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Transcript of Basic telecom
Copyright © 2011 LOGTEL 2
What are we selling ?
It’s all about customer satisfaction
customer satisfaction !
Copyright © 2011 LOGTEL
3
Course Content1. Introduction
• What is telecom ?
2. Telephony history – form Bell to analog switch
3. Telecom Network• Switching• telecom services
4. Moving to Digital
5. Basic Signaling (SS7)
6. ISP / Data network
7. Mobile
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Goals
4
• To understand the terminology• To know where did we come from• To understand the need and the various signaling
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What is Telecom?
5
Telecommunication is the transmission of information over significant distances to communicate.
Signaling:
the information exchange concerning the establishment and control of a telecommunication circuit and the management of the network, in contrast to user information transfer
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Switching Systems
Manual control—Switch/cord boards
Patch CordPairs
Off-Hook Indicator
Manual Ring
TipRing
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The Telephone: Tip and Ring
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Strowger switch (Step by Step) - 1891
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Signaling – E&M (Ear and Mouth) inbound
12
• On-hook• Off-hook• Line tone• Dialing• Ringing• Ring back tone• Busy tone
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Exchange A Exchange BAlice Bob
ringing tone
Bob answers
off-hook
connection ok
dial tone
Bob number
ringing tone
Setup of a PSTN call(meet Alice and Bob)
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Crossbar – 1920’s to 80’s
14
Now we can invent DTMF
and now we can have logic (!)
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Tone Dialing
1 2 3 A
4 5 6 B
7 8 9 C
* 0 # D
Dual Tone Multifrequency (DTMF)
1209 1336 1477 1633
697
770
852
941
Timing:60 ms Break40 ms Make
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N11 code
17
2-1-1: community services, United Way 3-1-1: municipal government services, non-
emergency 4-1-1: directory assistance 5-1-1: traffic information or police non-emergency
services 6-1-1: telephone company customer service and
repair 7-1-1: TDD relay for the deaf 8-1-1: underground public utility location,[1] in
Canada 8-1-1 is assigned for non-emergency health information and services
9-1-1: emergency services
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Telecom Network Elements
18
Core network SDH – Synchronous Digital Hierarchy (Europe) SONET – Synchronous optical networking (USA)
Switches Class 4 – network services Class 5 – Line services
Signaling IN – Intelligent Network SS7 – (Common Channel) Signaling System #7 SIP – Session Initiation Protocol
Access / Last mile Twisted per FTTx – fiber to the X Wireless
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Telecom Management – OSS/BSS
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• Network facing operational support systems
• Run by Network Operations• Typically including service
activation, provisioning, fault management, etc
• Cost-focused
• Customer facing business support systems
• Run by the IT department• Typically including billing
and CRM• Revenue-focused
OSS BSS
Traditional definitions
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eTOM – NGOSS - FrameWorX
20
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Classes 1-5
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CLASS (Custom Local Area Signaling Services)
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• AKA VSC (vertical service code) - developed by AT&T in the 1960s
• a special code dialed prior to (or instead of) a telephone number that engages some type of special telephone service
• Anonymous Call Rejection: start• Anonymous Call Rejection: cancel • Busy Number Redial : start• Busy Number Redial : cancel • Call Forwarding: start• Call Forwarding: cancel• Call Return (incoming)• Call Waiting disable• Caller ID Disable
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MDF - Main Distribution Frame
23
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MOVING TO DIGITAL
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Trunks to SDH
25
A trunk line is a circuit connecting telephone switchboards
(local loop circuit which extends from telephone exchange switching equipment to individual telephones)
• DS0 (Digital Signal 0) / T0 / E0 – 64Kb/s• DS1 / T1 – 1.5Mb/s E1 – 2Mb/s
• DS3 / T3 -
Nyquist rate
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Why 3.4 KHz?
Signal
Energy Distribution forHuman Speech
0 Hz 300 Hz 3,400 Hz 20 kHz
Bandwidth(3.1 kHz)
Bandpass Filtering
The human ear can hear sounds up to 20 kHz,but most sound is between 300 Hz and 3.4 kHz.The bandpass filter only passes this sound to reduce bandwidth.
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Time Division Multiplexing (TDM)
27
Used Used Used Used Used
Frame 1 Frame 2 Frame 3
Slot 1forCircuit A
Slot 3forCircuit C
Slot 2forCircuit B
TDM reserves capacityfor each circuit in each frame;assures speed but is wasteful
Time
Slot 1forCircuit A
Slot 1forCircuit A
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SONET and SDH
Synchronous Optical Network (SONET) High-speed, fiber optic networks organized in rings
Synchronous Digital Hierarchy (SDH) Fiber ring networks used internationally Essentially the same as SONET
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SONET and SDH (cont'd)
The basic measure of SONET speed is the Synchronous Transport Signal level 1 (STS-1) frame, which travels at 51.84 Mbps
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SONET and SDH (cont'd)
The basic unit for SDH is the Synchronous Transport Module (STM)-1 frame, which travels at 155.52 Mbps
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SONET and SDH (cont'd)
Benefits of using SONET/SDH You can use multiplexors and routers to combine
different data lines and streams onto one line One heterogeneous network can communicate with
another distant heterogeneous network via one fiber optic ring
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SDH Rings
34 Mb/s 2 Mb/s
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Introducing ISDN
Telephone companies developed ISDN (Integrated Services Digital Network) as part of an effort to standardize subscriber services.
This included the User-Network Interface (UNI), better known as the local loop.
The ISDN standards define the hardware and call setup schemes for end-to-end digital connectivity.
These standards help achieve the goal of worldwide connectivity by ensuring that ISDN networks easily communicate with one another.
In an ISDN network, the digitizing function is done at the user site rather than the telephone company.
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ISDN Advantages
ISDN also provides more bandwidth than a traditional 56 kbps dialup connection.
ISDN uses bearer channels, also called B channels, as clear data paths.
Each B channel provides 64 kbps of bandwidth. An ISDN connection with two B channels would provide a total
usable bandwidth of 128 kbps. Each ISDN B channel can make a separate serial connection
to any other site in the ISDN network. ISDN lines can be used in conjunction with PPP encapsulation.
