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Gsm system architecture

This document summarizes key aspects of the air interface in a GSM network. It describes the different radio transmission techniques including FDMA, TDMA, and CDMA. It then explains the different types of channels, including physical channels that transfer bits between network elements and logical channels distinguished by information type. Finally, it provides details on specific channels like the broadcast, common control, and dedicated control channels that are used for different functions like synchronization, paging, and signaling.

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Air Interface
Air Interface • Radio Transmission Techniques – FDMA – TDMA – CDMA • Channels – Physical channels – Logical channels
FDMA Time Frequency Channel
TDMA Time Frequency 0 1 2 3 4 5 6 7 Channel Time Slot
CDMA Frequency Time Code Code 1 Code 2 Code 3
Channels • Physical Channels – Associated with frequency bands, time slots, codes – Physical channels transfer bits from one network element to another • Logical Channels – Distinguished by the nature of carried information and the way to assemble bits into data units – Three types • one-to-one: traffic channels between a BTS and a MS • one-to-many: synchronization signals from BTS to MSs in a cell • many-to-one: from MSs to the same BTS
Air Interface Layers Radio Transmission Logical Channels Messages Radio Transmission Logical Channels Messages Terminal Base Station Layer 1 Bits Layer 2 Packets Layer 3 Messages
GSM Frame Structure 3 57 26 57 8.25 1 1 3 0 7 ... ... Superframe 6.12 sec 120 msec 4.615 msec 0.57692 msec 156.25 bits 51 Multiframe 26 Frames 8 Multiframe Coded data Midamble Tail bit Stealing Flag Guard period
• There are two types of multiframe – 26 TDMA-frame multiframe is used to carry TCH, SACCH and FACCH – 51 TDMA-frame multiframe is used to carry BCCH, CCH, SDCCH and SACCH Frame Types
Burst and Frames • The information contained in one time slot on the TDMA frame is call a burst. • Five types of burst – Normal Burst (NB) – Frequency Correction Burst (FB) – Synchronization Burst (SB) – Access Burst (AB) – Dummy Burst
Traffic channels (TCH) Signaling channel TCH/F: Full-rate Traffic Channel TCH/H: Half-rate Traffic Channel FCCH: Frequency correction SCH: Synchronization BCCH: Broadcast control PCH: Paging AGCH: Access grant RACH: Random access SDCCH: Stand-alone dedicated control SACCH: Slow associated control FACCH: Fast associated control Two-way Base-to- mobile Two-way Logical Channel List BCH CCCH DCCH
Logical Channels • Control Channels – Broadcast Channels (BCH) – Common Control Channels (CCCH) – Dedicated Control Channels (DCCH) • Traffic Channels (TCH) – Full Rate (TCH/F) – Half Rate (TCH/H)
UP / Down-Link • Down-link: the transmission path from Base Station to Mobile Station • Up-link: the transmission path from Mobile Station to Base Station
Control Channels • Broadcast Channels (BCH) – Frequency Correction Channel (FCCH) – Synchronization Channel (SCH) – Broadcast Control Channel (BCCH) • Common Control Channels (CCCH) – Paging Channel (PCH) – Random Access Channel (RACH) – Access Grant Channel (AGCH) • Dedicated Control Channels (DCCH) – Stand alone Dedicated Control Channel (SDCCH) – Cell Broadcast Channel (CBCH) – Slow Associated Control Channel (SACCH) – Fast Associated Control Channel (FACCH)
Message name Transmitted by AUTHENTICATION REQUEST AUTHENTICATION RESPONSE AUTHENTICATION REJECT IDENTITY REQUEST IDENTITY RESPONSE TSMI REALLOCATION COMMAND LOCATION UPDATING REQUET LOCATION UPDATING ACCEPT LOCATION UPDATING REJECT IMSI DETACH REQUEST CM SERVICE REQUEST CM RE-ESTABLISHMENT REQUEST MM-STATUS Base Mobile Base Base Mobile Base Mobile Base Base Mobile Mobile Mobile Mobile/Base Mobility Management Messages
Message name Starting a call Transmitted by SETUP EMERGENCY SETUP CALL PROCEEDING PROGRESS CALL CONFIRMED ALERTING CONNECT Mobile/base mobile base base mobile mobile/base mobile/base During a call START DTMF STOP DTMF MODIFY USER INFORMATION Mobile mobile mobile/base mobile/base Ending a call DISCONNECT RELEASE RELEASE COMPLET Mobile/base mobile/base mobile/base Abnormal conditions STATUS STATUS ENQUIRY CONGESTION CONROL Mobile/base mobile/base mobile/base Call management messages
Message name Logical channel Transmitted by SYNC CHANNEL INFORMATION SYSTEM INFORMATION (TYPE 1,2,3,4,5) SYSTEM INFORMATION (TYPE 6) CHANNEL REQUEST PAGING REQUEST (TYPE 1,2.3) IMMEDIATE ASSIGNMENT IMMEDIATE ASSIGNMENT EXTENDED IMMEDIATE ASSIGNMENT REJECT ASSIGNMENT COMMAND ADDITIONAL ASSIGNMENT PAGING RESPONSE MERSUREMENT REPORT HANDOVER COMMAND HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE CIPHERING MODE CHANNEL RELEASE PARTIAL RELEASE FREQUENCY REDEFINITION CLASSMARK CHANGE CHANNEL MODE MODIFY RR STATUS SCH BCCH SACCH RACH PCH AGCH AGCH AGCH FACCH FACCH SDCCH SACCH FACCH TCH FACCH FACCH FACCH FACCH FACCH SACCH FACCH SACCH FACCH FACCH FACCH SACCH Base Base Base Mobile Base Base Base Base Base Base Mobile Mobile Base Mobile Base Mobile Base Base Base Base Mobile Base Mobile/base Radio Resources Management Messages
Prior MSC Prior VLR HLR Serving VLR Serving MSC Serving Base Registration info Store info REGISTRATION NOTIFICATION INVOKE Store info Store info Change info remove info REGISTRATION NOTIFICATION INVOKE REGISTRATION NOTIFICATION RESULT REGISTRATION NOTIFICATION RESULT REGISTRATION CANCELLATION INVOKE remove info REGISTRATION CANCELLATION RESULT REGISTRATION CANCELLATION INVOKE REGISTRATION CANCELLATION RESULT QUALIFICATION REQUEST INVOKE QUALIFICATION REQUEST RESULT PROFILE REQUEST INVOKE PROFILE REQUEST RESULT Message sequence and system operations for registration of a terminal in a visited service area
Mobile station Base station Category Logical Channel SYNC CHANNEL INFORMATION Carrier sine wave SYSTEM INFORMATION TYPE3 CHANNEL REQUEST IMMEDIATE ASSIGNMENT LOCATION UPDATING REQUEST AUTHENTICATION REQUEST CIPHERING MODE COMMAND CIPHERING MODE ACK LOCATION UPDATING ACCEPT TMSI ALLOCATION COMPLETE AUTHENTICATION RESPONSE CHANNEL RELEASE RRM RRM RRM RRM MM MM MM MM MM RRM RRM RRM FCCH SCH BCCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH Location-Updating Procedure
Mobile station Base station Category Logical Channel RRM RRM RRM RRM RRM RRM MM MM RRM RRM CMCM CM CM RRM RRM CM CM CM CM RRM FCCH SCH BCCH PCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH FACCH TCH TCH FACCH FACCH FACCH FACCH Carrier sine wave SYNC CHANNEL INFORMATION SYSTEM INFORMATION PAGING REQUEST CHANNEL REQUEST IMMEDIATE ASSIGNMENT PAGING RESPONSE AUTHENTICATION REQUEST AUTHENTICATION RESPONSE CIPHERING MODE CIPHERING MODE ACK SETUP CALL CONFIRMED ALERTING CONNECT ASSIGNMENT COMMAND ASSIGNMENT ACK CONNECT ACK conversation conversation conversation DISCONNECT RELEASE RELEASE COMPLETE CHANNEL RELEASE Call Deliver to MH
Mobile-Assisted Handover Mobile station Base station Logical Channel TCH TCH SACCH TCH TCH TCH SACCH TCH FACCH new TCH TCH TCH TCH FACCH TCH TCH SACCH TCH TCH TCH SACCH TCH conversation conversation MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation HANDOVER COMMAND HANDOVER ACCESS HANDOVER ACCESS HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE conversation conversation MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation
Broadcast Channels (BCH) • To help the MH (Mobile Handset) measures – to turn to a BTS – to listen for the cell information • to start roaming, waiting for calls to arrive, making calls – Because BTSs are not synchronized with each other, every time a MH decides to camp to another cell, its FCCH, SCH, and BCCH must be read.
