Southern Methodist University Fall 2003 EETS 8316/NTU CC745-N Wireless Networks
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Transcript of Southern Methodist University Fall 2003 EETS 8316/NTU CC745-N Wireless Networks
#1EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Southern Methodist University Fall 2003
EETS 8316/NTU CC745-NWireless Networks
Lecture 4: GSM
Instructor: Jila Serajemail: [email protected]
http://www.engr.smu.edu/~jseraj/tel: 214-505-6303
#2EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review
In the last meeting we discussed
Handoff, challenges, solutions
Anchor MSC, path optimization
North American Numbering Plan
Numbers in GSM network
#3EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Handoff
Movement into a different cell requires MTSO to automatically transfer call to another base station without interruption
Two types of handoff, hard handoff and soft handoff
BSC decides on handoff in the first generation of mobile network
BSC together with handset decides on handoff, MAHO
#4EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Handoff, cont..
Phases of handoff are: handoff decision, resource reservation, execution, clearing resources.
Handoff challenges are: Performing handoff before signal strength becomes too low, do not perform unnecessary handoff, resource allocation, inter-MSC/inter-system handoff, handset capabilities
Anchor MSC remains in the call
#5EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Handoff, cont..
BS BS
Anchor MSC New Serving MSC PSTN
• What happens if we go back to the anchor MSC?• IS-41 has handoff back facility
• What if a third MSC gets involved?• Path minimization process
#6EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Handoff, cont..
BS
BS
Anchor MSC Target MSC
Serving MSC
BS
PSTN
HANDTHIRD
FACDIR
FACRELR
FACDIRR
1
3
2
4
HANDTHIRDR
6
5
7
MSONCH
10
8FACREL9
#7EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Handoff, cont..
BS
BS
Anchor MSC
MSC
BS
PSTN
Call Path after path minimization process
New Serving MSC
#8EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Registration, cont..
Registration, Power up/down, periodical, New system, Call origination
MS Service Qualification—validation information (billing)
—Service profile information, features, restrictions…
#9EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Roaming, cont..
MS Location Update occurs at registration, deregistration, new location area, new system
Deregistration is either triggered by mobile (power down registration), by MSC for inactivity, by HLR at registration in another MSC.
#10EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Border Case
If registration happens in several MSC, HLR decides which one is valid.
If registration happens in several BS, MSC determines which one is valid
#11EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Paging
Paging is used when there is a terminating call to a mobile station.
A termination call is routed towards gateway MSC, Gateway MSC consults HLR, HLR request paging from visiting MSC, visiting MSC pages the handset, when page response is received HLR is informed, HLR send the visiting MSC address to gateway MSC that routes the call to visiting MSC and the terminating call is established.
#12EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Paging, cont..
If multiple MSC responds to the page request, HLR chooses the valid page response
#13EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, North American Numbering Plan
North American Numbering Plan consists of 10 digits, NPA-NXX-XXXX
There is no way for a switch to identify that a number belongs to a mobile subscriber, nor can it identify the network provider.
Mobile network provider “buy” a certain number series in each area for their users.
Therefore we can not bill a caller to a mobile user for the air usage. They do it in other countries!
#14EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Primer on RF
The radio frequencies are grouped into bands.
Each set of bands are dedicated to different purposes by FCC
Each frequency is logically divided into time slots for communication between mobile station and the base station.
Some time slots are reserved for user traffic, such as voice and data and other for signaling purposes.
#15EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Review, Cellular DCCH Structure
DCCH
Reverse Forward
RACH SPACH BCCH SCF Reserved
PCH ARCH SMSCH FBCCH EBCCH SBCCH
#16EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM General Architecture
BSS
MSC
VLR
HLR
EIR
AUC
MTTE
MS
Um
A
PSTN
BSC
BTS BTS
OMC
NMC
ADC
OSS
BSS
MS
GSM Public land mobilenetwork (PLMN)
OSS: operation subsystemBSS: base station subsystemMS: mobile station
Abis
#17EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM
Several first generation analog cellular systems in Europe but incompatible - limited roaming
1987-1989 ETSI standards for pan-European Global System for Mobile Communications (GSM, originally Group Special Mobile) at 900 MHz—1992 GSM is launched
—1990-1993 Standards for Digital Cellular System at 1800 MHz (DCS 1800, recently renamed GSM 1800; US version is PCS 1900)
#18EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM, cont..