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Signaling Categories
Signaling categories: Supervision – detects changes to a particular line Addressing – responsible for routing signals to the correct
switch Alerting – audible alert signals Call progress – signals that maintain calls
Audible call progress tones: Dial tone Busy signal Receiver off hook too long Nonexistent number
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In-Band andOut-of-Band Signaling
In-band signaling The process of allowing the control signal to share the
same path as the voice and data AKA CAS (Channel Associated Signaling)
Out-of-band signaling The process of using a separate channel for signaling
purposes AKA CCS (Common Channel Signaling)
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Advantage of CCS over CAS
• Faster call setup• No interference between signaling tones by
network and frequency of human speech pattern.• Greater Trunking Efficiency: CCS has shorter call
set up and tear down times that result in less call holding time, thereby reducing the traffic on the network.
• Information Transfer: CCS allows the transfer of additional information along with the signaling traffic providing facilities such as caller identification and voice or data identification
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SS7 – Signaling System #7 (80’s)
SS7 network major components include: SSP (Service Switching Point) STP (Signaling Transfer Point) SCP (Service Control Point) SL (signaling link)
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SSP (Service Switching Point)
• SSP is the local exchange to the subscriber and the interface to the telephone network.
• The SS7 signaling information is produced at the sending SSP and is handled at the receiving SSP.
• It converts voice (in band) signaling into the SS7 signal units (out band), and vice versa.
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STP (Signaling Transfer Point)
• STP is the network node.• It works like a router to perform the routing of
messages to other signaling points.• It is usually paired to provide redundancy for a
reliable message transfer.• It is adjunct to a voice switch, and might stand
alone as a separate machine.(It’s the tandem in class 4/4)
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SCP (Service Control Point)
• SCP works as the interface with the databases, which contain the information of the subscribers, such as 800 service, calling cards, fraud data, etc.
• When receiving a request, it is triggered to handle the database queries, and returns a response with the results of the queries to the originating SSP.
Copyright © 2011 LOGTEL Slide 42
IP Formats in INs
SSP – Service Switching PointSS7
STP
STP
SMS
SCP
IP
SSP SSP
SMS – Service Management SystemSCP – Service Control PointSTP – Service Transfer Point
IP – Intelligent Peripheral
Basic Architecture of a IN
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Basic Call Setup Example
• Initial address message (IAM): contains all necessary information for a switch to establish a connection
• Address complete message (ACM): acknowledge to IAM; the required circuit is reserved and the “phone is ringing” (ring back tone)
• Answer message (ANM): occurs when the called party picks up the phone
• Release (REL): sent by the switch sensing that the phone hung up• Release complete (RLC): each exchange that receives REL, sends
an RLC message back (this acknowledges receipt of REL)
6,10
9
2
513
1
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Exchange A Exchange BTransit exchange Alice Bob
Setup IAMIAM
Setup
Alert
Connect
ACM
ANM
ACM
ANM
Alert
Connect
Charging of call starts now
Link-by-link routing (number analysis)Q.931
Link-by-link signalling (no number analysis)
Setup of a call using ISUP
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IAM – Initial Address Message
ACM – Address Complete Message
ANM – Answer Message
REL – Release Message
RLC – Release Complete
user A user B
Some basic ISUP messages
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Intelligence Network (90’s)
Before IN?
All services were to be implemented directly in the core switch systems.
Contact Vendors: Headache for service providers.
What actually is IN? An architecture that redistributes a portion of the call
processing, that is traditionally performed by tel-switches, to other nodes.
Two types of IN today:
Intelligence Network (IN) – standardized by ITU. Advanced Intelligent Network (AIN) - standardized by
Bellcore.
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Why Intelligent Networking?
Introduce new services rapidly: IN provides the capability to provision new services or modify existing services throughout the network with physical intervention.
Provide Service Customization: Service providers require the ability to change the service logic rapidly and efficiently. Customers are also demanding control of their own services to meet their individual needs.
Establish Vendor Independence: To develop the software for service providers quickly and efficiently, suppliers have to integrate commercially available software to create the applications required by service providers.
Create open interfaces: Open interfaces allow service providers to introduce network elements quickly for individualized customer services.
Capable to act appropriately in a changing environment
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IN service family
48
1. Number translating2. Billing modification
Reverse charging (800) Split charging (700) Premium rate (900) Personal services (600)
3. Centralize Voice Mail4. Pre Paid (node)
5. SMS – Short Massaging
in mobile networks IN CAMEL (Customised Applications for Mobile networks Enhanced Logic)
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Centrex
49
• Centrex is a PBX-like service providing switching at the central office instead of at the customer's premises. Typically, the telephone company owns and manages all the communications equipment and software necessary to implement the Centrex service and then sells various services to the customer.
• Today we use the terms: Hosted Stickiness Virtual Cloud
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PABX (voice) Services (1) Private (automatic) Branch eXchange
50
• Auto attendant• Automatic call distributor• Automated directory services (where callers can be routed to a given
employee by keying or speaking the letters of the employee's name)• Call accounting• Call blocking• Call forwarding on busy or absence• Call park• Call pick-up• Call transfer• Conference call• Custom greetings• Busy Override
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PABX service (2)
51
• Direct Inward Dialing (DID) – AKA DDI and DDO• Direct Inward System Access (DISA) (the ability to access internal features
from an outside telephone line)• Do not disturb (DND)• Follow-me, also known as find-me: Determines the routing of incoming calls.
The exchange is configured with a list of numbers for a person. When a call is received for that person, the exchange routes it to each number on the list in turn until either the call is answered or the list is exhausted (at which point the call may be routed to a voice mail system).
• Interactive voice response• Music on hold• Night service
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Signaling in VoIP networks
VoIP Network can carry SS7 over IP using protocols defined by Signaling Transport (SIGTRAN).
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DATA NETWORKING
53
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OSI 7 Layer Model
OSI - Open Systems Interconnection (Basic Reference Model)
Each level is an independent set of protocols
Each level can be change seamlessly
Application
Presentation
Session
Transport
Network
Data Link
Physical
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5 Layer model
Application
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
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5 Layer model (TCP/IP)
Application – Represent the end user and the application he use (mail, browse, FTP, etc.)
