer protocol. A packet assembler disassembler (PAD) is used at Layer :3 to connect networks using the X.25 interface with devices that are not equipped with a standard X.25 interface.
178
X.25 Link layer framesX.25 Link layer framesX.25 Link layer frames
n The message types are:Frame type Command/Response
» Information frame I frames C» Supervisory frames (S-frame)
• Receive Ready RR C/R• Receive Not Ready RNR C/R• Reject REJ C/R
» Unnumbered frames(U-frame)• Disconnect DISC C• Disc Mode DM R• Frame Reject FRMR R• Sync balance SABM C• Unnumbered Ack UA R
C = Command frameR = Response frame
179
Network/Packet layer Network/Packet layer Network/Packet layer
n Perform packet data switching, routing and recovery
n Supports permanent virtual circuits (PVC) and switched virtual circuits(SVC)
n Perform Flow control and call control (tear down and establishment).
n Assembly and disassembly of the packets.n Retransmission and error recoveryn Support of extended sequence number modulo
128 and modulo 8.
180
Chapter 2Chapter 2Chapter 2
n Overview of protocols and interfaces– Functional Planes– Basic Signaling Concepts and OSI (review)
n GSM Interfaces and Protocols– LAP-D and LAP-Dm– X.25 Signaling– SS7 Signaling Network
n MAPn Recap of GSM Protocols and Interfacesn GSM Call Flows and Short Message Subsystemn Summary and Discussions
181
What is SS7What is SS7What is SS7
n Signaling System No 7 is the ITU (formerly CCITT) standard that defines the communications protocol layers required to perform the call control signaling function.
n It is a synchronous protocol that performs the call control and transaction capabilities function for the GSM.
n It is designed based on the packet network technology.n It is designed to operate on a separate network than the
voice and user data network.n There are several versions of SS7 standards including
– CCITT International Telegraph and Telephone Consultative Committee, which operates under ITU
– ANSI, American National Standard Institute– BellCore
182
SS7 Network ElementsSS7 Network ElementsSS7 Network Elements
n Signaling Transfer Point (STP)– Is a stand-alone switch that relays SS7 messages from
one signaling link to another.– For reliability purposes STPs are installed in pairs
(mated).– Each STP can completely take over for its mate
without any performance degradation.
n Signaling Point (SP)– Is a switching system that interconnects input devices
(e.g. telephones, service terminals) with the SS7 Network.
– SP is able to originate call control messages only.
183
SS7 Network ElementsSS7 Network ElementsSS7 Network Elements
n Service Switching Point (SSP)– Is also a switching system that interconnects input
devices with the SS7 network. – SSP is able to originate database queries in addition
to call control messages.
n Service Control Point (SCP)– Is database that accepts queries and provides
responses over the SS7 network– For reliability purposes SCP’s are installed in pairs
(mated).– Example services: l-800, Line Information DataBase
(LIDB). Home Location Register (HLR).
184
SS7 NetworkSS7 NetworkSS7 Network
STP
STP
STP
STP
STP
STP
MSC
STP
STP
MSC
SP
PSTN
HLR
HLR
B BA
F
D
A
F
E
C
C
CC
A
185
n A-Link: Access Link– Connect SP / SSP / SCP to the home STP pair.
Deployed in a pair arrangement - at least one link to each STP. For Example The MSC and HLR interface to SS7 network use the A-link.
n B-Link: Bridge Link– Connect an STP pair to another STP pair, which is
in the same SS7 network.Deployed in a quad arrangement - four paths provided from each STP to the other STP pair.
n C-Link: Cross Link– Connect STP to its mate.
SS7 LinksSS7 LinksSS7 Links
186
SS7 LinksSS7 LinksSS7 Links
n D-Link: Diagonal Link– Connect an STP pair to another STP pair, which is NOT
in the same SS7 network. Deployed the same as B-Links.
n E-Link: Extended Link– Connect SP / SSP / SCP to a non-home STP or STP pair.
n F-Link: Fully Associated Links– Connect SP / SSP / SCP to another SP /SSP / SCP,
directly. For example the MSC to BSC interface use the F-link configuration.
187
Link ElementsLink ElementsLink Elements
SP/SSP
SLC00
SLC01
SLC02
SLC02
SLC00SLC01
Link
Link set
Combined Link Set
A Route Set Is an ordered list of combined linkset or link sets. In a given system each destination node or group of nodes is assigned a route set. The route set is accessed when determining which linkset should carry a message to a node.
188
SS7 and OSISS7 and OSISS7 and OSI
Physical
Link
Network
Transport
Application
OSI model SS7 Protocol Model
SessionPresentation
MTP Level 1
MTP Level 2
MTP Level 3
SCCP
ISUP
ISP
TCAP
OMAP ASE7
654
3
21
189
Network Service Part (NSP)Network Service Part (NSP)Network Service Part (NSP)
n The NSP provides ISDN nodes with a highly reliable and efficient means of exchanging signaling traffic using connectionless services.
n The SCCP in SS7 actually supports packet data network interconnections as well as connection-oriented networking to virtual circuit networks.
n The NSP allows network nodes to communicate throughout the world without concern for the application or context of the signaling traffic.
MTP Level 1
MTP Level 2
MTP Level 3
SCCP
ISUP
ISP
TCAP
OMAP ASE
190
Message Transfer PartMessage Transfer PartMessage Transfer Part
n The function of the MTP is to ensure that signaling traffic can be transferred and delivered reliably between the end-users and the network.
n MTP is provided at three levels with various functionalities.
Common TransferFunction
UserMessage
Processing
Common TransferFunction
UserMessage
Processing
Link Control
Functions
SignalingData Link
Link Control Function
Signaling Link
Message Transfer Part
191
MTP Level 1MTP Level 1MTP Level 1
n Signaling data link functions (MTP Level 1) provide an interface to the actual physical channel over which communication takes place.
n CCITT recommends that MTP Level 1 use 64 kbps transmissions, whereas ANSI recommends 56 kbps. The minimum data rate provided for telephony control operations is 4.8 kbps.
Common TransferFunction
UserMessage
Processing
Common TransferFunction
UserMessage
Processing
Link Control
Functions
SignalingData Link
Link Control Function
Signaling Link
Message Transfer Part
192
MTP Level 2MTP Level 2MTP Level 2
n Signaling link functions (MTP Level 2) correspond to the second layer in the OSI reference model and provide a reliable link for the transfer of traffic between two directly connected signaling points.
n MTP Level2 also provides flow control data between two signaling points as a means of sensing link failure.
Common TransferFunction
UserMessage
Processing
Common TransferFunction
UserMessage
Processing
Link Control
Functions
SignalingData Link
Link Control Function
Signaling Link
Message Transfer Part
193
MTP Level 3MTP Level 3MTP Level 3
n Signaling network functions (MTP Level 3) provide procedures that transfer messages between signaling nodes.
n As in ISDN, there are two types of MTP Level 3 functions: signaling message handling and signaling network management.
Common TransferFunction
UserMessage
Processing
Common TransferFunction
UserMessage
Processing
Link Control
Functions
SignalingData Link
Link Control Function
Signaling Link
Message Transfer Part
194
SCCPSCCPSCCP
n Signaling Connection Control Part (SCCP) is a layer on top of MTP layer 3.
n It provides enhancement to the addressing capabilities provided by the MTP.
n While the addressing capabilities of MTP are limited in nature, SCCP uses local addressing based on subsystem numbers (SSNs) to identify users at a signaling node.
n SCCP also provides the ability to address global title messages, such as
800 numbers or non billed numbers.
MTP Level 1
MTP Level 2
MTP Level 3
SCCP
ISUP
ISP
TCAP
OMAP ASE
195
SCCPSCCPSCCP
n SCCP is mainly used by the GSM A interface and provides global title translation function for the NSS.– Connection oriented
» The messages are not directly related to a single mobile» Reset or overload indications
– Connection less oriented» Separate independent connection for each MS» To distinguish transaction for each MS» The connections are established on the needed bases by the
BSC or MSC and release when the transactions complete.
196
SS7 User PartSS7 User PartSS7 User Part
n The SS7 User Part provides call control and management functions and call set-up capabilities to the network.
n These are the higher layers in the SS7 reference model, and utilize the transport facilities provided by the MTP and the SCCP. – The SS7 user part includes – ISDN User Part(ISUP). – Transaction Capabilities Application Part (TCAP) – Operations Maintenance and Administration Part
(OMAP).
197
ISDN User Part (ISUP)ISDN User Part (ISUP)ISDN User Part (ISUP)
n The Integrated Services Digital Network User Part (ISUP) provides the signaling functions for carrier and supplementary services for voice, data, and video in an ISDN environment.
n In the past, telephony requirements were lumped in the TUP, but this is now a subset of ISUP.
n ISUP uses the MTP for transfer of messages between different exchanges.
n concerned with remote operations. TCAP messages are used by IS-41.
198
SS7 ISUPSS7 ISUPSS7 ISUP
ResponsibilitiesControl circuit-switched connections between line exchanges.
Provide Basic Bearer & Supplementary Services
Basic Bearer ServicesCall Setup
Connection
Call Release
Supplementary ServicesRedirection of Calls
Malicious Caller Identification
Calling Line ID Identification
Called Line Identification
Closed User Groups
Completion of Calls to Busy Subscriber
MTP Level 1
MTP Level 2
MTP Level 3
SCCP
ISUP
ISP
TCAP
OMAP ASE
199
TCAPTCAPTCAP
n The Transaction Capabilities Application Part (TCAP) in SS7 refers to the application layer which invokes the services of the SCCP and the MTP in a hierarchical format.
n One application at a node is thus able to execute an application at another node and use these results.
n Thus, TCAP is concerned with remote operations.
MTP Level 1
MTP Level 2
MTP Level 3
SCCP
ISUP
ISP
TCAP
OMAP ASE
200
TCAP (cont.)TCAP (cont.)TCAP (cont.)
n Transaction Capabilities Application Part envelopes the mobility messages
n Provides the means to distinguish independent message flows– The transaction sub-layer ties the
messages in a dialogue and performs transaction management (begin, continue, end ..)
– And the component sub-layer handles the command /response of a dialogue. (Invoke, return result, reject)
201
TCAP in MAP and IS41TCAP in MAP and IS41TCAP in MAP and IS41
n Two types of Mobile application signaling takes advantage of TCAP– Mobile Application Part MAP, GSM DCS1800 and
DCS900. MAP defines the interfaces between different component in the GSM, (MSC <-> HLR, MSC<->MSC)
– IS41 Interim Standard 41 the TIA (U.S standard) and recently introduce as the ITU-R standard. This standard defines the interfaces between different component (MSC<->HLR, MSC<->MSC etc.)
202
OMAPOMAPOMAP
n Operation Maintenance and Administration Part (OMAP) functions include monitoring, coordination, and control functions to ensure that trouble free communications are possible.
n OMAP supports diagnostics are known throughout the global network to determine loading and specific subnetwork behaviors.
203
Mobile SS7 network elementsMobile SS7 network elementsMobile SS7 network elements
n The MSC is connected to both STP via A quad links. Each link (logical) run at 40% utilization.
n STPs are connected via the C link and A quad links to PSTN to avoid a single point of failure within a network.
n The SCP/HLR is also connected via A quad links to STPs.
n The PSTN to MSC is connected via the F link. ISUP application is used on these types of links.
204
Chapter 2Chapter 2Chapter 2
n Overview of protocols and interfaces– Functional Planes– Basic Signaling Concepts and OSI (review)
n GSM Interfaces and Protocols– LAP-D and LAP-Dm– X.25 Signaling– SS7 Signaling Network
n MAPn Recap of GSM Protocols and Interfacesn GSM Call Flows and Short Message Subsystemn Summary and Discussions
205
Mobile Application PartMobile Application PartMobile Application Part
n All non-call-associated signaling in GSM is grouped under MAP.
n Non-call-associated signaling implies all signaling dealing with – mobility management, – security, – activation/deactivation of supplementary services, and
so on.
n All protocols use SS7 lower three layers (i.e., MTP 1,2,3, SCCP layer, and TCAP layer). These protocols are used primarily for database queries and responses.
206
MAP Protocol ConnectionsMAP Protocol ConnectionsMAP Protocol Connections
BSS EIR
HLR
SMSGateway
GMSC
MSC
VLR
MAP/B
MSC
VLR
MAP/B
MAP/I
MAP/D
MAP/CMAP/CMAP/E
MAP/G
MAP/F
MAP/H
BSSMAP
RIL3
207
MAP-BMAPMAP--BB
n MAP-B is the interface between the MSC and its associated VLR. – Whenever the MSC needs data related to a given mobile
station currently located in its area, it interrogates the VLR. – When a subscriber activates a specific supplementary service
or modifies some data attached to a service, the MSC informs (via the VLR) the HLR that stores these modifications and updates the VLR if required.
– This interface between the MSC and the VLR is very heavily used, and hence the decision by several manufacturers to integrate the VLR functionality with the MSC.
208
MAP-CMAPMAP--CC
n MAP-C is the interface between the MSC and the HLR. – The gateway MSC queries the corresponding subscriber
HLR to determine the routing information for a call or a short message directed toward the user. This messaging is handled by the MAP-C protocol. Additional SMS and charging messages also form part of this interface message set.
209
MAP-DMAPMAP--DD
n MAP-D is the interface between the HLR and the VLR. – It is used to exchange data related to the location of
the mobile station and for the management of the subscriber.
– The VLR informs the HLR of the location of a mobile station managed by the latter and provides it with the roaming information for that subscriber.
– Exchanges of data may occur when the mobile subscriber requires a particular service, when changes to the subscription have to be done, or when some parameters of the subscription are modified by administrative means.
210
MAP-E & MAP-FMAPMAP--E & MAPE & MAP--FF
n MAP-E– This interface supports the necessary signaling support for the
handover function. – When a short message is to be transferred between a mobile
station and short message service center, this interface is usedto transfer the message between the MSC serving the mobile station and the MSC acting as the interface to the message center.
n MAP-F – is the interface between the MSC and the equipment identity
register (EIR). – It is used to exchange data to enable the EIR to verify the
mobile subscriber equipment
211
IS-41ISIS--4141
n It is a US standard that defines the inter-system operation that was develop by TIA, which is becoming an ITU-R standard.
n First revision in 1983 IS-41 Rev 0 only addressed Intersystem HO.
n Future revisions A,B,C and D addresses the following issues:– Automatic Roaming and call delivery in addition to– To add new subscribers features to the standardized set– To add functionality to support new network requirements
(IN and digital networks) – To add clarification and remove errors
212
IS-41 C ModelISIS--41 C Model41 C Model
AUC HLR
VLR
MSC
EIR
MCSME
MSC
BS
SME
MS
B
CH
E
D
NMM
MCM
Q
A
F
Ai
Di
PSTN
ISDN
All interfaces in bold are IS41C
213
IS41 ArchitectureIS41 ArchitectureIS41 Architecture
n The signaling backbone is based on SS7 protocoln It uses the MTP layer 1,2 and 3 the SCCP
connectionless protocol and TCAP layern Provides mobile application part MAP
functionality (MM, CM and RR) but incompatible with GSM MAP.
n Supports the air interfaces of AMPS/NAMPS and CDMA IS-95/IS136(800, 1900MHZ)
n Supports the MSC/BS interface IS-634 and IS-653n Support SMS and Authentication functionality
214
IS-41 and GSM inter-working ?ISIS--41 and GSM inter41 and GSM inter--working ?working ?
n Inter-working means the Mobile Application Part successful communications
n It requires an inter-working function IWF, a device that coverts protocols as well as performing database mapping
n There are market drivers, I.e international roamers and national roamers that uses a GSM based network (PCS 1.9)
215
FYI: Addressing and RoutingFYI:FYI: Addressing and RoutingAddressing and Routing
n Within the GSM network two types of routing can be described– SS7 addressing and message signaling routing– Call Control /number routing
216
SS7 addressing/routingSS7 addressing/routingSS7 addressing/routing
n As previously discussed the SS7 MTP layer 3 provides the routing function.– This layer is used to route within a local network using the Signaling
Point Code (OPC and DPC) addressing. Considering the OPC and DPC is known to each element.
– The routing is performed using the mapping of the DPC to a physical location (port).
n To interconnect all the local networks or the national SS7 networks the SCCP Global Title Translation (GTT) functionality is used.
n This SCCP functionality allows a centralized network to hold and maintain all the addresses and routing tables, centralizing the routing function.
217
GTTGTTGTT
n Global Title Translation is one of the strong routing capabilities of SS7 SCCP layer.
n For an MSC to send a message to a particular HLR, the MSC does not need to know each Mobile’s HLR point code. Only the adjacent STP point code and the dialed digits (MSISDN) needs to be provided to the STP in order to route the message to the HLR.
n The STP will perform the translation of the Dialed digits to physical point code (HLR or MSC etc.)
218
Example of GTT RoutingExample of GTT RoutingExample of GTT Routing
MSC/VLR
STP
STP
HLR
HLR
SS7 Network
B-links
B-links
A-links
A-links
Local SS7 network
Gateway network
STP performs GTTIMSI or MSISDN to HLR point code
SS7 Message from MSC/VLRSCCP Called address = IMSI or MSISDNMTP DPC = STP alias point code
Alias point code
219
GTT (cont.)GTT (cont.)GTT (cont.)
n The STP pair after checking the SCCP header information will determine the message requires GTT translation. It will then extract from the calling number address field in the SCCP header the IMSI of the subscriber and from a database table determines the HLR point code where the validation/authentication should be sent.
n As can be seen this will eliminate book keeping on every MSC and centralizes the routing/translation on the SS7 STP network.
220
Call control and number routingCall control and number routingCall control and number routing
n Two basic number routings are:– Routing of Mobile Terminating Calls (MTC) – Routing of Mobile Origination Calls (MTO)
221
Routing of MTCRouting of MTCRouting of MTC
n A land line calling party dial the GSM mobile directory number (MS ISDN number) the PSTN after performing the digits translation routes the call to the home PLMN GMSC.
n The GMSC contains either the routing tables to relate the MSISDN number with the corresponding HLR, or if the GMSC is connected to the SS7 network with the GTT functionality, theSS7 network will identify the HLR.
GMSC
HLR
VMSC
MSI
SDN
MSRN I
MS
I
MS
RN
MSRN
PSTNISDN
222
Routing of MTCRouting of MTCRouting of MTC
n Once the GMSC interrogate the HLR with the MSISDN number, the HLR determines the IMSI from MSISDN number. Note the HLR stores the subscriber’s information based on IMSI not MSISDN.
n The HLR locates the visiting MSC/VLR point code and if an MSRN available it will return the information to GMSC. If the HLR does not have the MSRN for the subscriber it will request one from the visiting MSC/VLR. The latter can be done via GTT if an SS7 backbone with GTT (IMSI to point code) functionality is available/supported.
n The GMSC once it receives the MSRN and the MSC/VLR point code it will route the call to the VMSC/VLR.
n The MSC/VLR will then page the subscriber.
223
Routing of MOC Routing of MOC Routing of MOC
n The call originating information including the dialed digits will be send to the MSC/VLR.
n The MSC/VLR with the subscriber's profile information performs digits translation (if supported) and routes the call either to the PSTN or to other MSCs (if a MTM call within the network) .
n If the MSC can not perform the digits translation it would route the call to GMSC for translation and routing.
224
Chapter 2Chapter 2Chapter 2
n Overview of protocols and interfaces– Functional Planes– Basic Signaling Concepts and OSI (review)
n GSM Interfaces and Protocols– LAP-D and LAP-Dm– X.25 Signaling– SS7 Signaling Network
n MAPn Recap of GSM Protocols and Interfacesn GSM Call Flows and Short Message Subsystemn Summary and Discussions
225
Protocols and InterfacesProtocols and InterfacesProtocols and Interfaces
n The distinction between an interface and a protocol is important. An interface represents the point of contact between two adjacent entities, and as such it can bear information flows pertaining to several different pairs of entities. i.e. several protocols.
n Signaling messages pertaining to a given protocol may be visible on several interfaces along their path. if the corresponding peer entities are not adjacent. The protocol then appears on several interfaces.
