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Full gsm overview (modified)


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Full GSM architecture valuable in Telecom companies

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Full gsm overview (modified)

  1. 1. GSM Global System for Mobiles
  2. 2. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTITIES USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  3. 3. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTITIES USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  4. 4. Telecom Basics <ul><li>Communication </li></ul><ul><ul><li>Voice and Data </li></ul></ul><ul><ul><li>Analog and Digital </li></ul></ul><ul><ul><li>Circuit Switched and Packet Switched </li></ul></ul><ul><ul><li>Media - Copper Wire, Co-axial cable, Air, Optical Fibre </li></ul></ul><ul><ul><li>Networks -PSTN, ISDN, PDN and Mobile Networks </li></ul></ul>
  5. 5. Background to GSM <ul><li>1G : Advanced Mobile Phone Service (AMPS) </li></ul><ul><ul><ul><li>Analog, Circuit Switched, FDMA, FDD </li></ul></ul></ul><ul><li>2G : Digital Advanced Mobile Phone Service (D-AMPS) </li></ul><ul><ul><ul><li>Digital, Circuit Switched, FDMA, FDD </li></ul></ul></ul><ul><li>2G : Global System for Mobile (GSM) </li></ul><ul><ul><ul><li>Digital, Circuit Switched, FDMA and TDMA, FDD </li></ul></ul></ul><ul><li>2G : Code Division Multiple Access (CDMA) </li></ul><ul><ul><ul><li>Digital, Circuit Switched, CDMA, FDD </li></ul></ul></ul>
  6. 6. GS M History
  7. 7. Development of the GSM Standard 1982: Groupe Spécial Mobile (GSM) created 1984: Description of GSM features 1985: List of recommendations settled 1987: Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries: 1988: Validation and trials, of the radio interface. 1991: First system trials are demonstrated at the Telecom 91 exhibition. 1992: Official commercial launch of GSM service in Europe. First Launch in Finland 1993: The GSM-MoU has 62 signatories in 39 countries worldwide. 1995: Specifications of GSM phase 2 are frozen. 1999: GSM MoU joins 3GPP (UMTS) GPRS Trials begins 2000: 480M GSM Network operators Worldwide First GPRS Networks roll out End 2002: 792M GSM Net work Operators Worldwide
  9. 9. Increasing GSM Data Rates <ul><li>Transmission Time </li></ul>GPRS = G eneral P acket R adio S ervice HSCSD = H igh S peed C ircuit S witched D ata EDGE = E nhanced D ata rate for G SM E volution UMTS = U niversal M obile T elecommunication S ystem 10 sec 1 min 10 min 1 hour 0 UMTS E/GPRS ISDN PSTN GSM web e-mail photo web photo e-mail web photo video clip report photo web photo e-mail video clip report video clip report video clip report video clip report
  10. 10. Wireless Data Technology Options throughput kbps 10 k 100 k 64 k 1 M 2 M 1 k 1998 1999 2000 2001 2002 Time frame UMTS GPRS HSCSD 9.6 14.4 packet GPRS = G eneral P acket R adio S ervice HSCSD = H igh S peed C ircuit S witched D ata EDGE = E nhanced D ata rate for G SM E volution UMTS = U niversal M obile T elecommunication S ystem EDGE circuit
  11. 11. Circuit-Switched or Packet-Switched Circuit mode Packet mode A -> F D -> H C -> G C -> G C -> G C -> G C -> G D -> H D -> H A -> F D -> H D -> H A -> F A -> F A -> F A B C D E F G H
  12. 12. GSM Concepts - Cellular Structure <ul><li>Cellular </li></ul><ul><ul><li>Networking technology that breaks geographic area into cells shaped like honey comb </li></ul></ul><ul><li>Cell </li></ul><ul><ul><li>is the radio coverage area of one base transceiver station </li></ul></ul>1 2 3 4 5 6 7 6 7 2 1 5
  13. 13. What are the types in GSM Network? <ul><li>GSM-900 (Channels 125 operating band 900Mhz carrier spacing 200khz spacing 45Mhz) </li></ul><ul><li>GSM -1800 (Channels 374 spacing 95Mhz) </li></ul><ul><li>GSM -1900(Used in USA) </li></ul>
  14. 14. Multiple Access Technique <ul><li>Multiple Access – Achieved by dividing the available radio frequency spectrum, so that multiple users can be given access at the same time. </li></ul><ul><li>FDMA - Frequency Division Multiple Access </li></ul><ul><ul><li>( eg: GSM each Frequency channel is 200KHz) </li></ul></ul><ul><li>TDMA - Time Division Multiple Access </li></ul><ul><ul><li>( eg: GSM each frequency channel is divided into 8 timeslots) </li></ul></ul><ul><li>CDMA - Code Division Multiple Access </li></ul><ul><ul><li>(eg: IS95- Each User data is coded with a unique code) </li></ul></ul>
  15. 15. Duplex Technique <ul><li>Duplex - How the up link and Down link of a user is separated </li></ul><ul><li>FDD - Frequency Division Duplex </li></ul><ul><ul><li>(eg:In GSM the up link and down link of a user is separated by 45MHz ) </li></ul></ul><ul><li>TDD - Time Division Duplex </li></ul><ul><ul><li>(the up link and down link of a user will be at the same frequency but at different Time ) </li></ul></ul>
  16. 16. GSM System specifications Frequency band Uplink 890 - 915 MHz Downlink 935 - 960MHz Duplex Frequency Spacing 45MHz Carrier separation 200KHz Frequency Channels 124 Time Slots /Frame(Full Rate) 8 Voice Coder Bit Rate 13Kbps Modulation GMSK Air transmission rate 270.833333 Kbps Access method FDMA/TDMA Speech Coder RPE-LTP-LPC