Frequency Correction Channel (FCCH) • Provide MH with the frequency reference of the system – To enable the Mobile Handset (MH) to synchronize with the frequency • Transmission properties – Transmit on the down-link – Point to multi-point.
Synchronization Channel (SCH) • MH synchronize with the structure within the locative cell – MH can receive information from the proper time slots on the TDMA structure • To ensure a GSM BTS is chose – The Base Station Identity Code (BSIC) can only be decoded by a GSM BTS • Transmission properties – Transmit on down-link – Point to multi-point.
Broadcast Control Channel (BCCH) • BTS broadcast cell information to MH – LAI ( Location Area Identity), to start roaming, waiting for calls to arrive, making calls – maximum output power allowed in the cell – information about BCCH carriers for the neighboring cells • MH will perform measurement to BTS • Transmission properties – Transmit on down-link – Point to multi-point
Common Control Channels (CCCH) • CCCH support the establishment of a dedicated communication path (dedicated channel) between the MH and the BTS • Three types of CCCH – Paging Channel (PCH) – Random Access Channel (RACH) – Access Grant Channel (AGCH)
Paging Channel (PCH) • Used by BTS to page particular MH in the cell – MH actively listen to PCH to check contact info within certain time – Contact could be incoming call or short message • Contact info on PCH include – IMSI (MH’s identity number), or – TMSI (temporary number) • Transmission properties – Transmit on down-link – point to point
Random Access Channel (RACH) • Used by MH to request a dedicated channel for call setup – Shared by any MH attempts to access the network – Channel request message contains the reason for the access attempt • Transmission properties – Transmit on up-link – Point to pint.
Access Grant Channel (AGCH) • The network assigns a signaling channel via AGCH – A Stand alone Dedicated Control Channel (SDCCH) is assigned • Transmission properties – Transmit on down-link – Point to point
Dedicated Control Channels (DCCH) • DCCH are used for transferring nonuser information between the network and the MH – Messages on DCCH Including • channel maintenance • mobility management • radio resource management • Four kinds of DCCH – Stand alone Dedicated Control Channel (SDCCH) – Cell Broadcast Channel (CBCH) – Slow Associated Control Channel (SACCH) – Fast Associated Control Channel (FACCH)
Stand alone Dedicated Control Channel (SDCCH) • Transfer signaling information between the BTS and the MH • Typically used for location updating prior to use of a traffic channel • Transmission properties – Bidirectional channel, transmit on both up and down-link – Point to point.
Cell Broadcast Channel (CBCH) • To carry Short Message Service Cell Broadcast (SMSCB) • Use the same physical channel as SDCCH • Transmission properties – Transmit on down-link – Point to multi-point
Slow Associated Control Channel (SACCH) • Carries control and measurement parameters along with routine data necessary to maintain a radio link between the MH and the BTS – On the uplink, MS sends averaged measurements (signal strength and quality) of current and neighboring BCCH – On downlink, MS receives information about transmitting power to use and an instruction with time advance/retard • Transmission properties – Bidirection channel, transmit on both up and down link – Point to point
Fast Associated Control Channel (FACCH) • An FACCH is used over a TCH where it steals time slots from a TCH – a 20 ms segment of speech is stolen to carry handover signaling information • Appears on demand
Traffic Channels (TCH) • TCH transport user information (speech/data) • TCH are bidirectional dedicated channels between the network and the MH
Mobile station Base station Category Logical Channel SYNC CHANNEL INFORMATION Carrier sine wave SYSTEM INFORMATION TYPE3 CHANNEL REQUEST IMMEDIATE ASSIGNMENT LOCATION UPDATING REQUEST AUTHENTICATION REQUEST CIPHERING MODE COMMAND CIPHERING MODE ACK LOCATION UPDATING ACCEPT TMSI ALLOCATION COMPLETE AUTHENTICATION RESPONSE CHANNEL RELEASE RRM RRM RRM RRM MM MM MM MM MM RRM RRM RRM FCCH SCH BCCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH Location-Updating Procedure
Mobile station Base station Category Logical Channel RRM RRM RRM RRM RRM RRM MM MM RRM RRM CMCM CM CM RRM RRM CM CM CM CM RRM FCCH SCH BCCH PCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH FACCH TCH TCH FACCH FACCH FACCH FACCH Carrier sine wave SYNC CHANNEL INFORMATION SYSTEM INFORMATION PAGING REQUEST CHANNEL REQUEST IMMEDIATE ASSIGNMENT PAGING RESPONSE AUTHENTICATION REQUEST AUTHENTICATION RESPONSE CIPHERING MODE CIPHERING MODE ACK SETUP CALL CONFIRMED ALERTING CONNECT ASSIGNMENT COMMAND ASSIGNMENT ACK CONNECT ACK conversation conversation conversation DISCONNECT RELEASE RELEASE COMPLETE CHANNEL RELEASE Call Deliver to MH
Mobile-Assisted Handover Mobile station Base station Logical Channel TCH TCH SACCH TCH TCH TCH SACCH TCH FACCH new TCH TCH TCH TCH FACCH TCH TCH SACCH TCH TCH TCH SACCH TCH conversation conversation MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation HANDOVER COMMAND HANDOVER ACCESS HANDOVER ACCESS HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE conversation conversation MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation
Burst • The information contained in one time slot is a burst • Five types of burst – Normal Burst (NB) • To carry information on traffic and control channels – Frequency Correction Burst (FB) • To synchronize the frequency of the mobile – Synchronization Burst (SB) • To synchronize the frames of the mobile – Access Burst (AB) • For random and handover access – Dummy Burst • For padding the frame
Bursts and Frames • There are two types of multiframe – 26 TDMA-frame multiframe is used to carry TCH, SACCH and FACCH – 51 TDMA-frame multiframe is used to carry BCCH, CCH, SDCCH and SACCH