Transport - end-to-end message transfer, along with error control, fragmentation and flow control.
Network (AKA Internet) – responsible on getting packets of data from source to destination.
Link - processes of transmitting receiving packets on a given link layer
Application
Transport - TCP
Network - IP
Link
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TCP/IP Connection
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TCP - Transmission Control Protocol
Connection oriented - Reliable stream transport Conceptually, two ends communicate to agree
on details After agreeing application notified of connection During transfer, ends communicate continuously
to verify data received correctly When done, ends tear down the connection
Provides buffering and flow control Takes care of lost packets, out of order,
duplicates, long delays Usually used for browsing, FTP, Mail, etc.
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read(s1, dataBlock)
Transport (TCP)
Network (IP)
Link (WLAN)
Web serverSamuel
Web Site
send(s2, dataBlock)
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
Network (IP)
Link
1 2 3
1 2 3
Transport (TCP)
Browser
1 2 3 4 5
Network (IP)
Link (WLAN)
Physical
Router
1 2 3
1 2 3 4 5
1 2 3 4 5
PhysicalPhysical
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UDP- User Datagram Protocol
Connectionless Datagram- Not Reliable transport Minimal overhead, high performance No setup/teardown, 1 datagram at a time Application responsible for reliability
Includes datagram loss, duplication, delay, out-of-sequence, multiplexing, loss of connectivity
Usually used for Voice & Video streaming, broadcasting, etc.
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TCP vs. UDP data format
Source port Destination port
Sequence number
0 8 16 3124
Acknowledgement number
4
Hlen
Resv
Code Window
Urgent ptrChecksum
Options (if any) Padding
Data if any
…
Source port Destination port
UDP message len
Checksum (opt.)
0 8 16 3124
Data
…
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TCP data format
Port - TCP port numbers to ID applications at both ends of connection
Sequence number - ID position in sender’s byte stream
Acknowledgement - identifies the number of the byte the sender of this segment expects to receive next
Hlen - specifies the length of the segment header in 32 bit multiples. If there are no options, the Hlen = 5 (20 bytes)
Code - used to determine segment purpose, e.g. SYN, ACK, FIN, URG
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TCP data format (cont.)
Window - Advertises how much data this station is willing to accept. Can depend on buffer space remaining.
Checksum -Verifies the integrity of the TCP header and data. It is mandatory.
Urgent pointer - used with the URG flag to indicate where the urgent data starts in the data stream. Typically used with a file transfer abort during FTP or when pressing an interrupt key in telnet.
Options -used for window scaling, SACK, timestamps, maximum segment size etc.
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IP Address
Unique addresses in the world An IP address is 32 bits, noted in dotted decimal
notation: 192.78.32.2
Host and Prefix Part An IP address has a prefix and a host part:
prefix:host Prefix identifies a subnetwork
used for locating a subnetwork – routing Prefix is usually identified in a host using a “subnet mask”
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Using a mask: address + mask
the mask is the dotted decimal representation of the string made of : 1 in the prefix, 0 elsewhere
bit wise address & mask gives the prefix example 1: 128.178.156.13 mask
255.255.255.0 here: prefix is 128.178.156.0
example 2: 129.132.119.77 mask 255.255.255.192 Q1: what is the prefix ? Q2: how many host ids can be allocated ?
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Address + Mask (example 2)
129.132.119.77 mask 255.255.255.192▪ Q1: what is the prefix ? A: 129.132.119.64
Q2: how many host ids can be allocated ? ▪ A: 64 (minus the reserved addresses: 62)
1000 00011000 01000111 01110100 1101
1111 11111111 11111111 11111100 0000
129
255
132
255
119
255 192
77
64 addresses
26 6
1000 00011000 01000111 01110100 0000129 132 119 64
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IP v.4 header
Version (4 bits) – 6 or 4 Hlen (4 bits) - Header length in 32 bit words,
without options (usual case) = 20 Type of Service (TOS 8 bits): now being used for
QoS Total length (16 bits) - length of datagram in bytes,
includes header and data Time to live (TTL 8bits) - specifies how long
datagram is allowed to remain in internet (how many hops)
Protocol (8 bits) - specifies the format of the data area Protocol numbers administered by central authority to
guarantee agreement, e.g. TCP=6, UDP=17 …68
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IP v.6 header
Version (4 bits) – 6 or 4 Traffic Class (8 bits) - traffic priority delivery value. Flow Label. 20 bits.
Used for specifying special router handling from source to destination(s) for a sequence of packets.
Payload Length (16 bits) - Specifies the length of the data
Hop Limit (8 bits) - the same as TTL in the IPv4 Source address. 16 bytes. Destination address. 16 bytes.
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IPv6 address – 128 bit
IPv6 address is made of two parts: prefix and suffix (I.e interface-ids)
and hierarchical structure (that depends on format prefix, FP) prefix:
suffix:
Link-local address (mandatory) is unique within a "link".
64 bits suffix
64 bits prefixFP TLA NLA SLA
Interface ID
64 bits suffix
54 '0' bits
1111111010
FP – Format prefixTLA - Top-Level Aggregators NLA - Next-Level Aggregators SLA – Service level Agreements
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71
IPv6 Autoconfiguration and Renumbering
RFC 2462, IPv6 Stateless Address Autoconfiguration. IPv6 includes stateless address autoconfiguration feature, which
allows a host to determine its own IPv6 address from its Layer 2 address.