BTS
BSCBSC
HLR
MSCVLR
SS
MM+CM
RR
Air Interface
Abis Interface
AInterface
226
GSM Network InterfacesGSM Network InterfacesGSM Network Interfaces
n GSM has created a set of standard interfaces which allows an open system architecture.
n An operator can mix and match different vendors' equipment as elements in the network. Previously, each vendor had a closed system and each element was proprietary and restricted to the vendors equipment.
n In GSM it is possible for an operator to choose the BSS (BSC and BTS) from one vendor, the MSC and VLR from another, and the HLR from still another.Interworking is simpler due to the standardized interfaces among all of these entities.
227
Air Interface (Um)Air Interface (Um)Air Interface (Um)
n The radio interface between the BTS and the mobile station is known as the air interface or Um (user interface-mobile).
n The radio interface uses RF signaling as the layer one and modification of integrated digital services network (ISDN) protocol as layers two and three.
n This interface has been very well documented in the GSM standards and all mobile station and BTS vendors adhere to it strictly.
n Each RF channel on the air interface is broken down into time slots wherein mobile subscribers can transmit information.
228
A-bis InterfaceAA--bisbis InterfaceInterface
n A-bis interface is the interface between the BTS and the BSC.
n All the connections from the BSC to the BTS utilize a modification of ISDN signaling for layer three and use ISDN signaling for layer two.
n The physical interface is an E1. Since speech is compressed in GSM, each 64-kbps channel on the El supports four TDMA time slots (i.e., four users). There is a separate signaling channel used for control of the BTS that is also transported via an El time slot.
229
A InterfaceA InterfaceA Interface
n The A interface uses SS7 for the lower three layers to transport modified ISDN call-control signaling.
n The information carried on this interface pertains to management of the BSS, call handling, and mobility management.
n The SCCP and MTP layers provide for data transport. SCCP is implemented in two classes-0 and 2. – Class 0 (connectionless) is for messages for the BSC, – while class 2 (connection oriented is for messages to a
particular mobile station or logical connection.
n BSSMAP controls base-station functions and manages the physical connection between the BSS and the MSC. It also controls allocation of radio channels and intra-BSShandover.
230
The A interfaceThe A interfaceThe A interface
n Two message sets are defined– DTAP (Direct Transfer Application Part)
» These are messages between MS and MSC.– BSSMAP (BSS Management Part)
» The messages between the BSC and MSC» The BSSMAP messages originates or end in BSC.
n The distribution of the messages are performed by a distribution function on top of SCCP.
n The distribution function will add a header on top of application message to indicate DTAP or BSSMAP.
231
PSTN InterfacesPSTN InterfacesPSTN Interfaces
n These are the interfaces between the MSC and the PSTN.
n All of these protocols are grouped under call-associated signaling. T
n hey are not specific to GSM and are commonly used in PSTNs for call setup.
n The GSM architecture is based on ISDN access and as such the MSC is based on an ISDN switch.
n To take full advantage of all the ISDN services the MSC should be connected to the PSTN via CCS7-based protocols such as ISUP.
232
GSM ProtocolsGSM ProtocolsGSM Protocols
n Using the OSI model, the GSM system can be described by considering several functional layers arranged in hierarchical form. These consist of the physical layer, data link layer, and the so-called “Layer 3”
n Layer 3 functions are designated as the application layer and should not be confused with the standard layer 3 functions of the OSI model.
233
Layer 1: Physical LayerLayer 1: Physical LayerLayer 1: Physical Layer
n The lowest layer of the radio interface, layer 1, provides functions necessary to transfer bit streams on the physical radio links. – Digital signal processing techniques are used to
perform equalization functions that recover transmitted bit patterns from signals distorted by the radio environment and channel coding functions (due to band limiting) that multiplex signaling and data channels onto the radio path, providing a level of immunity to errors.
– Speech coding functions also use complex digital signaling techniques to compress speech information into a manageable data rate and vice versa.
234
Layer 2Layer 2Layer 2
n Layer 2 provides a reliable dedicated signaling link connection between the MS and the BS. – The layer 2 protocol is based on the ISDN link
access procedure (LAP-D) but adopted to take account of the limitations using a radio path. On the other hand, standard LAP-D protocol is used internally within BSS (between BTS and BSC).
– The Message Transfer Part (MTP) of SS7 is used on the BSC-to-MSC interface to provide a reliable data link service.
– The same protocol (MTP1) is kept between MSCs, between MSC to HLR/AUC, AUC to GMSC, as well as between GMSC and PSTN.
235
Layer 3Layer 3Layer 3
n The application layer is composed of three sublayers: RR, MM, and CM.
n The RR, together with the data link layer and the physical layer, provide the means for point-to-point radio connections on which MM and CM messages are carried.
n The overall objectives of layer 3 are to provide the means for the following.– The establishment, operation, and release of a dedicated radio
channel connection (RR);– Location update, authentication, and TMSI reallocation (MM);– The establishment, maintenance, and termination of a circuit-
switched call(CCM); SS support; SMS support
236
RR ProtocolsRR ProtocolsRR Protocols
n The RR protocol entity provides control functions for the operation of common and dedicated channels. – The RIL3 RR protocols establishes and releases radio
connections between the MS and various BSCs for the duration of a call and, despite user movements, provides system information broadcasting, inter- and intracellchange of channels, and ciphering mode setting, for example.
– The Radio Subsystem Management (RSM) protocol provides RR functions between the BTS and BSC.
» The Direct Transfer Application Part (DTAP) protocols provide RR messages between the MS and MSC.
» The BSS Management Application Part (BSSMAP) protocols provide RR messages between the BSC and MSC. The distinction between DTAP and BSSMAP is provided by a small “Distribution" protocol below them.
237
MM ProtocolsMM ProtocolsMM Protocols
n Mobility management, which best defines the dialog between MS and the network, deals with the management of MS location and the security functions authentication and ciphering key management) necessary for mobile application.
n In addition to these functions, the MM sublayer also provides connection management services to the CC layer.
n The higher layer that sits over MM is called the CM. The CM protocol controls the end-to-end call establishment (both mobile originating and terminating) and, in general, all functions related to call management.
238
Other ProtocolsOther ProtocolsOther Protocols
n In addition to the aforementioned protocols, there are other protocols such as
n MTP3 and SCCP that are used above the data link layer between BSCs and MSCs and also between MSCs and different databases.
n TCAP protocol, which sits above SCCP, supports various transactions between two nodes of the network. TCAP manages the transaction on an end-to-end basis.
n MAP protocol is used between MSC, VLR, HLR, and AUC in the form of query and response messages. These protocols are designated as MAP/B through MAP/H.
239
Chapter 2Chapter 2Chapter 2
n Overview of protocols and interfaces– Functional Planes– Basic Signaling Concepts and OSI (review)
n GSM Interfaces and Protocols– LAP-D and LAP-Dm– X.25 Signaling– SS7 Signaling Network
n MAPn Recap of GSM Protocols and Interfacesn GSM Call Flows and Short Message Subsystemn Summary and Discussions
240
Call Flow DiscussionsCall Flow DiscussionsCall Flow Discussions
n Mobile to Land Calln land to Mobile Calln Mobile Initiated Call Clearingn Inter BSS Handovern Location Updaten Authentication and Cipheringn EIR Identificationn IMSI Attach/Detach
241
MSC VLR HLR EIR
Channel Request <RACH>
<SDCCH>
<AGCH>
<SDCCH>
(Call Info)
CR
CC
DCCH Assign
Signaling LinkEstablished
Request For Service
Authentication
Set Cipher Mode
Set Up
1
4
3
2
MS BSS
Equipment ID Request5
Mobile to Land SequenceMobile to Land SequenceMobile to Land Sequence
PSTN
242
MSC VLR HLR EIR PSTN
Channel Request <RACH>
<SDCCH>
<AGCH>
<SDCCH>
(Call Info)
CR
CC
DCCH Assign
Signaling LinkEstablished
Request For Service
Authentication
Set Cipher Mode
Set Up
1
4
3
2
MS BSS
Equipment ID Request5
Mobile to Land SequenceMobile to Land SequenceMobile to Land Sequence
243
MS BSS MSC EIR PSTN
MS Hears RingtoneFrom Land Phone
RingtoneStops
(Call Data,
TMSI)<SDCCH>
<SDCCH>
(Channel)
<SDCCH>
<FACCH>
<FACCH>
<FACCH>
<TCH>
(Circuit)
Complete Call
Call Processing
Assignment Command
Assignment Complete
IFAM
ACM
Alerting
Answer (ANS)
Connect
Connect Acknowledge BILLING STARTS “Hello ..10
9
8
7
6VLR HLR
Mobile to Land SequenceMobile to Land SequenceMobile to Land Sequence
244
MS BSS MSC EIR PSTN
MS Hears RingtoneFrom Land Phone
RingtoneStops
(Call Data,
TMSI)<SDCCH>
<SDCCH>
(Channel)
<SDCCH>
<FACCH>
<FACCH>
<FACCH><TCH>
(Circuit)
Complete Call
Call Processing
Assignment Command
Assignment Complete
IFAM
ACM
Alerting
Answer (ANS)
Connect
Connect Acknowledge BILLING STARTS “Hello ..10
9
8
7
6VLR HLR
Mobile to Land SequenceMobile to Land SequenceMobile to Land Sequence
245
Land to Mobile SequenceLand to Mobile SequenceLand to Mobile Sequence
MS BSS MSC VLR HLR GMSC PSTN
Routing Info. Ack
Send Info For I/C Call Setup
Signaling Link Established<SDCCH>
<PCH>
(MSISDN)
(MSISDN)(IMSI)
(MSRN)(MSRN)
(MSRN)
(MSRN)Information Request And ExchangeVLR-HLR *
<SDCCH>
(TMSI)
(TMSI &
Status) (Status)
<AGCH>
<RACH>
(TMSI) (TMSI)
(LAI&
TMSI)
1
6
54
32
IFAM
Send Routing Info
IFAM
Page
Paging Request
Channel Request
DCCH Assign
Page Response
246
Land to Mobile SequenceLand to Mobile SequenceLand to Mobile Sequence
MS BSS MSC VLR HLR GMSC PSTN
Routing Info. Ack
Send Info For I/C Call Setup
Signaling Link Established<SDCCH>
<PCH>
(MSISDN)
(MSISDN)(IMSI)
(MSRN)(MSRN)
(MSRN)
(MSRN)Information Request And ExchangeVLR-HLR *
<SDCCH>
(TMSI)
(TMSI &
Status) (Status)
<AGCH>
<RACH>
(TMSI) (TMSI)
(LAI&
TMSI)
1
6
54
32
IFAM
Send Routing Info
IFAM
Page
Paging Request
Channel Request
DCCH Assign
Page Response
247
MS BSS MSC VLR HLR GMSC PSTN
Complete Call
*Authentication
<FACCH>
<FACCH>
<TCH>
BILLING STARTS
Ring-tone at Land Phone
Ringing Stops At
Land Phone
<SDCCH>
(Call Info) (Call Info)
<SDCCH>
<TMSI>
<SDCCH>
(channel)
(circuit)
<FACCH>
<FACCH>
Setup
Call Information
Assignment Command
Assignment Complete
ACM
ConnectSubscriber Picks up
Connect Ack Answer (ANS)
10
98
7
Alert Ringtone at MS
Land to Mobile SequenceLand to Mobile SequenceLand to Mobile Sequence
248
MS BSS MSC VLR HLR GMSC PSTN
Complete Call
*Authentication
<FACCH>
<FACCH>
<TCH>
BILLING STARTS
Ring-tone at Land Phone
Ringing Stops At
Land Phone
<SDCCH>(Call Info) (Call Info)
<SDCCH>
<TMSI>
<SDCCH>(channel)
(circuit)
<FACCH>
<FACCH>
Setup
Call Information
Assignment Command
Assignment Complete
ACM
ConnectSubscriber Picks up
Connect Ack Answer (ANS)
10
98
7
Alert Ringtone at MS
Land to Mobile SequenceLand to Mobile SequenceLand to Mobile Sequence
249
Mobile Release Complete
PSTN Release Complete
Disc
PSTN Release
Mobile Release
UA
RLSD
Release Complete
MS BSS MSC VLR HLR PSTN<FACCH>
<FACCH>
<FACCH>
1
5
4
3
2
Channel Release
Clear Complete
Clear Command
Disconnect
<FACCH>
<FACCH>
<FACCH>
Mobile Initiated Call ClearingMobile Initiated Call ClearingMobile Initiated Call Clearing
250
Mobile Release Complete
PSTN Release Complete
Disc
PSTN Release
Mobile Release
UA
RLSD
Release Complete
MS BSS MSC VLR HLR PSTN<FACCH>
<FACCH>
<FACCH>
1
5
4
3
2
Channel Release
Clear Complete
Clear Command
Disconnect
<FACCH>
<FACCH>
<FACCH>
Mobile Initiated Call ClearingMobile Initiated Call ClearingMobile Initiated Call Clearing
251
Periodic Measurement Reports
Handover Command
Information Interchange
Periodic Measurement Reports
MS BSS BSS MSC HLR PSTN
<FACCH>
<SACCH>
<FACCH>
(TMSI cct. code) nBSS Assigns Air-Interface Traffic Channel(HO Ref. No.)
(HO Ref. No.) nBSS establishes level 2 signaling link on dedicated control channel and sends Timing Advance Cell ID Info. Etc.
<SACCH>
1
654
32
9
87 Handover Complete
Clear Command
Handover Req. Ack
Handover Request
Hanover Required
Inter - BSS Handover SequenceInter Inter -- BSS Handover SequenceBSS Handover Sequence
252
Periodic Measurement Reports
Handover Command
Information Interchange
Periodic Measurement Reports
MS BSS BSS MSC HLR PSTN
<FACCH>
<SACCH>
<FACCH>
(TMSI cct. code) nBSS Assigns Air-Interface Traffic Channel(HO Ref. No.)
(HO Ref. No.) nBSS establishes level 2 signaling link on dedicated control channel and sends Timing Advance Cell ID Info. Etc.
<SACCH>
1
654
32
9
87 Handover Complete
Clear Command
Handover Req. Ack
Handover Request
Hanover Required
Inter - BSS Handover SequenceInter Inter -- BSS Handover SequenceBSS Handover Sequence
253
Location Update Request
TMSI Reallocate Complete
TMSI Ack
(TMSI)
1
6
5
4
3
2
<RACH>
<AGCH>
<SDCCH>
MS BSS MSC VLR HLR PSTN
(LAI & TMSI)
<SDCCH>
(TMSI)
<SDCCH>
<SDCCH>
<SDCCH>
Only sent to HLR If this is the first time the
MS has Location Updated in this VLR.
DCCH Assign
Channel Request
Authentication
Ciphering
Forward New TMSI
Location Update Accept
Clear Command
Clear Complete
Location Update SequenceLocation Update SequenceLocation Update Sequence
254
MS BSS MSC VLR HLR PSTN EIRPre-Send Triples
to VLR
Authentication
Start Ciphering
Authentication Request
Authentication Response
Cipher Mode Command
Cipher Mode Complete
<SDCCH>
(Rand)
(Rand)
<SDCCH>
<SDCCH>
<SDCCH>
1
5
4
3
2
(SRES)
Authentication and CipheringAuthentication and CipheringAuthentication and Ciphering
255
MS BSS MSC VLR HLR PSTN EIR
Equipment ID Request
ID Response
Note: IMEI check may be deferred until after traffic channel has been established.
Check IMEI
Check IMEI Response
<SDCCH>
<SDCCH>
(IMEI)
1
3
2
Equipment IdentificationEquipment IdentificationEquipment Identification
256
IMSI Attach/DetachIMSI Attach/DetachIMSI Attach/Detach
n When a mobile station is switched off (or when the SIM is removed by the user), the calls toward the corresponding subscriber can no longer be completed.
n Important resources are then consumed, and even not paid for, for nothing, whwnwver the mobile is paged.
n Upon a Mobile terminated call/SMS request, the establishment of the first part of the circuit (before HLR interrogation) cannot be avoided.
n However, the second portion, between the point where HLR interrogation is done and the visited MSC, can be avoided using the IMSI Attach/Detachmechanism.
257
IMSI Attach Status IMSI Attach Status IMSI Attach Status
n The subscriber's record in the MSC/VLR contains a binary information called Attach Status indicating whether it is useful or not to try to complete a call toward this subscriber.
n The mobile station triggers an IMSI Detach when it goes inactive, and either a location updating procedure (if in a new' location area) or an IMSI Attach procedure when it comes back on (in the same location area).
258
IMSI Attach/DetachIMSI Attach/DetachIMSI Attach/Detach
n When a mobile station is switched off (or when the SIM is removed by the user), the calls toward the corresponding subscriber can no longer be completed.
n Important resources are then consumed, and even not paid for, for nothing, whwnwver the mobile is paged.
n Upon a Mobile terminated call/SMS request, the establishment of the first part of the circuit (before HLR interrogation) cannot be avoided.
n However, the second portion, between the point where HLR interrogation is done and the visited MSC, can be avoided using the IMSI Attach/Detachmechanism.
259
IMSI Attach Status IMSI Attach Status IMSI Attach Status
n The subscriber's record in the MSC/VLR contains a binary information called Attach Status indicating whether it is useful or not to try to complete a call toward this subscriber.
n The mobile station triggers an IMSI Detach when it goes inactive, and either a location updating procedure (if in a new' location area) or an IMSI Attach procedure when it comes back on (in the same location area).
260
Call Rejection by MSC/VLRCall Rejection by MSC/VLRCall Rejection by MSC/VLR
n The basic scenario of a mobile terminating call set-up attempt requires an interrogation of the visited MSC/VLR by the HLR before the latter provides the information necessary for the continuation of the routing.
n This phase allows the visited MSC/VLR to reject the call on the basis of the attach status before the costly set up of the traffic circuit. – If it does so, call forwarding if applied can potentially
be controlled by the HLR. – Another possibility is that the visited MSC/VLR
accepts the call, and applies the call forwarding itself if required.
261
IMSI DetachIMSI DetachIMSI Detach
n The IMSI Detach procedure consists of a single message, the RIL-3 MM IMSI Detach message, from the mobile station to the visited MSC/VLR.
n This message is not acknowledged, simply because it has been considered that the mobile station is typically switched off, or more generally not in a position to receive an answer from the network.
n The mobile station keeps no track of having asked for a detach (for instance by storage in the SIM): the state of the attach/detach information in the network is not monitored by the mobile station.
262
IMSI AttachIMSI AttachIMSI Attach
n The MS starts an IMSI Attach procedure, that is to say (except for a negligible detail) a location updating procedure.– if attach is indicated as supported in the cell the it has
chosen at switch-on (or SIM insertion) and– if the it knows the subscriber is already registered in
the same location area.
263
SimilaritiesSimilaritiesSimilarities
n Periodic location updating and the IMSI Attach procedure, over the air, are almost identical to location update procedures. Their main differences are mostly the events that trigger them..
n These IMSI Attach/Detach procedures are very close functionally to the call forwarding supplementary services in the case where the mobile station is not deregistered.
IMSI Attach/Detach
Call ForwardingLocation Update
264
Short Message Service (Rev.)Short Message Service (Rev.)Short Message Service (Rev.)
n Unlike circuit switch communication such as speech and video, short message services do not require the end-to-end establishment of a traffic path.
n A short message communication is limited to one message or in other words the transmission of one message is a communication all by itself.
n SMS service is asymmetric, so the Mobile Originating Short Message transmission is considered as a different service from the Mobile Terminating Short Message transmission.
265
Short Message Service CenterShort Message Service CenterShort Message Service Center
n The transmission of a message is always relayed by a Short Message Service Center (SM-SC), considered to be outside the GSM specifications.– Therefore, the transfer of a short message always takes
place between a mobile station and some SM-SC from the point of view of the GSM infrastructure.