Objectives:
—Broad offering of speech and data services
—Compatible with wireline networks, eg, ISDN
—Automatic roaming and handoff
—Highly efficient use of frequency spectrum
—Support for different types of mobile terminal equipment (eg, cars, portable handsets)
#19EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM, cont..
Objectives:
—Digital signaling and transmission
—Low cost infrastructure and terminal equipment
#20EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM, cont..
13 recommendations—R.00: Preamble—R.01: General structure of
recommendations, GSM overview—R.02: Service aspects: types of
services—R.03: Network aspects: architecture,
call routing, performance objectives—R.04: Mobile/base station interface
and protocols
#21EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM, cont..
—R.05: Physical layer on radio path: multiple access, channel coding, modulation, transmission
—R.06: Speech coding aspects
—R.07: Terminal adaptors for mobile stations
—R.08: Base station and mobile switching center (MSC) interface
—R.09: Interworking with PSTN and packet data networks
#22EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM, cont..
—R.10: Service interworking, short message service
—R.11: Equipment specification
—R.12: Operation and maintenance, tariffs, traffic administration
#23EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM, cont..
Summary of features
Channel bandwidth 200 kHz
Multiple access TDMA
Users/carrier 8
Speech coding rate 13 kb/s
FEC coded speech rate 22.8 kb/s
#24EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM, cont..
Summary of service quality requirements
Speech intelligibility 90%
Max one-way delay 90 ms
Max handoff gap 150 ms if intercell
Time to alert mobile ofinbound cell
4 sec first attempt, 15 sec final attempt
Release time to callednetwork
2 sec
Connect time to callednetwork
4 sec
#25EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM General Architecture, cont..
Mobile station (MS) communicates to base stations through radio interface Um
Mobile termination (MT) supports physical channel between MS and base station (radio transmission, channel coding, speech coding)
#26EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM General Architecture, cont..
Terminal equipment (TE), eg, telephone set. Contains terminal/user-specific data in form of smart card (subscriber identify module or SIM card), plugs into any GSM terminal like credit card and identifies user to network for personal mobility (in addition to terminal mobility) and security
#27EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM General Architecture, cont..
Base station Subsystem (BSS) communicates with mobile switching center through network interface A
Base Transceiver Station (BTS) handles channel allocation, signaling, frequency hopping, handover initiation, etc.
BTS communicates with BSC using Abis interface
#28EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM General Architecture, cont..
Base station controller (BSC) manages radio channels, paging, handoff for several BTSs
BSC communicates with MSC using A interface
Mobile switching center (MSC) is gateway to PSTN and packet data networks
Performs switching, paging functions, MS location updating, handoff control, etc.
#29EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM General Architecture, cont..
Home location register (HLR) stores subscriber info and part of MS’s location info to route incoming calls to visitor location register (VLR) where mobile is roaming
VLR registers users roaming in its area and assigns roaming numbers
#30EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM General Architecture, cont..
Authentication center (AUC) is accessed by HLR to authenticate a user for service. It contains authentication and encryption keys for subscribers
Equipment identity register (EIR) allows stolen or fraudulent mobile stations to be identified
#31EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM General Architecture, cont..