  17. 17. Access Techniques Uplink 890 MHz to 915 MHz Down Link 935 MHz to 960 MHz 25 MHz divided into 125 channels of 200 KHz bandwidth 890.0 890.2 890.4 914.8 915.0 935.0 935.2 935.4 959.8 960.0 UP DOWN
  18. 18. Access Techniques ... <ul><li>Time Division Multiple Access </li></ul><ul><ul><li>Each carrier frequency subdivided in time domain into 8 time slots </li></ul></ul><ul><ul><li>Each mobile transmits data in a frequency, in its particular time slot - Burst period = 0.577 milli secs. </li></ul></ul><ul><ul><li>8 time slots called a TDMA frame. Period is .577 * 8 = 4.616 milli secs </li></ul></ul>0 1 2 3 4 5 6 7 4.616 ms 0.577 ms
  19. 20. GSM in comparison with other Standards <ul><li>GSM gives mobility without any loss in Audio quality </li></ul><ul><li>Encryption techniques used gives high security in the air Interface and also use of SIM. </li></ul><ul><li>Bit Interleaving for high efficiency in Transmission. </li></ul><ul><li>Variable Power (Power budgeting- extend battery life) </li></ul><ul><li>Minimum Interference. </li></ul><ul><li>Features-CCS7 Signaling </li></ul><ul><ul><ul><ul><li>SMS (Short Message Services) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Emergency Calls </li></ul></ul></ul></ul><ul><ul><ul><ul><li>CELL Broadcast </li></ul></ul></ul></ul>
  20. 21. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTITIES USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  21. 22. GSM - Network Structure AuC MS MS BTS BTS BTS BSC BSC MSC MSC VLR VLR GMSC HLR PSTN EIR Um Abis Abis A A OMC Server Um B E E X.25 C F H X.25
  22. 23. GSM Network OMC AUC HLR MSC EIR VLR BSC BTS MS External PSTN & PDN N/W SS BSS Switching System Base Station System MS Mobile Station BTS Base transceiver System BSC Base Station Controller MSC Mobile Switching Center HLR Home Location Register VLR Visitor Location Register EIR Equipment Identity Register AUC Authentication Center OMC Operation And Maintenance Center
  23. 24. GSM Architecture HLR VLR EIR AUC MSC B S C B S C SMSC PSTN VMSC Mobile Station GSM Air interface OMCR TRAU Base Station System Network and switching subsystem A interface SS7 / speech SS7 X.25 BTS BTS BTS BTS BTS BTS Abis interface A interface OMCS
  24. 25. Fundamentals GSM utilizes two bands of 25 MHz. 890-915 MHz band is used for uplink while the 935-960 MHz is used for downlink. The frequency bands are divided into 200 KHz wide channels called ARFCNs (Absolute Radio Frequency Channel Numbers) i.e. there are 125 ARFCNs out of which only 124 are used. Each ARFCN supports 8 users with each user transmitting / receiving on a particular time slot (TS). 960 MHz 959.8MHz 200KHz 935 MHz 935.2 Mhz 915 MHz 200KHz 45 MHz Downlink (TDMA frame) = 8 TS Uplink (TDMA frame) Delay TS: Time slot 914.8 MHz 890.2 MHz 890 MHz DOWNLINK UPLINK Therefore 1 TDMA frame = 156.25 x 8 = 1250 bits and has a duration of 576.92  s x 8 = 4.615 ms The technology 1 2 …… …… . 123 124 1 2 …… …… . 123 124 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 Data burst = 156.25 bit periods = 576.9  s
  25. 26. Mobile Station (MS) <ul><li>Hand portable unit </li></ul><ul><li>Contains Mobile Equipment(ME) and Subscriber Identity Module (SIM) </li></ul>
  26. 27. Mobile Equipment(ME) <ul><li>Frequency and Time Synchronization </li></ul><ul><li>Voice encoding and transmission </li></ul><ul><li>Voice encryption/decryption functions </li></ul><ul><li>Power measurements of adjacent cells </li></ul><ul><li>Display of short messages </li></ul><ul><li>International Mobile Equipment Identifier (IMEI) </li></ul>
  27. 28. SIM <ul><li>Portable Smart Card with memory (ROM-6KB to 16KB-A3/A8 algorithm, RAM- 128KB TO 256KB, EEPROM- 3KB to 8KB ) </li></ul><ul><li>Static Information </li></ul><ul><ul><li>International Mobile Subscriber Identity(IMSI) </li></ul></ul><ul><ul><li>Personal Identification Number (PIN) </li></ul></ul><ul><ul><li>Authentication Key (Ki) </li></ul></ul><ul><li>Dynamic Information </li></ul><ul><ul><li>Temporary Mobile Subscriber Identity(TMSI) </li></ul></ul><ul><ul><li>Location Area Identity (LAI) </li></ul></ul><ul><ul><li>Phone memories, billing information </li></ul></ul><ul><ul><li>Ability to store Short Messages received </li></ul></ul>
  28. 29. Base Transceiver Station (BTS) <ul><li>Handles the radio interface to the mobile station. </li></ul><ul><li>Consists of one or more radio terminals for transmission and reception </li></ul><ul><li>Each Radio terminal represents an RF Channel </li></ul><ul><li>TRX and MS communicates over Um interface </li></ul><ul><li>Received data transcoding </li></ul><ul><li>Voice encryption/decryption </li></ul><ul><li>Signal processing functions of the radio interface </li></ul><ul><li>Uplink Radio channel power measurements </li></ul>
  29. 30. Base Station Controller (BSC) <ul><li>Provides all the control functions and physical links between the MSC and BTS </li></ul><ul><li>External Interfaces </li></ul><ul><ul><li>‘ Abis’ interface towards the BTS </li></ul></ul><ul><ul><li>‘ A’ interface towards the MSC </li></ul></ul><ul><li>Monitors and controls several BTSs </li></ul><ul><li>Management of channels on the radio interface </li></ul><ul><li>Alarm Handling from the external interfaces </li></ul><ul><li>Performs inter-cell Handover </li></ul><ul><li>Switching from ‘Abis’ link to the ‘A’ link </li></ul><ul><li>Interface to OMC for BSS Management </li></ul>