– However, for the user, the message has also an ultimate destination or origin, identified by some field in the message, but relevant only for the user and the SM -SC not for the GSM infrastructure.
n The SM-SC – Sorts and store the messages– Delivery the messages to the MS– Provides Billing data– And user data administration
266
SM-GatewaySMSM--GatewayGateway
n The point-to-point short message services defined in GSM enable the transfer of short messages between the mobile station and a short message service center which is in contact with GSM networks through specific MSCs called SMS-GMSC (for Mobile Terminating Short Messages) or SMS-IWMSC (for Mobile Originating Short Messages), referred hereafter, both as SMS-gateway
267
SMS ArchitectureSMS ArchitectureSMS Architecture
SM-SC
HLR
MSC/VLR
SMS-GW
SM_TP
SM-RP SM-CP
MAP-D (location of MS)
MAP-H(forward messages)
MAP-C(routing)
268
SMS ProtocolsSMS ProtocolsSMS Protocols
The protocols involved in SMS management includen the mobile station to SM-SC protocol, called Short Message
Transport Protocol (SM-TP)), enables the transport of short messages, whether from or to the mobile station.
n the protocol between the SMS-gateway and HLR enables the SMS-gateway to interrogate the HLR in search of the address of the subscriber when reachable; it is part of the MAP/C protocol
n the protocol between MSC and HLR. as well as the protocol between HLR and SMS-gateway. enable the alerting of the SM-SC when a mobile station has missed a message while it was out of reach but has subsequently become reachable. This function must also be supported on the interface between the SMS-gateway and the SM-SC, but the protocols on this interface are not defined in the specifications.
269
SM-MO/PPSMSM--MO/PPMO/PP
n Allows the mobile to send short message to other mobile or otherdevices(devices that are located within the PSTN,PSDN, LAN, WAN) via the signaling channel. This allows the mobile to send amessage while in a call.
n The MS must send the content of the message along with the address of the receiver and the address of the SM_SC.
n The SM-TP protocol will be used to send the messages to the SM-SC and an acknowledgment is send back to the MS that the SM_SC has received the message.
n This service will impact the network planning, depending on number of subscribers using the service
270
SM-MT/PPSMSM--MT/PPMT/PP
n Allows the mobile subscriber to receive short message via the signaling channel from the SM-SC.
n The short message will be delivered from the SM-SC to the MSC via the SM-TP protocol indicating the ID of the sender and time stamp of the message received.
n In order for the message to reach its destination, the HLR of the subscriber must be interrogated .– is the MS subscribed for this service? – is there any call barring active etc.)by the SM-
GW(finding the HLR based on the MSISDN) .
271
SM-MT/PP (cont.)SMSM--MT/PP (cont.)MT/PP (cont.)
n Once the MSC/VLR of the subscriber has been identified and it is reachable the message is forwarded to the MSC. The MSC/VLR after successful determination of the location of the MS will attempt paging the MS in the location area.
n If the subscriber is not able to receive the short message (either SIM does not have enough memory or the paging of the subscriber is unsuccessful or etc.) the message will be kept in the SM-SC for later delivery, the HLR /VLR will take a note of this for when the subscriber is available again.
272
Chapter 2: Review and DiscussionsChapter 2: Review and DiscussionsChapter 2: Review and Discussions
Signaling NetworkProtocols and InterfacesCall Flows & SMS
273
Chapter 3:Chapter 3:Chapter 3:
n Review of Probability Theory– Review of Basic Probability Concepts– Useful Distributions– Basics of Statistical Methods
n Basic Traffic Model– Arrival Process,– Erlang and Blocking Definition– Queuing Strategy and Markov Chain Formulation– Erlang B, C and Poisson Models and Calculations
n Contention Based Multiple Access Protocols– P-ALOHA and S-ALOHA– CSMA and ISMA
n Subscriber Forecast and Demographic Analysisn Summary and Discussions
274
Review of Probability Theory Review of Probability Theory Review of Probability Theory
n Distribution Function– Probability Density Function– Probability Mass Function– Commutative Distribution Function
n Independencen Expected Value
– Mean– Variance
n Correlation
0 0 1 . 5
0 . 2 0 . 0 9 9 5 0 1 2
0 . 4 0 . 1 9 6 0 4
0 . 6 0 . 2 8 6 7 9 9
0 . 8 0 . 3 6 9 2 4 7
1 0 . 4 4 1 2 4 8
1 . 2 0 . 5 0 1 1 6 2
1 . 4 0 . 5 4 7 8 9 3
1 . 6 0 . 5 8 0 9 1 9
1 . 8 0 . 6 0 0 2 7 9
2 0 . 6 0 6 5 3 1
2 . 2 0 . 6 0 0 6 8 2
2 . 4 0 . 5 8 4 1 0 3
2 . 6 0 . 5 5 8 4 2 5
2 . 8 0 . 5 2 5 4 3 6
3 0 . 4 8 6 9 7 9
3 . 2 0 . 4 4 4 8 6
3 . 4 0 . 4 0 0 7 6 8
3 . 6 0 . 3 5 6 2 1 8
3 . 8 0 . 3 1 2 5 0 1
4 0 . 2 7 0 6 7 1
4 . 2 0 . 2 3 1 5 2 6
4 . 4 0 . 1 9 5 6 2 8
P o i s s o n D i s t r i b u t i o n
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
00.
61.
21.
82.
4 33.
64.
24.
85.
4 66.
67.
27.
88.
4 99.
6
N u m b e r o f U s e r s
Pro
ba
bil
ity
De
ns
ity
Fu
nc
tio
n
275
Quick QuestionQuick QuestionQuick Question
n Find the end-to-end service availability from point A to D, assuming the given set of availability of links and network elements.
n Answer:
αα γγ
ββ
ββA B
PA-B = α.[1α.[1−−(1(1−−β)β)22].γ].γ
276
Exponential DistributionExponential DistributionExponential Distribution
n Let τ τ be a random variable, denoting the duration of a certain event, e.g. call duration.
n ΤΤ has a Exponential distribution if
Where λλ is some positive constant n The mean time duration time is
n The variance of time duration is
22 1
1)T(E
otherwise0
0ife)(f
λ=σ
λ=
≥τλ
=τ
Τ
λτ−
Τ
277
Properties of Exponential DistributionProperties of ExponentialProperties of Exponential DistributionDistribution
n An exponential random process is Memoryless
n The minimum of a group of N exponential random variables with parameters µµi is an exponential random variable with parameter
∑=
µ=µN
1ii
Pr( | ) Pr( )X a b X a X a bn n n>> ++ == == >> ++−−1
278
Poisson DistributionPoisson DistributionPoisson Distribution
n Let N be a random variable, denoting the number of occurrences of a certain event, e.g. call arrivals, during a time interval of duration T.
n N has a Poisson distribution if
Where λλ is some positive constant n The mean number of events (arrivals) during time
interval of T is
The variance of the number of events (arrivals) during time interval of T is
T
T)N(E
e!n
)T()nN(P
2N
Tn
λ=σ
λ=
λ== λ−
σσ λλN T==
279
Why Poisson?Why Poisson?Why Poisson?
n A Poisson process is generally considered to be a good model for the aggregate traffic of a large number of similar and independent users.
n Theorem: Suppose that we merge n independent and identically distributed packet arrival processes. – Each process has arrival rate λλ/n, so that the aggregate process
has arrival rate λλ. – The interarrival times ττ between packets of the same process
have a given distribution F(s ) = P{ ττ < s} and are independent [ F(s ) need not be an exponential distribution].
– Then under relatively mild conditions on F, e.g. F(0)=0 anddF(0)/ds > 0, the aggregate arrival process can be approximated well by a Poisson process with rate λλ when n is large.
280
Properties of Poisson ArrivalsProperties of Poisson ArrivalsProperties of Poisson Arrivals
n The number of arrivals n in any time interval of duration T is given by a Poisson distribution
Where λλ is some positive constant n The number of arrivals in disjoint time intervals are
independent.
Tn
e!n
)T()nN(P λ−λ==
281
Properties of Poisson ArrivalsProperties of Poisson ArrivalsProperties of Poisson Arrivals
n The inter-arrival time or the time between successive arrivals τ τ is an exponentially distributed random variable with parameter λλ .
n Inter-arrival times are independent random variables.
nn Question: What is theQuestion: What is the cdfcdf of this process.of this process.
≥τλ
=τλτ−
Τotherwise0
0ife)(f
282
Properties of Poisson ArrivalsProperties of Poisson ArrivalsProperties of Poisson Arrivals
Let X be a Poisson arrival process,n The probability of a new arrival within the next t unit
of time is essentially proportional to h with λλ being the constant of proportionality
so that for small t
Similarlyso that for small t
n So Pr( 2 or more arrivals during t) is O(t) or essentially zero.
n Arrivals during disjoint intervals are independent.
t
)t(ot)arrivalnew1Pr(
λ≈+λ=
t1
)t(ot1)arrivalNoPr(
λ−≈+λ−=
283
Poisson Arrivalwith Rate λ1
Poisson Arrivalwith Rate λ2
Which Distribution?What Rate?
Independent
Merging Poisson ArrivalsMerging Poisson ArrivalsMerging Poisson Arrivals
n Theorem & Proof !!
284
Splitting Poisson ArrivalsSplitting Poisson ArrivalsSplitting Poisson Arrivals
n If a Poisson process is split into two other processes by independently assigning each arrival to the first (second) of these processes with probability p (1 - p, respectively). The two arrival processes thus obtained are Poisson.
Poisson Arrivalwith Rate λ1
Poisson Arrivalwith Rate λ
Which Distributions?What Rate?
S
S2S1
285
Alternative ModelsAlternative ModelsAlternative Models
n Due to – Variations in of service statistics– User’s preferences and usage patterns– and emerging new services, e.g. circuit and packet switch data
The classical Poisson models may not be appropriate in certain applications and markets.
n Therefore new empirical or theoretical models have to be developed.
n These models need to be confirmed and tested against measure statistics.
286
Statistical MethodsStatistical MethodsStatistical Methods
n One of the objectives of statistical methods is to test the validity of a model.
n The first step is to obtain a random sample, e.g. of size n, for X.
n Generate the sample cdf of X, FS(x)n Consider the cdf of candidate distribution, FC(x) n Compute the maximum difference between the two
functions |)x(F)x(F|supD SCxn −=
287
K-S TestKK--S TestS Test
n Kolmogorov-Smirnov Test Says:– The hypothesis that a given sample comes
from a candidate distribution can be accepted or rejected with a confidence level based on the value of cdf of
– Y=sqrt(n) * Dn
22yi2
1i
1i
nn
e)1(21
)y(H)yDnPr(lim
−∞
=
−
∞→
∑ −−=
≡≤
288
ExampleExampleExample
n A random sample of call holding times have been measured. The sample size is 400.
n Sample cdf is generatedn An exponential distribution is considered as
candidate.– The maximum difference between the candidate and
sample cdf is computed to be 0.05.– Y=sqrt(400)*0.05=1.0– H(1)=0.73
n Thus the probability that the sample size indeed come from the candidate exponential distribution, or the confidence level, is 0.73.
289
Chapter 3:Chapter 3:Chapter 3:
n Review of Probability Theory– Review of Basic Probability Concepts– Useful Distributions– Basics of Statistical Methods
n Basic Traffic Model– Arrival Process,– Erlang and Blocking Definition– Queuing Strategy and Markov Chain Formulation– Erlang B, C and Poisson Models and Calculations
n Contention Based Multiple Access Protocols– P-ALOHA and S-ALOHA– CSMA and ISMA
n Subscriber Forecast and Demographic Analysisn Summary and Discussions
290
Traffic ModelTraffic ModelTraffic Model
n In traffic engineering problems typically the following assumptions are made– Call arrivals form a Poisson process with
average call arrival rate of λλ– The duration of each call (often called the
holding time) is an exponentially distributed random variable with parameter µµ, which is independent from other calls’ duration and the system load.
» This implies that the average call duration is ……..
291
Service Time StatisticsService Time StatisticsService Time Statistics
n Our assumption regarding the service process is that the Customer service times have an exponential distribution with parameter µµ ,
n The parameter µµ is called the service rate and represents the rate (in customers served per unit time) at which the server operates when busy.
n Furthermore. the service times sn are mutually independent and also independent of all interarrival times.
n An important fact regarding the exponential distribution is its memoryless character. – This means that the additional time needed to complete
a customer's service in progress is independent of when the service started.
– Similarly, the time up to the next arrival is independent of when the previous arrival occurred,
292
Traffic Model (cont.)Traffic Model (cont.)Traffic Model (cont.)
n The amount of traffic load is proportional to – average arrival rate λλ– average call holding time or call duration 1/µµ
n Therefore the product of call arrival rate and call duration is a dimensionless quantity A=λ/µλ/µdenoted as “Erlangs” measuring the offered load.
n For Example:– If the average call arrival rate is 10 calls per minute
and an average call last for 2 minutes, then the offered load is 10 x 2=20 A or 20 Erlangs.
293
Some Parameters of InterestSome Parameters of InterestSome Parameters of Interest
n We are typically interested in estimating quantities such as.– The average number of customers in the system (i.e. the
“typical" number of customers either waiting in queue or undergoing service)
– The average delay per customer (i.e. the “typical" time a customer spends waiting in queue plus the service time).
n These quantities will be estimated in terms of known information such as:– The customer arrival rate (i.e.. the “typical" number of
customers entering the system per unit time)– The customer service rate (i.e., the “typical” number of
customers the system serves per unit time when it is constantly busy)
294
Arrivals & Departures Arrivals & Departures Arrivals & Departures
αα(t)
ββ(t)
N(t)
time
Nu
mb
er o
f A
rriv
als
αα(t
)N
um
ber
of
Dep
artu
res
ββ(t)
295
Defining ParametersDefining ParametersDefining Parameters
N N where Nt
N d
wheret
t
T T where TT
t
t t t
t
tt t
t t t
ii
t
= =
= =
= =
→∞
→∞
→∞
=
∫
∑
lim ( )
lim( )
lim( )
( )
10
0
τ τ
λ λ λα
α
α
Steady State Number of Customers in the System
Steady State Arrival Rate
Steady State Time Average Customer Delay
n N(t)=Number of customers in the system at time tn αα(t)= Number of customers arrived in the interval [0 , t]n Ti = Time spent in the system by the ith arriving customer
296
Little’s Theorem Little’sLittle’s Theorem Theorem
n Little's Theorem establishes the following relationN=λλT
between the basic quantities,– N = Average number of customers in the system – T = Average customer time in the system
n Application of the same idea to a queuing system results in
NQ=λλW – NQ = Average number of customers waiting in queue– W= Average customer waiting time in queue
n However, N, T, NQ, and W cannot be specified further unless we know something more about the statistics of the system.
λ
T
N=λλT
297
Application of Little’s TheoremApplication ofApplication of Little’sLittle’s TheoremTheorem
n Given system statistics, we will be able to derive the
steady-state probabilities
n ππi= Probability of i customers in the system, i = 0.1,….n From these probabilities, we can get
n and using Little's Theorem,
n Similar formulas exist for NQ and W.
N i
TN
ii
=
=
=
∞
∑ π
λ
0
298
0 0 1.5
0.2 0.099501 2
0.4 0.19604
0.6 0.286799
0.8 0.369247
1 0.441248
1.2 0.501162
1.4 0.547893
1.6 0.580919
1.8 0.600279
2 0.606531
2.2 0.600682
2.4 0.584103
2.6 0.558425
2.8 0.525436
3 0.486979
3.2 0.44486
3.4 0.400768
3.6 0.356218
3.8 0.312501
4 0.270671
4.2 0.231526
4.4 0.195628
Poisson Dist r ibut ion
0
0 .1
0 .2
0 .3
0 .4
0 .5
0 .6
0 .7
00.6 1.2 1.8 2.4 3
3.6 4.2 4.8 5.4 66.6 7.2 7.8 8.4 9
9.6
Number o f Users
Pro
ba
bil
ity
De
ns
ity
F
un
cti
on
Blocking ConceptsBlocking ConceptsBlocking Concepts
BlockingProbability
λ/µ
The number of active calls is a Poisson random
variable of mean λ/µ.
299
Classical M/D/m/n NotationClassical M/D/m/n NotationClassical M/D/m/n Notation
n the number of users in the system, including users in the queue.
n the number of servers.n the probability distribution of
the service times (e.g., M, G, and D stand for exponential, general, and deterministic distributions, respectively).
n the nature of the arrival process {e.g., M: for memoryless, G for general distribution, D for deterministic interarrival time.
M/D/m/nM/D/m/n
300
Chapter 3:Chapter 3:Chapter 3:
n Review of Probability Theory– Review of Basic Probability Concepts– Useful Distributions– Basics of Statistical Methods
n Basic Traffic Model– Arrival Process,– Erlang and Blocking Definition– Queuing Strategy and Markov Chain Formulation– Erlang B, C and Poisson Models and Calculations
n Contention Based Multiple Access Protocols– P-ALOHA and S-ALOHA– CSMA and ISMA
n Subscriber Forecast and Demographic Analysisn Summary and Discussions
301
Queuing StrategyQueuing StrategyQueuing Strategy
n We assume– All circuits or servers are the same– No special priority is considered– and if a circuit is available it will be allocated to a
requested call
n There are three common strategies for handling arriving requests:– Blocked Calls Cleared (Erlang B Model)– Blocked Calls Delays (Erlang C Model)– Block Calls Held (Poisson Model)
302
Markov Chain FormulationMarkov Chain FormulationMarkov Chain Formulation
n An important consequence of the memoryless property is that it allows the use of the theory of Markov chains.
n Indeed. this property, together with our earlier independence assumptions on interarrival and service times, imply that – once we know the number N(t) of customers in the system at
time t, the times at which customers will arrive or complete service in the future are independent of the arrival times of the customers presently in the system and of how much service the customer currently in service (if any) has already received.
– This means that the future numbers of customers depend on past numbers only through the present number: that is, {N(t) >0} is a continuous-time Markov chain,
303
System State TransitionSystem State TransitionSystem State Transition
i i+1
ππi,i+1
n Under these assumptions the state of the system forms a Markov Chain.
n In such a formulation, being in State i implies that there are i users in the system.
n The probability of transition from one state to another as result of a new call arrival or termination, depends on the queuing strategy of the system
n Flow Conservation Law is
ππi+1,i
P Pi i i i i i× = ×+ + +π π, ,1 1 1
ππi,i
ππi+1,i+1
304
Erlang B State TransitionErlangErlang B State TransitionB State Transition
0 1 2 3 N-1 N…...
λλ
µµ
λλ
2µ2µ
λλ
3µ3µ
λλ
4µ4µ
λλ
(Ν(Ν−−1)µ1)µ
λλ
ΝµΝµ
( )
λ µλ µλ µ
λ µ
λ µ λ µ
p p
p p
p p
p N p
p N p pN
p
N N
N NN N
N
0 1
1 2
2 3
1
0 0
2
3
1
===
=
= ⇒ =
−
!!
/
305
Erlang B, Blocking Probability ErlangErlang B, Blocking Probability B, Blocking Probability
n The fraction of time that all N servers are busy or the blocking probability is the probability that an arbitrary arrival find the system in the Nth state.
n This is a traditional M/M/N/N system in queuing theory.
∑=
=N
1i
i
N
B
!iA!N
A
)N,A(P
=π++π+π+π
π
µλ
=π
1...
!N
1
N321
0
N
N ( )pN
p
p p p p
N
N
N
=
+ + + + =
1
1
0
0 1 2
!/
...
λ µ
306
Offered vs. Carried vs. TrafficOffered vs. Carried vs. TrafficOffered vs. Carried vs. Traffic
n The offered load is split into– Carried Calls C(A,N), and – Blocked calls B(A,N) or overflow traffic
n Utilization can be defined as the ratio between carried load and the number of channels or circuits.
U(A,N)=C(A,N)/N
A = A * PB(A,N) + A * ( 1 - PB(A,N) )
Offered Traffic
CarriedTraffic
OverflowTraffic
307
PeakednessPeakednessPeakedness
n Peakedness of a random process is measured as ratio between its variance and average squared.
n Peakedness of random traffic is an important factor to be considered in design of trunking systems.
σσ
Variance σσ22
(Average)2 m2
m
Peakedness = =
308
PeakednessPeakednessPeakedness
n A Poisson arrival has a peakedness of ………n How about carried traffic or blocked (or
overflow) traffic?
1M
Z
1M
Z
2B
2B
B
2C
2C
C
>σ
=
<σ
=
Arrived Traffic
CarriedTraffic
OverflowTraffic
309
Utilization vs. NUtilization vs. NUtilization vs. N
n Using Erlang B Table:n Generate a curve for Utilization as a function of Number
of channels, assuming %1 blocking probability.
310
Utilization vs. BlockingUtilization vs. BlockingUtilization vs. Blocking
n Using Erlang B Table:n Generate a curve for Utilization as a function of blocking
probability, assuming 50 channels.