Operation subsystem (OSS) contains: operations and maintenance center (OMC), network management center (NMC), and administration center (ADC) . These network elements work together to monitor, control, maintain, and manage the network
#32EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical and Physical Channels
Um interface: various logical channels are mapped to physical channels
A physical channel is a timeslot with timeslot number in a sequence of TDMA frames
8 physical channels mapped onto 8 timeslots within TDMA frame per frequency carrier
#33EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Physical Channels
::
Frequency 124
Frequency 2
Frequency 1 Ch 1
Timeslot 1
Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
::
2 3 4 5 6 7 8
TDMA frame = 4.615 ms
#34EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical Channel Structure
CCH
TCH/F TCH/H
BCH CCCH DCCH
FCCH SCH BCCH PCH AGCH RACH
TCH CBCH
ACCH SDCCH
FACCHSACCH
#35EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical Channels
3 groups of logical channels, TCH, CCH and CBCH
TCH is used to carry voice or data traffic
CCH is used for control functions
CBCH is used for broadcast functions
#36EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical Channels, cont..
Logical traffic channels = full rate (TCH/F) at 22.8 kb/s or half rate (TCH/H) at 11.4 kb/s
Physical channel = full rate traffic channel (1 timeslot) or 2 half rate traffic channels (1 timeslot in alternating frames)
Full rate channel may carry 13 kb/s speech or data at 12, 6, or 3.6 kb/s
Half rate channel may carry 6.5 kb/s speech or data at 6 or 3.6 kb/s
#37EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical Channels, cont..
CCH consists of 3 groups of logical control channels, BCH, CCCH and DCCH
BCH (broadcast channel): point-to-multipoint downlink only. Contains three sub-channels, BCCH, FCCH and SCH
—BCCH (broadcast control channel): send cell identities, organization info about common control channels, cell service available, etc
#38EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical Channels
—FCCH (frequency correction channel): send a frequency correction data burst containing all zeros to effect a constant frequency shift of RF carrier
—SCH (synchronization channel): send TDMA frame number and base station identity code to synchronize MSs
#39EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical Channels, cont…
CCCH (common control channel): Consists of three sub-channels, PCH, AGCH and RACH. This channels is used for paging and access
—PCH (paging channel): to page MSs
—AGCH (access grant channel): to assign MSs to stand-alone dedicated control channels for initial assignment
—RACH (random access channel): for MS to send requests for dedicated connections
#40EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical Channels, cont…
DCCH (dedicated control channel): bi-directional point-to-point -- main signaling channels. Consist of two sub-channels, SDCCH and ACCH
—SDCCH (stand-alone dedicated control channel): for service request, subscriber authentication, equipment validation, assignment to a traffic channel
#41EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Logical Channels, cont…
—SACCH consist of two sub-channels, SACCH and FACCH
•SACCH (slow associated control channel): for out-of-band signaling associated with a traffic channel, eg, signal strength measurements
•FACCH (fast associated control channel): for preemptive signaling on a traffic channel, eg, for handoff messages
#42EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
OSI Model for SS7
TCAP MAPISUP INAPMUP OMAPLayer 4-7
SCCP
MTPLayer 3
Signaling link function, Signaling link physical requirementLayer 1-2
#43EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Interfaces, cont..
RF
LAPD
MM
RRM
CM
RRM
RF
LAPD LAPD
RF
RRM
RF
LAPD LAPD
RF
SCCP
RF
LAPD
MM
RRM
CM
SCCP
Air InterfaceUm Abis A
#44EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Protocol Layers
RF : Physical Layer
LAPD: Link Layer, ISDN protocol based
SCCP: Signal Connection Control Layer, part of link layer
RR: Radio Resource
MM: Mobility Management
CC: Call Control
#45EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Network Layer
Network layer consists of 3 sublayers
Radio resource management (RR) sublayer—Establishment, maintenance, and termination of
radio channel connections
Mobility management (MM) sublayer—Registration, authentication, and location tracking
Call control (CC) sublayer—Establishment, maintenance, and termination of
circuit-switched calls
#46EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Interfaces
MSC
AUC
Base Station SubsystemBSS
Switching System
BSSAP
VLR HLREIR
MAP
MAP
MAP
VLR
MAP
#47EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Interfaces, cont…
MS
BTS
BSC
LAPD
Base Station SubsystemBSS
Switching System
BSSAP
#48EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers
International mobile station equipment identity (IMEI). IMEI= TAC + FAC + SNR + SP— TAC = Type Approval Code, 6 decimals
— FAC = Final Assembly Code, 6 decimals, assigned by manufacturer
— SNR = Serial Number, 6 decimals, assigned by manufacturer
— SP = Spare, 1 decimal place
EIR has while, black and optionally grey list.
