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GSM

GSM. Global System for Mobiles. TOPICS. GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT. TOPICS. GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS

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GSM

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  1. GSM Global System for Mobiles

  2. TOPICS • GSM CONCEPTS • GSM SYSTEM ARCHITECTURE • IDENTITIES USED IN GSM • GSM CHANNELS • GSM RADIO LINK • MOBILITY MANAGEMENT • CALL MANAGEMENT • RADIO RESOURCE MANAGEMENT

  3. TOPICS • GSM CONCEPTS • GSM SYSTEM ARCHITECTURE • IDENTITIES USED IN GSM • GSM CHANNELS • GSM RADIO LINK • MOBILITY MANAGEMENT • CALL MANAGEMENT • RADIO RESOURCE MANAGEMENT

  4. Telecom Basics • Communication • Voice and Data • Analog and Digital • Circuit Switched and Packet Switched • Media - Copper Wire, Co-axial cable, Air, Optical Fibre • Networks -PSTN, ISDN, PDN and Mobile Networks

  5. Background to GSM • 1G : Advanced Mobile Phone Service (AMPS) • Analog, Circuit Switched, FDMA, FDD • 2G : Digital Advanced Mobile Phone Service (D-AMPS) • Digital, Circuit Switched, FDMA, FDD • 2G : Global System for Mobile (GSM) • Digital, Circuit Switched, FDMA and TDMA, FDD • 2G : Code Division Multiple Access (CDMA) • Digital, Circuit Switched, CDMA, FDD

  6. GSM History

  7. Development of the GSM Standard 1992: Official commercial launch of GSM service in Europe. First Launch in Finland 1982: Groupe Spécial Mobile (GSM) created 1984: Description of GSM features 1993: The GSM-MoU has 62 signatories in 39 countries worldwide. 1985: List of recommendations settled 1995: Specifications of GSM phase 2 are frozen. 1987: Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries: 1999: GSM MoU joins 3GPP (UMTS) GPRS Trials begins 1988: Validation and trials, of the radio interface. 2000: 480M GSM Network operators Worldwide First GPRS Networks roll out 1991: First system trials are demonstrated at the Telecom 91 exhibition. End 2002: 792M GSM Net work Operators Worldwide

  8. 01 SERIES GENERAL 12 SERIES OPERATION AND MAINTENANCE 02 SERIES SERVICE ASPECTS 03 SERIES NETWORK ASPECTS 11 SERIES EQUIPMENT AND TYPE APPROVAL SPECIFICATIONS 04 SERIES MS-BSS INTERFACE AND PROTOCOLS 10 SERIES SERVICE INTERWORKING 09 SERIES NETWORK INTERWORKING 05 SERIES PHYSICAL LAYER ON THE RADIO PATH. 08 SERIES BSS TO MSC INTERFACES 06 SERIES SPEECH CODING SPECIFICATIONS 07 SERIES TERMINAL ADAPTERS FOR MOBILE STATIONS GSM Specifications

  9. report video clip photo UMTS video clip web photo report E/GPRS video clip e-mail web photo report ISDN video clip e-mail web photo report PSTN video clip report e-mail web photo GSM 0 10 sec 1 min 10 min 1 hour Increasing GSM Data Rates Transmission Time GPRS = GeneralPacketRadioService HSCSD=HighSpeedCircuit SwitchedData EDGE=Enhanced Data rate for GSM Evolution UMTS = Universal Mobile Telecommunication System

  10. Wireless Data Technology Options 2 M UMTS 1 M EDGE packet throughput kbps GPRS 100 k circuit HSCSD 64 k 14.4 10 k 9.6 Time frame 1 k 1998 1999 2000 2001 2002 GPRS=GeneralPacketRadioService HSCSD=HighSpeedCircuit SwitchedData EDGE=Enhanced Data rate for GSM Evolution UMTS = Universal Mobile Telecommunication System

  11. A F B C G D H E Circuit-Switched or Packet-Switched Circuit mode Packet mode A→F A→F D→H A→F C→G C→G D→H A→F C→G A→F D→H C→G C→G D→H D→H

  12. What are the types in GSM Network? • GSM-900 (Channels 125 operating band 900Mhz carrier spacing 200khz spacing 45Mhz) • GSM -1800 (Channels 374 spacing 95Mhz) • GSM -1900(Used in USA)