311
Erlang vs. NErlangErlang vs. Nvs. N
n Using Erlang B Table:n Generate a curve for Supported erlangs as a function of
number of channels, assuming %2 blocking.
312
Erlang vs. GoSErlangErlang vs.vs. GoSGoS
n Using Erlang B Table:n Generate a curve for Supported erlangs as a function of
Blocking, assuming 50 channels.
313
ExerciseExerciseExercise
n 60 channels are to be allocated to a BTS are there are two choices: (Both configurations have the same coverage)– Use an omnidirectional cell and assign all 60 channels to it.– Use a sectorize cell and allocate 20 channels to each sector.
n Which choice will carry higher traffic load?
n What is the impact of sectorization on trunking efficiency?n What is the impact of sectorization on cell capacity?n What is the impact of sectorization on system capacity?
60 20 20
20
314
Blocked Calls Delayed ModelBlocked Calls Delayed ModelBlocked Calls Delayed Model
0 1 2 N-1 N…...
λλ
µµ
λλ
2µ2µ
λλ
3µ3µ
λλ
(Ν(Ν−−1)µ1)µ
λλ
ΝµΝµ
λλ
ΝµΝµ
N+1 N+2 …...
λλ
ΝµΝµ
λλ
ΝµΝµ
n This model assumes N servers (or channels) and an infinite queue size.
n It is usually considered as an M/M/m system.n The corresponding state transition diagram is
shown.
315
Erlang CErlangErlang CC
n The pdf of number of users in the system can be calculated using the diagram and similar procedures to what we used for Erlang B model.
n The result is
where
>
≤= −
Nkif!N
NAP
Nkif!k
AP
P kNk
0
k
0
k
NA&
AN
N
!N
A
!k
A
1P
1N
0k
Nk0 <
−+
=
∑−
=
316
Blocking in Erlang-CBlocking inBlocking in ErlangErlang--CC
n Probability of a call waiting in the queue for a time T exceeding t is given by:
n Therefore the probability of “having to wait” or PQ is
n The following equation is usually referred to as Erlang C Formula
NA
)1N,A(APAN
1
1
)0T(PP)QueueingPr(
e)N,A(P))N,A(P1(AN
N)tT(P
B
Nkk
t)AN(B
B
≤
−−+
=
>==
−−=>
∑∞
=
µ−−
Pp A
NN
N AQ
N
=−
0
!
317
Notice:Notice:Notice:
n Note that PQ(A,N)|Erlang C > PB(A,N) |Erlang B
n It is not correct to directly compare these two probabilities, because they apply to different models and they have totally different meanings.
n Erlang C model has no blocking, it merely has queuing.
n Keeping this in mind it is sometimes useful to compare blocking probability of one model with the those obtained using other models.
318
Users in Queue or SystemUsers in Queue or SystemUsers in Queue or System
n When A < NThe average number of calls waiting is
and the mean waiting time of a call is
n For A > N both E(N) and E(W) tend to infinity.n The average user time in the system and average
number of users in the system are:
NA)AN(
1)0TPr()W(E
NAAN
A)N,A(P)N(E Q
<−µ
>=
<−
=
T W
N AA
N Ac
= +
= +−
1/ µ
319
Some ObservationsSome ObservationsSome Observations
n The average waiting time depends on– the average holding time– and the amount of load in Erlangs
n These equations – hold only for systems which have a non-biased
service discipline such as LIFO or FIFO– do not hold for systems which have a biased service
discipline such as shortest service time first. The distribution of the waiting time, however, does depend on the choice of service discipline.
320
Poisson Model: Blocked Calls HeldPoisson Model: Blocked Calls HeldPoisson Model: Blocked Calls Held
n In Poisson Model blocked arrivals – wait for a random amount of time, the distribution
of which is assumed to be the same as holding time distribution.
– clears the system once the Waiting Timer expires– arrivals, not served immediately are considered
blocked
n The Blocking Probability for system based on Poisson Model using similar assumptions about the arrival process is
∑−
=
−−=1N
1i
iA
P !i
Ae1)Blocking(P
321
Poisson Model (cont.)Poisson Model (cont.)Poisson Model (cont.)
n Poisson model can be considered as classical model.
n Poisson Model is an intermediate and to some extent more realistic than Erlang B and C models. (Why?)– In many cases where fast redialing is very common
this model reflects the traffic dynamics more closely.
– However, in systems where the blocked calls can be rerouted to other servers, Erlang B model seems to be more appropriate.
∞/M/M
322
Chapter 3:Chapter 3:Chapter 3:
n Review of Probability Theory– Review of Basic Probability Concepts– Useful Distributions– Basics of Statistical Methods
n Basic Traffic Model– Arrival Process,– Erlang and Blocking Definition– Queuing Strategy and Markov Chain Formulation– Erlang B, C and Poisson Models and Calculations
n Contention Based Multiple Access Protocols– P-ALOHA and S-ALOHA– CSMA and ISMA
n Subscriber Forecast and Demographic Analysisn Summary and Discussions
323
Contention Based (Random) MAContention Based (Random) MAContention Based (Random) MA
n With the contention multiple access protocols there is no scheduling of transmissions. This means that a user getting ready to transmit does not have exact knowledge of when it can transmit without interfering with the transmissions of other users.
n This possible transmission failure makes the occurrence of a successful transmission a more or less random process.
n The random access protocol should resolve the contention that occurs when several users transmit simultaneously.Collision
ChannelIdle
Successful TX
WastedChannel
324
ThroughputThroughputThroughput
n In a random access channel time can be divided into– Idle Time, No packet is transmitted– Colliding Time, more than one packet transmitted – Successful Time, One packet is successfully transmitted
n The fraction of successful time to total time can be thought of as the throughput of the system.
n It is the fraction of messages that are send successfully sent/received to how many could be sent/received, should we had a perfect scheduling/controller.
Collision
ChannelIdle
Successful TX
WastedChannel
325
Contention Based MAContention Based MAContention Based MA
n We can subdivide the contention multiple access protocols into two groups,
n Repeated random access protocols – With every transmission there is a possibility of
contention and
n Random access protocols with reservation. – only in its first transmission does a user not know how
to avoid collisions with other users. However, once a user has successfully completed its first transmission (once the user has access to the channel), future transmissions of that user will be scheduled in an orderly fashion so that no contention can occur.
326
Repeated Random Access ProtocolsRepeated Random Access ProtocolsRepeated Random Access Protocols
n At the start of each transmission by a user, the user does not know if other users will also begin transmitting. Therefore, contention will occur if two or more users start transmitting at more or less the same time.
n If the users are also not able to detect an ongoing transmission, then contention will also occur if a new user starts a transmission while another user is already busy.
n If a user can sense an ongoing transmission, it can defer its own transmission until the channel is free. Contention can then only occur if two or more users start transmitting at the same time.
327
Repeated Random Access ProtocolsRepeated Random Access ProtocolsRepeated Random Access Protocols
n In this section some of the following repeated random access protocols are described:– pure (p)-ALOHA, – slotted (s)-ALOHA, – carrier sense multiple access (CSMA), – inhibit sense multiple access (ISMA), – and stack algorithm.
328
p-ALOHApp--ALOHAALOHA
n The Aloha network was developed around 1970 to provide radio communication between the central computer and various data terminals at the campuses of the university of Hawaii
n Immediately after a user has generated a packet it will transmit this packet on the uplink channel.
– If no other users transmit, the base station will receive a correct transmission and send an acknowledgment packet on the down link channel. On reception of the acknowledgment, the user knows its transmission has been successful.
329
p-ALOHApp--ALOHAALOHA
– If two or more users transmit simultaneously, a collision will occur. The base station recognizes this occurrence because it receives a garbled transmission and does not transmit an acknowledgment. When a user does not receive an acknowledgment, it assumes its transmission has collided so it will have to retransmit.
– Simply retransmitting after a fixed time interval will not do, because two users that transmitted at the same time will find out about the collision at about the same time and therefore retransmit at the same time, thus creating another collision.
– To avoid this deadlock situation, a user experiencing a collision will wait a random amount of time beforeretransmitting.
330
p-ALOHA (cont.)pp--ALOHA (cont.)ALOHA (cont.)
n As figure shows that user 1 starts transmission at t=t0. Assume a transmission takes T seconds, so the transmission of user 1 ends at t=t0+T. As can be seen from the figure, the transmission of a user starting anywhere within the time period between t0-T to t0+T will collide with the transmission of user 1 (indicated as the shadedarea in the Figure).
n As a result the transmission of user 1 there is a vulnerable period of 2T (2 times the duration of a transmission). Note that we assumed the propagation delay to be negligible compared to the time needed to transmit a packet.
t0-T t0+Tt0 t0+2T
Other Users
User 1
331
Pure Aloha ThroughputPure Aloha ThroughputPure Aloha Throughput
n Assuming Poisson Arrivals with an arrival rate of G arrivals/slot the throughput rate S for p-ALOHA is given by:
Pure ALOHA
0
0.02
0.040.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 2 4 6 8
G
S
332
Slotted AlohaSlotted AlohaSlotted Aloha
n One way to improve the performance of p-ALOHA protocol is to try and make the vulnerable period smaller. This can be done by dividing the transmission time axis into time slots and requiring that a user is only permitted to start its transmission at the start of a time slot.
n The transmission of this packet is delayed until time t=T (indicated by an arrow followed by the packet) and only those users that generated a packet between time 0 and T will also transmit at time T and collide with the transmission of user 1. Users that generate a packet after time t=T will not start transmission until time i=2T and will therefore not collide with the transmission of user 1.
n The vulnerable period of a transmission is now only T so it is halved compared to p-ALOHA. This doubles the maximum channel throughput to 36%. The resulting protocol is called the slotted (s-)ALOHA protocol.
0 2TT 3T
Other Users
User 1
333
Slotted Aloha Slotted Aloha Slotted Aloha
n Assuming Poisson Arrivals with an arrival rate of G arrivals/slot the throughput rate S is given by:
Slotted ALOHA
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 1 2 3 4 5 6
G
S
S Ge G= −
334
Equilibrium PointEquilibrium PointEquilibrium Point
n In equilibrium the arrival rate, λλ, to the system should be the same as the departure rate, Ge-G.
n This relationship is illustrated in Figure.n We see that the maximum possible departure rate
(according to the argument above) occurs at G = 1 and is l/e=0.368.
Slotted ALOHA
0
0.050.1
0.15
0.20.25
0.3
0.350.4
0 1 2 3 4 5 6
G
S
Departure Rate S
Arrival Rate λλ
335
Operating PointOperating PointOperating Point
n In G > 1 region the system is unstable, because the accumulation of retransmissions saturates the channel resulting in 0 throughput.
n The G=1 point is the unset of instability and therefore is not a good operating point.
n Usually the 0.3 < G < 0.5 region is considered to be feasible.
n Obviously the system behavior highly depends on the retransmission strategy defined in the protocol. For example
– Random Attempts– Max. No. Attempts
– Access Classes
336
0 0 00.2 0.163746 0.1340640.4 0.268128 0.1797320.6 0.329287 0.1807170.8 0.359463 0.161517
1 0.367879 0.1353351.5 0.334695 0.074681
2 0.270671 0.0366312.5 0.205212 0.016845
3 0.149361 0.0074363.5 0.105691 0.003192
4 0.073263 0.0013424.5 0.04999 0.000555
5 0.03369 0.0002276 0.014873 3.69E-057 0.006383 5.82E-06
ALOHA vs. Slotted ALOHA
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 2 4 6 8
G
S
Aloha vs. Slotted Aloha Aloha vs. Slotted Aloha Aloha vs. Slotted Aloha
S Ge G= −2
S Ge G= −s-ALOHA
p-ALOHA
337
S-ALOHA vs. TDMSS--ALOHA vs. TDMALOHA vs. TDM
n The basic idea of s-ALOHA algorithm is that eachunbacklogged node simply transmits a newly arriving packet in the first slot after the packet arrival. Thus risking occasional collisions but achieving very' small delay if collisions are rare.
n This approach should be contrasted with TDM in which, with m nodes, an arriving packet would have to wait for an average of m/2 slots for its turn to transmit.
n Thus, slotted Aloha transmits packets almost immediately with occasional collisions. whereas TDM avoids collisions at the expense of large delays.
338
Example 1: Low Traffic, No MobilityExample 1: Low Traffic, No MobilityExample 1: Low Traffic, No Mobility
n Suppose the base station has only 7 traffic channeln GoS is %2n Also Assume
– Very low degree of mobility, No location update, No SMS traffic
n The average call holding time is 2 minutesn Then we have:
– N=7 (why?) and B=0.02 From Erlang B table: A= 2.93
– 1/µµ=2min arrival rate is λλ =2.93/2=1.46 calls/minute– Then
So There is no problem at all!!
G arrivalsm
G arrivals slot
= =×
= <<
1 46146 4 6
600 0001 0 2
. / min. . sec
sec. / .
339
Ex. 2: Low Traffic & High MobilityEx. 2: Low Traffic & High MobilityEx. 2: Low Traffic & High Mobility
n Suppose the base station has 47 traffic channeln GoS is %2n Also Assume
– Very high degree of mobility, high rate of registration and location update. So for every user originating call there are 100 users performing location updates and registration.
n The average call holding time is 2 minutesn Then we have:
– N = 47 and B=0.02 From Erlang B table: A= 37.4
– 1/µµ=2min arrival rate is λλ =37.4/2=18.7 calls/minute– Then
So There is still no problem.
G arrivals
Gm slot
G arrivals slot
= × + =
=× ×
= <
18 7 100 1
189 10 4 6
600145 0 2
3
. ( ) / min
. . sec/
sec. / .
340
Ex. 3: High Traffic & High MobilityEx. 3: High Traffic & High MobilityEx. 3: High Traffic & High Mobility
n Suppose the base station has 119 Traffic channeln GoS is %2n Also Assume
– Very high degree of mobility, high rate of registration and location update. So for every user originating call there are 100 users performing location updates and registration.
n The average call holding time is 2 minutesn Then we have:
– N = 119 and B=0.02 From Erlang B table: A= 106.4
– 1/µµ=2min arrival rate is λλ =106.4/2=53.2 calls/minute– Then G arrivals
Gm slot
G arrivals slot
= × + =
=× ×
= >
532 100 1
537 10 4 660
0 411 0 2
3
. ( ) / min
. . sec/sec
. / .
So the system is almost unstable and there is a problem.
341
Carrier Sense MACarrier Sense MACarrier Sense MA
n CSMA is a class of protocols which we can divide into two subclasses: – the nonpersistent CSMA protocols and – the p-persistent CSMA protocols.
n In the nonpersistent CSMA protocols, a user that has generated a packet first "listens" to (senses) the channel for transmissions of other users. – If it senses the channel idle, it will transmit; – otherwise the user will wait a random time and then try again.
342
Carrier Sense MA (cont.)Carrier Sense MA (cont.)Carrier Sense MA (cont.)
n Figure shows a transmission from user 1 that starts at t0. With a propagation delay between user I and user 2 of tp , user 2 will sense the channel idle between t0and t0+tp Therefore, if user 2 generates a packet within this time a colliding transmission will result.
n A user is informed of a collision by the absence of an acknowledgment packet from the receiving station. Upon detecting the collision, the packet is rescheduled for transmission a random time later.
t0 t0+tp
User 1
User 2
time
343
1-Persistent CSMA11--Persistent CSMAPersistent CSMA
n A special case of the p-persistent CSMA protocols is the 1-persistent CSMA protocol.
n The protocol is the same as the nonpersistent CSMA protocol except when a user senses the channel busy. In this case the transmission is not rescheduled a random time later but instead the user keeps sensing the channel until it becomes idle and then immediately transmits its packet.
n As a result of this, all users that become ready during a busy channel will transmit as soon as the channel becomes idle, which leads to a high probability of a collision at the end of a successful transmission.
344
1-Persistent CSMA11--Persistent CSMAPersistent CSMA
n To avoid the collision of packets accumulated while the channel was busy, the start of the transmission times of the accumulated packets can be randomized.
n This can be done by letting all users that generate a packet during a busy channel transmit as soon as the channel becomes idle with a probability p.
n With a probability 1-p they will defer their transmission for ττ seconds (with ττ being the maximum propagation delay between any two users in the system). After the ττ seconds the deferred terminal will sense the channel again and apply the same algorithm as before.
345
CSMA-CDCSMACSMA--CDCD
n With the nonpersistent and p-persistent CSMA protocols, a user will not learn about a collision until after its whole packet has been transmitted. – The reason for this is, of course, that an acknowledgment packet
will only be sent after the complete packet has been received bythe receiving user.
– Since a collision can only occur within the propagation delay after the start of the transmission, it is a waste of time to transmit more of the packet if a collision has occurred within this period.
n For this reason the CSMA-CD (carrier sense multiple access with collision detect) protocols have been developed. With these protocols a user keeps monitoring the channel while it is transmitting. If it detects a collision, it aborts its transmission as soon as possible thus saving time.
346
ISMAISMAISMA
n With the CSMA protocols each user must be able to detect (to sense) the transmissions of all other users. However, especially in radio channels, this may prove to be very difficult because in such channels it can easily happen that two users are hidden from each other by a building or some other obstacle.
n This hidden terminal problem severely degrades the performance of CSMA. As a solution the Inhibit Sense MA or ISMA (also called the BTMA, busy tone multiple access) protocol is proposed.
347
ISMAISMAISMA
n The ISMA protocol is identical to the CSMA protocol except for the way in which the users sense the channel for transmissions of other users. – In CSMA the sensing is done by listening to the channel
on which the users transmit. – In ISMA there is a base station that transmits a busy/idle
signal on a separate channel to indicate the presence or absence of a transmission of one of the users.
RACH isBusy/Idle
348
ISMA (cont.)ISMA (cont.)ISMA (cont.)
n The channel on which the users transmit to the base station is called the inbound channel and the channel on which the base station broadcasts to the users is called the outbound channel. – As soon as the base station receives a transmission
from a user on the inbound channel, it will generate a busy signal on the outbound channel.
– If the transmission ends, the base station will transmit an idle signal.
– Now if two users are hidden from each other but not from the base station they will still be able to determine if the other user is transmitting or not.
349
Random Access With ReservationRandom Access With ReservationRandom Access With Reservation
n The difference between a reservation protocol and a pure random access protocol arises when a user successfully transmits its first packet in a row of packets. Now a fixed part of the channel capacity is allocated to the user for the transmissions of the rest of the packets. The user obtains a reservation.
n All users are aware of what parts of the channel are allocated to the reserved users. Therefore the transmissions of these users are carried out without contention, and the transmissions are scheduled.
350
RA with Reservation (cont.)RA with Reservation (cont.)RA with Reservation (cont.)
n Once a user has transmitted its whole row of packets, it will return the allocated capacity (give up its reservation) so it can be used by other users.
n If the user wants to transmit a new row of packets, the first packet will again have to contend for the channel.
n There are many protocols that fall within the category of random access with reservation. Many of those protocols (probably most) use slotted ALOHA as the random access method to obtain a reservation.
n These protocols are collectively known as the reservation ALOHA or r-ALOHA protocols
351
Chapter 3:Chapter 3:Chapter 3:
n Review of Probability Theory– Review of Basic Probability Concepts– Useful Distributions– Basics of Statistical Methods
n Basic Traffic Model– Arrival Process,– Erlang and Blocking Definition– Queuing Strategy and Markov Chain Formulation– Erlang B, C and Poisson Models and Calculations
n Contention Based Multiple Access Protocols– P-ALOHA and S-ALOHA– CSMA and ISMA
n Subscriber Forecast and Demographic Analysisn Summary and Discussions
352
Joint Radio & Traffic Design Joint Radio & Traffic Design
n In principle radio coverage and traffic distribution are to be considered jointly.
n However, due to the inherent task complexity, the procedure calculates – first of all a suitable radio coverage for the service area, – Then it verifies if that coverage can fulfill the cell capacity
requirements deriving from the traffic forecasting. n These two very strictly dependent steps are iterated
until a satisfactory solution is derived. n The factors conditioning the resulting cell layout come
from either propagation or traffic constraints, depending on the most critical conditions.