Bursts and Frames ... 2047 2046 2045 2044 2043 1 0 2 3 4 5 ... 0 1 2 3 50 49 48 47 0 1 25 24 ... 0 1 25 24 ... 0 1 50 49 ... 0 1 2 3 4 5 6 7 1 hyperframe = 2048 superframes = 2,715,648 TDMA frames (3 hours 28 minutes 53 seconds 760 microseconds) 1 superframe = 1326 TDMA frames (6.12 seconds) = 51 (26-frame) multiframes or 26 (51-frame) multiframes 1TDMA frame = 8 timeslots (120/26 =~ 4.615 ms) 1 (26-frame) multiframe = 26 TDMA frames (120 ms) 1 (51-frame) multiframe = 51 TDMA frames (120 ms)
Bursts and Frames 0 1 2 3 4 5 6 7 GP 8.25 TB 3 Encrypted bits 57 flag 1 Training sequence 26 flag 1 Encrypted bits 57 TB 3 TB 3 Fixed bits 142 GP 8.25 TB 3 GP 8.25 TB 3 TB 3 Encrypted bits 39 Synchronization sequence 64 Encrypted bits 39 TB 3 Synchronization sequence 41 Encrypted bits 36 TB 3 GP 68.25 GP 8.25 TB 3 TB 3 Mixed bits 58 Training sequence 26 Mixed bits 58 Normal Burst (NB) Frequency correction burst (FB) Synchronization burst (SB) Access burst (AB) Dummy burst (DB) TB: Tail bits GP: Guard period 1 TDMA frame = 8 timeslots 1 timeslot = 156.25 bit durations (15/26 =~ 0.577 ms) (1 bit duration 48/13 =~ 3.69 micro sec)
Normal Burst T3 Coded Data 57 Training Sequence 26 Coded Data 57 GP 8.25 S1 S1 T3 148 bits = 0.54612 msec This burst is used to carry information on TCH and on the control channels BCCH, PCH, AGCH, SDCCH, ASCCH and FACCH. Note: GP (Guard Period)
Random Access Burst T8 Synchronization sequence 41 Coded Data 36 Guard Period 68.25 T3 88 bits = 0.32472 msec 68.25 bits = 0.252 msec which is equivalent to 75.5 km propagation delay. That is, the max. allowed distance between mobile station and BTS is 37.75 km. Based on other system parameters, the max cell size is 35 km in GSM.
Logical Channels Characteristics Logical Channel Uplink- only Downlink- only Both uplink &downlink Point- to-pint Broadcast Dedicated shared BCCH FCCH SCH RACH PCH AGCH SDCCH SACCH FACCH TCH √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √
GSM Architecture
GSM System Architecture PSTN Data Terminal HLR/ VLR MSC BSC OMC (Operation & Maintenance Center) Operation Terminal BTS Handset A X.25 A-bis SS7 Network sub-system PSTN Radio sub-system Mobile station UM SIM card
GSM Network Elements • Handset • BTS: Base Transceiver Station • MSC: Mobile Switching Center • BSC: Base Station Controller • HLR/VLR: Home Location Register/Visiting Location Register • SIM Card: Subscriber Identity Module Card • Service Centers: USSD, SMS, ...
Mobile Handset (MH) • Used by the subscriber to access the GSM network via the air interface • Contains the hardware and software specific to the radio interface • Need a Subscriber Identity Module (SIM) which contains the subscriber-specific data to access GSM network, except emergency call
Base Transceiver Station (BTS) / Base Station • Responsible for communication to and from MHs via air interface – MH communicates with the mobile system using a radio channel to a BTS • BTS comprises radio transmission and reception devices – Including the antennae and signaling processing specific to the radio interface • BTS separates the speech and control signaling associated with a MH and sends them to the BSC on separate channels
Mobile services Switching Center (MSC) • Responsible for all switching functions related to call processing – Coordinate the setting up of calls to and from GSM users • MSC is the interface between GSM network & PSTN (Public Switched Telephone Network)
Base Station Controller (BSC) • Monitor and Control several base stations – Frequency administration, control of BTSs, exchange functions • Responsible for all the radio interface management – Channel allocation and release, handover management • BSC is the interface between MSC and BTS – BSC is connected on one side to several BTSs and on the other side to the MSC
Home Location Register (HLR) • A database in charge of the management of mobile subscribers • Contains information of network subscribers – Information on teleservices and bearer services subscription, service restrictions, and supplementary services – The data stored in HLR is of a semipermanent nature and does not usually change from call to call
Visitor Location Register (VLR) • Contains the relevant data of all MHs currently located in a serving MSC – The permanent data is the same as data in the HLR – The temporary data includes • Temporary Subscriber Identity (TMSI) • Location Area Identity (LAI) of an MH – VLR allocates mobile subscriber roaming numbers (MSRNs) for the incoming call setup
Subscriber Identity Module (SIM) • Subscriber Identity Module – Contains • phone number (MSISDN) • international mobile subscriber identity (IMSI) • status of SIM • service code • authentication key • PIN (personal identification code) • PUK (personal unlock code)
SIM Cards • SIM cards are embedded with a microprocessor – Stores customer identity information and is made to fit inside the cellular phone • Memory capacity – 1K, 3K, 8K, 16K – With/Without OTAC (Over The Air Customization) • Two types of SIM card form factors – ID-1 SIM – Plug-In SIM
Application Service Centers • Responsible for GSM network add-on services – Operation and Maintenance Center (OMC) • Monitoring and control the network • Usually connect with MSC, BSC, HLR, and other service centers – Short Message Service Center (SMSC) • provide short message services • usually connect to MSC – Unstructured Supplementary Service Data Center (USSDC) • provide USSD service in the form of *ID*ID*info# • usually connect to HLR
Geographical Network Structure • Location Units – Cell – Location Area (LA) – MSC/VLR Service Area – PLMN (Public Land Mobile Network) Service Area – GSM Service Area • Cell Planning
Location Information -- GSM Service Area Hierarchy • The area in which a subscriber can access the network. cell Location Area MSC/VLR PLMN Service Area (one per operator) GSM Service Area
Cell Characteristics • The Basic Union In The System – defined as the area where radio coverage is given by one base station. • Addressed by Cell Global Identity (CGI) • A cell has one or several frequencies, depending on traffic load. – Frequencies are reused, but not used in neighboring cells due to interference.