The concept: A device generates a temporary address until it can determine the characteristics of the network it is on. Then creates a permanent address it can use based on that information. In the case of multi-homed devices: Autoconfiguration is
performed for each interface separately
Stateless address autoconfiguration
No central server needed to aid in address configuration Node forms its own suffix, checks if it is uniqueNode obtains prefix(es) from the nearest router
Stateful address autoconfiguration
Central server allocates full addresses to nodes on requestDHCPv6 is the current protocol for stateful address autoconfiguration
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IPv6 Extended Unique Identifier (EUI-64)
RFC 2464 IPv6 link-local addresses and statelessly autoconfigured
addresses on Ethernet networks used in Router Solicitation, Router Advertisement, Neighbor
Solicitation, Neighbor Advertisement and Redirect messages
48-bit MAC address
64-bit IPv6 EUI
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IPv6 address Types
73
Unicast (1:1)
Anycast addresses : nearest node of a set of nodes
currently only used to address routers
Multicast (1:n) communicate group of computers
No more broadcast in use
communicate specified one computer
RFC 4291 currently specifies the following restrictions on anycast addresses: An anycast address must not be used as the source address of a packet.Any anycast address can only be assigned to a router
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Representation of IPv6 addresses
Colon hexadecimal notation - 805B:2D9D:DC28:0000:0000:FC57:D4C8:1FFF
Leading zeroes can be suppressed in the notation 805B:2D9D:DC28:0:0:FC57:D4C8:1FFF Zero Compression in IPv6 Addresses
805B:2D9D:DC28::FC57:D4C8:1FFF The double-colon can appear only once in any IP address. IPv6 addresses can embed IPv4. The notation has the first
96 bits in colon hex notation, and the last 32 bits in dotted decimal. eg ::212.200.31.255
Prefix notation can be used as with classless IPv4 addressing with CIDR.
Example: 805B:2D9D:DC28::FC57:D4C8:1FFF/48
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So why isn’t it here yet?
No clear move to IPv6 Lack of smooth migration plans Investments in IPv4 Software availability - Available from Microsoft Windows XP
sp2 Developments in IP v4
Use of NAT CIDR Planning of Hierarchies and use of Autonomous Areas IPsec implemented in IPv4
Other Points Router Upgrades to handle IPv6 – OSPFv3
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Tunneling IPv6 over IPv4
IPv6 can operate within a closed or private network environment Currently across a public networks, such as the Internet, have to
cross an IPv4 domain IPv6 packets can be encapsulated within IPv4 Encapsulated packets can then travel transparently across an IPv4
routing domain Tunneling can be used by routers and hosts
IPv4IPv6 Network
IPv6 Network
Tunnel: IPv6 in IPv4 packet
IPv6 Host
Dual-Stack Router
Dual-Stack Router
IPv6 Host
IPv6 HeaderIPv6 HeaderIPv4 HeaderIPv4 Header
IPv6 HeaderIPv6 Header Transport Header
Transport Header DataData
DataDataTransport Header
Transport Header
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MOBILE NETWORKS
77
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Cellular Technology Defined :
A communications system which serves users via radio waves (a “radio air interface”) by connecting the user’s mobile terminal to the antennas at the nearest “cell base station”. The cell base station antennas can be tower mounted; rooftop mounted; mounted on water tanks; or hidden from sight for aesthetic purposes. Average base station coverage area today: 2-5 miles radius.
The system functions by re-using frequencies at the low-powered cell base stations throughout a cellular market area, and handing off calls in progress from one cell base station to another as users move throughout the market area.
Copyright © 2011 LOGTEL
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Course Content1. Introduction
• What is telecom ?
2. Telephony history – form Bell to analog switch
3. Telecom Network• Switching• telecom services
4. Moving to Digital
5. Basic Signaling (SS7)
6. ISP / Data network
7. Mobile
Copyright © 2011 LOGTEL
Telecom Network Elements
80
Core network SDH – Synchronous Digital Hierarchy (Europe) SONET – Synchronous optical networking (USA)
Switches Class 4 – network services Class 5 – Line services
Signaling IN – Intelligent Network SS7 – (Common Channel) Signaling System #7 SIP – Session Initiation Protocol
Access / Last mile Twisted per FTTx – fiber to the X Wireless
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Call Base Station Photos
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Stealth Cell Sites
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Mobile Telephone (Cellular Technology)
Wireless service is founded on one key concept known as “frequency re-use”
Cellular service launched in Chicago in 1983Traditionally, to engineer a cell network to support millions of
users in a metropolitan area, or thousands in a rural area, markets are broken down into cells. Cells are geographic areas that use their own sets of frequencies (channels) to support dozens of users simultaneously.
Frequency re-use is accomplished by breaking down all available frequencies into groups of 7 (N=7).
Each cell base station has its own transmission system (antennas) and set of assignable channels.
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N=7 Frequency Re-Use Cluster. Each hexagon represents a base station with distinct set of frequencies. Note how identicalfrequency sets are laid out symmetrically. This facilitates designand engineering.
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Two Antenna Types:
Omnidirectional: propagates radio signal equally 360 degrees, aka “omni”. Also called “stick” antennas. (Lamp With No Shade)
Directional: radio energy is focused in a specific direction at a specific beamwidth, based on a reflector within the antenna housing. (Flashlight)
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Five Key Components To Every (Macro) Wireless Network:
Mobile phone, aka “UE” (user equipment) or “mobile terminal”
Cell Base StationFixed network, AKA “backhaul network”Mobile Switching Center (MSC)Interconnection to PSTN and Internet
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BTS
BSC
MSC
VLR HLR AuC EIR
PSTN,ISDN...
OMCOMC
NMCX.25 links
GSM interfaces
Voicemail Server
SM-SC
MS (Mobile Station)
BSS (Base Station System)
NSS (Network Switching Subsystem)
OMM (Operations & Maintenance Management)
MS
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Key design and engineering concepts that drive cellular technology:
Frequency Re-Use – supports simultaneous use of hundreds or thousands of frequencies (channels) to exponentially increase system capacity
Call Handoffs – seamless transfer of a call / transmission in progress from one base station to an adjacent (neighbor) base station
Frequency Agility: in handsets / terminals – ability of cell phones to operate on any one of dozens or hundreds of possible frequencies. Call handoff cannot occur without this ability.
Working together, these concepts support basic cellular operation.
Copyright © 2011 LOGTEL
Generations Of WirelessWireless Service(s)
Cellular service first launched in 1983 in Chicago, Illinois by Illinois Bell.