  30. 31. Mobile Switching Center (MSC) <ul><li>Performs call switching </li></ul><ul><li>Interface of the cellular network to PSTN </li></ul><ul><li>Routes calls between PLMN and PSTN </li></ul><ul><li>Queries HLR when calls come from PSTN to mobile user </li></ul><ul><li>Inter-BSC Handover </li></ul><ul><li>Paging </li></ul><ul><li>Billing </li></ul>
  31. 32. Home Location Register (HLR) <ul><li>Stores user data of all Subscribers related to the GMSC </li></ul><ul><ul><li>International Mobile Subscriber Identity(IMSI) </li></ul></ul><ul><ul><li>Users telephone number (MS ISDN) </li></ul></ul><ul><ul><li>Subscription information and services </li></ul></ul><ul><ul><li>VLR address </li></ul></ul><ul><ul><li>Reference to Authentication center for key (Ki) </li></ul></ul><ul><li>Referred when call comes from public land network </li></ul>
  32. 33. Visitor Location Register (VLR) <ul><li>Database that contains Subscriber parameters and location information for all mobile subscribers currently located in the geographical area controlled by that VLR </li></ul><ul><li>Identity of Mobile Subscriber </li></ul><ul><li>Copy of subscriber data from HLR </li></ul><ul><li>Generates and allocates a Temporary Mobile Subscriber Identity(TMSI) </li></ul><ul><li>Location Area Code </li></ul><ul><li>Provides necessary data when mobile originates call </li></ul>
  33. 34. Authentication Center (AuC) <ul><li>Stores Subscriber authentication data called Ki, a copy of which is also stored in in the SIM card </li></ul><ul><li>Generates security related parameters to authorize a subscriber (SRES-Signed RESponse) </li></ul><ul><li>Generates unique data pattern called Cipher key (Kc) for user data encryption </li></ul><ul><li>Provides triplets - RAND, SRES & Kc, to the HLR on request. </li></ul>
  34. 35. EIR (Equipment Identity Register) <ul><li>EIR is a database that contains a list of all valid mobile station equipment within the network, where each mobile station is identified by its International Mobile Equipment Identity(IMEI). </li></ul><ul><li>EIR has three databases., </li></ul><ul><ul><li>White list - For all known,good IMEI’s </li></ul></ul><ul><ul><li>Black list - For all bad or stolen handsets </li></ul></ul><ul><ul><li>Grey list - For handsets/IMEI’s that are on observation </li></ul></ul>
  35. 36. Interfaces and Protocols Um Abis A C B E D F Digital Networks POTS TUP ISUP MAP MAP MAP BSSAP LAPD LAPDm G
  36. 37. GSM Entities and Signaling Architecture
  37. 38. GSM Protocols <ul><li>CM - Connection Management </li></ul><ul><li>MM - Mobility Management </li></ul><ul><li>RR - Radio resource </li></ul><ul><li>LAPDm - LAPD for mobile </li></ul><ul><li>LAPD - Link Access Procedure for D channel </li></ul><ul><li>BTSM - BTS Management Part </li></ul><ul><li>BSSAP - BSS Application Part (BSC - MSC) </li></ul><ul><li>DTAP - Direct Transfer Application Part (MS - MSC) </li></ul><ul><li>MAP - Mobile Application Part </li></ul><ul><li>MTP - Message Transfer part of SS7 </li></ul><ul><li>SCCP - Signalling Connection Control Part of SS7 </li></ul><ul><li>TCAP - Transaction Capabilities Application Part </li></ul><ul><li>ISUP - ISDN User Part </li></ul>
  39. 40. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTIFIERS USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  40. 41. Subscriber Identity -MSISDN <ul><li>The MSISDN is a GSM directory number which uniquely identifies a mobile subscription in the Public Switched Telephone Network (PSTN). </li></ul><ul><li>Calls will be routed from the PSTN and other networks based on the Mobile Subscribers’ MSISDN number. </li></ul><ul><li>MSISDN= CC + NDC + SN </li></ul><ul><ul><li>CC= Country Code (91) </li></ul></ul><ul><ul><li>NDC= National Destination Code(98370) </li></ul></ul><ul><ul><li>SN= Subscriber Number (12345) </li></ul></ul>
  41. 42. International Mobile Subscriber Identity [IMSI] <ul><li>Subscriber always identified within the GSM network by the IMSI </li></ul><ul><li>This is used for all signaling in the PLMN stored in SIM and HLR/VLR </li></ul><ul><li>The IMSI consists of three different parts </li></ul><ul><ul><li>MCC = Mobile Country Code(3 Digits) </li></ul></ul><ul><ul><li>MNC = Mobile Network Code(2 Digits) </li></ul></ul><ul><ul><li>MSIN = Mobile Station Identification Number(Upto 10 digits) </li></ul></ul>
  42. 43. Temporary Mobile Subscriber Identity [TMSI] <ul><li>The TMSI is used for the subscriber’s confidentiality. </li></ul><ul><li>It should be combined with the LAI to uniquely identify a MS. </li></ul><ul><li>Since the TMSI has only local significance (that is, within the MSC/VLR area), the structure may be chosen by each administration. </li></ul><ul><li>The TMSI should not consist of more than four octets. </li></ul>