  13. Multiple Access Technique • Multiple Access – Achieved by dividing the available radio frequency spectrum, so that multiple users can be given access at the same time. • FDMA - Frequency Division Multiple Access • ( eg: GSM each Frequency channel is 200KHz) • TDMA - Time Division Multiple Access • ( eg: GSM each frequency channel is divided into 8 timeslots) • CDMA - Code Division Multiple Access • (eg: IS95- Each User data is coded with a unique code)

  14. Duplex Technique • Duplex - How the up link and Down link of a user is separated • FDD - Frequency Division Duplex • (eg:In GSM the up link and down link of a user is separated by 45MHz ) • TDD - Time Division Duplex • (the up link and down link of a user will be at the same frequency but at different Time )

  15. 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

  16. UP 890.0 890.2 890.4 914.8 915.0 DOWN 935.0 935.2 935.4 959.8 960.0 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

  17. 0.577 ms 0 1 2 3 4 5 6 7 4.616 ms Access Techniques ... • Time Division Multiple Access • Each carrier frequency subdivided in time domain into 8 time slots • Each mobile transmits data in a frequency, in its particular time slot - Burst period = 0.577 milli secs. • 8 time slots called a TDMA frame. Period is .577 * 8 = 4.616 milli secs

  18. GSM in comparison with other Standards • GSM gives mobility without any loss in Audio quality • Encryption techniques used gives high security in the air Interface and also use of SIM. • Bit Interleaving for high efficiency in Transmission. • Variable Power (Power budgeting- extend battery life) • Minimum Interference. • Features-CCS7 Signaling • SMS (Short Message Services) • Emergency Calls • CELL Broadcast

  19. TOPICS • GSM CONCEPTS • GSM SYSTEM ARCHITECTURE • IDENTITIES USED IN GSM • GSM CHANNELS • GSM RADIO LINK • MOBILITY MANAGEMENT • CALL MANAGEMENT • RADIO RESOURCE MANAGEMENT

  20. GSM - Network Structure MS Um HLR BTS VLR BSC Abis MSC B A H C AuC MS GMSC BTS E F Abis EIR A E MSC PSTN BSC Um BTS X.25 VLR X.25 OMC Server

  21. GSM Network Switching System SS AUC External PSTN & PDN N/W VLR HLR EIR OMC MSC 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 Base Station System BSS BSC BTS MS

  22. GSM Architecture VMSC SMSC GSM Air interface B S C AUC A interface HLR Abis interface PSTN TRAU MSC VLR B S C BTS BTS EIR OMCS BTS BTS BTS BTS Network and switching subsystem Mobile Station A interface SS7 / speech OMCR X.25 SS7 Base Station System

  23. Fundamentals 960 MHz TS: Time slot 959.8MHz 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). DOWNLINK Downlink (TDMA frame) = 8 TS 200KHz 935.2 Mhz 935 MHz 915 MHz 914.8 MHz 45 MHz Delay 200KHz UPLINK Uplink (TDMA frame) 890.2 MHz 890 MHz 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

  24. Mobile Station (MS) • Hand portable unit • Contains Mobile Equipment(ME) and Subscriber Identity Module (SIM)

  25. Mobile Equipment(ME) • Frequency and Time Synchronization • Voice encoding and transmission • Voice encryption/decryption functions • Power measurements of adjacent cells • Display of short messages • International Mobile Equipment Identifier (IMEI)

  26. SIM • Portable Smart Card with memory (ROM-6KB to 16KB-A3/A8 algorithm, RAM- 128KB TO 256KB, EEPROM- 3KB to 8KB ) • Static Information • International Mobile Subscriber Identity(IMSI) • Personal Identification Number (PIN) • Authentication Key (Ki) • Dynamic Information • Temporary Mobile Subscriber Identity(TMSI) • Location Area Identity (LAI) • Phone memories, billing information • Ability to store Short Messages received

  27. Base Transceiver Station (BTS) • Handles the radio interface to the mobile station. • Consists of one or more radio terminals for transmission and reception • Each Radio terminal represents an RF Channel • TRX and MS communicates over Um interface • Received data transcoding • Voice encryption/decryption • Signal processing functions of the radio interface • Uplink Radio channel power measurements

  28. Base Station Controller (BSC) • Provides all the control functions and physical links between the MSC and BTS • External Interfaces • ‘Abis’ interface towards the BTS • ‘A’ interface towards the MSC • Monitors and controls several BTSs • Management of channels on the radio interface • Alarm Handling from the external interfaces • Performs inter-cell Handover • Switching from ‘Abis’ link to the ‘A’ link • Interface to OMC for BSS Management