First generation (1G) service: All analog, more prone to noise, crosstalk, call drops Limited system capacity Used 850 Mhz frequency spectrum 1983 – 1994 KEY DIFFERENTIATOR: first instance of frequency re-use to
exponentially increase capacity over previous mobile systems
Second generation (2G) service: Also known as “PCS” (Personal Communication Service) Co-existed with analog service for 15 years Used different frequency spectrum (1900 Mhz / 1.9 Ghz) KEY DIFFERENTIATOR: all digital service
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Wireless Service(s) Continued:Third generation (3G) service:
All digital “Always On” Internet access High-speed access and transmission (> 384 Kbps) Technologies: UMTS (GSM-based), CDMA 1X-EVDO KEY DIFFERENTIATOR: supports sustainable multimedia
transmissions (i.e. voice, video, text, image, video)Fourth generation (4G)
Launching in 2009 with Clearwire WiMax launch Key technologies: WiMax (802.16) and LTE (Long Term
Evolution) KEY DIFFERENTIATOR: super-fast access and transmissions –
tens of Megabits. Technology built into laptops.
Generations Of Wireless
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– 1983 – Present: The “NIMBY” phenomenon. “Not In My Backyard”. Wireless subscribers desire – demand – great cellular coverage but protest when base station towers are installed in areas where “ugly towers” are not desired.
– 2006 – Present: Backhaul network congestion and bottlenecking due to proliferation and popularity of wireless data technologies and services, based on 3G rollouts.• Traditionally, base station-to-MSC (switch) connections
have been one or two DS-1 circuits. This traditional model is quickly becoming outmoded as the backhaul network now has huge potential to become a bottleneck. Adding more and more DS-1 circuits becomes expensive. Solution? Ethernet in the backhaul network: simple, known technology. Ultimately less expensive than multiple DS-1 circuits.
– 2010: Radio spectrum is becoming a precious and increasingly scarce commodity. Also, data traffic vs. revenue dichotomy.
Major Challenges:
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INCREASED CAPACITY
• number of cells in the reuse patteThe GSM system provides a greater subscriber capacity than analogue systems.
• GSM allows 25 kHz per user, that is, eight conversations per 200 kHz channel pair (a pair comprising one transmit channel and one receive channel).
• Digital channel coding and the modulation used makes the signal resistant to interference from cells where the same frequencies are re-used (co-channel interference); a Carrier to Interference Ratio (C/I) level of 12 dB is achieved, as opposed to the 18 dB typical with analogue cellular.
• This allows increased geographic reuse by permitting a reduction in the rn.
FEATURES OF GSM (1)
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AUDIO QUALITY
• Digital transmission of speech and high performance digital signal processors provide good quality speech transmission.
• Since GSM is a digital technology, the signals passed over a digital air interface can be protected against errors by using better error detection and correction techniques.
• In regions of interference or noise-limited operation the speech quality is noticeably better than analogue.
USE OF STANDARDISED OPEN INTERFACES• Standard interfaces such as C7 and X25 are used throughout the
system. Hence different manufacturers can be selected for different parts of the PLMN.
• There is a high flexibility in where the Network components are situated.
FEATURES OF GSM (2)
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IMPROVED SECURITY AND CONFIDENTIALITY
• GSM offers high speech and data confidentiality.• Subscriber authentication can be performed by the system to check if
a subscriber is a valid subscriber or not.• The GSM system provides for high degree of confidentiality for the
subscriber. Calls are encoded and ciphered when sent over air. • The mobile equipment can be identified independently from the mobile
subscriber. The mobile has a identity number hard coded into it when it is manufactured. This number is stored in a standard database and whenever a call is made the equipment can be checked to see if it has been reported stolen.
FEATURES OF GSM (3)
Copyright © 2011 LOGTEL
CLEANER HANDOVERS
• GSM uses Mobile assisted handover technique.• The mobile itself carries out the signal strength and quality
measurement of its server and signal strength measurement of its neighbors.
• This data is passed on the Network which then uses sophisticated algorithms to determine the need of handover.
SUBSCRIBER IDENTIFICATION• In a GSM system the mobile station and the subscriber are
identified separately.• The subscriber is identified by means of a smart card known as a
SIM. • This enables the subscriber to use different mobile equipment
while retaining the same subscriber number.
FEATURES OF GSM (4)
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GSM Voice and Data Call Architecture
Voice Calls Path
Data Calls PathPacket Data
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MS Mobile Station = phone + SIM card
BTS Base Transceiver Station BSC Base Station Controller HLR Home Location Register MSC Mobile services Switching
Centre VLR Visitor Location Register AUC Authentication Centre
Stand-alone or integrated in HLR
EIR Equipment Identity RegisterFor blacklisting stolen and
unwanted equipment SMSC Short Message Service
”Support” Centre VMS Voice Messaging System PrePaid Node Hosting prepaid service
system IN Intelligent Network services PSTN Public Switched Telephone
Network PABX Private Automatic Branch
Exchange
MSC/VLR
IN
BSC
SMSC
EIR
INTERNET
MobilinkPSTN
BSC
PrePaidNode
VMS
HLR
MSCw
AUC
NETWORK COMPONENTS
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• The Mobile services Switching Centre (MSC) co-ordinates the setting up of calls to and from GSM users.
• It is the telephone switching office for MS originated or terminated traffic and provides the appropriate bearer services, teleservices and supplementary services.
• It controls a number of Base Station Sites (BSSs) within a specified geographical coverage area and gives the radio subsystem access to the subscriber and equipment databases.
• The MSC carries out several different functions depending on its position in the network.
• When the MSC provides the interface between PSTN and the BSS in the GSM network it is called the Gateway MSC.
• Some important functions carried out by MSC are Call processing including control of data/voice call setup, inter BSS & inter MSC handovers, control of mobility management, Operation & maintenance support including database management, traffic metering and man machine interface & managing the interface between GSM & PSTN N/W.
Mobile Switching Centre (MSC)
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Mobile Station (MS)The Mobile Station consists of the Mobile Equipment (ME) and the
Subscriber Identity Module (SIM). Mobile EquipmentThe Mobile Equipment is the hardware used by the subscriber to
access the network. The mobile equipment can be Vehicle mounted, with the antenna
physically mounted on the outside of the vehicle or portable mobile unit, which can be handheld.
Mobiles are classified into five classes according to their power rating.