  43. 44. Mobile Station Roaming Number[MSRN] <ul><li>HLR knows in what Service area the subscriber is located. </li></ul><ul><li>In order to provide a temporary number to be used for routing, the HLR requests the current MSC/VLR to allocate a Mobile Station Roaming Number(MSRN) to the called subscriber and to return it. </li></ul><ul><li>At reception of the MSRN, HLR sends it to the MSC, which now can route the call to the VLR where the called subscriber is currently registered. </li></ul>
  44. 45. International Mobile Equipment Identity [IMEI] <ul><li>The IMEI is used for equipment identification. An IMEI </li></ul><ul><li>uniquely identifies a mobile station as a piece or assembly of equipment. </li></ul><ul><li>IMEI = TAC + FAC + SNR + sp </li></ul><ul><ul><li>TAC= Type Approval Code (6 digits),determined by GSM body </li></ul></ul><ul><ul><li>FAC= Final Assembly Code (2 digits), identifies themanufacturer </li></ul></ul><ul><ul><li>SNR= Serial Number (6 digits), uniquely identifying all equipment within each TAC and FAC </li></ul></ul><ul><ul><li>sp = Spare for future use (1 digit) </li></ul></ul>
  45. 46. Location Area Identity <ul><li>LAI identifies a location area which is a group of cells.. </li></ul><ul><li>It is transmitted in the BCCH. </li></ul><ul><li>When the MS moves into another LA (detected by monitoring LAI transmitted on the BCCH) it must perform a LU. </li></ul><ul><li>LAI = MCC + MNC + LAC </li></ul><ul><ul><li>MCC= Mobile Country Code(3 digits), identifies the country </li></ul></ul><ul><ul><li>MNC= Mobile Network Code(1-2 digits), identifies the GSM-PLMN </li></ul></ul><ul><ul><li>LAC= Location Area Code, identifies a location area within a GSM PLMN network. The maximum length of LAC is 16 bits,enabling 65536 different location areas to be defined in one GSM PLMN. </li></ul></ul>
  46. 47. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTITIES USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  47. 48. Channels : differentiating between Physical and Logical channels Physical channels : The combination of an ARFCN and a time slot defines a physical channel. Logical channels : These are channels specified by GSM which are mapped on physical channels.
  48. 49. Channel concept Physical channel : One timeslot of a TDMA-frame on one carrier is referred to as a physical channel. There are 8 physical channels per carrier in GSM,channel 0-7(timeslot 0-7) Logical channel: A great variety of information must be transmitted between BTS and the MS,for e.g. user data and control signaling.Depending on the kind of information transmitted we refer to different logical channels.These logical channels are mapped on physical channel.
  50. 51. Frequency plan and importance of BCCH B3 B2 B9 B6 B4 B1 Sectored antennas MS ( monitoring the broadcast radio B1 in ‘idle mode’ ) F0 F50 F2 F3 F4 F5 F10 F11 F1 <ul><li>F,S,B exist in time slot 0 of each frame </li></ul>B7 B8 B5 B10 B11 B12 BPL frequency plan : Broadcast frequencies : 15 Broadcast channels = 48-62 15 Hopping channels = 32-46 … .. … .. S F I … .. B B B B S F
  51. 52. Broadcast channels BCH <ul><li>Broadcast Channel-BCH </li></ul><ul><ul><li>Alloted one ARFCN & is ON all the time in every cell. Present in TS0 and other 7 TS used by TCH. </li></ul></ul><ul><li>Frequency correction channel-FCCH </li></ul><ul><ul><li>To make sure this is the BCCH carrier. </li></ul></ul><ul><ul><li>Allow the MS to synchronize to the frequency. </li></ul></ul><ul><ul><li>Carries a 142 bit zero sequence and repeats once in every 10 frames on the BCH. </li></ul></ul><ul><li>Synchronization Channel-SCH </li></ul><ul><ul><li>This is used by the MS to synchronize to the TDMA frame structure within the particular cell. </li></ul></ul><ul><ul><li>Listening to the SCH the MS receives the TDMA frame number and also the BSIC ( in the coded part- 39 bits). </li></ul></ul><ul><ul><li>Repeats once in every 10 frames. </li></ul></ul>
  52. 53. Back <ul><li>The MS is monitoring the BCCH and has all the decoded information stored on the SIM ( including the LAC) </li></ul><ul><li>As soon as the mobile is on a TCH it sends the signal strength indication on the corresponding SACCH </li></ul><ul><li>The BSC monitors the signal strengths and on analysis sends a ‘handoff request’ on FACCH. The handoff process is completed on the FACCH. </li></ul><ul><li>After the completion of call, the MS starts monitoring the BCCH again. On finding the LAC (stored on SIM) and that decoded from the BCCH to be different , the MS requests a ‘Location Update’ through SDCCH. </li></ul>
  53. 54. Broadcast channels BCH ... <ul><li>BCH </li></ul><ul><ul><li>The last information the MS must receive in order to receive calls or make calls is some information concerning the cell. This is BCCH. </li></ul></ul><ul><ul><li>This include the information of Max power allowed in the cell. </li></ul></ul><ul><ul><li>List of channels in use in the cell. </li></ul></ul><ul><ul><li>BCCH carriers for the neighboring cells,Location Area Identity etc. </li></ul></ul><ul><ul><li>BCCH occupies 4 frames (normal bursts) on BCH and repeats once every Multiframe. </li></ul></ul><ul><ul><li>This is transmitted Downlink point to multipoint. </li></ul></ul><ul><li>Cell Broadcast Channel - CBCH </li></ul><ul><ul><li>Used for the Transmission of generally accessible information like Short Message Services(SMS) </li></ul></ul>