Cell Planning • Reusing frequencies in different geographic areas: – 7 cell repeat pattern is typical, but other patterns are also common A3 A1 A2 G3 G1 G2 C3 C1 C2 B3 B1 B2 F3 F1 F2 D3 D1 D2 E3 E1 E2 G3 G1 G2 F3 F1 F2 C3 C1 C2 A3 A1 A2 B3 B1 B2 E3 E1 E2 D3 D1 D2 7-cell reuse pattern Frequency reuse
Cell Patterns 1 3 2 3 2 7 1 6 4 5 K=3 K=7
Frequency Utilization v.s. K • Frequency can’t be reused in the same pattern • Larger K – More channels in a pattern – Higher subscriber number – Worse frequency reusability • Smaller K – Less channels in a pattern, high channel distortion – Smaller subscriber number – Better frequency reusability
Numbering & Routing
Numbering • Mobile Subscriber ISDN Number (MSISDN) – Mapping to Mobile Station Roaming Number (MSRN) by HLR • International Mobile Subscriber Identify (IMSI) – Stored in SIM/HLR • Temporary Mobile Subscriber Identity (TMSI) – Assigned by VLR, Stored in VLR • International Mobile Equipment Identity (IMEI) – Unique ID to handset, used by air interface
ID-Numbers • MSISDN = CC + NDC + SN – MSISDN: Mobile Station ISDN Number – CC Country Code – NDC National Destination Code – SN Subscriber Number • IMSI = MCC + MNC + MSIN – IMSI International Mobile Subscriber Identity – MCC Mobile Country Code – MNC Mobile Network Code – MSIN Mobile Station Identification Number
ID-Numbers (cont.) • IMEI = TAC + FAC + SNR + spare – IMEI Internal Mobile Equipment Identity – TAC Type Approval Code, determined by a central GSM/PCS body – FAC Final Assembly Code, identifies the manufacturer – SNR Serial Number, uniquely identifies all equipment within each TAC and FAC • IMEISV = TAC + FAC + SNR + SVN – IMEISVInternational Mobile Equipment Identity and Software Version Number – SVN Software Version Number
ID-Numbers (cont.) • MSRN = CC + NDC + SN – MSRN Mobile Station Roaming Number – CC Country Code – NDC National Destination Code – SN Subscriber Number. In this case, the address to the serving MSC • LAI = MCC + MNC + LAC – MCC Mobile Country Code – MNC Mobile Network Code – LAC Location Area Code
ID-Numbers (cont.) • CGI = MCC + MNC + LAC + CI – CGI Cell Global Identity – CI Cell Identity • BSIC = NCC + BCC – BSIC Base Station Identity Code – NCC Network Color Code (3bits) – BCC Base Station Color Code (3bits) • LN = CC + NCD + LSP – LN Location Number – CC Country Code – NCD National Destination Code – LSP Locally Significant Part
ID -Numbers (cont.) • LN = CC + NCD + LSP – LN Location Number – CC Country Code – NCD National Destination Code – LSP Locally Significant Part • RSZI = CC + NDC + ZC – RSZI Regional Subscription Zone Identity – CC Country Code – NDC National Destination Code – ZC length of the Zone code (2 octets)
Routing • Information resident in MS & SIM – IMSI, TMSI, IMEI, and misc. information • Routing Information used by Network – MSISDN, MSRN
Location Registry
Location Registry • Registration Message Flow – Inter-LA movement • In the same MSC – Inter-MSC movement • In the same GSM Operator – Inter-VLR movement
Registration Message Flow -- Inter-LA Movement 1 2 3 4 HLR MSC2 LA2 LA1 MSC1 VLR2 VLR1
Registration Message Flow -- Inter-MSC Movement 1 2 3 4 5 6 LA2 MSC2 HLR LA1 MSC1 VLR1 VLR2
HLR VLR1 VLR2 LA1 LA2 Registration Message Flow -- Inter-VLR Movement 1 6 7 8 3 2 4 5 MSC2 MSC1
Prior MSC Prior VLR HLR Serving VLR Serving MSC Serving Base Registration info Store info REGISTRATION NOTIFICATION INVOKE Store info Store info Change info remove info REGISTRATION NOTIFICATION INVOKE REGISTRATION NOTIFICATION RESULT REGISTRATION NOTIFICATION RESULT REGISTRATION CANCELLATION INVOKE remove info REGISTRATION CANCELLATION RESULT REGISTRATION CANCELLATION INVOKE REGISTRATION CANCELLATION RESULT QUALIFICATION REQUEST INVOKE QUALIFICATION REQUEST RESULT PROFILE REQUEST INVOKE PROFILE REQUEST RESULT Message sequence and system operations for registration of a terminal in a visited service area
Call Setup
MS BSS MSC/VLR HLR PSTN Channel REQuest IMMediate ASSign Complete layer 3 Info, AUThentication REQuest TMSI REALlocation CoMmanD SETUP Mobile-originated call, mobile to land call flow (part 1 of 2) AUThentication RESponse Cipher Mode Complete Cipher Mode CMD Cipher Mode CMD Cipher Mode Complete TMSI REALlocation COMplete
MS BSS MSC/VLR HLR PSTN CALL PROCeeding Mobile-originated call, mobile to land call flow (part 2 of 2) Assignment Request ASSignment CoMmanD Assignment Complete Assignment Complete Initial Address Message (IAM) Address Complete message (ACM) Alerting Answer Signal/answer Message(ANM) connect Connect Acknowledge
Prior MSC Prior VLR HLR Serving VLR Serving MSC Serving Base Call setup to a roaming subscriber Receive call setup request LOCATION REQUEST INVOKE ROUTE REQUEST INVOKE ROUTE REQUEST INVOKE ROUTE REQUEST RESULT ROUTE REQUEST RESULT LOCATION REQUEST RESULT Call setup request (temporary phone number) Page command PAGE Delete MIN conversation VMPS call setup
GMSC MSC/VLR BSC HLR BTS BTS BTS MSISDN MSISDN MSRN IMSI MSISDN-->IMSI--> MSC/VLR Service Area IMSI<-->MSRN 6. 1. 3. 5. 4. 7. 8. 8. 9. 2. PSTN 5. Call Delivery
MS BSS MSC/VLR HLR PSTN Mobile-terminated call, land to mobile call flow (part 1 of 2) Send routing info. Provide roaming number Roaming number Routing information Initial address message Paging command Paging request Channel request Immediate assign Complete layer 3 info. Authentication request Authentication response Cipher mode cmd Cipher mode cmd Cipher mode cmd Cipher mode complete
Mobile-terminated call, mobile to land call flow (part 2 of 2) MS BSS MSC/VLR HLR PSTN TMSI reallocation command TMSI reallocation complete SETUP Call confirmed Assignment request Assignment command Assignment complete Assignment complete alerting connect Connect acknowledge Address complete message Answer signal /answer message
Example of call management scenarios Fig. 4.5 Busy indication to caller Action by serving MSC Announcement to caller HLR sends call forwarding number to home MSC Terminal idle and subscriber responds Terminal busy No answer or no page response Unconditional call forwarding Call request at home MSC Call waiting Call forwarding
Handover
MS BSS MSC VLR HLR VLR Location Update in new MSC Authenticate Authentication Resp, Start ciphering Forward new TMSI Loc.n area up. acc Send para (authentication) Authentication Prar. Update location Insert subscriber data Subs. Data Ins. Acc. Loc.n update acc Cancel location Loc.n cancellation acc. Location update call flow
Inter-MSC handover BSS1 MSC-A MSC-B BSS2 VLR-B Handover request MS Perform handover Allocate handover number Handover request Send handover report Handover request ack Radio channel ack Initial address message Address complete message Handover command Handover command Handover access Handover detect physical information Handover complete Handover complete Answer signal Send end signal Clear command Clear complete End signal Remove handover report
HLR VLR GMSC MSC MSISDN MSISDN MSRN MSRN IMSI IMSI MSRN MSRN 1 2 3 4 5 6 The Use of MSRN PSTN

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Gsm system architecture

  • 1.
  • 2.
    Air Interface • RadioTransmission Techniques – FDMA – TDMA – CDMA • Channels – Physical channels – Logical channels
  • 3.
  • 4.
    TDMA Time Frequency 0 1 23 4 5 6 7 Channel Time Slot
  • 5.
  • 6.