CLASS POWER OUTPUT1 20W2 8W3 5W4 2W5 0.8W
MS & ME
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The SIM is a removable card that plugs into the ME.It identifies the mobile subscriber and provides information about the
service that the subscriber should receive.The SIM contains several pieces of information
– International Mobile Subscribers Identity (IMSI) - This number identifies the mobile subscriber. It is only transmitted over the air during initializing.
– Temporary Mobile Subscriber Identity ( TMSI ) - This number also identifies the subscriber. It can be alternatively used by the system. It is periodically changed by the system to protect the subscriber from being identified by someone attempting to monitor the radio interface.
– Location Area Identity ( LAI ) - Identifies the current location of the subscriber.
– Subscribers Authentication Key ( Ki ) - This is used to authenticate the SIM card.
– Mobile Station International Standard Data Number ( MSISDN ) - This is the telephone number of the mobile.
SIM (1)
Copyright © 2011 LOGTEL
• Most of the data contained within the SIM is protected against reading (eg Ki ) or alterations after the SIM is issued.
• Some of the parameters ( eg. LAI ) will be continuously updated to reflect the current location of the subscriber.
• The SIM card can be protected by use of Personal Identity Number( PIN ) password.
• The SIM is capable of storing additional information such as accumulated call charges.
G S M
FULL SIZE SIM CARD MINI SIM CARD
SIM (2)
Copyright © 2011 LOGTEL
98 XXX 12345CCNDCSN
CC NDC SN
= Country code= National Destination Code= Subscriber Number
Mobile Station International Subscribers Dialling Number ( MSISDN ) :Human identity used to call a MSThe Mobile Subscriber ISDN (MSISDN) number is the telephone number
of the MS.This is the number a calling party dials to reach the subscriber.It is used by the land network to route calls toward the MSC.
MSISDN
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MCC MNC MSIN
404 XX 12345..10
MCCMNCMSIN
= Mobile Country Code ( 3 Digits )= Mobile Network Code ( 2 Digits )= Mobile Subscriber Identity Number
International Mobile Subscribers Identity ( IMSI ) :Network Identity Unique to a MSThe International Mobile Subscriber Identity (IMSI) is the primary identity
of the subscriber within the mobile network and is permanently assigned to that subscriber.
The IMSI can be maximum of 15 digits.
IMSI
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TAC FAC SNR
6 2 6 1
TACFACSNRSP
SP
= Type Approval Code= Final Assembly Code= Serial Number= Spare
International Mobile Equipment Identity ( IMEI ) :IMEI is a serial number unique to each mobileEach MS is identified by an International Mobile station Equipment Identity
(IMEI) number which is permanently stored in the Mobile Equipment. On request, the MS sends this number over the signaling channel to the
MSC.The IMEI can be used to identify MSs that are reported stolen or operating
incorrectly.
IMEI
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• The HLR contains the master database of all subscribers in the PLMN.• This data is remotely accessed by the MSC´´s and VLRs in the network.
The data can also be accessed by an MSC or a VLR in a different PLMN to allow inter-system and inter-country roaming.
• A PLMN may contain more than one HLR, in which case each HLR contains a portion of the total subscriber database. There is only one database record per subscriber.
• The subscribers data may be accessed by the IMSI or the MSISDN.• The parameters stored in HLR are
– Subscribers ID (IMSI and MSISDN )– Current subscriber VLR.– Supplementary services subscribed to.– Supplementary services information (eg. Current forwarding
address ).– Authentication key and AUC functionality.– TMSI and MSRN
HOME LOCATION REGISTER (HLR)
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• The Visited Location Register (VLR) is a local subscriber database, holding details on those subscribers who enter the area of the network that it covers.
• The details are held in the VLR until the subscriber moves into the area serviced by another VLR.
• The data includes most of the information stored at the HLR, as well as more precise location and status information.
• The additional data stored in VLR are– Mobile status ( Busy / Free / No answer etc. )– Location Area Identity ( LAI )– Temporary Mobile Subscribers Identity ( TMSI )– Mobile Station Roaming Number ( MSRN )
• The VLR provides the system elements local to the subscriber, with basic information on that subscriber, thus removing the need to access the HLR every time subscriber information is required.
VISITOR LOCATION REGISTER (VLR)
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• The AUC is a processor system that perform authentication function.
• It is normally co-located with the HLR.• The authentication process usually takes place each time
the subscriber initializes on the system.• Each subscriber is assigned an authentication key (Ki) which
is stored in the SIM and at the AUC.• A random number of 128 bits is generated by the AUC &
sent to the MS.• The authentication algorithm A3 uses this random number
and authentication key Ki to produce a signed response SRES( Signed Response ).
• At the same time the AUC uses the random number and Authentication algorithm A3 along with the Ki key to produce a SRES.
• If the SRES produced by AUC matches the one produced by MS is the same, the subscriber is permitted to use the network.
Authentication Centre (AUC)
Copyright © 2011 LOGTEL
HLR AUC
TRIPLESRAND, Kc , SRESVLR
RAND Kc SRES
RAND
SRES
SRES
SRES = SRESBTS
A5 , HYPERFRAME NUM
Kc
AIR INTERFACE ENCRYPTION
MS
A3 , A8 , A5 , Ki
SRES = A3 (RAND , Ki )
Kc = A8 (RAND , Ki )
Ki, A3, A8A3 ( RAND, Ki ) = SRES
A8 ( RAND, Ki ) = KcTriples
Generated
AUTHENTICATION PROCESS
Copyright © 2011 LOGTEL
HANDOVER
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• The GSM handover process uses a mobile assisted technique for accurate and fast handovers, in order to:
– Maintain the user connection link quality.
– Manage traffic distribution• The overall handover process is implemented in the
MS,BSS & MSC. • Measurement of radio subsystem downlink performance
and signal strengths received from surrounding cells, is made in the MS.
• These measurements are sent to the BSS for assessment. • The BSS measures the uplink performance for the MS being
served and also assesses the signal strength of interference on its idle traffic channels.
• Initial assessment of the measurements in conjunction with defined thresholds and handover strategy may be performed in the BSS. Assessment requiring measurement results from other BSS or other information resident in the MSC, may be perform. in the MSC.