  54. 55. What information does Broadcast Control channel (BCCH) contain? <ul><li>Serves as a Beacon for the Cell </li></ul><ul><li>Country Code (CC) and the Network Code (NC) </li></ul><ul><li>Location Area Identity (LAI) </li></ul><ul><li>List of neighboring cells which should be monitored by MS </li></ul><ul><li>List of frequencies used in the cell </li></ul><ul><li>Cell identity </li></ul>Back
  55. 56. Common Control Channels CCCH <ul><li>CCCH- </li></ul><ul><ul><li>Shares TS-0 with BCH on a Multiframe. </li></ul></ul><ul><li>Random access channel-RACH: </li></ul><ul><ul><li>Used by Mobile Station for requesting for a channel. When the mobile realizes it is paged it answers by requesting a signaling channel (SDCCH) on RACH. RACH is also used by the MS if it wants to originate a call. </li></ul></ul><ul><ul><li>Initially MS doesn’t know the path delay (timing advance), hence uses a short burst (with a large guard period = 68.25 bits). </li></ul></ul><ul><ul><li>MS sends normal burst only after getting the timing advance info on the SACCH. </li></ul></ul><ul><ul><li>It is transmitted in Uplink point to point. </li></ul></ul>
  56. 57. Common Control Channels CCCH .. <ul><li>Access Grant Channel-AGCH </li></ul><ul><ul><li>On request for a signaling channel by MS the network assigns a signaling channel(SDCCH) through AGCH. AGCH is transmitted on the downlink point to point. </li></ul></ul><ul><li>Paging Channel-PCH </li></ul><ul><ul><li>The information on this channel is a paging message including the MS’s identity(IMSI/TMSI).This is transmitted on Downlink, point-to-multipoint. </li></ul></ul>
  57. 58. Dedicated Control Channels-DCCH <ul><li>Stand alone dedicated control channel(SDCCH) </li></ul><ul><li>AGCH assigns SDCCH as signaling channel on request by MS.The MS is informed about which frequency(ARFCN) & timeslot to use for traffic. </li></ul><ul><li>Used for location update, subscriber authentication, ciphering information, equipment validation and assignment of TCH. </li></ul><ul><li>This is used both sides, up and Downlink point-point. </li></ul>
  58. 59. Dedicated Control Channels-DCCH <ul><li>Slow associated control channel-SACCH </li></ul><ul><ul><li>Transmission of radio link signal measurement, power control etc. </li></ul></ul><ul><ul><li>Average signal strengths(RXLev) and quality of service (RXQual) of the serving base station and of the neighboring cells is sent on SACCH (on uplink). </li></ul></ul><ul><ul><li>Mobile receives information like what TX power it has to transmit and the timing advance. It is associated with TCH or SDCCH </li></ul></ul><ul><li>Fast associated control channel-FACCH </li></ul><ul><ul><li>Used for Hand over commands and during call setup and release. FACCH data is sent over TCH with stealing flag set </li></ul></ul>
  59. 60. Traffic Channels-TCH <ul><li>TCH carries the voice data. </li></ul><ul><li>Two blocks of 57 bits contain voice data in the normal burst. </li></ul><ul><li>One TCH is allocated for every active call. </li></ul><ul><li>Full rate traffic channel occupies one physical channel(one TS on a carrier) and carries voice data at 13kbps </li></ul><ul><li>Two half rate (6.5kbps) TCHs can share one physical channel. </li></ul>
  60. 61. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTITIES USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  61. 62. GSM Radio Link <ul><li>Speech Coding -Done at Transcoder of BSC and MS </li></ul><ul><ul><li>The Linear Predictive Coder uses RPE-LTP(Regular Pulse Excitation- Long Term Prediction) </li></ul></ul><ul><ul><li>Converts 64kbps voice to 13kbps(260 bits every 20ms) </li></ul></ul><ul><li>Channel Coding - Done at BTS and MS </li></ul><ul><ul><li>Uses Convolution Coding and CRC (Cyclic Redundancy Check) </li></ul></ul><ul><ul><li>Converts 13 kbps to 22.8 kbps (456 bits per 20ms) </li></ul></ul>
  62. 63. GSM Radio Link <ul><li>Bit Interleaving - Done at BTS and MS </li></ul><ul><li>Encryption - Done at BTS and MS </li></ul><ul><ul><li>EX OR data with cipher block, which is generated by applying A5 Algorithm to the Ciphering Key(Kc) </li></ul></ul><ul><li>Multiplexing - Done at BTS </li></ul><ul><li>Modulation - Done at BTS and MS </li></ul><ul><ul><li>GMSK(Gaussian filtered Minimum Shift Keying) </li></ul></ul><ul><ul><li>Phase change of +90 for 0 and -90 for 1 </li></ul></ul>
  63. 64. Speech Coding BP A/D SPEECH ENCODER CHANNEL CODING LP D/A SPEECH DECODER CHANNEL DECODING BAND PASS 300 Hz - 3.4 kHZ Every 125  s value is sampled from analog signal and quantised by 13 bit word Data rate = 13/125*10 -6 = 104 kbps Every 20ms 160 samples taken Data rate = 160 * 13/20ms = 104 kbps Linear Predictive Coding & Regular Pulse Excitation Analysis 1. Generates 160 filter coeff 2. These blocks sorted in 4 sequence 1,5,9,…37 / 2,6,10----38/ 3,7,11…39/8,12,16…40 3. Selects the sequence with most energy So data rate = 104/4 = 26 kbps Long term prediction analysis 1. Previous sequences stored in memory 2. Find out the correlation between the present seq. And previous sequences 3. Select the highest correlation sequence 4. Find a value representing the difference between the two sequences. Reduces data rate = 26 kbps/2 = 13 kbps ie 260 bits in 20ms 50 132 78 1A 1B 2 1A = Filter Coeff block ampl, LTP params 1B = RPE pointers & pulses 2 = RPE pulse & filter params 50 3 132 4 3 crc bits Four 0 bits for codec 378 coded bits Conv coding rate = 1/2 delay = 4 78 456 bits in 20 ms = 22.8 kbps 57 x 8 = 456 To modulator