    Channels • Physical Channels –Associated with frequency bands, time slots, codes – Physical channels transfer bits from one network element to another • Logical Channels – Distinguished by the nature of carried information and the way to assemble bits into data units – Three types • one-to-one: traffic channels between a BTS and a MS • one-to-many: synchronization signals from BTS to MSs in a cell • many-to-one: from MSs to the same BTS
  • 7.
  • 8.
    GSM Frame Structure 357 26 57 8.25 1 1 3 0 7 ... ... Superframe 6.12 sec 120 msec 4.615 msec 0.57692 msec 156.25 bits 51 Multiframe 26 Frames 8 Multiframe Coded data Midamble Tail bit Stealing Flag Guard period
  • 9.
    • There aretwo types of multiframe – 26 TDMA-frame multiframe is used to carry TCH, SACCH and FACCH – 51 TDMA-frame multiframe is used to carry BCCH, CCH, SDCCH and SACCH Frame Types
  • 10.
    Burst and Frames •The information contained in one time slot on the TDMA frame is call a burst. • Five types of burst – Normal Burst (NB) – Frequency Correction Burst (FB) – Synchronization Burst (SB) – Access Burst (AB) – Dummy Burst
  • 11.
    Traffic channels (TCH) Signaling channel TCH/F: Full-rate TrafficChannel TCH/H: Half-rate Traffic Channel FCCH: Frequency correction SCH: Synchronization BCCH: Broadcast control PCH: Paging AGCH: Access grant RACH: Random access SDCCH: Stand-alone dedicated control SACCH: Slow associated control FACCH: Fast associated control Two-way Base-to- mobile Two-way Logical Channel List BCH CCCH DCCH
  • 12.
    Logical Channels • ControlChannels – Broadcast Channels (BCH) – Common Control Channels (CCCH) – Dedicated Control Channels (DCCH) • Traffic Channels (TCH) – Full Rate (TCH/F) – Half Rate (TCH/H)
  • 13.
    UP / Down-Link •Down-link: the transmission path from Base Station to Mobile Station • Up-link: the transmission path from Mobile Station to Base Station
  • 14.
    Control Channels • BroadcastChannels (BCH) – Frequency Correction Channel (FCCH) – Synchronization Channel (SCH) – Broadcast Control Channel (BCCH) • Common Control Channels (CCCH) – Paging Channel (PCH) – Random Access Channel (RACH) – Access Grant Channel (AGCH) • Dedicated Control Channels (DCCH) – Stand alone Dedicated Control Channel (SDCCH) – Cell Broadcast Channel (CBCH) – Slow Associated Control Channel (SACCH) – Fast Associated Control Channel (FACCH)
  • 15.
    Message name Transmittedby AUTHENTICATION REQUEST AUTHENTICATION RESPONSE AUTHENTICATION REJECT IDENTITY REQUEST IDENTITY RESPONSE TSMI REALLOCATION COMMAND LOCATION UPDATING REQUET LOCATION UPDATING ACCEPT LOCATION UPDATING REJECT IMSI DETACH REQUEST CM SERVICE REQUEST CM RE-ESTABLISHMENT REQUEST MM-STATUS Base Mobile Base Base Mobile Base Mobile Base Base Mobile Mobile Mobile Mobile/Base Mobility Management Messages
  • 16.
    Message name Starting acall Transmitted by SETUP EMERGENCY SETUP CALL PROCEEDING PROGRESS CALL CONFIRMED ALERTING CONNECT Mobile/base mobile base base mobile mobile/base mobile/base During a call START DTMF STOP DTMF MODIFY USER INFORMATION Mobile mobile mobile/base mobile/base Ending a call DISCONNECT RELEASE RELEASE COMPLET Mobile/base mobile/base mobile/base Abnormal conditions STATUS STATUS ENQUIRY CONGESTION CONROL Mobile/base mobile/base mobile/base Call management messages
  • 17.
    Message name Logicalchannel Transmitted by SYNC CHANNEL INFORMATION SYSTEM INFORMATION (TYPE 1,2,3,4,5) SYSTEM INFORMATION (TYPE 6) CHANNEL REQUEST PAGING REQUEST (TYPE 1,2.3) IMMEDIATE ASSIGNMENT IMMEDIATE ASSIGNMENT EXTENDED IMMEDIATE ASSIGNMENT REJECT ASSIGNMENT COMMAND ADDITIONAL ASSIGNMENT PAGING RESPONSE MERSUREMENT REPORT HANDOVER COMMAND HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE CIPHERING MODE CHANNEL RELEASE PARTIAL RELEASE FREQUENCY REDEFINITION CLASSMARK CHANGE CHANNEL MODE MODIFY RR STATUS SCH BCCH SACCH RACH PCH AGCH AGCH AGCH FACCH FACCH SDCCH SACCH FACCH TCH FACCH FACCH FACCH FACCH FACCH SACCH FACCH SACCH FACCH FACCH FACCH SACCH Base Base Base Mobile Base Base Base Base Base Base Mobile Mobile Base Mobile Base Mobile Base Base Base Base Mobile Base Mobile/base Radio Resources Management Messages
  • 18.
    Prior MSC Prior VLR HLR Serving VLR Serving MSC Serving Base Registration info Storeinfo REGISTRATION NOTIFICATION INVOKE Store info Store info Change info remove info REGISTRATION NOTIFICATION INVOKE REGISTRATION NOTIFICATION RESULT REGISTRATION NOTIFICATION RESULT REGISTRATION CANCELLATION INVOKE remove info REGISTRATION CANCELLATION RESULT REGISTRATION CANCELLATION INVOKE REGISTRATION CANCELLATION RESULT QUALIFICATION REQUEST INVOKE QUALIFICATION REQUEST RESULT PROFILE REQUEST INVOKE PROFILE REQUEST RESULT Message sequence and system operations for registration of a terminal in a visited service area
  • 19.
    Mobile station Base station Category Logical Channel SYNC CHANNELINFORMATION Carrier sine wave SYSTEM INFORMATION TYPE3 CHANNEL REQUEST IMMEDIATE ASSIGNMENT LOCATION UPDATING REQUEST AUTHENTICATION REQUEST CIPHERING MODE COMMAND CIPHERING MODE ACK LOCATION UPDATING ACCEPT TMSI ALLOCATION COMPLETE AUTHENTICATION RESPONSE CHANNEL RELEASE RRM RRM RRM RRM MM MM MM MM MM RRM RRM RRM FCCH SCH BCCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH Location-Updating Procedure
  • 20.
    Mobile station Base station Category Logical Channel RRM RRM RRM RRM RRM RRM MM MM RRM RRM CMCM CM CM RRM RRM CM CM CM CM RRM FCCH SCH BCCH PCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH FACCH TCH TCH FACCH FACCH FACCH FACCH Carrier sinewave SYNC CHANNEL INFORMATION SYSTEM INFORMATION PAGING REQUEST CHANNEL REQUEST IMMEDIATE ASSIGNMENT PAGING RESPONSE AUTHENTICATION REQUEST AUTHENTICATION RESPONSE CIPHERING MODE CIPHERING MODE ACK SETUP CALL CONFIRMED ALERTING CONNECT ASSIGNMENT COMMAND ASSIGNMENT ACK CONNECT ACK conversation conversation conversation DISCONNECT RELEASE RELEASE COMPLETE CHANNEL RELEASE Call Deliver to MH
  • 21.