HANDOVER
Copyright © 2011 LOGTEL
• The MS assists the handover decision process by performing certain measurements.
• When the MS is engaged in a speech conversation, a portion of the TDMA frame is idle while the rest of the frame is used for uplink (BTS receive) and downlink (BTS transmit) timeslots.
• During the idle time period of the frame, the MS changes radio channel frequency and monitors and measures the signal level of the six best neighbor cells.
• Measurements which feed the handover decision algorithm are made at both ends of the radio link.
HANDOVER (Cont)
Copyright © 2011 LOGTEL
• At the MS end, measurements are continuously signalled, via the associated control channel, to the BSS where the decision for handover is ultimately made.
• MS measurements include:
– Serving cell downlink quality (bit error rate (BER) estimate).
– Serving cell downlink received signal level, and six best neighbor cells downlink received signal level.
• The MS also decodes the Base Station ID Code (BSIC) from the six best neighbor cells, and reports the BSICs and the measurement information to the BSS.
MS END
HANDOVER
Copyright © 2011 LOGTEL
The BTS measures the uplink link quality, received signal level, and MS to BTS site distance.
The MS RF transmit output power budget is also considered in the handover decision.
If the MS can be served by a neighbor cell at a lower power, the handover is recommended.
From a system perspective, handover may be considered due to loading or congestion conditions. In this case, the MSC or BSC tries to balance channel usage among cells.
BTS END
HANDOVER
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During the conversation, the MS only transmits and receives for one eighth of the time, that is during one timeslot in each frame.
During its idle time (the remaining seven timeslots), the MS switches to the BCCH of the surrounding cells and measures its signal strength.
The signal strength measurements of the surrounding cells, and the signal strength and quality measurements of the serving cell, are reported back to the serving cell via the SACCH once in every SACCH multiframe.
This information is evaluated by the BSS for use in deciding when the MS should be handed over to another traffic channel.
This reporting is the basis for MS assisted handovers.
MS IDLE TIME REPORTING
HANDOVER
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MEASUREMENT IN ACTIVE MODE
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2
Frame 24 Frame 25 Idle Frame Frame 0
Frame 24 Frame 25 Idle Frame Frame 0
1 2 3 1 2 1 2
1. MS receives and measures signal strength on serving cell(TS2).
2. MS transmits3. MS measures signsl strength for at least one neighbor
cell.4. MS reads BSIC on SCH for one of the 6 strongest
neighbor.
4
Downlink
Uplink
HANDOVER
Copyright © 2011 LOGTEL
Maximum 32 averaging of RSS takes place.Practically a cell neighbors can be equipped for a cell.If high numbers of neighbors are equipped, then the accuracy
of RSS is decreased as should have 8 to 10 neighbors.
T15
T5
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I25
NUMBER OF NEIGHBORS
HANDOVER
Copyright © 2011 LOGTEL
NUMBER OF NEIGHBORS
In one SACCH multiframe there are 104 TDMA frames.Out of this 104 frames 4 frames are idle and are used to
decode the BSIC.Remaining 100 TDMA frames are used to measure
RSS( Received Signal Strength) of the neighbor.If 25 neigbors are equipped, then in one SACCH multiframe
each neigbor is measured 100/25 = 4 times and averaged out. This produces a less accurate value.
If 10 neigbors are equipped, then in one SACCH multiframe each neigbor is measured 100/10 = 10 times and averaged out. This produces a more accurate value.
HANDOVER
Copyright © 2011 LOGTEL
GSM causes its own time interference.
The MS has a omni-directional antenna. Much of the MS power goes to the server but a lot is interfering with surrounding cells using the same channel.
The TDMA frames of adjacent cell are not aligned since they are not synchronised. Hence the uplink in the surrounding cell suffers from interference.
INTERFERENCE ON IDLE CHANNEL
Channel 10Cell 1
1 2 3 4 5
1 2 3 4 5
UPLINK CELL1
UPLINK CELL2
Channel 10Cell 2
HANDOVER
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The BSS keeps on measuring the interference on the idle timeslots.
Ambient noise is measured and recorded 104 times in one SACCH multiframe.
These measurements are averaged out to produce one figure.
The BSS then distributes the idle timeslots into band 0 to band 5.
Since the BSS knows the interference level on idle timeslots, it uses this data to allocate the best channel first and the worst last.
INTERFERENCE ON IDLE CHANNEL
0 1 2 3 4 5 6 7
Inteference on idle channel measured on Idle Timeslot by BSS
HANDOVER
Copyright © 2011 LOGTEL
The following measurements is be continuously processed in the BSS :i) Measurements reported by MS on SACCH - Down link RXLEV - Down link RXQUAL - Down link neighbor cell RXLEV ii) Measurements performed in BSS - Uplink RXLEV - Uplink RXQUAL - MS-BS distance - Interference level in unallocated time slots
Every SACCH multiframe (480 ms) a new processed value for each of the measurements is calculated..
HANDOVER
HANDOVER
Copyright © 2011 LOGTEL
Handover is done on five conditions– Interference– RXQUAL– RXLEV– Distance or Timing Advance– Power Budget
Interference - If signal level is high and still there is RXQUAL problem, then the RXQUAL problem is because of interference.RXQUAL - It is the receive quality. It ranges from 0 to 7 , 0 being the best and 7 the worstRXLEV - It is the receive level. It varies from -47dBm to -110dBm.Timing Advance - Ranges from 0 to 63.Power budget - It is used to save the power of the MS.
HANDOVER CONDITIONS
HANDOVER
Copyright © 2011 LOGTEL
Handover takes place in the same cell from one timeslot to another timeslot of the same carrier or different carriers( but the same cell).
Intra-cell handover is triggered only if the cause is interference.Intra-cell handover can be enabled or disabled in a cell.
HANDOVER TYPESIntra-Cell Handover
BSC
BTSCall is handed
from timeslot 3 to timeslot 5
0 1 2 3 4 5 6 7
HANDOVER
Copyright © 2011 LOGTEL
Handover takes place between different cell which are controlled by the same BSC.