353
Traffic AnalysisTraffic Analysis
n As for the traffic modeling,n the service area must be characterized based on
subscribers' density and distribution. n Geographical maps or territorial databases are utilized
to identify the main roads, inhabitant densities, and business areas. Urban and geographical analysis can be integrated, when necessary, with data relevant to the fixed telecommunication users distribution.
n In this step also mobility attributes are modeled, since they affect significantly signaling network and distributed data base dimensioning.
354
Subscriber ForecastSubscriber ForecastSubscriber Forecast
n Demographics– Service Penetration– Total Number of
Subscribers– Distribution of
Subscribers
n Mobility of subscribers– Handoff Rates– Location Update Rate
n Service Types and percentages– Voice– Short Messages– Fax– Later on: Data/Internet
Transactions.....
n Service Statistics– Average Call Duration– Erlangs/Sub– Outgoing vs. Incoming Call
Ratios.....
355
Demographics AnalysisDemographics AnalysisDemographics Analysis
n Demographics Analysis is predicting the subscribers density in different areas based on demographic data such as– Population Density, ( Layered by Age Classes)– Income Distribution– Household Distribution– Highways and Vehicular Traffic Distribution– Business Area Maps
n The estimate is usually obtained by a weighted combination of these distributions.
$$$$$
$$$$$$$
356
Demographics AnalysisDemographics AnalysisDemographics Analysis
%30 %20
%40%10
%50 %0
%50%0
%25 %25
%25%25
%? %?
%?%?
Income Dist.Vehicular Traffic Dist. Population Dist.
Subscribers Dist.
W1 W3W2
357
Subs/CellSubs/CellSubs/Cell
Composite Coverage Design(Cell Footprints)
Subscriber Distribution Map
358
Alternative Subscriber ForecastAlternative Subscriber Forecast
Total PopulationService Penetration Factor
Total No. of Subscribers
Subscribers’ Density
Market Area
# Subs/Cell
Cell Area
LBA
MAPL Prop. Model
359
Traffic Analysis for BTS Traffic Analysis for BTS
# Subs/Cell
Erlangs/Cell
Voice Channels/Cell
RF Channels/Cell
Erlang/Subs
Erlangs Model GoS
Channelization
360
Chapter 3: Review and DiscussionsChapter 3: Review and DiscussionsChapter 3: Review and Discussions
Review of ProbabilityTraffic ModelsErlang CalculationRandom AccessSubscriber Forecast
361
Chapter 4.Chapter 4.Chapter 4.
n Introduction: » Planning Process, Objectives and Concepts
n Planning Inputs» Traffic, Call and Mobility Models» Basic Concepts and Calculations
n Dimensioning (New System)» BTS
• Traffic Channels• Control Channels
» Links to/from BSC (Voice & Signaling)» BSC» Links to/from MSC/VLR » MSC» HLR/AC
n Section Summary and Discussions
362
Day 4: Network planningDay 4: Network planning
n Introduction» Planning Process, Objectives and Concepts
n Planning Inputs» Traffic, Call and Mobility Models» Basic Concepts and Calculations» Availability and Utilization
363
Scope of Fixed Network planningScope of Fixed Network planning
n The scope of Fixed Network Planning (FNP) covers the dimensioning and planning of the NSS and part of BSS network elements and their interconnections.
n FNP is not the same as RF planning or cell site planning, but it requires input from it.
n Objective:– The primary network planning objective is to design
a network that offers a desired set of communication services at a specific performance and acceptable cost over a period of time.
364
Planning Considerations Planning Considerations
n How to best balance CPRS– Cost
» Operations» Maintenance» Expandability
– Performance» Fast response
– Reliability» Availability .01 down » Fault tolerance
– Service» Latest features (now and future)
365
Objectives and ConstraintsObjectives and Constraints
n Objectives:– Business Objective
» Time to Market, Competitive price and services– Technical Objective
» performance and reliability» Services and Quality of Service» Quality
n Constraints– Time/Resources– Cost– Technology– Network Elements limitations
366
GrowthGrowth
n The future network capacity/growth is based on the validity of the current measurement and statistical analysis under growth conditions.
n The future capacity calculation depends on the traffic pattern and traffic sensitivity.– Current traffic patterns are scaleable to estimate the
future. For Example:» Future (2 years from now) average number of call attempts =
current average number of call attempts * (1 + growth ) **2. – -And each elements voice or signaling traffic
characteristics will not change.
367
Data services growth Data services growth Data services growth
n The growth rate of Data services will have an impact on Fixed Network planning.– Some operators believe their Mobile data may
account for 12-15% of Revenue by 2000.– And 10 -15% of the GSM users will be data users by
year 2000.– This rate of growth will equate to 20-25% of the
traffic on the GSM network.
n The impact of the data services– Circuit switch Data Impacts
» MSC/VLR and the Control channels– Packet Switch Impacts
» IWF and the control channel usage
368
Mobility Impact on Planning Mobility Impact on Planning
n In a none mobile environment the planning process is trivial. Where the growth of the subscribers and call setup have is a linear function
n In a Mobile environment as the number of the subscribers/cells grow the load from mobility registration, HO will grow none linear, while the call setup load continue to be a linear function.
Number of subscribers
Mob
ile sy
stem
loa
d
Call setup
Registration and HO
369
Network Design ActivityNetwork Design Activity
n Setting Business Objective– determine subscriber growth– Establish planning interval– Target new services– Decrease cost /sub
n Network service Requirements– Specify the requirements for services and the network
n RF Engineering – Plan the Cell Sites and Optimize the topology for Maximum
coveragen Network engineering/ Network capacity /reliability
– Service Planning– Capacity /Performance Planning– Availability Planning– Cost Planning
370
Planning IssuesPlanning Issues
n Service Planning– Based on the service being provided by the GSM network,
must define all aspect of the services including the Quality of Service that affects the technical objectives
n Capacity /Performance Planning– Characterize the offered traffic for each element based on
» Traffic Model and Mobility Model» Call Mix Model and Service Mix Model
n Availability Planning– A hard number that must be given to the network planner for
each network element. % availability
n Cost Planning– Perform a cost analysis on each alternative proposed.
371
Alternatives Alternatives
n Alternative network plans must be devised until the overall objectives are satisfied
n Provide as many alternative as possible, if required breakdown the alternatives into phases for a given period.
n comparative analysis of alternatives provides the basis for selection
n Real measured data is preferable to estimatesn A quantitative basis for selection is preferablen Acquire tools and models for various aspects of the
network.
372
Chapter 4.Chapter 4.Chapter 4.
n Introduction: » Planning Objectives, Concepts
n Planning Inputs» Traffic, Call and Mobility Models» Basic Concepts and Calculations
n Dimensioning (New System)» BTS
• Traffic Channels• Control Channels
» Links to/from BSC (Voice & Signaling)» BSC» Links to/from MSC/VLR » MSC» HLR/AC
n Section Summary and Discussions
373
Modeling ConceptsModeling Concepts
n A model provides a structure to describe the elements of the planning problem, their relationships, the type of information required, the methods of analysis to use.
n Models can be either– Logical (functional)
» Switching» Database HLR/VLR » Protocols
– Computational (quantitative) based on analytical and simulation
» Traffic and Queuing Model» Mobility Model
374
Analytical vs. SimulationAnalytical vs. Simulation
n For Analytical model: the randomness of the events is described by equations describing probability distribution– can provide quick results, using spreadsheets and
software scripts.
n For simulation model: the randomness of the events is described by algorithms that simulate the probability distribution (Monte Carlo).– The accuracy of the result depends on number of
runs and granularity
375
Purpose of ModelsPurpose of Models
n Network Capacity/ Performance Model purpose– For a given network architecture, models each element
utilization as offered traffic increases due to subscribers growth, new services and increase use.
– Computes the required number of network elements to meet performance objective
n Availability Model– From statistical data collected shows the system availability as
minutes of outage/week/months etc.– Determines average service availability to the end user.
n Functional Model– Network diagram showing all the elements to support the
servicesn Cost Model
– For a given network architecture and growth estimate based on the network capacity model computes the capital cost for the planning interval.
376
Two Types of TrafficTwo Types of Traffic
n The traffic capacity of the wireline/wireless network can be categorized as – Voice/Data traffic (Erlang traffic)– Control/Signaling traffic (events traffic)
n The signaling traffic capacity calculation is based on occurrence of an event , Call Attempt (CA)and does not involve the duration of the call,
n where as calculation of the voice traffic considers the duration(Erlang) and the measurement of the voice traffic is based on ErlangB(blocked calls are not retried).
377
Logically Different PathsLogically Different Paths
n The signaling traffic will impact– The Signaling links – The Databases (HLR/VLR)– Data storage– Computer hardware (processors)
n The voice traffic will impact– The Transcoder– The Switch/ voice trunk– Voice Mail
378
Signaling TrafficSignaling Traffic
n Following events have major impact on the traffic calculations and processor utilization.– Call Origination– Call Termination– Authentication– Handover– Location Update– IMSI Attach/Detach– SMS Services– Data Services
379
HO impactHO impact
n No of HO/CA can impact many areas of the system– Inter BSC HO, intra-MSC HO
» The BSC and the MSC Call Processing
– Intra-BSC HO» The BSC call processing » No effect on MSC (depending on implementation)
– Inter MSC HO (Anchor MSC)» MSC » BSC
380
Location UpdateLocation Update
n Possible location update procedures:– MS location update to MSC/VLR– HLR updating of the location at the MSC/VLR
request– Removal of the subscriber record from MSC/VLR at
the HLR request– Periodic location update is performed to keep the
MSC/VLR and HLR in check when a failure occurs on any of the elements.
» The period can be controlled by the operator
381
Traffic ModelTraffic Model
n The traffic Models are based on two factors– Experiences/measurement from existing systems– Assumptions, some arbitrary
n All the traffic data varies in time – Subscriber’s use– New features– New elements supporting the features
n A traffic model with peak busy hour must be used
382
Traffic ModelTraffic Model
n Traffic model includes– GOS or blocking factor (Grade Of Service or blocking
probability)– Busy Hour Call Attempts (BHCA) /sub.– Erlang /sub– No of subscribers and the growth over the planning period
n Example:Parameter ValueGoS, Air Interface 2%GoS, BSC-MSC 0.1%GoS, MSC-PSTN 0.01%BHCA/sub 1.5 (assume all active mobiles)Duration of a call 120 secErlang/sub .05Growth of the subscribers 20%/yr
383
Mobility & HandoverMobility & HandoverMobility & Handover
n Handover rates and location updating rates depend on the movements of the users.
n The estimation of this signaling load must be based on statistics concerning these movements.
n To give an idea on the order of magnitude, we can make very simple assumptions. – First we will take the assumption that the speed of 70% of the
users is zero, and that the speed of the other 30% is 30 km/h. – Then, we will assume an average cell diameter of 3 km. and
translate this into a mean lifetime in a cell for the moving users of 4.5 minutes, that is to say an average of around one handoverevery two communications.
384
Mobility & Location UpdateMobility & Location UpdateMobility & Location Update
n A related point is the location updating traffic. Different reasons may lead to location updating, – movements of users between cells, – switch on and off, – periodic updating.
n While the two last terms can be considered roughly proportional to the traffic in the cell (within a given traffic model), the first one varies from 0 to a high value depending on the proportion of the boundary' of the cell which corresponds to a boundary between location areas.
385
Mobility ModelMobility Model
n Average User’s Speedn Average Cells Sizen Average Location Area Sizen Location Update Times
n Example*
n No of HO per call n Ratio of Location Update
(LU) to calls
Parameter ValueNo of HO /call 2In t r a MSC HO 80%
• In t ra BSC HO 80%• In te rBSC HO 20%
Inte rMSC HO 20%Ratio of LU to Call 1.8• intra VLR 80%• inter VLR 20%
386
Call Mix ModelCall Mix Model
n Call Mix Consists of – Mobile Origination Call (MOC) %– Mobile Termination Call (MTC) %– Mobile to Mobile (MTM) Attempts %– Mobile Call Completion %
Example:Parameter Value CompletionMOC(M-L) 60% %70MTM(M-M) 5% %40MTC(L-M) 35% %40
387
Service Mix ModelService Mix Model
n Service Mix Model includes the probability of using various services per user per call.
n For exampleParameter ValueRatio of SMS per call 0.1Fax/Data Calls 0.05Ratio of Voice Mail per call 0.1
388
TransactionsTransactions
* The SMS message size can vary depending on the use
n Other Transactions include mobile station attach/detach procedures.
Transactions #of MSC->BSC #of BSC->MSCCallsetup/clearing 5M/30O 6M/26OHandover 4M/ 37O 5M/38OLocation Update 5M/30O 6M/26OSMS 7M/30-126O 7M/30-126O*Paging 1M/30O
#Messages(M) and # Octets (O)
389
Processes in Network Elements Processes in Network Elements
n Each of fixed network elements perform one or all of the following processes/functions
n There is a capacity or limit for each process or function
I/OCommunications
(Data link)
DATABASE
ADMINISTRATION, O&M(Billing, User Interaction)
APPLICATIONCall processing, Mobility
390
Capacity LimitsCapacity Limits
n The Maximum network capacity (voice/signaling) is given for each network element.
n Each element system limit is provided for future expansions/ (Max number of processors)
n For a voice sensitive element/link ( ie. MSC, MC) maximum number of– Erlangs– Subscribers– Trunks
n For a signaling sensitive element (HLR, VLR,SM_SC) maximum number of– Transactions/Sec– Data links– Subscribers
391
NSS Elements LimitsNSS Elements Limits
n The BSC limits are:– Maximum no of BTS that can be supported/controlled – Maximum no of Call Attempt (CA)– Maximum no of voice ports it can support (I/O)– Maximum no of Signaling link can be supported
n The MSC limits are:– Maximum no of BSC that can be supported/controlled – Maximum no of Call Attempt (CA)– Maximum no of voice ports it can support (I/O)– Maximum no of Signaling link can be supported
392
NSS Elements Limits (cont.)NSS Elements Limits (cont.)
n The VLR limits are:– Maximum no of subscribers (Size of the Memory!)– Maximum no of transaction/sec processing on the
VLR database
n The HLR limits are:– Maximum no of subscribers (Size of Memory )– Maximum no of Signaling link can be supported– Maximum no of transaction/sec processing on the
VLR database
393
Chapter 4.Chapter 4.Chapter 4.
n Introduction: » Planning Objectives, Concepts
n Planning Inputs» Traffic, Call and Mobility Models» Basic Concepts and Calculations
n Dimensioning (New System)» BTS
• Traffic Channels• Control Channels
» Links to/from BSC (Voice & Signaling)» BSC» Links to/from MSC/VLR » MSC» HLR/AC
n Section Summary and Discussions
394
Calculating BH Call Attempt Calculating BH Call Attempt
n BHCA is the rate of call attempts, both mobile originated or terminated, per unit of time during peak traffic hours.
n CA rate can be calculated from Erlangs A, and Average Service Time or Call Duration µµ
CA Erlang Average Call Duration
Number of CallsA
in ondsA
==
== == ××
/
/ sec/ ( sec )1 µµ
µµ
395
Transactions/secTransactions/sec
n For each network element, e.g. MSC and HLR, the number of transactions per second is
n the summations of the number of transactions/call attempt for all truncations involving that element
n Times the number of CA/sec
» P SMS = No. SMS/Call Ratio» P Loc = No.Location Updates/Call
N CA P P
N N CATranactions SMS Loc
Tranactions Tranactions
/ ....
/ sec / sec
= + += ×
396
Signaling Octets/secSignaling Octets/sec
» N S/C = No. of call setup/clearing messages
» L S/C = Average message size of call setup/clearing
» P SMS = No. SMS/Call Ratio
» N SMS = No. of SMS messages
» L SMS = Average message size for SMS
» M SMS = Average Data size for SMS
» P Loc = No.Location Updates/Call
» N Loc = No of Location Update messages
» L Loc = Average message size for Location Update
» R S = Signaling Rate bits/sec
# ./ ( )
# / sec # / . / ( . . )
. / sec # / sec /
/ /Oct Call N L P N L M P N L
Octets Octets Call No Calls Sec i e
Signaling Rate R No bits Octets bits byte
S C S C SMS SMS SMS SMS Loc Loc Loc
S
== ×× ++ ×× ×× ++ ++ ×× ××== ××
== == == ××λλ
8
397
#of Signaling Channels#of Signaling Channels
» R S = Signaling Rate bits/sec
» N E0 = No. of 64kbps E0 channels needed
» U =Utilization of the Link
NR
kbps UES
0 64=
×
398
Link UtilizationLink Utilization
n Each signaling capacity is designated as 64 Kbit sec (E0).n The signaling link capacity is consumed by control
information as well as the application data. When calculating the number of signaling links it is important to factor in the control and overhead information and plan for less than the maximum rate (64 K).
n Usually a link utilization factor is used :– For LAPD Abis link this utilization is 75% to 80% of
maximum rate. – For SS7 links the utilization is 20% . (SS7 links load
share/redundancy and we should count for link failures)
399
SS7 Link General Rules: FSS7 Link General Rules: F--linkslinks
n When planning For a SS7 F-link– Number of links
– If number of links = 1 then add 1; minimum of 2 link /link set
– Configure one linkset with the number of links
NR
kbps US==
××64
400
SS7 Link General Rules: A-linkSS7 Link General Rules: ASS7 Link General Rules: A--linklink
n For a SS7 A- link– Number of links
– If number of links are < 1 or odd add a 1 and then – Number of links per link set = Number of links / 2– Plan for 2 link sets each to an STP pair and configure
the link set as a combined link set
NR
kbps US==
××64
401
ExerciseExerciseExercise
402
Chapter 4.Chapter 4.Chapter 4.
n Introduction: » Planning Objectives, Concepts
n Planning Inputs» Traffic, Call and Mobility Models» Basic Concepts and Calculations
n Dimensioning (New System)» BTS
• Traffic Channels• Control Channels
» Links to/from BSC (Voice & Signaling)» BSC» Links to/from MSC/VLR » MSC» HLR/AC
n Section Summary and Discussions
403
Joint Radio & Traffic Design (Rev.) Joint Radio & Traffic Design (Rev.)
n In principle radio coverage and traffic distribution are to be considered jointly.
n However, due to the inherent task complexity, the procedure calculates – first of all a suitable radio coverage for the service area, – Then it verifies if that coverage can fulfill the cell capacity
requirements deriving from the traffic forecasting. n These two very strictly dependent steps are iterated
until a satisfactory solution is derived. n The factors conditioning the resulting cell layout come
from either propagation or traffic constraints, depending on the most critical conditions.
404
Traffic AnalysisTraffic Analysis
n As for the traffic modeling,n the PCS service area must be characterized based on
subscribers' density and distribution. n Geographical maps or territorial databases are utilized
to identify the main roads, inhabitant densities, and business areas. Urban and geographical analysis can be integrated, when necessary, with data relevant to the fixed telecommunication users distribution.
n In this step also mobility attributes are modeled, since they affect significantly signaling network and distributed data base dimensioning.
405
Subscriber ForecastSubscriber Forecast
Total PopulationPCS Market Penetration Factor
Total No. of Subscribers
Subscribers’ Density
Market Area
# Subs/Cell
Cell Area
LBA
MAPL Prop. Model
406
BTS Traffic AnalysisBTS Traffic Analysis
# Subs/Cell
Erlangs/Cell
Voice Channels/Cell
RF Channels/Cell
Erlang/Subs
Erlangs Model GoS
Channelization
407
BTS DimensioningBTS Dimensioning
n Step 1:– For each sector estimate the required number of
» traffic channels (TCH’s) » control channels (BCCH, CCCH and SDCCH) to support TCH’s
– RF channels or TRX’s / BTS– Perform Feasibility Analysis Against Limitation
n Step 2:– For the entire BTS
» estimate the total number of E0 channels needed» estimate #E1’s/BTS or #BTS’s/E1 !!!
BTS
408
BTS Dim. Voice ChannelsBTS Dim. Voice Channels
n Step 1: review
# Subs/Cell
Erlangs/Cell
Erlang/Subs
Erlangs Model GoS
Voice Channels/Sector
BTS
409
BTS Dim. Control ChannelsBTS Dim. Control Channels
n The required number of BCCH, CCCH and A=SDCCCH channels have to be estimated
n The number of air interface forward control channels required depends on the rates of:– Pages– Location Updates– Short Messages– Call Setups
n Only the numbers of pages and access grants affects the CCCH. The other information uses SDCCH.