  64. 65. Interleaving 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 Encoded speech blocks - Diagonal Interleaving Even bits Odd bits Tb 3 Coded Data 57 F 1 Training Sequence 26 F 1 Coded Data 57 Tb 3 Gp 8.25 Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 Encoded control channel blocks - Rectangular Interleaving Even bits Odd bits Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3
  65. 66. Burst <ul><li>The information format transmitted during one timeslot in the TDMA frame is called a burst. </li></ul><ul><li>Different Types of Bursts </li></ul><ul><ul><li>Normal Burst </li></ul></ul><ul><ul><li>Random Access Burst </li></ul></ul><ul><ul><li>Frequency Correction Burst </li></ul></ul><ul><ul><li>Synchronization Burst </li></ul></ul>
  66. 67. Normal Burst T 3 Coded Data 57 S 1 T. Seq. 26 S 1 Coded Data 57 T 3 GP 8.25 Tail Bit(T) :Used as Guard Time Coded Data :It is the Data part associated with the burst Stealing Flag :This indicates whether the burst is carrying Signaling data (FACCH) or user info (TCH). Training Seq. :This is a fixed bit sequence known both to the BTS & the MS.This takes care of the signal deterioration. 156.25 bits 0.577 ms
  67. 68. T 3 Training Sequence 41 Coded Data 36 T 3 GP 68.25 Random Access Burst T 3 Fixed Bit Sequence 142 T 3 GP 8.25 T 3 Coded Data 39 Training Sequence 64 Coded Data 39 T 3 GP 8.25 Synchronization Burst 156.25 bits 0.577 ms 156.25 bits 0.577 ms 156.25 bits 0.577 ms Freq. Correc. Burst
  68. 69. Transmission on the radio channels <ul><li>A timeslot has a duration of .577 m seconds (148 Bits) </li></ul><ul><li>8 timeslots(8 x 0.577 = 4.62 ms) form a TDMA frame </li></ul><ul><li>If a mobile is assigned one TS it transmits only in this time slot </li></ul><ul><li>and stays idle for the other 7 with its transmitter off, called bursting </li></ul><ul><li>The start on the uplink is delayed from downlink by 3 TS periods </li></ul><ul><li>One TS = duration of 156.25 bits, and its physical contents is </li></ul><ul><li>called a burst </li></ul>Downlink BTS > MS Uplink MS > BTS Offset 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 3 4 5 6 7
  69. 70. Timing Advance 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 MS1 near MS2 far 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 At BTS 0 1 2 3 4 5 6 7 MS1 near 0 1 2 3 4 5 6 7 MS2 far 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 At BTS
  70. 71. Frames Types On Um Interface <ul><li>TDMA Frame </li></ul><ul><ul><li>8 Time slots (Burst Period) </li></ul></ul><ul><ul><li>Length is 4.62 ms(8 * 0.577ms) </li></ul></ul><ul><li>26-TDMA Multiframe </li></ul><ul><ul><li>26 TDMA Frames (24 TCH, SACCH, Idle) </li></ul></ul><ul><ul><li>120 ms (26 * 4.62ms) </li></ul></ul><ul><li>51-TDMA Multiframe </li></ul><ul><ul><li>26 TDMA Frames (FCCH, SCH, BCCH, SDCCH, CCCH) </li></ul></ul><ul><ul><li>235.6 ms (51 * 4.62ms) </li></ul></ul>
  71. 72. Frames Types On Um Interface <ul><li>Super Frame </li></ul><ul><ul><li>51* 26 TDMA Frames </li></ul></ul><ul><ul><li>6.12 S </li></ul></ul><ul><li>Hyper Frame </li></ul><ul><ul><li>2048 * 51* 26 TDMA Frames </li></ul></ul><ul><ul><li>3 Hours, 28 Minutes, 53 Secs and 760 ms </li></ul></ul>
  72. 73. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTITIES USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  73. 74. Mobility Management <ul><li>Mobility Management (MM) </li></ul><ul><li>Location updating- normal,periodic, IMSI attach </li></ul><ul><li>Paging </li></ul><ul><li>Security Management </li></ul><ul><ul><li>Preventing unauthorized users- authentication </li></ul></ul><ul><ul><li>Maintaining Privacy of users- ciphering </li></ul></ul><ul><li>Providing roaming facility </li></ul><ul><li>MM functionality mainly handled by MS, HLR, MSC/VLR. </li></ul>
  74. 75. Network Attachment <ul><ul><ul><li>Cell Identification </li></ul></ul></ul><ul><ul><ul><ul><li>MS scans complete GSM frequency band for highest power </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Tunes to highest powered frequency and looks for FCCH. Synchronizes in frequency domain </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Get training sequence from SCH which follows FCCH. Synchronizes in time domain. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Accesses BCCH for network id, location area and frequencies of the neighboring cells. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Stores a list of 30 BCCH channels </li></ul></ul></ul></ul>
  75. 76. Network Attachment….. <ul><ul><ul><li>PLMN Selection </li></ul></ul></ul><ul><ul><ul><ul><li>Get the operator information from SIM. </li></ul></ul></ul></ul><ul><ul><ul><li>Cell Selection </li></ul></ul></ul><ul><ul><ul><ul><li>Selected cell should be a cell of the selected PLMN </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Signal strength should be above the threshold. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Cell should not be barred </li></ul></ul></ul></ul><ul><ul><ul><li>Location Update </li></ul></ul></ul><ul><ul><ul><ul><li>Register with the network by means of location updation procedures. </li></ul></ul></ul></ul>