HANDOVER TYPESIntra-BSC Handover
BSC1
BTS1Call is handed from timeslot 3 of cell1 to timeslot 1 of cell2 . Both the cells are controlled
by the same BSC.
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
HANDOVER
Copyright © 2011 LOGTEL
Handover takes place between different cell which are controlled by the different BSC.
HANDOVER TYPESInter-BSC Handover
BSS1
BTS1Call is handed from timeslot 3 of cell1 to timeslot 1 of cell2 . Both the cells are controlled
by the different BSC.
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7BSS2
MSC
BTS2
HANDOVER
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Handover takes place between different cell which are controlled by the different BSC and each BSC is controlled by different MSC.
HANDOVER TYPESInter-MSC Handover
BSS1
BTS1Call is handed from timeslot 3 of cell1 to timeslot 1 of cell2 . Both the cells are controlled
by the different BSC, each BSCbeing controlled by different MSC.
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7BSS2
MSC1
BTS2
MSC2
HANDOVER
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LOCATION UPDATE
Copyright © 2011 LOGTEL
MSC should always know the location of the MS so that it can contact it by sending pages whenever required.
The mobile keeps on informing the MSC about its current location area or whenever it changes from one LA to another.
This process of informing the MSC is known as location updating.
The new LAI is updated in the VLR.LAI = MCC + MNC + LAC
MCC MNC LAC
3 digits 1-2 digits Max 16 bits
MCC = Mobile country code.MNC = Mobile Network Code.LAC = Location area code. Identifies a location area within a GSM PLMN network. The maximum length of LAC is 16 bits. Thus 65536 different LA can be defined in one GSM PLMN.
LOCATION UPDATE
Copyright © 2011 LOGTEL
• Normal location update• Periodic location update• IMSI attach
Normal Location Update1. Mobile powers on and is idle.2. Reads the LAI broadcast on the BCCH.3. Compares with the last stored LAI and if it is different does a
location update.
LOCATION UPDATE TYPES
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LTE
Copyright © 2011 LOGTEL
The driving forces – The telco point of view
Addressing the trend of declining ARPU Delivery of higher bandwidth services and
capacity Reducing OPEX & Cost/MB Proliferation of emerging devices, with rich
mobile applications and video Quad-play (bundle) Multiple screen offerings
Addressing shortage in bandwidth Leveraging existing 3G infrastructure
Regulation Re-allocation of older spectrum for 4G
technologies Open access & net neutrality
130
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Standards bodies
131
IMT-Advanced
802.X – LAN/WLAN
Copyright © 2011 LOGTEL
IMT Expected Targets
IMT- Advanced (IMT-2000 – become 3G) high quality mobile services user equipment suitable for worldwide use user‐friendly applications, services and equipment worldwide roaming capability Improve wireless performance
Better signal reception and better coverage Increase spectrum efficiency
More subscribers and more data transfer in the same spectrum Flat all-IP network architecture High mobility up to 500 Km/H enhanced peak data rates to support advanced services
and applications 100 Mbit/s (UL 50 Mbit/s DL) for high mobility 1 Gbit/s for low mobility
Low latency <50ms
132
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4G Enabling Technology
Some key technologies made 4G possible
Both WiMAX and LTE use: OFDM, OFDMA and SC-FDMA Channel dependent scheduling Adaptive coding and modulation (ACM) Multiple-In-Multiple-Out (MIMO) antenna
processing Turbo coding and decoding
133
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OFDMA Flexibility
With OFDMA the user allocation is flexible Can change from frame to frame Multiple allocations for several applications
Allocation changes In WiMAX every 5 ms In LTE every 1 ms
134
frequency
frequency
time
OFDMA
Burst
Burst Burst
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Single Carrier FDMA (SC-FDMA) A major problem with OFDM and OFDMA is
high peak-to-average power ratio (PAPR) Transmitted amplitude with large variation Requires a linear amplifier at transmitter Linear amplifies consumes high power OK at base station For mobile station, this consumes battery
LTE uses a solution for UL: SC-FDMA Single carrier transmission
135
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MIMO
Transmit diversity: Same modulation symbols sent from all Tx M
antennas Receiver combines the signal from N antennas Useful to increase performance against fading
Spatial multiplexing: Different modulation symbols sent from M Tx
antennas Receiver received the signal from N antennas Useful to increase data rate if channel is good
WiMAX uses up to 2x2. LTE uses up to 4x4
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MIMO Radio Channel
Multiple antennas at both the base station and terminal can significantly increase data rates with sufficient multipath
Reduce noise Reduce handoffs and disconnecting
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So, What will be the bandwidth?
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LOCATION UPDATE
MS MSCBSS
RACH
Imme. Assign
Location update request
Authentication request
Authentication response
DTI<CICMD>
DTI<CICMP>
Cipher mode command
Cipher mode complete
Location update accepted
Copyright © 2011 LOGTEL
IMSI ATTACHSaves the network from paging a MS which is not active in the system.When MS is turned off or SIM is removed the MS sends a detach signal to
the Network. It is marked as detached.When the MS is powered again it reads the current LAI and if it is same does
a location update type IMSI attach.Attach/detach flag is broadcast on the BCCH sys info.
PERIODIC LOCATION UPDATEMany times the MS enters non-coverage zone.The MS will keep on paging the MS thus wasting precious resources.To avoid this the MS has to inform the MSC about its current LAI in a set
period of time.This time ranges from 0 to 255 decihours.Periodic location timer value is broadcast on BCCH sys info messages.
Copyright © 2011 LOGTEL
During conversation user talks alternatively.In DTX mode of operation the transmitter are switched on only for
frames containing useful information.Helps to increase battery life and reduce interference level.
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DISCONTINOUS TRANSMISSION
SID
Copyright © 2011 LOGTEL
IMPLEMENTATION OF DTXVoice Activity Detector ( VAD )
Determines which specific block of 20ms from the speech coder contains speech.
Removes stationary noise.Inserts comfort noise.The frames containing this background noise are called SID frames and
are sent in blocks of 8 frames within every 104 frame block.
VAD Speech / No speech20 ms speech
block
Copyright © 2011 LOGTEL
144
Thank You!!!