Voice Channels/Sector
Total RF channels
Control Channels/Sector
BTS
410
Number of CCCH’s Number ofNumber of CCCH’s CCCH’s
n Each CCCH block can carry one message, hence the capacity of 4.25 messages/sec.
n The AGCH can carry– immediate assignment message for upto 2 users or– immediate assignment reject message for upto 4 users.
n Each PCH message can carry pages for upto 4 MS’s using TMSI or 2 MS’s using IMSI.
n It is usually assumed that once the down link CCCH is correctly dimensioned the uplink RACH capacity is sufficient.
411
Number of CCCH’s (Cont.)Number ofNumber of CCCH’sCCCH’s (Cont.)(Cont.)
n Paging parameters, e.g. the number of paging groups. (Trade Off?)
n Access parameters, e.g. maximum number of MS reattempts, Waiting time between Reattempts.
N N N U
where
Ncalls
calls msg msg blk
Np calls
calls msg mess blk
CCCH AGCH PCH CCCH
AGCHC Loc SMS
PCH
== ++
==++ ++
××
==××
( ) /
( ) / sec
( / ( . / sec) / )
/ sec
( / ( . / sec) / )
λλ λλ λλ2 4 25
2 4 25
412
No. SDCCH’sNo.No. SDCCH’sSDCCH’s
n SDCCH carries a large portion of call setup messaging, therefore SDCCH dimensioning is an important part of BTS planning process.
n The number of required SDCCH’s depends on the – Call Attempt rates (MO and MT)– Location Updates and– SMS rate (Which SMS’s go to SDCCH?)
N T T TSDCCH C C Loc Loc SMS SMS= × + × + ×λ λ λ
CA Rate
Avg. Call Setup Time
Loc. UpdateRate
Avg. Loc. UpdateTime Duration
Avg. SMSTime Duration
SMSRate
413
Control Channel ConfigurationsControl Channel ConfigurationsControl Channel Configurations
n There are three configurations of the control channels.– A combined Control Channel
» 1 BCCH+3 CCCH + 4 SDCCH– Non-Combined Control Channel
» 1 BCCH + 9 CCCH (no SDCCH)– SDCCH Channel
» 8 SDCCH
n If the CCCH has a low traffic requirement, the CCCH can share its time slot with SDCCHs.
n At least one of the first two configurations is needed. (Why?)
414
Control Channel AssignmentsControl Channel AssignmentsControl Channel Assignments
n Typically the first control channel assigned comprises one BCCH, 3 CCCHs and 4SDCCHs. When subscriber growth demands for additional control channels
n 8 SDCCH may be added to a second time slot to give a total of 12 SDCCH’s
n Also the configuration on the first channel may change to provide no SDCCH’s, resulting in the total of 8 SDCCH and 9 CCCH.
415
BTS Dim. Control ChannelsBTS Dim. Control Channels
n Number of Control channel required
BTS
Use of Time Slots#TRX’s #TCH’s #Erlangs #SDDCH’s TS0 Other TS’s
1 7 2.94 4 1 BCCH+3CCCH+4SDCCH
2 14 6.2 8 1BCCH+9CCCH 8 SDDCH3 22 14.9 8 1BCCH+9CCCH 8 SDCCH4 30 21.9 12 1BCCH+
3CCCH+4SDCCH8 SDCCH
5 38 29.2 12 1BCCH+3CCCH+4SDCCH
8 SDCCH
6 45 35.6 16 1BCCH+9CCCH 2 x 8 SDCCH7 53 43.1 16 1BCCH+9CCCH 2 x 8 SDCCH8 61 50.6 20 1BCCH+
3CCCH+4SDCCH2 x 8 SDCCH
9 69 58.2 20 1BCCH+3CCCH+4SDCCH
2 x 8 SDCCH
10 77 65.8 20 1BCCH+3CCCH+4SDCCH
2 x 8 SDCCH
Note: CBCH uses one SDCCH
416
BTS Dim. : Number ofBTS Dim. : Number of TRX’sTRX’s
n The maximum number of RF Channels per BTS is limited by:– Manufacturers Hardware Limitations– Avaliable Spectrum and Target Reuse factor
n If the numbers RF’s needed is not feasible cell splitting or more sectorization may be needed.
n At the end of this step all BTS’s should have acceptable number of RF channels.
BTS
Voice Channels/Sector
Total RF channels
Control Channels/Sector
417
Step 2: Backhaul ConsiderationStep 2: Backhaul Consideration
n Add the number of TCH’s needed on all sectors and calculate the numbers of E0’s needed.– If TRAU is at the BTS
» # E0 Channels = # TCH’s
– If TRAU is at BSC or MSC» # E0 Channels = # TCH’s/4, rounded up
n Add One or two E0’s for Signaling/Control Information, or wait till next section!!
n Estimate the number of E1’s needed» Total # E0 channels/30 = # E1 links
418
Step 2: Step 2:
n If #E0/30 > 1– more than one E1 is needed– One may limit the #E1/BTS to one. In such a case
the number of TCH’s per BTS may be limited by E1 capacity, i.e. roughly 28*4=112 TCH’s per BTS.
n If #E0/30 < 1– Multiple BTS’s may be connected in a Daisy Chain
Configuration.
BTS
BTS
BTS
BSC
419
ExerciseExerciseExercise
420
Exercise Exercise Exercise
n The cell design in a cellular market is based on the following assumptions, n The total number of subscribers is projected to be 100,000.n the subcriber usage and grade of service in regions A and B are different.
– Case 1: Each of regions A and B are covered by 50 BTS’s, uniformly distributed. Find the number of TRX’s needed for each BTS in regions A and B.
– Case 2: Assuming the maximum number of TRX’s per BTS is 3, find the minimum number of BTS’s needed to support the traffic in this market.
Region A
Region B
DemographicsDistributions
WeighingFactor
Region A Region B
Population 0.5 %40 %60Income 0.3 %80 %20Vehicular Traffic 0.2 %50 %50
Traffic Paramters Region A Region B
Erlangs/Subs 50mA/sub 20mA/subGoS %1 %2
421
Exercise: Case 1 Exercise: Case 1 Exercise: Case 1
DemographicsDistributions
WeighingFactor
Region A Region B
Population 0.5 %40 %60Income 0.3 %80 %20Vehicular Traffic 0.2 %50 %50
Average Percentage of subscribersNo. of subscribers in each regionTotal Erlangs in Each RegionErlangs/BTSNumber of TRX’s/BTS
422
Exercise: Case 2 Exercise: Case 2 Exercise: Case 2
DemographicsDistributions
WeighingFactor
Region A Region B
Population 0.5 %40 %60Income 0.3 %80 %20Vehicular Traffic 0.2 %50 %50
Average Percentage of subscribersNo. of subscribers in each regionTotal Erlangs in Each RegionMaximum Erlangs per BTSNumber of BTS’s
423
Chapter 4.Chapter 4.Chapter 4.
n Introduction: » Planning Objectives, Concepts
n Planning Inputs» Traffic, Call and Mobility Models» Basic Concepts and Calculations
n Dimensioning (New System)» BTS
• Traffic Channels• Control Channels
» Links to/from BSC (Voice & Signaling)» BSC» Links to/from MSC/VLR » MSC» HLR/AC
n Section Summary and Discussions
424
BSC interfaces ReviewBSC interfaces Review
n BSC <-> BTS– Voice Ports (E1 trunk)– Abis Ports (64kpbs LAPD link)
n BSC <-> MSC/VLR– Voice Ports (E1 trunk)– A link (64kbps SS7 F link)
n BSC <-> OMC (R)– Data link (X.25 data link)
BSC
MSCMSC
BTS2BTS2
OMCOMC
BTSnBTSnBTS1BTS1
425
BSC <=> BTS LinkBSC <=> BTS Link
n No of the voice ports (E0) required between the BTS(s) and BSC is determined by the BTS and the traffic channels allocated for the offered traffic.
n The of number of signaling link required can be derived form the number of traffic channels allocated.– Normally an E0 link will be sufficient
to carry the maximum voice/signaling data to/from a BTS.
BTS
BSC
426
BSC <=> BTS Voice PortsBSC <=> BTS Voice Ports
n If TRAU is at the BTS– Total voice ports = total TCH used by the BTS (all of
the sectors)
n If TRAU is at BSC or MSC– Total voice ports = total TCH used by the BTS (all of
the sectors)/ 4, rounded up!
BTS
BSC
n It is possible that a full E1 link may not be required by a BTS in this case BTS’s can be connected to E1 in Daisy Chain Configuration.
427
BSC <=> BTS Signaling PortsBSC <=> BTS Signaling Ports
n The number of Abis signaling links can be determined from – BHCA or call arrival rate obtained from
» Total Erlangs From all BTS sectors to BSC» and Average Call Duration
– Number of SMS and Location Updates /Call– Abis Message Sizes
BTS
BSC
428
BTS<=>BSC Signaling PortsBTS<=>BSC Signaling Ports
n N S/C = No. of call setup/clearing messages
n L S/C = Average message size of call setup/clearing
n P SMS = No. SMS/Call Ration N SMS = No. of SMS messagesn L SMS = Average message size for SMSn M SMS = Average SMS data sizen P Loc = No.Location Updates/Call
No Bytes Call N L P N L M
P N L P N L
R No Bytes Call bits byte No Calls Sec i e
NR
kbps U
S C S C SMS SMS SMS SMS
Loc Loc Loc HO HO HO
S
ES
Abis
. / ( )
. / / . / ( . . )
/ /== ×× ×× ++ ×× ×× ++ ++++ ×× ×× ++ ×× ××
== ×× ××
==××
1
8
640
λλ
n N Loc = No of Location Update messagesn L Loc = Average message size for
Location Updaten N HO = No of Handoff’sn L HO = Average message size of
Handoff’sn R S = Signaling Rate bits/secn N E0 = No. of 64kbps E0 channels
neededn U Abis =Utilization of the Abis Link
429
BSC<=>MSC/VLR: Voice PortsBSC<=>MSC/VLR: Voice Ports
n Aggregate the Erlang from all of the BTS’s, call it eBTS-BSC
n Perform an Erlang B look up with a GoS of BSC (usually smaller than BTS GOS) and eBTS-BSC to determine the number of voice channels required.
n from number of Voice Channels find the number of E0 channels needed– If TRAU is at the BSC # E0’s = # Voice CH’s– If TRAU is at the MSC # E0’s = # Voice CH’s/4, rounded up
BTS1BTS1
BTS2BTS2BBSSCC
TRAUTRAU
e1
e2
BTS2BTS2en
eBTS-MSC
MSCMSC
430
BSC<=> MSC/VLR Signaling linkBSC<=> MSC/VLR Signaling link
n N S/C = No. of call setup/clearing messages
n L S/C = Average message size of call setup/clearing
n P SMS = No. SMS/Call Ration N SMS = No. of SMS messagesn L SMS = Average message size for SMSn M SMS = Aveage SMS data size.n P Loc = No.Location Updates/Call
n N Loc = No of Location Update messages
n L Loc = Average message size for Location Update
n N HO = No of Handoff’s
n L HO = Average message size for Handoff’s
n R S = Signaling Rate bits/sec
n N E0 = No. of 64kbps E0 channels needed
n U A =Utilization of the A Link
No Bytes Call N L P N L M
P N L P N L
R No Bytes Call bits byte No Calls Sec i e
NR
kbps U
S C S C SMS SMS SMS SMS
Loc Loc Loc HO HO HO
S
ES
A
. / ( )
. / / . / ( . . )
/ /= × × + × × + ++ × × + × ×
= × ×
=×
1
8
640
λ
Note that these messages sizes are not the same as Abis link messages. (Why?)
431
BSC <BSC <--> OMC(R)> OMC(R)
n The data interface between the BSC and OMC is based on the X.25 data protocol.
n A single X.25 data link can be planned for this OMC interface. The capacity of this link depends on the BSC sizing and number of BTSs connected.
n 19.9kbps or higher is recommendedn Usually a 64kbps E0 link is sufficient.n The connection from BSC to OMC may be
indirect through MSC.BSCOMC
432
BSC Dimensioning (review)BSC Dimensioning (review)
n The BSC capacity in general is Its ability to connect to and process information received by all the signaling links from BTS(s), MSC and OMC.
n This capacity is usually expressed in terms of– Max_BTS: Total No of BTS that can be supported/controlled,– Max_TRX: Maximum number of TRX’s in the connected BTS’s.– Max_CA: Maximum number of CA– Max_PORT: Total Number of Ports, (input and output together)
BTS BSC
MSC/VLR
BTS
BTS
OMC
433
BSC DimensioningBSC Dimensioning
n For a given system once all of the trunk traffic to the BSC has been identified the capacity requirement can be determined.– The Total Erlang (or BHCA) from all of the BTS < Max_CA – The total number of ports required by the BSC< Max_PORT– Number of Connected BTS’s < Max_BTS– Number of TRX’s on Connected BTS’s < Max_TRX– The total number of Signaling links < Maximum No. of signaling
links supported
n Once the capacity and performance requirement has been identified the equipment (no of boards etc.) can be determined.
434
Chapter 4.Chapter 4.Chapter 4.
n Introduction: » Planning Objectives, Concepts
n Planning Inputs» Traffic, Call and Mobility Models» Basic Concepts and Calculations
n Dimensioning (New System)» BTS
• Traffic Channels• Control Channels
» Links to/from BSC (Voice & Signaling)» BSC» Links to/from MSC/VLR » MSC» HLR/AC
n Section Summary and Discussions
435
MSC/VLR InterfacesMSC/VLR Interfaces
n MSC/VLR voice interfaces– BSC’s– MSCs – PSTN– MC (VMS)
n MSC/VLR signaling link interfaces– BSC’s– SS7 Network (Redundant SS7 A-link)
» HLR/AC» SM-gateway
– PSTN (SS7 ISUP Signaling)– MSC (SS7 F-link)
n EIR (SS7 F-link)n OMC (X.25 link)
MSC
PSTNPSTN
OtherOtherMSC2MSC2
OMCOMC
MCMCBSC’sBSC’s
HLR/ACHLR/AC SMSM--GWGW
SS7 Network
EIREIR
436
MSC/VLR <MSC/VLR <--> BSC Voice Ports> BSC Voice Ports
n The Number of MSC ports, needed for MSC to BSC voice transmissions is the sum of all E0 channels from all of the BSCs
MSC
BSC3BSC3BSC2BSC2BSCnBSCnBSC1BSC1
Nports = NBSC1 + NBSC2 +...+ NBSCn
437
MSC/VLR <MSC/VLR <--> MSC Voice Ports > MSC Voice Ports
n MSC/VLR <->MSC» Voice trunks are required between MSCs to support » MTM calls without routing the call to the PSTN » inter MSC HO» MC traffic across MSC’s
n Initially an E1 link will be planned between each MSC pair which are subject to inter MSC handover.
MSC1
MSC2
438
MSC/VLR<MSC/VLR<-->PSTN>PSTN
n The Number of Voice Ports can be determine from– Total erlangs from all of the BSCs (already calculated)– GoS from the traffic model– Erlang B table
MSC PSTN
eBSC1
eBSC2
eBSCn GoSMSC
439
MSC/VLR<MSC/VLR<-->MC (VMS)>MC (VMS)
n The Number of voice ports can be estimated using the – Incoming Erlang to MC, which is the product of
» % of calls terminating to voice mail which is • % of subscribers provisioned for the service times • % of subscribers either not answering the call or call forwarded
the calls
» Total incoming erlangs to the switch* % of call terminated to voice mail
– With GoS of VMS = 0.01 %– Erlang B MSC
MCMC
440
MSC/VLR Signaling linksMSC/VLR Signaling links
n The SS7 backbone has been planned and designed (assumption here is that an existing network is used).
n And that the SS7 network is designed to handle the traffic from the PLMN that is being planned.
n Planning a fix SS7 packet network is a major task. Many large operators design their own SS7 network (STPs).
441
MSC/VLR<MSC/VLR<-->BSC A Signaling Link>BSC A Signaling Link
n To determine the total no of MSC-BSC signaling links required add the numbers of links from each BSC from earlier calculations.
MSC
BSC3BSC3BSC2BSC2BSCnBSCnBSC1BSC1
442
MSC/VLR <MSC/VLR <-->SS7 Network>SS7 Network
n To determine the number of links required for connection to the SS7 network must calculate the following:
n The sum of the signaling traffic – To/from the HLR-AC– To/from SM gateway – To/from the MSCs outside the network is
required.(this is considered negligible)
MSC
HLR/ACHLR/AC SMSM--GWGW
SS7 Network
443
HLR transactionsHLR transactions
n Traffic to/from HLR-AC is calculated base on the following transactions– Authentication – Termination – Location Updating– SMS messages (send routing information, Set
Message Waiting etc.)– HLR Interrogation
HLR/AC
444
HLR transactions: AuthenticationHLR transactions: Authentication
n No of octet/sec to/from HLR related to Authentication is computed in two steps:– Calculate total #authentication transactions/sec
» Assuming authentication is performed n=1 times every CA» Total no of Auth transactions/sec = total CA /sec * n
– Calculate total number of Auth octets/sec» Total no of octet for Auth/sec = 2 Message per transactions*
30 Octet per message * total no of Auth transactions/sec
445
HLR transaction: TerminationsHLR transaction: Terminations
n No of octet for to/from the HLR related to Termination is computed in two steps:– Calculate total #termination transactions/sec
» Total no of terminations transactions /sec =• Total CA/sec *( MCM + MTM)%
– Calculate total #termination octets/sec» Total no of termination octets /sec =
• total No of Termination transactions/sec *• 2 message per transaction * • 30 octet per message
446
HLR Trans. : Location UpdatesHLR Trans. : Location Updates
n No of octet for to/from the HLR related to Location Update is computed in two steps:– Calculate total number of Location Update
transactions• Total no of Location Update transactions /sec = Total
CA/sec * Ratio of Location Updates
– Calculate total number of Location Update octets/sec
• Total no of location update octets/sec = total no of location update transactions/sec * call attempts * 2 messages call attempts * 25 octet per message
447
HLR transactions: SMSHLR transactions: SMS
n No of octet for to/from the HLR related to MT and MO SMS is computed in two steps:– Calculate total number of SMS transactions
» Total no of SMS transactions /sec = Total CA/sec * Ratio of SMS
– Calculate total number of SMS octets/sec» Total no of SMS octets/sec = Total no of SMS transactions
/sec * 2 Messages per call * of 33 octet per message
448
SMSM--gateway transactionsgateway transactions
Traffic to/from SM gatewayn The SMS Gateway will support both the MO
SMS as well as MT SMS services.n To calculate the number of octet to/from SM-
gateway– Calculate total number of SM gateway transactions/sec
» Total no of SM gateway transactions/sec = Ratios of SMS calls * CA/sec
– Calculate total number of SM gateway octets» Total no of SM gateway octets/sec = Total number of SM
gateway transactions/sec * 2 message per call * 100 octet per message
449
Signaling Rate on MSCSignaling Rate on MSC--SS7 LinksSS7 Links
n The total MSC transactions/sec is the sum of – Total number of SM gateway transactions/sec – Total no of Auth transactions/sec– Total no of Terminations transactions /sec– Total no of Location Update transactions /sec– Total no of SMS transactions/sec
n The total no of octets/sec is the sum of– Total no of SM-gateway octets/sec– Total no of Auth octet/ sec – Total no of Termination octets/sec– Total no of Location Update octets/sec– Total no of SMS octets/sec
450
MSC/VLR<MSC/VLR<-->SS7 network>SS7 network
n No of MSC signaling links to SS7 network is
n Since this is an SS7 A-link connection, a pair of link set is required to each STP pair. Follow the SS7 link rules to determine no of links required.
NOctets
kbps U A
==××
××/ sec 8
64
MSC
HLR/ACHLR/AC SMSM--GWGW
SS7 Network
451
MSC/VLR PSTN signaling linkMSC/VLR PSTN signaling link
n To calculate the no of SS7 ISUP links required– Determine No of ISUP messages per call attempts
» Assume 5 messages
– Determine number of octets per message» Assume 25 octets per message
– 5 messages * 25 bytes/ message * No. Call attempts/sec / 64 Kbps * SS7 link utilization
Normally an SS7 F link is configured. Follow the SS7 link guide line to allocate no of links required.