  76. 77. MS Location Update (registration) MS BTS BSC (G)MSC VLR HLR Action Channel Request (RACH) Channel Assignment (AGCH) Authentication Request (SDCCH) Authentication Response (SDCCH) Comparison of Authentication params Accept LUP and allocTMSI (SDCCH) Ack of LUP and TMSI (SDCCH) Entry of new area and identity into VLR and HLR Channel Release (SDCCH) Location Update Request (SDCCH) TMSI + old LAI
  77. 78. Security - Authentication <ul><ul><li>Authentication center provides RAND to Mobile </li></ul></ul><ul><ul><li>AuC generates SRES using Ki of subscriber and RAND </li></ul></ul><ul><ul><li>Mobile generates SRES using Ki and RAND </li></ul></ul><ul><ul><li>Mobile transmits SRES to BTS </li></ul></ul><ul><ul><li>BTS compares received SRES with one generated by AuC </li></ul></ul>MS Ki RAND A3 SRES RAND SRES SRES Auth Result AuC BTS MS
  78. 79. Security - Ciphering <ul><ul><li>Data sent on air interface ciphered for security </li></ul></ul><ul><ul><li>A5 and A8 algorithms used to cipher data </li></ul></ul><ul><ul><li>Ciphering Key is never transmitted on air </li></ul></ul>MS Ki RAND A8 Kc MS Network Um interface A5 A5 Kc Kc Data Data Ciphered Data
  79. 80. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTITIES USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  80. 81. Communication Management (CM) <ul><li>Setup of calls between users on request </li></ul><ul><li>Routing function i.e. Choice of transmission segments linking users </li></ul><ul><li>Point to Point Short message services </li></ul>
  81. 82. Mobile Originated Call <ul><ul><ul><li>Request for Service </li></ul></ul></ul><ul><ul><ul><li>Authentication </li></ul></ul></ul><ul><ul><ul><li>Ciphering </li></ul></ul></ul><ul><ul><ul><li>Equipment Validation </li></ul></ul></ul><ul><ul><ul><li>Call Setup </li></ul></ul></ul><ul><ul><ul><li>Handovers </li></ul></ul></ul><ul><ul><ul><li>Call Release </li></ul></ul></ul>
  82. 83. MS MS BTS BTS BTS BSC BSC MSC VLR GMSC HLR PSTN EIR AuC  Mobile Originated Call Req for dedicated channel for signaling (RACH) Give SDCCH Allocates SDCCH using the AGCH Sends call set-up request including dialled digits on SDCCH Call set-up forwarded to BSC Call set-up forwarded to MSC Authentication request (SDCCH) Authentication response (SDCCH) Authentication response (SDCCH) Assigns TCH Req Activate TCH TCH assigned Assn complete Release SDCCH SDCCH released ACM Ring tone over FACCH Ring alert Called Sub answers Connect message Ring tone ceases over FACCH Speech path enabled
  83. 84. Mobile Terminated Call <ul><ul><ul><li>Paging </li></ul></ul></ul><ul><ul><ul><li>Authentication </li></ul></ul></ul><ul><ul><ul><li>Ciphering </li></ul></ul></ul><ul><ul><ul><li>Equipment Validation </li></ul></ul></ul><ul><ul><ul><li>Call Setup </li></ul></ul></ul><ul><ul><ul><li>Handovers </li></ul></ul></ul><ul><ul><ul><li>Call Release </li></ul></ul></ul>
  84. 85. Mobile Terminated Call Authentication and Ciphering procedure done as seen in Location Updation MS MS BTS BTS BTS BSC BSC MSC VLR GMSC HLR PSTN EIR AuC Land to Mobile call (MSISDN) Query for VLR info Reply (MSRN) Route to MSC Query VLR for LAC and TMSI Paging the area (+TMSI) TMSI Paged on PCH Paging Ch. REQ over RACH Allocate SDCCH over AGCH Page RESP on SDCCH ( TMSI + LAI) Page RES Page RES Assign. REQ Assignment CMD (= TCH) on SDCCH * MS tunes * Assgn CMP * Phone rings Connect traffic trunk frees SDCCH Assgn CMP Network Alerting
  85. 86. TOPICS <ul><li>GSM CONCEPTS </li></ul><ul><li>GSM SYSTEM ARCHITECTURE </li></ul><ul><li>IDENTITIES USED IN GSM </li></ul><ul><li>GSM CHANNELS </li></ul><ul><li>GSM RADIO LINK </li></ul><ul><li>MOBILITY MANAGEMENT </li></ul><ul><li>CALL MANAGEMENT </li></ul><ul><li>RADIO RESOURCE MANAGEMENT </li></ul>
  86. 87. Radio Resource Management <ul><li>Establish maintain and release stable connections between MS and MSC </li></ul><ul><li>Manage Limited Radio and Terrestrial resources </li></ul><ul><li>Handover process is the sole responsibility of the RR Layer </li></ul><ul><li>Functions of RR layer are performed by MS and BSC and partly by MSC </li></ul>
  87. 88. Radio Resource Management <ul><ul><ul><li>Power Control </li></ul></ul></ul><ul><ul><ul><li>Hand over Control </li></ul></ul></ul><ul><ul><ul><li>Discontinuous Transmission </li></ul></ul></ul><ul><ul><ul><li>Frequency Hopping </li></ul></ul></ul>
  88. 89. Power Control BTS commands MS at different distances to use different power levels so that the power arriving at the BTS’s Rx is approximately the same for each TS - Reduce interference - Longer battery life
  89. 90. Handover <ul><li>Means to continue a call even a mobile crosses the border of one cell to another </li></ul><ul><li>Procedure which made the mobile station really roam </li></ul><ul><li>Handover causes </li></ul><ul><ul><li>RxLev (Signal strength , uplink or downlink) </li></ul></ul><ul><ul><li>RxQual (BER on data) </li></ul></ul><ul><ul><li>O & M intervention </li></ul></ul><ul><ul><li>Timing Advance </li></ul></ul><ul><ul><li>Traffic or Load balancing </li></ul></ul>