    Mobile-Assisted Handover Mobile station Base station Logical Channel TCH TCH SACCH TCH TCH TCH SACCH TCH FACCH new TCH TCH TCH TCH FACCH TCH TCH SACCH TCH TCH TCH SACCH TCH conversation conversation MEASUREMENTREPORT conversation conversation conversation MEASUREMENT REPORT conversation HANDOVER COMMAND HANDOVER ACCESS HANDOVER ACCESS HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE conversation conversation MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation
  • 22.
    Broadcast Channels (BCH) •To help the MH (Mobile Handset) measures – to turn to a BTS – to listen for the cell information • to start roaming, waiting for calls to arrive, making calls – Because BTSs are not synchronized with each other, every time a MH decides to camp to another cell, its FCCH, SCH, and BCCH must be read.
  • 23.
    Frequency Correction Channel (FCCH) •Provide MH with the frequency reference of the system – To enable the Mobile Handset (MH) to synchronize with the frequency • Transmission properties – Transmit on the down-link – Point to multi-point.
  • 24.
    Synchronization Channel (SCH) •MH synchronize with the structure within the locative cell – MH can receive information from the proper time slots on the TDMA structure • To ensure a GSM BTS is chose – The Base Station Identity Code (BSIC) can only be decoded by a GSM BTS • Transmission properties – Transmit on down-link – Point to multi-point.
  • 25.
    Broadcast Control Channel (BCCH) •BTS broadcast cell information to MH – LAI ( Location Area Identity), to start roaming, waiting for calls to arrive, making calls – maximum output power allowed in the cell – information about BCCH carriers for the neighboring cells • MH will perform measurement to BTS • Transmission properties – Transmit on down-link – Point to multi-point
  • 26.
    Common Control Channels (CCCH) •CCCH support the establishment of a dedicated communication path (dedicated channel) between the MH and the BTS • Three types of CCCH – Paging Channel (PCH) – Random Access Channel (RACH) – Access Grant Channel (AGCH)
  • 27.
    Paging Channel (PCH) •Used by BTS to page particular MH in the cell – MH actively listen to PCH to check contact info within certain time – Contact could be incoming call or short message • Contact info on PCH include – IMSI (MH’s identity number), or – TMSI (temporary number) • Transmission properties – Transmit on down-link – point to point
  • 28.
    Random Access Channel(RACH) • Used by MH to request a dedicated channel for call setup – Shared by any MH attempts to access the network – Channel request message contains the reason for the access attempt • Transmission properties – Transmit on up-link – Point to pint.
  • 29.
    Access Grant Channel(AGCH) • The network assigns a signaling channel via AGCH – A Stand alone Dedicated Control Channel (SDCCH) is assigned • Transmission properties – Transmit on down-link – Point to point
  • 30.
    Dedicated Control Channels (DCCH) •DCCH are used for transferring nonuser information between the network and the MH – Messages on DCCH Including • channel maintenance • mobility management • radio resource management • Four kinds of DCCH – Stand alone Dedicated Control Channel (SDCCH) – Cell Broadcast Channel (CBCH) – Slow Associated Control Channel (SACCH) – Fast Associated Control Channel (FACCH)
  • 31.
    Stand alone DedicatedControl Channel (SDCCH) • Transfer signaling information between the BTS and the MH • Typically used for location updating prior to use of a traffic channel • Transmission properties – Bidirectional channel, transmit on both up and down-link – Point to point.
  • 32.
    Cell Broadcast Channel(CBCH) • To carry Short Message Service Cell Broadcast (SMSCB) • Use the same physical channel as SDCCH • Transmission properties – Transmit on down-link – Point to multi-point
  • 33.
    Slow Associated ControlChannel (SACCH) • Carries control and measurement parameters along with routine data necessary to maintain a radio link between the MH and the BTS – On the uplink, MS sends averaged measurements (signal strength and quality) of current and neighboring BCCH – On downlink, MS receives information about transmitting power to use and an instruction with time advance/retard • Transmission properties – Bidirection channel, transmit on both up and down link – Point to point
  • 34.
    Fast Associated ControlChannel (FACCH) • An FACCH is used over a TCH where it steals time slots from a TCH – a 20 ms segment of speech is stolen to carry handover signaling information • Appears on demand
  • 35.
    Traffic Channels (TCH) •TCH transport user information (speech/data) • TCH are bidirectional dedicated channels between the network and the MH
  • 36.
    Mobile station Base station Category Logical Channel SYNC CHANNELINFORMATION Carrier sine wave SYSTEM INFORMATION TYPE3 CHANNEL REQUEST IMMEDIATE ASSIGNMENT LOCATION UPDATING REQUEST AUTHENTICATION REQUEST CIPHERING MODE COMMAND CIPHERING MODE ACK LOCATION UPDATING ACCEPT TMSI ALLOCATION COMPLETE AUTHENTICATION RESPONSE CHANNEL RELEASE RRM RRM RRM RRM MM MM MM MM MM RRM RRM RRM FCCH SCH BCCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH Location-Updating Procedure
  • 37.
    Mobile station Base station Category Logical Channel RRM RRM RRM RRM RRM RRM MM MM RRM RRM CMCM CM CM RRM RRM CM CM CM CM RRM FCCH SCH BCCH PCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH FACCH TCH TCH FACCH FACCH FACCH FACCH Carrier sinewave SYNC CHANNEL INFORMATION SYSTEM INFORMATION PAGING REQUEST CHANNEL REQUEST IMMEDIATE ASSIGNMENT PAGING RESPONSE AUTHENTICATION REQUEST AUTHENTICATION RESPONSE CIPHERING MODE CIPHERING MODE ACK SETUP CALL CONFIRMED ALERTING CONNECT ASSIGNMENT COMMAND ASSIGNMENT ACK CONNECT ACK conversation conversation conversation DISCONNECT RELEASE RELEASE COMPLETE CHANNEL RELEASE Call Deliver to MH
  • 38.
    Mobile-Assisted Handover Mobile station Base station Logical Channel TCH TCH SACCH TCH TCH TCH SACCH TCH FACCH new TCH TCH TCH TCH FACCH TCH TCH SACCH TCH TCH TCH SACCH TCH conversation conversation MEASUREMENTREPORT conversation conversation conversation MEASUREMENT REPORT conversation HANDOVER COMMAND HANDOVER ACCESS HANDOVER ACCESS HANDOVER ACCESS PHYSICAL INFORMATION HANDOVER COMPLETE conversation conversation MEASUREMENT REPORT conversation conversation conversation MEASUREMENT REPORT conversation
  • 39.
    Burst • The informationcontained in one time slot is a burst • Five types of burst – Normal Burst (NB) • To carry information on traffic and control channels – Frequency Correction Burst (FB) • To synchronize the frequency of the mobile – Synchronization Burst (SB) • To synchronize the frames of the mobile – Access Burst (AB) • For random and handover access – Dummy Burst • For padding the frame
  • 40.
    Bursts and Frames •There are two types of multiframe – 26 TDMA-frame multiframe is used to carry TCH, SACCH and FACCH – 51 TDMA-frame multiframe is used to carry BCCH, CCH, SDCCH and SACCH
  • 41.