MSC
PSTN
452
Other ConnectionsOther Connections
n The MSC/VLR-OMC interface is based on X.25 – One E0 link is sufficient to handle the traffic.
n The MSC/VLR-EIR interface is based on the SS7 signaling and it is operator dependent. – A single SS7 E0 link is recommended. – The operators normally provide this functionality as
part of OSS (Operations Sub-System).
453
MSC/VLR DimensioningMSC/VLR Dimensioning
n The MSC/VLR capacity in general is– Its ability to connect to and process information
received by all the signaling links from BSC(s), HLR and OMC.
– The MSC capacity usually expressed in terms of» Maximum no of BSC that can be supported/controlled (a
hard value)» Maximum no of Call Attempt (CA)» Maximum no of voice ports it can support (I/O)» Maximum no of Signaling link can be supported
– The VLR capacity limits are based on» Number of subscribers (less and less of limiting factor)» Transaction/sec processing on the VLR database
454
MSC Dimensioning (cont.)MSC Dimensioning (cont.)
n For a given system once all of the voice port and signaling link to the MSC has been identified the size of MSC can be determined. – The total Erlang from all of the BSCs < Maximum
erlang supported by the MSC– The total number of voice ports required <
Maximum ports supported by the MSC– The total CA from all of the BSCs < Maximum CA
supported by the MSC– The total number of signaling links required <
Maximum signaling links supported by the MSC
455
MSC Dimensioning (cont.)MSC Dimensioning (cont.)
n The VLR limitations must also be met» Total number of subscribers < Maximum no of subscribers» Total number of transactions/sec < Maximum no of
transaction/sec
n If required traffic is greater than the MSC/VLR limits then provide different alternatives
» Possible add to the number of MSCs or a plan for a larger MSC/VLR
» Or if other MSCs already exist determine the possibility of sharing with the other MSCs
n Based on the constraint select the best alternatives
456
ExerciseExerciseExercise
n Using the information provided in page 4-25, 4-27 and 4-28 estimate the number of signaling ports between BSC and MSC.
n Assuming the total Erlang at the BSC is 1000 and average call duration is 120sec.
BSC
MSCMSC
457
HLR/AC TransactionsHLR/AC Transactions
n Major HLR/AC transactions that effects HLR sizing– Authentication – Termination validation– Location Updating– Subscriber provisioning (add/delete/update)
» Which is not considered for traffic calculations
– SMS messages (send routing information, Set Message Waiting etc.)
– HLR Interrogation
MSCVLR
MSCVLR
HLR/ACHLR/AC
SS7 network
SM-GMSC
458
HLR/AC interfacesHLR/AC interfaces
n The HLR will interface to the SS7 network via the SS7 A-link.
n To plan for the A-link the traffic from various elements must be considered– MSC/VLRs – SMS-gateway
n Based on previous calculations ( MSC to SS7 network) determine the no of signaling link required for HLR to SS7 network.
n Note: the total call attempts will be the sum of call attempts from all the MSCs.
459
HLR/AC Dimensioning HLR/AC Dimensioning
n Many HLR/AC platforms can support millions of subscribers in their database. The traffic load is critical issue.
n It is important that the HLR/AC supports the present maximum traffic and allow for growth of the number of subscribers and transactions.
n The HLR limits are– Number of transactions/sec
– Number of signaling links
– Number of Subscriber
460
HLR Dimensioning HLR Dimensioning
n The total number of transactions from all the elements < Maximum number of transactions supported by the HLR
Aggregate Transactions
Processor
Utilization
10000 20000 30000 40000 50000
20
4
060
80
100
The Planning Limit
461
Chapter 4.Chapter 4.Chapter 4.
n Introduction: » Planning Objectives, Concepts
n Planning Inputs» Traffic, Call and Mobility Models» Basic Concepts and Calculations
n Dimensioning (New System)» BTS
• Traffic Channels• Control Channels
» Links to/from BSC (Voice & Signaling)» BSC» Links to/from MSC/VLR » MSC» HLR/AC
n Section Summary and Discussions
462
Chapter 4: Review and DiscussionsChapter 4: Review and DiscussionsChapter 4: Review and Discussions
Planning ConceptsDimensioningNetwork Elementsand Interconnects
463
Chapter 5.Chapter 5.Chapter 5.
n Fixed Network Configurations Rules/ Planning Options
n Network Expansion for Existing Systemn Trends in GSM Networks and Future Mobile
Networks– UMTS and IMT2000 Perspectives
n Course Summary and Discussions
464
Planning/Configuration StepsPlanning/Configuration StepsPlanning/Configuration Steps
n Review Inputs: – Average Size and Capacity of Links
and Network Elements– BTS Locations
n BSC Planning– Preferred Locations– BTS-BSC Configurations– BTS-BSC Assignment
n GMSC/MSC Planning– MSC Preferred Locations– BSC-MSC assignment
n HLR Location, Redundant HLRn OMC Location
From Dimensioning
From RF Design
465
ConfigurationConfigurationConfiguration
n Once the dimensioning of the elements and link requirements have been identified consider– Where and how to lay out each element and interconnect– What kind of circuits to use for interconnect E0,E3.– Fiber v.s Microwave what is available? What is more economical?
Perform cost analysis– Is it better to size the HLR based on current requirements and
growth, how costly is it to expand later?– Try different interconnects. Is there a saving to be made?– Identify MSC to MSC interconnects, a ring or a star configuration.
466
AlternativesAlternativesAlternatives
n Compare the alternatives you have devised based on – COST– Time frame– Features– Demand– Technology
n Select the best alternative and be flexible to changes (customer is right !)
467
BackboneBackboneBackbone
n The backbone is the transmission facility that allows the interconnects of the GSM elements via the E0/E1 links.
n Decide on the type of backbone, before planning any of the equipment.– This decision is mostly based on
» Availability » Cost » Reliability
n Make sure the same clock source is used for synchronization of the entire backbone
468
TransportTransportTransport
n How to interconnect the elements in the GSM network? What facilities to use?
n This one of planners concerns– BTS to BSCs– BSCs to MSCs– MSCs to PSTN
?
469
Digital Transmission Digital Transmission Digital Transmission
n Digital Transmission – The analog signals are sampled, coded and
multiplexed into a digital bit-stream which is modulated into digital carrier (electrical, microwave or optical)
– One single channel has a rate of 64 Kbs, Several voice channels are multiplexed into this bit-stream.
» Voice channels sampled at the twice the rate therefore
• 4Khz * 2 * 8bits = 64Kbps.» The GSM air interface uses a vocoding (Voice
coder/decoder) to compress the 4 Khz bandwidth to 8Kbps digital bits.
470
Digital TransmissionDigital TransmissionDigital Transmission
n Digital hierarchy– E0 64Kbps 1VC– E1 2.048Mbps 30E0– E2 8.4Mbps 4 E1– E3 34.3Mbps 16E1– E4 139.2Mbs 64E1– E5 565.1Mbps 256E1
n Devices based on the hierarchy are
Channel Bank Intelligent Channel Bank
MUX Digital Cross Connect
Voice&Other signals
E1
Flexible assignment of channels to E1s
1 E3
16 E1 E0 E1E1
471
Synchronous HierarchySynchronous HierarchySynchronous Hierarchy
n Two standards exist ITU standard describes the Synchronous Digital Hierarchy (SDH) and the other is the North American ANSI standard that describes the Synchronous Optical NETwork(SONET) with optics rate in mind.
472
Microwave OptionMicrowave OptionMicrowave Option
n Provides transmission– When right of way is difficult to obtain– Rapid deployment is required
n Available in wide range of capacities– E1 and Lower rates– SDH and SONET rates
n Wide range of frequenciesn Atmospheric conditions affect the quality of
transmission.n Sometimes less expensive than the leased lines
473
Cost AnalysisCost AnalysisCost Analysis
n A transport network design – Fiber optic link (option 1)– Microwave lease (option 2)
n From cost analysis of the two options it may be concluded that after the second year option 1 will pay for itself and a fiber optic backbone will be more cost effective in long run.
n List other pros and cons
474
Cost analysis exampleCost analysis exampleCost analysis example
This is an example of a cost analysis for a backbone network. Two options are presented, One with a leased links as an interconnect method and the other purchase of microwave radio. Assuming the following configuration for a leased line
A
B
C
D
E
f
gh
i
475
Option 1: Leased LineOption 1: Leased LineOption 1: Leased Line
PathNo of links
Launch Year1
Distancein Kms
AmountLaunch Year 1
A - i
A-f
A-g
A-h
B-C
C-D
D-E
E-A
2 5 135 $342K $856K
1 2 35 $86K $171K
1 2 55 $114K $228K
1 1 70 $114K $114K
1 100 $171K
1 30 $86K
4 200 $856K
2 265 $428K
Total $656K $2910K
Option I :COST of leased line (assume $2856/Km)
476
Option 2: Microwave costOption 2: Microwave costOption 2: Microwave cost
Option II :Cost of Microwave infrastructure for 1 year
PathDistancein Kms
Cost of Tower includingRoyalty
A - i
A-f
A-g
A-h
B-C
C-D
D-E
E-A
135 $320K $100K
35 $80K
55 $140K $30K
70 $140K $30K
100 $192K $110K
30 $64K
200 $640K $270K
265 $640K $270K
Sub-total $2216K $900K
Cost of MicrowaveEquipment
Total $3116K
477
AnalysisAnalysisAnalysis
n Obvious comparison shows the cost of leased line (option 1) for the first year is lower than the microwave cost. But the second year the microwave infrastructure pays for it self and there are other advantages :
n Possible earned revenue by leasing the extra bandwidth available to private network operators.– Save on leased links required for other interfaces like billing,
OMC, NMS etc.– Increased system reliability, therefore satisfied customers.– No wait delay in ordering new links
478
Cell PlanningCell PlanningCell Planning
n Our assumption is that the Cell Planning has been done based on coverage, capacity and interference analysis.
n Do we know these steps?– coverage,– capacity and– interference analysis
479
Abis InterfaceAbisAbis InterfaceInterface
n Abis links can represent a substantial part of the running costs of a PLMN.
n If each BTS site requires a relatively small number of circuits, economies can be obtained if the drop and insert , or Daisy Chain connection method can be used at the BTS. – This technique provides the ability to share a 2 Mbit/s
multiplex between several BTS sites, and to decrease the number of leased or installed transmission links.
480
BTS TRAU BSC MSC To Fixed Networks
To MS
BTS MSC To Fixed Networks
To MS BSC TRAU
BTS MSC To Fixed Networks
To MS BSC TRAU
AInterface
A-bisInterface
RF AirInterface
13 kbps encoded voice / 12 kbps data
16 kbps transmission
64 kbps transmission
Physical site
TRAU LocationTRAU LocationTRAU Location
481
Low and High Traffic AreasLow and High Traffic AreasLow and High Traffic Areas
n In rural areas, most BSs are installed to provide maximum coverage rather than maximum capacity. High levels of traffic are not problems in those areas.
n If the cells are not colocated, the BSS will be split between BSC and BTS where BSC will then be connected to severalBTSs.
n For high-traffic surroundings in urban areas, MSC can be connected to a number of BSSs via A-interfaces. Some of the BSSs are multicell (sectored) sites.
n Several groups of omnidirectional as well as sectorized BTSs may be tied into a common remote BSC via combinations of star, chain, and multidrop connections.
482
BSC Location/Capacity BSC Location/Capacity BSC Location/Capacity
n The location and capacity range of the BSCs is a debated point. – Some operators want small BSCs on the BTS sites. – Some other operators want big BSCs on the MSC sites.
even possibly a single BSC per MSC. – Others want independent BSCs with a capacity
intermediate between a BTS's and an MSC's, and which can potentially be sited in any location, not necessarily with a BTS or an MSC.
n If more than one BSC is used do not co-locate the BSC to avoid any natural disaster disturbing the operations of all of the BSCs
483
BSC LocationBSC LocationBSC Location
n Various considerations will dictate the choice. – A BSC has three main functions: it acts as a circuit
concentrator, and as such its position impacts the running costs of the transmission lines between BTSsand MSCs.
– A BSC is also an operation and maintenance agent; we will see that the BTSs are not linked directly to the OSS, but through their BSC.
– Finally, a BSC is where handovers are controlled. Bigger BSCs lead to a smaller number of handovers which must be handled by the MSC and the bigger the BSC the wider the knowledge concerning the traffic used to decide on handovers.
484
BSC Location (cont.)BSC Location (cont.)BSC Location (cont.)
The list of preferred BSC location should be prepared based on
n Low Cost, client owned/leased buildings.n Availability of backhaul links n Access, Utilities, Security and maintainability
Considerationsn Easy connection to BTS’sn Being in the center of cluster of cells,
– Having BTS’s in LOS, if Microwave link are to used– Having MSC in LOS, if Microwave link are to used
485
BTS to BSC AssignmentBTS to BSC AssignmentBTS to BSC Assignment
n Starting from the most preferred BSC location, a group of BTS’saround a that BSC are assign to it Considering:
n The BSC limitations (# BTS’s, #TRX’s,.#Erlangs...)
n Short/easy connections, The BSC may be co-located with one of BTS’sin the middle of the cluster.
n Possibility of daisy chain connection of some of BTS’s using E1 or E3 links
n Minimization of inter-BSC handovers rates, by not leaving major highways and intersections at the boundary of BSC coverage area.
486
BSCBSCBSC
n Once a set of BTS’s are assigned to a BSCn The total voice and signaling traffic on
Abis links should be checked.n At this point alternative BTS-BSC
connection configurations should be of considered for best utilization of the links.
n Total Voice and signaling traffic from all selected BTS’s to BSC should be checked against BSC size and capacity selected as part of dimensioning.
487
BTS-BSC ConfigurationsBTSBTS--BSC ConfigurationsBSC Configurations
n There are several BTS-BSC configurations: – single site, single cell; – single site, multicell; and– multisite, multicell.
n These configurations are chosen based on the rural or urban applications. These configurations make the GSM system economical since the operation has options to adapt the best layout based on the traffic requirements.
n System optimization is possible by the proper choice of the configurations
488
BTS-BSC ConfigurationBTSBTS--BSC ConfigurationBSC Configuration
n Some of BTS-BSC Configurations include– omnidirectional rural configurations where the BSC and
BTS are on the same site; – chain and multidrop loop configurations in which
several BTSs are controlled by a single remote BSC with a chain or ring connection topology;
– rural star configurations in which several BTSs are connected by individual lines to the same BSC; and
– sectorized urban configurations in which three BTSsshare the same site and are controlled by either a collocated or remote BSC.
489
Omnidirectional Configuration
Omnidirectional Configuration
BTS BTS BTS
A - Interface
A - Interface
1
2
Star Configuration
BTS BTS A - Interface
3BSC
BTS
BTS BTS BTSA - Interface
4BSCMultidrop Configuration
BSC
BTS
BSC
BTS-BSC ConfigurationsBTSBTS--BSC ConfigurationsBSC Configurations
490
BSC
A - Interface
6
Sectorized Configuration with remote BSC and MSC-BSS configuration
BTS1 BTS2 BTS3
BSC
A - Interface
5Sectorized Configuration
BTS-BSC Configurations (cont.)BTSBTS--BSC Configurations (cont.)BSC Configurations (cont.)
BTS1 BTS2 BTS3
BTS1 BTS2 BTS3
491
ExerciseExerciseExercise
n A cellular network consists of 100 BTS’s, 50 of which are in central downtown area and 50 of them are in the suburbs. The BTS’s are uniformly distributed.– Each BSC can handle upto 30 BTS’s. – How do you place the BSC’s and how do you assign BTS’s to
BSC’s.Hwy 1
Hwy 2
492
MSCMSCMSC
n The trend is to have MSCs of as high a capacity as possible with the present switch technology.
n Currently the order of magnitude of an MSC capacity is tens of thousands of Erlangs.
n For a network with a 10% penetration of the population and 0.02 Erlang per subscriber, a 2000 Erlang MSC is suitable for an area with 1000 000 inhabitants.
n This is commensurate with the present density of PSTN switch locations. MSCs can then be sited in rather important towns, and will cover a part of the biggest towns or a medium town and the surrounding area.
493
Distributed v.s. CentralizedDistributed v.s. CentralizedDistributed v.s. Centralized
n Comparison of distributed design vs. centralized Distributed design Centralized
– Allows for easy expansion Not as easy– Reliability/availability Any minor change may
effect the system– Easier to adapt to IN standard Harder to adopt– Faster introductions of services Slower– Less complex and easier to maintain Harder to maintain– (it is logically divided into sub-system)– Cost More (facilities to interconnect) Less costly
MSCSTP
HLR/ACHLR/AC
VLRVLR
EIREIR MSC/VLR/HLR/AC/EIR
494
MSC ConfigurationMSC ConfigurationMSC Configuration
n MSC functionality– Some manufactures of the MSCs can provide one or all
of the following functionality within the MSC platform» VLR, MSC, HLR, EIR, STP in addition to SSP functionality
n When considering small PLMN network (less than 3MSCs) it is more economical and efficient to design a non distributed (centralized) system.
495
MSC LocationsMSC LocationsMSC Locations
n Generate a list of best candidates for MSC locations, considering:
n The required number of MSC’s predicted (as part of Dimensioning), consider centralized and distributed options separately.– Low Cost, client owned/leased buildings.– Availability of links to PSTN – Access, Utilities, Security and maintainability
Considerations– Possibility of Expansion – Easy connection to BSC’s
496
Low Cost Configuration OptionsLow Cost Configuration OptionsLow Cost Configuration Options
CO
CO
CO
CO
CO
CO
CO
CO
MSC
BSC
BSC
BSC
497
MSC ConfigurationMSC ConfigurationMSC Configuration
n Normally the MSC and VLR functionality are combined.
n One MSC within the PLMN must perform Gateway functionality to route the incoming calls from PSTN to the MSC/VLR
n Plan to have MSCs of as high a capacity as possible for a given number of subscriber and BHCA.
n Depending on the services provided plan to support IWF and SM gateway interfaces/functionality.
498
MSC/VLR interconnectsMSC/VLR interconnectsMSC/VLR interconnects
n The system interconnect can be divided into– Voice interconnects– Signaling /Data interconnects
n The MSCs voice/signaling interconnect may be designed to allow for alternate routing within the PLMN. If Route AB fails route AC to CB can succeed
GMSC/VLRA
MSC/VLRB
MSC/VLRC
499
MSC signaling InterconnectsMSC signaling InterconnectsMSC signaling Interconnects
n The MSC SS7 signaling interconnects can be planned using an STP pair (a separate hardware) or one of the MSCs in the network can perform STP functionality (if supported by the switch manufacturer).
GMSC/VLRSTP
MSC/VLRB
MSC/VLRC
National SS7 network
500
MSC Planning ConsiderationsMSC Planning ConsiderationsMSC Planning Considerations
n For a small network (< 3 MSCs) it is recommended to configure the MSC to perform STP functions.
n As the network expands it may be feasible to plan for local STP pairs which can then connect to the national STP network.
n Some of the important factors in deciding the need are:– Complexity of the network
» Too many voice and signaling interconnect through the MSC
– Maintainability » As the network becomes larger it may be harder to maintain, so it is
better to separate the packet switching from the circuit switching functions.
501
NSS ConfigurationNSS ConfigurationNSS Configuration
n The operator may or may not, depending on the terms of its license, have the right to mesh its MSCs and GMSCsand have its own transit exchanges.
n Similarly, the operator may have the right to set up its own signaling links between NSS machines and have its own Signaling Transfer Points (STPs).
n In either case, operators must decide on the number and location of the GMSCs (e.g., in the same machine as an MSC or not), the interworking functions with the fixed networks and the SMS-GW for short messages etc.
502
Possible SSS configurationsPossible SSS configurationsPossible SSS configurations
n The following shows an example of SSS star trunk configuration where A,B, C and D are gateways to their respective SSS network.