#49EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers
International mobile station equipment identity (IMEI). IMEI= TAC + FAC + SNR + SP— TAC = Type Approval Code, 6 decimals
— FAC = Final Assembly Code, 6 decimals, assigned by manufacturer
— SNR = Serial Number, 6 decimals, assigned by manufacturer
— SP = Spare, 1 decimal place
EIR has while, black and optionally grey list
#50EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers, cont…
International mobile Subscriber Identity (IMSI). Stored on the SIM (Subscriber Identity Module) card. IMSI is obtained at the time of subscription. IMSI is not made public.
IMSI = MCC + MNC + MSIN
MCC = Mobile Country Code, 3 decimals
MNC = Mobile Network Code, 2 decimals
#51EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers, cont…
MSIN = Mobile Subscriber Identification Number, maximum 10 decimal digits
Mobile Station ISDN number (MSISDN), is the real phone number of the subscriber. Stored in HLR and on SIM card
MSISDN = CC + NDC + SN
CC = Country Code, up to 3 decimals
#52EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers, cont…
NDC = National Destination Code, typically 2-3 decimals
SN = Subscriber Number, maximum 10 decimals.
Mobile Station Roaming Number (MSRN), same format as MSISDN. A temporary location dependent ISDN number.
Is assigned in two cases, at registration or at call set up.
#53EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers, cont…
Location Area Identity (LAI). Regularly sent on BCCH LAI = CC + MNC + LAC,
LAC = Location Area Code, max 5 decimals (<FFFFhex).
Temporary Mobile Subscriber Identity (TMSI). Stored only in the VLR and SIM card. Consists of 4*8 bits excluding value FFFF FFFFhex
#54EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers, cont…
TMSI has only local meaning and can be defines according to operator’s specifications.
LAI + TMSI uniquely identifies the user, I.e. IMSI is no longer needed for ongoing communication
#55EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers, cont..
Local Mobile Subscriber Identity (LMSI). Created in VLR and stored in HLR.
Like TMSI is operator defined.
Used in communication with VLR to speed the search for mobile records.
Speed is essential to achieve short call setup times.
#56EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers, cont…
Global Cell Id = LAI + CI
CI = Cell id, unique id within the LAI. Maximum 2*8 bits
Base Transceiver Station Identity Code (BSIC) = NCC + BCC
#57EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Numbers, cont…
BSIC is broadcast periodically by the base station on the synchronization channel.
NCC = Network Color Code, 3 bits
BCC = Base Station Color Code, 3 bits
#58EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Roaming From Another PLMN
VLR registers users roaming in its area
—Recognizes mobile station is from another PLMN
—If roaming is allowed, VLR finds the mobile’s HLR in its home PLMN
—VLR constructs a global title from IMSI to allow signaling from VLR to mobile’s HLR via public telephone network
#59EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Roaming, cont...
VLR registers users roaming in its area
—VLR generates a mobile subscriber roaming number (MSRN) used to route incoming calls to mobile station
—MSRN is sent to mobile’s HLR
#60EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Roaming, cont…
VLR contains
—MSRN
—TMSI
—Location area where mobile station has registered
—Info for supplementary services (if any)
—IMSI
—HLR or global title
—Local identity for mobile station (if any)
#61EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Security
3 security problems: unauthorized access, privacy from eavesdropping, protection of subscriber identity/location
Unauthorized (fraudulent) access
—GSM handsets must be presented with a subscriber identity module (SIM)
—SIM must be validated with personal identification number (PIN)
#62EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Security, cont…
Unauthorized (fraudulent) access
—SIM also stores subscriber authentication key, authentication algorithm, cipher key generation algorithm, encryption algorithm
—During registration (when roaming), mobile station receives “challenge” and uses authentication key and authentication algorithm to generate “challenge response” to verify user’s identity
#63EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Security, cont…
Privacy from eavesdropping
—Temporary encryption key is used for privacy of data, signaling, and voice
—Info is encrypted before transmission
#64EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Security, cont…
Anonymity of users
—Supported by temporary mobile subscriber ID (TMSI)
—When registered, mobile station sends globally-unique international mobile subscriber ID (IMSI) to network
—Network assigns TMSI for use during call - IMSI is not sent over radio link
#65EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Security, cont…
Anonymity of users
—Only network and mobile station know true identity
—New TMSI is assigned when roam into new area
#66EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Security, cont..