    Bursts and Frames ...2047 2046 2045 2044 2043 1 0 2 3 4 5 ... 0 1 2 3 50 49 48 47 0 1 25 24 ... 0 1 25 24 ... 0 1 50 49 ... 0 1 2 3 4 5 6 7 1 hyperframe = 2048 superframes = 2,715,648 TDMA frames (3 hours 28 minutes 53 seconds 760 microseconds) 1 superframe = 1326 TDMA frames (6.12 seconds) = 51 (26-frame) multiframes or 26 (51-frame) multiframes 1TDMA frame = 8 timeslots (120/26 =~ 4.615 ms) 1 (26-frame) multiframe = 26 TDMA frames (120 ms) 1 (51-frame) multiframe = 51 TDMA frames (120 ms)
  • 42.
    Bursts and Frames 01 2 3 4 5 6 7 GP 8.25 TB 3 Encrypted bits 57 flag 1 Training sequence 26 flag 1 Encrypted bits 57 TB 3 TB 3 Fixed bits 142 GP 8.25 TB 3 GP 8.25 TB 3 TB 3 Encrypted bits 39 Synchronization sequence 64 Encrypted bits 39 TB 3 Synchronization sequence 41 Encrypted bits 36 TB 3 GP 68.25 GP 8.25 TB 3 TB 3 Mixed bits 58 Training sequence 26 Mixed bits 58 Normal Burst (NB) Frequency correction burst (FB) Synchronization burst (SB) Access burst (AB) Dummy burst (DB) TB: Tail bits GP: Guard period 1 TDMA frame = 8 timeslots 1 timeslot = 156.25 bit durations (15/26 =~ 0.577 ms) (1 bit duration 48/13 =~ 3.69 micro sec)
  • 43.
    Normal Burst T3 CodedData 57 Training Sequence 26 Coded Data 57 GP 8.25 S1 S1 T3 148 bits = 0.54612 msec This burst is used to carry information on TCH and on the control channels BCCH, PCH, AGCH, SDCCH, ASCCH and FACCH. Note: GP (Guard Period)
  • 44.
    Random Access Burst T8Synchronization sequence 41 Coded Data 36 Guard Period 68.25 T3 88 bits = 0.32472 msec 68.25 bits = 0.252 msec which is equivalent to 75.5 km propagation delay. That is, the max. allowed distance between mobile station and BTS is 37.75 km. Based on other system parameters, the max cell size is 35 km in GSM.
  • 45.
    Logical Channels Characteristics Logical Channel Uplink- only Downlink- only Bothuplink &downlink Point- to-pint Broadcast Dedicated shared BCCH FCCH SCH RACH PCH AGCH SDCCH SACCH FACCH TCH √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √ √
  • 46.
  • 47.
    GSM System Architecture PSTN DataTerminal HLR/ VLR MSC BSC OMC (Operation & Maintenance Center) Operation Terminal BTS Handset A X.25 A-bis SS7 Network sub-system PSTN Radio sub-system Mobile station UM SIM card
  • 48.
    GSM Network Elements •Handset • BTS: Base Transceiver Station • MSC: Mobile Switching Center • BSC: Base Station Controller • HLR/VLR: Home Location Register/Visiting Location Register • SIM Card: Subscriber Identity Module Card • Service Centers: USSD, SMS, ...
  • 49.
    Mobile Handset (MH) •Used by the subscriber to access the GSM network via the air interface • Contains the hardware and software specific to the radio interface • Need a Subscriber Identity Module (SIM) which contains the subscriber-specific data to access GSM network, except emergency call
  • 50.
    Base Transceiver Station(BTS) / Base Station • Responsible for communication to and from MHs via air interface – MH communicates with the mobile system using a radio channel to a BTS • BTS comprises radio transmission and reception devices – Including the antennae and signaling processing specific to the radio interface • BTS separates the speech and control signaling associated with a MH and sends them to the BSC on separate channels
  • 51.
    Mobile services Switching Center(MSC) • Responsible for all switching functions related to call processing – Coordinate the setting up of calls to and from GSM users • MSC is the interface between GSM network & PSTN (Public Switched Telephone Network)
  • 52.
    Base Station Controller(BSC) • Monitor and Control several base stations – Frequency administration, control of BTSs, exchange functions • Responsible for all the radio interface management – Channel allocation and release, handover management • BSC is the interface between MSC and BTS – BSC is connected on one side to several BTSs and on the other side to the MSC
  • 53.
    Home Location Register(HLR) • A database in charge of the management of mobile subscribers • Contains information of network subscribers – Information on teleservices and bearer services subscription, service restrictions, and supplementary services – The data stored in HLR is of a semipermanent nature and does not usually change from call to call
  • 54.
    Visitor Location Register(VLR) • Contains the relevant data of all MHs currently located in a serving MSC – The permanent data is the same as data in the HLR – The temporary data includes • Temporary Subscriber Identity (TMSI) • Location Area Identity (LAI) of an MH – VLR allocates mobile subscriber roaming numbers (MSRNs) for the incoming call setup
  • 55.
    Subscriber Identity Module(SIM) • Subscriber Identity Module – Contains • phone number (MSISDN) • international mobile subscriber identity (IMSI) • status of SIM • service code • authentication key • PIN (personal identification code) • PUK (personal unlock code)
  • 56.
    SIM Cards • SIMcards are embedded with a microprocessor – Stores customer identity information and is made to fit inside the cellular phone • Memory capacity – 1K, 3K, 8K, 16K – With/Without OTAC (Over The Air Customization) • Two types of SIM card form factors – ID-1 SIM – Plug-In SIM
  • 57.
    Application Service Centers •Responsible for GSM network add-on services – Operation and Maintenance Center (OMC) • Monitoring and control the network • Usually connect with MSC, BSC, HLR, and other service centers – Short Message Service Center (SMSC) • provide short message services • usually connect to MSC – Unstructured Supplementary Service Data Center (USSDC) • provide USSD service in the form of *ID*ID*info# • usually connect to HLR
  • 58.
    Geographical Network Structure •Location Units – Cell – Location Area (LA) – MSC/VLR Service Area – PLMN (Public Land Mobile Network) Service Area – GSM Service Area • Cell Planning
  • 59.
    Location Information -- GSMService Area Hierarchy • The area in which a subscriber can access the network. cell Location Area MSC/VLR PLMN Service Area (one per operator) GSM Service Area
  • 60.
    Cell Characteristics • TheBasic Union In The System – defined as the area where radio coverage is given by one base station. • Addressed by Cell Global Identity (CGI) • A cell has one or several frequencies, depending on traffic load. – Frequencies are reused, but not used in neighboring cells due to interference.
  • 61.
    Cell Planning • Reusingfrequencies in different geographic areas: – 7 cell repeat pattern is typical, but other patterns are also common A3 A1 A2 G3 G1 G2 C3 C1 C2 B3 B1 B2 F3 F1 F2 D3 D1 D2 E3 E1 E2 G3 G1 G2 F3 F1 F2 C3 C1 C2 A3 A1 A2 B3 B1 B2 E3 E1 E2 D3 D1 D2 7-cell reuse pattern Frequency reuse
  • 62.
  • 63.
    Frequency Utilization v.s.K • Frequency can’t be reused in the same pattern • Larger K – More channels in a pattern – Higher subscriber number – Worse frequency reusability • Smaller K – Less channels in a pattern, high channel distortion – Smaller subscriber number – Better frequency reusability
  • 64.
  • 65.