A
C
B
D
503
Tandem SwitchesTandem SwitchesTandem Switches
n The system complexity and interconnect can be eliminated by adding Tandem switch which performs trunk routing functionality (E an F can perform tandem switch functionality in addition to other functionality)
AC
BD
E F
504
NSS Configuration (Cont.)NSS Configuration (Cont.)NSS Configuration (Cont.)
n A daisy chain configuration may be effective for small network with a few interconnects (up to 4).
n It is recommended when expanding such a network a Tandem switch with trunk routing capabilities be added, so that the daisy chain configuration will be changed to a star interconnect configuration.
b d
c
a c
b d
c
a
505
GMSC, HLR, IWFGMSC, HLR, IWFGMSC, HLR, IWF
n Select one centralized location for GMSC, this location should have easy/low cost access to public networks, such as PSTN, ISDN, PSPDN,..
n Usually IWF is co-located with GMSC.n To ensure the availability of HLR, at least two
HLRs are usually planned. n One HLR can be co-located with GMSC and
the other HLR at a different location preferably co-located with one of other MSC’s.
506
GMSC Connections (option 1)GMSC Connections (option 1)GMSC Connections (option 1)
GMSC
MSC
MSC
HLR
P S T N
P S T N
507
GMSC Connection (option 2)GMSC Connection (option 2)GMSC Connection (option 2)
GMSC
MSC
MSC
HLR
SS7 Packet Switch
Network
P S T N
P S T N
508
HLR/AC planningHLR/AC planning
n The HLR/AC can be part of the MSC or in a distributed architecture a separate platform. With in the IN architecture the HLR is an SCP (Service Control Point) which will perform service definition/execution environment.
n The HLR/AC must be planned as a pair to avoid single point of the failure.
n Generally the operator’s network can be supported by a pair of HLR/AC supporting multiple MSCs.
n Choose the fastest/relatively economical hardware platform since the computer technology is at high gear. Chose an HLR platform that is expandable.
509
HLR/ACHLR/ACHLR/AC
n Plan for the HLR/AC to be on a separate platform than the switch.– Allows for easier introduction of services
when integrated with the SCP.– Since it is based on computer platforms/and
not a switching platform, it will be » Easier to maintain/upgrade» Easier to expand» More cost effective in the long run» Faster processing power and more capacity
(memory) in short time.
510
EIREIREIR
n Initially plan to include the EIR in the HLR or MSC depending on the configuration supported by the manufacturer.
n As the network grows follow the distributed architecture
511
Chapter 5.Chapter 5.Chapter 5.
n Fixed Network Configurations Rules/ Planning Options
n Network Expansion for Existing Systemn Trends in GSM Networks and Future Mobile
Networks– UMTS and IMT2000 Perspectives
n Course Summary and Discussions
512
Planning Exiting NetworkPlanning Exiting NetworkPlanning Exiting Network
The purpose of the planning for existing network is usually – System improvement
» To expand the system» To introduce new elements to the network» To increase system reliability» To add new features/services
– System Problem identification and resolution
513
Approach Approach Approach
n After determining the objective and purpose of planning
n Perform the following steps as required by the objective before any new services or additional growth can be planned. – Functional Model– Traffic Flow (only when adding new service or new
elements)– Data collection– Cost analysis
514
ApproachApproachApproach
n Functional Model– A network block diagram defining the interfaces
» Signaling interfaces» Voice Trunk interconnects» Number Routing and address routing information
n Traffic Flow (only when adding new service or new elements)
515
Approach (cont.)Approach (cont.)Approach (cont.)
n Data collection– For a fix period of time (i.e 10 days) collect statistical
data from each network element that is effected by the objective. The statistical data normally is collected by the by the OMC. For specific data sometimes it is required to execute a batch file on the OMC or on the specific network element.
– Data Analysis– Analyze the data collected to meet the objective.
n Cost analysis– Perform the transport network cost analysis– Physical space cost analysis– Equipment life cycle analysis v.s cost
516
Traffic FlowsTraffic FlowsTraffic Flows
n When adding a new service/subscriber feature or a new network element to the network the effect of the change must be identified.
n Obtain the message flow diagram showing all the elements involved, including– The number of messages– The size of each message– % of subscribers expected to use the service/feature– Estimate the number of transaction/sec – Estimate Call mix, traffic model and service mix model impact
n These information will be required later to identify whether or not the current system can support the feature.
517
Data CollectionData CollectionData Collection
n Collect the data from each network element that is affected, on an hourly basis (Some network elements have the flexibility to present the data in many forms e.g. plots, charts etc.)
n Collect the information required from the MSC/VLR and the HLR to construct – The Call Mix – The Traffic model– The service mix model– Collect the processor utilization usage.
» Collect Call attempts /hr from the MSC/VLR» Collect number of Transactions /hr from the HLR or VLR» Plot the MSC processor utilization v.s Call attempts /hr» Plot the HLR or VLR processor utilization v.s number of
transactions/hr
518
Data Collection Data Collection Data Collection
n Signaling links statistical data from each data link that is to be effected. Specifically the– Number of frame rejects/hr – Number of frame retries/hr – Number of signaling information frames/hr– Total number of messages /hr– Total number of bytes/hr– Obtain the link utilization for the element
» total number of bytes per hr * 8 / 3600 / maximum link speed
n Voice trunk utilization– Obtain the voice trunk utilization from the BSC or
the MSC
519
Processes Within a Network Element Processes Within a Network Element Processes Within a Network Element
n Note: Each fixed network elements processor can perform anyone or all of the following functions, therefore it is very important when collecting/analyzing the data to know how each processor is used
I/OCommunications
(Data link)
DATABASE
ADMINISTRATION, O&M(Billing, User Interaction)
APPLICATIONCall processing, Mobility
520
Data Analysis (Call mix)Data Analysis (Call mix)Data Analysis (Call mix)
n From the Call mix, Traffic model and Service model – Compare the Call mix model obtained to the model initially used
to plan the network if the call mix ratios varies more than a few % an overall system data collection/analysis is required. Otherwise no action is required from the call mix.
– Compare the traffic model data obtained to the model initially used to plan the network if the BHCA or no of HO has increased (%25)and the system experiencing unexplained problems perform an overall system data collection/analysis. Otherwise noaction is required.
– Compare the service model data obtained to the model initially used to plan the network if the ratio of service usage has increased more than 25% identify the the elements/signaling links that are effected by the service. Perform data collections and analysis of the element(s).
521
Data Analysis (Processors)Data Analysis (Processors)Data Analysis (Processors)
n From the MSC processor utilization v.s Call attempts /hr plot – If the Processor utilization exceed the planning limit
(recommend 75 to 80%) for a the Maximum BHCA supported and if this condition consistently (more than once) occurs for a given period (i.e 10 days) then a
» A Processor upgrade or» A system expansion or » A system rerouting /reconfiguration is required.
– Otherwise if the Processor utilization is not reaching the planning limits use the data to estimate capacity limits for future growth. Share the data with customer/marketing.
522
Processor utilizationProcessor utilizationProcessor utilization
Call attempts /hr
Processor
Utilization
1000 2000 3000 4000 5000
20
4
060
80
100
The Planning Limit
Day 1Day 2
523
Data Analysis (signaling link)Data Analysis (signaling link)Data Analysis (signaling link)
n From the data link utilization %– If this is an SS7 link and link utilization for each link
in the link set is over 40% consider adding another link.
– Forecast system growth/ additional traffic can be supported
– Note: When adding a new service/element the traffic impact must be added to the collected data.
n From excessive number of frames rejects & retries– Can detect possible physical layer problems – Processors over load and possible bottlenecks
» Rejects >= Retries > 5% Physical Link has problem» Retry- Reject > 1% Processor is overloaded
524
Data Analysis (Voice Trunks)Data Analysis (Voice Trunks)Data Analysis (Voice Trunks)
n Voice Trunk utilization– One can estimate the voice link utilization by:– Observing the busy/idle status of each time slot (e.g. in the E1
link)– Compute the percentage of busy cases for each time slot over a
period of time, e.g. 10 days.– Average over all time slots to obtain the overall link utilization.
n If utilization is above the target need to add links, why?
# busy / #Total
525
Data Analysis: Service AvailabilityData Analysis: Service AvailabilityData Analysis: Service Availability
n Service Availability data can help identify– System problems /failures – Further data collection may be required on each
element to identify the cause of system failures.
n Service Availability – Collect each network elements availability and use the
following rules to calculate the service/system availability
» % of the time the service is available for a given period.
n Plot the result of service availability v.s hr
526
Example :MSC/VLR processes Example :MSC/VLR processes Example :MSC/VLR processes
n Call Processing(CP) and Mobility management processors can be monitored for their utilization. A Plot of the BHCA v.s CP processor utilization % or call/sec v.s processor load can determine – The need for CP processor expansion or upgrade
The new Services effect on the processorsn I/O and communications processors can be monitored for
its utilization. A plot of no of messages/sec v.s the I/O processor utilization % can determine– The need for I/O processor expansion or upgrade
The links statistics can be monitored for no of messages/sec to determine link overload. Statistics collected based on % of frame retries should lead to identifying network problems.
527
Example: HLR/Auc Example: HLR/Example: HLR/Auc Auc
n Collect hourly statistics data base on the following transactions. Determine average hourly transactions.– Authentication– Location Updates– Terminations
n Collect hourly data on processor utilization. Determine average hourly utilization
n Plot no of transactions/hr v.s processor utilizationn Identify bottlenecks. I/O, application or database
528
ExerciseExerciseExercise
529
Chapter 5.Chapter 5.Chapter 5.
n Fixed Network Configurations Rules/ Planning Options
n Network Expansion for Existing Systemn Trends in GSM Networks and Future Mobile
Networks– UMTS and IMT2000 Perspectives
n Course Summary and Discussions
530
ITU and IMT2000ITU and IMT2000ITU and IMT2000
n Studies in the International Telecommunications Union’s Radio-communication Sector (ITU-R) on Future Public Land Mobile Telecommunication Systems (FPLMTS), are aimed at providing mobile telecommunications -Anywhere - Anytime.
n These studies are intended to develop systems that could be used around the year 2000 and will operate in a frequency band around 2000 MHz.
n A new name has been proposed because FPLMTS is difficult to pronounce in any of the ITU languages!
n The proposed new name is International Mobile Telecommunications - 2000 (IMT-2000).
531
IMT2000 (Cont.)IMT2000 (Cont.)IMT2000 (Cont.)
n IMT-2000 are third generation systems which aim to unify the diverse systems we see today into a radio infrastructure capable of offering a wide range of services around the year 2000 in many different operating environments.
n A number of different radio environments are involved covering very small indoor cells with high capacity all the way through large outdoor terrestrial cells to satellite coverage.
n A major focus is to maximize the commonality between the various radio interfaces involved in order to simplify the task of building multi-mode mobile terminals covering more than one operating environment.
532
IMT2000 (cont.)IMT2000 (cont.)IMT2000 (cont.)
n Initial studies were aimed at defining the objectives for FPLMTS and the resulting spectrum requirements as part of the ITU-R (ex-CCIR) input to the World Administrative Radio Conference in February 1992 (WARC-92).
n WARC-92 identified the bands – 1885 - 2025 MHz and
– 2110 - 2200 MHz,
n on a global basis for FPLMTS n This includes the bands 1980 - 2 010 and 2170 - 2200
MHz for the satellite component of FPLMTS.
533
IMT2000 & Developing CountriesIMT2000 & Developing CountriesIMT2000 & Developing Countries
n An important part of the ITU-R studies on FPLMTS/IMT-2000 is the potential for these new mobile radio technologies to provide cost effective and flexible access to the global telecommunications networks in developing countries and under-developed parts of developed countries.
n The close relationship between the satellite and terrestrial components of FPLMTS/IMT-2000 enables the deployment of service via satellite initially, where there is little or no existing fixed infrastructure with the conversion to terrestrial infrastructure in areas as development conditions permit.
534
Next Generation PCSNext Generation PCSNext Generation PCS
ETSISMG2
200 KHz GSM EvolutionIncluding EDGE
FMA1
FRAMESFRAMES
FMA2 ARIB
ITU-R TIA
Harmonization
535
ETSI and 3G Radio Interface ETSI and 3G Radio Interface ETSI and 3G Radio Interface
n On 28-29 January 1998 in Paris, France, an agreement was reached by consensus on the radio interface for third generation mobile system, UMTS (Universal Mobile Telecommunications System).
n The solution, called UTRA, draws on both W-CDMA and TD-CDMA technologies. The Solution is as follows:– In the paired band (FDD - Frequency Division
Duplex) of UMTS the system adopts the radio access technique formerly proposed by the W-CDMA group.
– In the unpaired band (TDD - Time Division Duplex) the UMTS system adopts the radio access technique proposed formerly by the TD-CDMA group.
536
ObjectivesObjectivesObjectives
n Following objectives have to be achieved through the process of selecting parameter of FDD/TDD mode– Low Cost Terminal– Harmonization with GSM– FDD/TDD dual mode operation– Fit into 2*5MHz spectrum allocation
537
SupportersSupportersSupporters
n The parties that made the proposal leading to this new solution included– Alcatel, Bosch, Ericsson, Fujitsu, Italtel, Matsushita (Panasonic),
Mitsubishi Electric, Motorola, NEC, Nokia, Nortel,Siemens and Sony as well as Analog Devices, Cegetel, Cellnet, CSEM/Pro Telecom, DeutscheTelekom, France Telecom, Mannesman Mobilfunk, NTT DoCoMo, Samsung Electronics, SFR, T-Mobil, Telecom Finland, Telia,TexasInstruments, TIM and Vodafone.
n NTT DoCoMo, the leading Japanese cellular network operator, participated in the meeting as an observer, welcomed the solution reached and expressed full support.
n The agreed solution offers a competitive continuation for GSM evolution to UMTS and will position UMTS as a leading member of the IMT-2000 family of systems recommendations being developed in the ITU
538
Enhanced Data GSM EvolutionEnhanced Data GSM EvolutionEnhanced Data GSM Evolution
EDGE System Level Descriptionn EDGE uses the same 8 Time Slot / 200KHz
channelization in GSM, but uses a different modulation than GMSK.
n This modulation is called Quarternary Offset QAM or Binary Offset QAM, which provides higher spectral efficiency than GMSK.
n Using Q-OQAM and time slot aggregation, EDGE claims to support high speed data upto384kbps over 200khz channel.
539
EDGE (cont.)EDGE (cont.)EDGE (cont.)
n Channel Reuse: EDGE claims to be able to use a 1/3 (cells/sector) reuse factor. This reuse factor is claimed to be feasible even with fixed channel assignment.
n Another system aspect of EDGE is its rate adaptation, meaning selecting the best combination of coding and modulation to meet the Eb/No at maximum throughput or user data rate.
n The rate adaptation relies on the mobile and base stations measurements of the channel under bursty interference/fading conditions.
540
EDGE: Pedestrian EnvironmentEDGE: Pedestrian EnvironmentEDGE: Pedestrian Environment
n For Microcells with pedestrian mobile speeds of up to 10 km/hr the following is proposed:
n Carrier Spacing 200 kHzn Modulation Quaternary-Offset-QAM, Binary-
Offset-QAM
n Time Slot duration 576.92 µµsecn Time Slots 8n Gross Carrier rate Up to 521.6 kbpsn User Data Rate >384 kbps with 8 time slots
541
EDGE: Low Speed Vehicular Env.EDGE: Low Speed VehicularEDGE: Low Speed Vehicular EnvEnv..
n For Macrocells with vehicular mobile speeds of up to 100 km/hr the following is
n proposed:n Carrier Spacing 200 kHzn Modulation Quaternary-Offset-QAM, Binary-
Offset-QAM, GMSK
n Time Slot duration 576.92 µµsecn Time Slots 8n Gross Carrier rate Up to 521.6 kbpsn User Data Rate >384 kbps with 8 time slots
542
EDGE: High Speed Vehicular Env.EDGE: High Speed VehicularEDGE: High Speed Vehicular EnvEnv..
n For Macrocells with vehicular mobile speeds of from 100 km/hr to 500 km/hr the
n following is proposed:n Carrier Spacing 200 kHzn Modulation Binary-Offset-QAM, GMSK
n Time Slot duration 576.92 µµsecn Time Slots 8n User Data Rate >144 kbps with 8 time slots
543
EDGE: Indoor OfficeEDGE: Indoor OfficeEDGE: Indoor Office
n For Picocells with mobile speeds of 0 km/hr the following is proposed:
n Carrier Spacing 200 kHzn Modulation Quaternary-Offset-QAM
n Time Slot duration 576.92 µµsecn Time Slots 8n Gross Carrier rate 521.6 kbpsn User Data Rate >1920 kbps with 5 aggregated
carriers each with 8 time slots
544
FYI: IN and GSM FYI: IN and GSM FYI: IN and GSM
n Intelligent Network is a technology that allows the rapid introduction of the new features/services within a network (wireless or wire-line)
n The technology is base on a distributed network which offloads the traditional switching platform from performing service creation and feature development. Perform service creation function on computing platforms.
n Allows inter-working between different standards.
n The backbone is based on SS7.
545
Current IN ArchitectureCurrent IN ArchitectureCurrent IN Architecture
SCP
HLR
IP
IP
IP
SSF
MSC
SSF
MSC
SMP SCE
SMS
MAP MAP
IN CS1
IN CS1
546
IN /CAMEL Architecture IN /CAMEL Architecture IN /CAMEL Architecture
n Customized Application for Mobile Enhanced Logic (CAMEL) is a GSM standard that addresses IN. (GSM 01.78,02.78,03.78,04.78)
n ITU-T Q1224 recommendation for IN CS-2 (Capability Set 2) describes Functional Entities (FE). ACF Authentication Control functionCCF Call Control Function LRF Location Registration FunctionRACF Radio Access Control FunctionRCF Radio Control FunctionRTFRadio Terminal FunctionSCEF Service Creation Environment functionSCF Service Control FunctionSDF Service Data FunctionSMAF Service Management Access FunctionSMF Service Management FunctionSRF Specialized Resource FunctionSSF Service Switching Function
547
GSM and IN MappingGSM and IN MappingGSM and IN Mapping
MSC/VLR
CCFSSF
RACFLRFSRFACF
PSTNISDNPSPDN
CCF
SNSCPIP
BSSMS
HLRAC
LRFSCFSDF
ACF
RCFRTF
SCFSDFSRF
SCFSDF
SRF
548
INININ
n Call models and triggers are the functional bases for Call processing (CCF) in IN.
n The call models are the states machines.– Origination Call Model– Termination Call Model– Registration Call Model
n Triggers are the events that suspends the call processing. (when an * is detected suspend processing and send a message to the HLR)
n Origination triggers Termination Triggers• All Calls No Answer• 0-15 digits Busy• Feature codes No page response• specific
549
IN (cont.)IN (cont.)IN (cont.)
n Within a call model there are – Point in Call (PICs) Null , Collect information,
select_Facility analyze information etc.)– Detection Point (DPs) Origination attempt,
origination attempt authorized etc.. Note: example of termination call model (this is not a complete call model),
T_Null
Select_Facility
Authorize_termination-attempt
T_exception
Termination_Attempt DP
Termination_Attempt_Authorized DP
T_abandon DP
T_Busy DP
No triggers are defined for these DP
550
FutureFutureFuture
n Alignment with Fixed network e.g CS2/CS3n Exploiting the mobile capabilities available in
GSM n Capabilities for GSM/IN/Internet convergence
versus the traditional INn GSM and CAMEL -core for next generation
systems UMTS switchingn Future services,
– Virtual Private Networks– Call Screening Applications– Location dependent services
551
Chapter 5: Review and DiscussionsChapter 5: Review and DiscussionsChapter 5: Review and Discussions
Configuration RulesPlanning Existing SystemNext Generation Systems
552
Course SummaryCourse SummaryCourse Summary
GSM ProtocolChennelization & Network Elements
Fixed NetworkPlanning
Signaling Protocols & Interfaces
NetworkDimensioning Traffic Theory
553
ReferencesReferencesReferences
n “An Introduction to GSM”, Siegmund M. Redl, Matthias K. Weber and Malcolm W. Oliphant, Artech House Publishers, 1995
n “The GSM System for Mobile Communications”, Michel Moulyand Marie B. Pautet, 1995
n “GSM System Engineering”, Asha Mehrotra, Artech House Publishers, 1997.
n “Wireless Communications, Principles and Practice”, Theoddore Rappaport, Prentice Hall/IEEE Press 1996.
n IEEE Communications Magazinen IEEE Personal Communications Magazine
554
Congratulations!!!Congratulations!!!Congratulations!!!
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