Fetched triplets are stored in VLR—Every call uses up one triplet (discarded)
—Another set must be fetched when exhausted
Visited system
Registration requestIMSI/TMSI identifies user, LAI points to old VLR,requests data toauthenticate user
IMSI/TMSI + LAI
Subscriber data
Old VLR
#67EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Assignment
Wireless personal communications, Chapter 7
Rappaport what pages
#68EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Security, cont..
Visited system
Challenge
Requests tripletsfrom home system,chooses a tripletCalculates
responseby authen-
ticationalgorithm
Challenge response Compares to storedresponse in triplet, registration successfulif matches
New TMSI
Acknowledge
Assigns new TMSI
#69EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Security, cont..
Visited system
Registrationcancel
Location update
AcknowledgeHLR
Old VLR
#70EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Handoffs
3 types of handoffs
—Intra-BSS: if old and new BTSs are attached to same base station
•MSC is not involved
—Intra-MSC: if old and new BTSs are attached to different base stations but within same MSC
—Inter-MSC: if MSCs are changed
#71EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Intra-MSC Handoff
Mobile station monitors signal quality and determines handoff is required, sends signal measurements to serving BSS
Serving BSS sends handoff request to MSC with ranked list of qualified target BSSs
MSC determines that best candidate BSS is under its control (assumed here)
MSC reserves a trunk to target BSS
#72EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Intra-MSC Handoff, cont..
Target BSS selects and reserves radio channels for new connection, sends Ack to MSC
MSC notifies serving BSS to begin handoff, including new radio channel assignment
Serving BSS forwards new radio channel assignment to mobile station
Mobile station re-tunes to new radio channel, notifies target BSS on new channel
#73EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Intra-MSC Handoff, cont..
Target BSS notifies MSC that handoff is detected
Target BSS and mobile station exchange messages to synchronize transmission in proper timeslot
MSC switches voice connection to target BSS, which responds when handoff is complete
MSC notifies serving BSS to release old radio traffic channel
#74EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Inter-MSC Handoff
Mobile station monitors signal quality and determines handoff is required, sends signal measurements to serving BSS
Serving BSS sends handoff request to MSC with ranked list of qualified target BSSs
Serving MSC determines that best candidate BSS is under control of a target MSC (assumed here) and calls target MSC through PSTN
#75EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Inter-MSC Handoff, cont..
Target MSC notifies its VLR to assign a TMSI
Target VLR returns TMSI
Target MSC reserves a trunk to target BSS
Target BSS selects and reserves radio channels for new connection, sends Ack to target MSC
Target MSC notifies serving MSC that it is ready for handoff
#76EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Inter-MSC Handoff, cont..
Serving MSC notifies serving BSS to begin handoff, including new radio channel assignment
Serving BSS forwards new radio channel assignment to mobile station
Mobile station re-tunes to new radio channel, notifies target BSS on new channel
Target BSS notifies target MSC that handoff is detected
#77EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
GSM Inter-MSC Handoff, cont..
Target BSS and mobile station exchange messages to synchronize transmission in proper timeslot
Voice connection is switched to target BSS, which responds when handoff is complete
Target MSC notifies serving MSC
Old network resources are released
#78EETS 8316/NTU TC 745, Fall 2003 ENGINEERINGSMU
Reading Suggestion
Wireless Communications: Principles and Practice, Rappaport, sections 2.1
Wireless personal communications systems, Goodman, Chapter 7