  90. 91. Handover Types <ul><li>Internal Handover (Intra-BSS) </li></ul><ul><ul><li>Within same base station - intra cell </li></ul></ul><ul><ul><li>Between different base stations - inter cell </li></ul></ul><ul><li>External Handover (Inter-BSS) </li></ul><ul><ul><li>Within same MSC -intra MSC </li></ul></ul><ul><ul><li>Between different MSCs - inter-MSC </li></ul></ul>
  91. 92. Handover Types BSC BSC BSC BSC MSC MSC GMSC C-1 C-2 C-3 C-4
  92. 93. Periodic Measurement Reports (SACCH) Cell 1 Cell 2 BSC BTS 1 BTS 2 Intra BSC handover Periodic Measurement Reports (SACCH) Periodic Measurement Reports HO required Activate TCH(facch) with HoRef# if 1. Check for HO passed 2. Channel avail in new BTS Acknowledges and alloctes TCH (facch) HO cmd with HoRef# Receives new BTS data(FACCH) MS tunes into new frequency and TS and sends HO message to new BTS (facch) HO performed Release TCH
  93. 94. Discontinuous Transmission <ul><li>Discontinuous Transmission(DTX) allows the radio transmitter to be switched off most of the time during speech pauses. </li></ul><ul><li>A Silence Indicator Block is transmitted at 500bps, which generates a comfort noise </li></ul><ul><li>Down Link interference is decreased. </li></ul><ul><li>Up link battery is saved </li></ul>
  94. 95. Frequency Hopping <ul><li>Frequency Hopping permits the dynamic switching of radio links from one carrier frequency to another. </li></ul><ul><li>Base Band Hopping </li></ul><ul><ul><li>At the BTS each the timeslot is shifted to another transceiver, which is transmitting at the hop frequency. User will be connected to different Transceivers depending on hop sequence. </li></ul></ul><ul><li>Synthesis Hopping </li></ul><ul><ul><li>At the BTS transceiver changes the frequencies used. The user will be connected to only one transceiver. </li></ul></ul><ul><li>Decreases the probability of interference </li></ul><ul><li>Suppresses the effect of Rayleigh fading </li></ul>
  95. 96. Wireless Data 98 99 2000 2001 GSM DATA HSCSD GPRS EDGE UMTS SIM Toolkit WAP Data Application Time Circuit Switched technology Packet Switched technology Technology for Applications SMS Data: 160  -numeric characters User Data Rate : 9.6kbps One time slot over the air interface High Speed Circuit Switched Data User Data Rate:14.5kbps Use multiple timeslots (max=8), hence max rate = 115.2kbps. Needs a duplexor in MS for simultaneous Tx and Rx <ul><li>Add-on to GSM network : </li></ul><ul><li>PCU; Packet Segmentation/re-assembly and scheduling </li></ul><ul><li>Radio channel access control and management </li></ul><ul><li>Transmission error detection and retransmission. </li></ul><ul><li>Power control </li></ul><ul><li>SGSN: GPRS mobility </li></ul><ul><li>Encryption </li></ul><ul><li>Charging </li></ul><ul><li>GGSN : Interface to the PDN, Internet </li></ul><ul><li>Max user data rate : 21.4 kbps </li></ul><ul><li>Dynamic rate adaptation to suit the radio conditions at </li></ul><ul><li>that time ( 9.05 kbps, 13.4 kbps, 15.6 kbps 21.4 kbps) </li></ul>W@P Gateway W@P Service W @ P F o n e Internet Mobile Network <ul><li>Surf the Internet while on the move </li></ul><ul><li>W@P Gateway : </li></ul><ul><li>Adaptation of the information to the mobile </li></ul><ul><li>Compression of the data </li></ul><ul><li>Buffering of the information </li></ul><ul><li>Enhanced Data rate for GSM Evolution </li></ul><ul><li>EDGE is an enhancement of GPRS and CSD technologies. </li></ul><ul><li>Based on the current GSM technology - same TDMA frame structure, same bandwidth (200 kHz). </li></ul><ul><li>Uses 8-PSK modulation instead of GMSK. </li></ul><ul><li>Requires good propagation conditions. </li></ul><ul><li>Allows upto 48 kbps (EGPRS) and upto 28.8 kbps (ECSD) on every radio channel </li></ul><ul><li>EDGE helps GSM-Only operators to compete with UMTS. </li></ul><ul><li>Universal Mobile Telecommunication Standards </li></ul><ul><li>Innovative Service Architecture : VHE Concept - providing the us </li></ul><ul><li>the same look and feel of its personalized services independent of network and terminal. </li></ul><ul><li>Global Convergence : Fixed/Mobile, Telecom/Datacom, public/private </li></ul><ul><li>Mobile Multimedia driven market. </li></ul><ul><li>Wideband bearers - 2GHz band ( 5 MHz per carrier), -max. 2Mbps </li></ul>
  96. 97. References <ul><li>Wireless and Personal Communication Systems. Vijay.K.Garg and Wilkes </li></ul><ul><li>Overview of the GSM System and Protocol Architecture, IEEE Comm. Magazine, Moe Rahnema. </li></ul><ul><li>The GSM System for Mobile Communications- Michel Mouly & Marie-Bernadette Pautet </li></ul><ul><li>Overview of the GSM Comm- John Scourias. </li></ul>
  97. 98. Thank you
  98. 99. Location Updates Location Updates can be classified into two: Periodic Location Updates: This occurs as per the timer set by the network operator. If the MS does not perform this update the MSC marks the MS as ‘Detached’ on the VLR. Location Update on a handover: This occurs if during a handover the MS is moved into a new Location Area Code (LAC).