    Numbering • Mobile SubscriberISDN Number (MSISDN) – Mapping to Mobile Station Roaming Number (MSRN) by HLR • International Mobile Subscriber Identify (IMSI) – Stored in SIM/HLR • Temporary Mobile Subscriber Identity (TMSI) – Assigned by VLR, Stored in VLR • International Mobile Equipment Identity (IMEI) – Unique ID to handset, used by air interface
  • 66.
    ID-Numbers • MSISDN =CC + NDC + SN – MSISDN: Mobile Station ISDN Number – CC Country Code – NDC National Destination Code – SN Subscriber Number • IMSI = MCC + MNC + MSIN – IMSI International Mobile Subscriber Identity – MCC Mobile Country Code – MNC Mobile Network Code – MSIN Mobile Station Identification Number
  • 67.
    ID-Numbers (cont.) • IMEI= TAC + FAC + SNR + spare – IMEI Internal Mobile Equipment Identity – TAC Type Approval Code, determined by a central GSM/PCS body – FAC Final Assembly Code, identifies the manufacturer – SNR Serial Number, uniquely identifies all equipment within each TAC and FAC • IMEISV = TAC + FAC + SNR + SVN – IMEISVInternational Mobile Equipment Identity and Software Version Number – SVN Software Version Number
  • 68.
    ID-Numbers (cont.) • MSRN= CC + NDC + SN – MSRN Mobile Station Roaming Number – CC Country Code – NDC National Destination Code – SN Subscriber Number. In this case, the address to the serving MSC • LAI = MCC + MNC + LAC – MCC Mobile Country Code – MNC Mobile Network Code – LAC Location Area Code
  • 69.
    ID-Numbers (cont.) • CGI= MCC + MNC + LAC + CI – CGI Cell Global Identity – CI Cell Identity • BSIC = NCC + BCC – BSIC Base Station Identity Code – NCC Network Color Code (3bits) – BCC Base Station Color Code (3bits) • LN = CC + NCD + LSP – LN Location Number – CC Country Code – NCD National Destination Code – LSP Locally Significant Part
  • 70.
    ID -Numbers (cont.) •LN = CC + NCD + LSP – LN Location Number – CC Country Code – NCD National Destination Code – LSP Locally Significant Part • RSZI = CC + NDC + ZC – RSZI Regional Subscription Zone Identity – CC Country Code – NDC National Destination Code – ZC length of the Zone code (2 octets)
  • 71.
    Routing • Information residentin MS & SIM – IMSI, TMSI, IMEI, and misc. information • Routing Information used by Network – MSISDN, MSRN
  • 72.
  • 73.
    Location Registry • RegistrationMessage Flow – Inter-LA movement • In the same MSC – Inter-MSC movement • In the same GSM Operator – Inter-VLR movement
  • 74.
    Registration Message Flow --Inter-LA Movement 1 2 3 4 HLR MSC2 LA2 LA1 MSC1 VLR2 VLR1
  • 75.
    Registration Message Flow --Inter-MSC Movement 1 2 3 4 5 6 LA2 MSC2 HLR LA1 MSC1 VLR1 VLR2
  • 76.
    HLR VLR1 VLR2 LA1 LA2 RegistrationMessage Flow -- Inter-VLR Movement 1 6 7 8 3 2 4 5 MSC2 MSC1
  • 77.
    Prior MSC Prior VLR HLR Serving VLR Serving MSC Serving Base Registration info Storeinfo REGISTRATION NOTIFICATION INVOKE Store info Store info Change info remove info REGISTRATION NOTIFICATION INVOKE REGISTRATION NOTIFICATION RESULT REGISTRATION NOTIFICATION RESULT REGISTRATION CANCELLATION INVOKE remove info REGISTRATION CANCELLATION RESULT REGISTRATION CANCELLATION INVOKE REGISTRATION CANCELLATION RESULT QUALIFICATION REQUEST INVOKE QUALIFICATION REQUEST RESULT PROFILE REQUEST INVOKE PROFILE REQUEST RESULT Message sequence and system operations for registration of a terminal in a visited service area
  • 78.
  • 79.
    MS BSS MSC/VLRHLR PSTN Channel REQuest IMMediate ASSign Complete layer 3 Info, AUThentication REQuest TMSI REALlocation CoMmanD SETUP Mobile-originated call, mobile to land call flow (part 1 of 2) AUThentication RESponse Cipher Mode Complete Cipher Mode CMD Cipher Mode CMD Cipher Mode Complete TMSI REALlocation COMplete
  • 80.
    MS BSS MSC/VLRHLR PSTN CALL PROCeeding Mobile-originated call, mobile to land call flow (part 2 of 2) Assignment Request ASSignment CoMmanD Assignment Complete Assignment Complete Initial Address Message (IAM) Address Complete message (ACM) Alerting Answer Signal/answer Message(ANM) connect Connect Acknowledge
  • 81.
    Prior MSC Prior VLR HLR Serving VLR Serving MSC Serving Base Call setupto a roaming subscriber Receive call setup request LOCATION REQUEST INVOKE ROUTE REQUEST INVOKE ROUTE REQUEST INVOKE ROUTE REQUEST RESULT ROUTE REQUEST RESULT LOCATION REQUEST RESULT Call setup request (temporary phone number) Page command PAGE Delete MIN conversation VMPS call setup
  • 82.
    GMSC MSC/VLR BSC HLR BTS BTS BTS MSISDN MSISDN MSRN IMSI MSISDN-->IMSI--> MSC/VLRService Area IMSI<-->MSRN 6. 1. 3. 5. 4. 7. 8. 8. 9. 2. PSTN 5. Call Delivery
  • 83.
    MS BSS MSC/VLRHLR PSTN Mobile-terminated call, land to mobile call flow (part 1 of 2) Send routing info. Provide roaming number Roaming number Routing information Initial address message Paging command Paging request Channel request Immediate assign Complete layer 3 info. Authentication request Authentication response Cipher mode cmd Cipher mode cmd Cipher mode cmd Cipher mode complete
  • 84.
    Mobile-terminated call, mobileto land call flow (part 2 of 2) MS BSS MSC/VLR HLR PSTN TMSI reallocation command TMSI reallocation complete SETUP Call confirmed Assignment request Assignment command Assignment complete Assignment complete alerting connect Connect acknowledge Address complete message Answer signal /answer message
  • 85.
    Example of callmanagement scenarios Fig. 4.5 Busy indication to caller Action by serving MSC Announcement to caller HLR sends call forwarding number to home MSC Terminal idle and subscriber responds Terminal busy No answer or no page response Unconditional call forwarding Call request at home MSC Call waiting Call forwarding
  • 86.
  • 87.
    MS BSS MSCVLR HLR VLR Location Update in new MSC Authenticate Authentication Resp, Start ciphering Forward new TMSI Loc.n area up. acc Send para (authentication) Authentication Prar. Update location Insert subscriber data Subs. Data Ins. Acc. Loc.n update acc Cancel location Loc.n cancellation acc. Location update call flow
  • 88.
    Inter-MSC handover BSS1 MSC-AMSC-B BSS2 VLR-B Handover request MS Perform handover Allocate handover number Handover request Send handover report Handover request ack Radio channel ack Initial address message Address complete message Handover command Handover command Handover access Handover detect physical information Handover complete Handover complete Answer signal Send end signal Clear command Clear complete End signal Remove handover report
  • 89.