  29. Mobile Switching Center (MSC) • Performs call switching • Interface of the cellular network to PSTN • Routes calls between PLMN and PSTN • Queries HLR when calls come from PSTN to mobile user • Inter-BSC Handover • Paging • Billing

  30. Home Location Register (HLR) • Stores user data of all Subscribers related to the GMSC • International Mobile Subscriber Identity(IMSI) • Users telephone number (MS ISDN) • Subscription information and services • VLR address • Reference to Authentication center for key (Ki) • Referred when call comes from public land network

  31. Visitor Location Register (VLR) • Database that contains Subscriber parameters and location information for all mobile subscribers currently located in the geographical area controlled by that VLR • Identity of Mobile Subscriber • Copy of subscriber data from HLR • Generates and allocates a Temporary Mobile Subscriber Identity(TMSI) • Location Area Code • Provides necessary data when mobile originates call

  32. Authentication Center (AuC) • Stores Subscriber authentication data called Ki, a copy of which is also stored in in the SIM card • Generates security related parameters to authorize a subscriber (SRES-Signed RESponse) • Generates unique data pattern called Cipher key (Kc) for user data encryption • Provides triplets - RAND, SRES & Kc, to the HLR on request.

  33. EIR (Equipment Identity Register) • 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). • EIR has three databases., • White list - For all known,good IMEI’s • Black list - For all bad or stolen handsets • Grey list - For handsets/IMEI’s that are on observation

  34. GSM Entities and Signaling Architecture

  35. GSM Protocols • CM - Connection Management • MM - Mobility Management • RR - Radio resource • LAPDm - LAPD for mobile • LAPD - Link Access Procedure for D channel • BTSM - BTS Management Part • BSSAP - BSS Application Part (BSC - MSC) • DTAP - Direct Transfer Application Part (MS - MSC) • MAP - Mobile Application Part • MTP - Message Transfer part of SS7 • SCCP - Signalling Connection Control Part of SS7 • TCAP - Transaction Capabilities Application Part • ISUP - ISDN User Part

  36. Functional Plane of GSM MS BTS BSC MSC/VLR HLR GMSC CC MM RR Trans MS BTS BSC MSC/ HLR GMSC VLR

  37. TOPICS • GSM CONCEPTS • GSM SYSTEM ARCHITECTURE • IDENTIFIERS USED IN GSM • GSM CHANNELS • GSM RADIO LINK • MOBILITY MANAGEMENT • CALL MANAGEMENT • RADIO RESOURCE MANAGEMENT

  38. Subscriber Identity -MSISDN • The MSISDN is a GSM directory number which uniquely identifies a mobile subscription in the Public Switched Telephone Network (PSTN). • Calls will be routed from the PSTN and other networks based on the Mobile Subscribers’ MSISDN number. • MSISDN= CC + NDC + SN • CC= Country Code (91) • NDC= National Destination Code(98370) • SN= Subscriber Number (12345)

  39. International Mobile Subscriber Identity [IMSI] • Subscriber always identified within the GSM network by the IMSI • This is used for all signaling in the PLMN stored in SIM and HLR/VLR • The IMSI consists of three different parts • MCC = Mobile Country Code(3 Digits) • MNC = Mobile Network Code(2 Digits) • MSIN = Mobile Station Identification Number(Upto 10 digits)

  40. Temporary Mobile Subscriber Identity [TMSI] • The TMSI is used for the subscriber’s confidentiality. • It should be combined with the LAI to uniquely identify a MS. • Since the TMSI has only local significance (that is, within the MSC/VLR area), the structure may be chosen by each administration. • The TMSI should not consist of more than four octets.

  41. Mobile Station Roaming Number[MSRN] • HLR knows in what Service area the subscriber is located. • 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. • 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.

  42. International Mobile Equipment Identity [IMEI] • The IMEI is used for equipment identification. An IMEI • uniquely identifies a mobile station as a piece or assembly of equipment. • IMEI = TAC + FAC + SNR + sp • TAC= Type Approval Code (6 digits),determined by GSM body • FAC= Final Assembly Code (2 digits), identifies themanufacturer • SNR= Serial Number (6 digits), uniquely identifying all equipment within each TAC and FAC • sp = Spare for future use (1 digit)

  43. Location Area Identity • LAI identifies a location area which is a group of cells.. • It is transmitted in the BCCH. • When the MS moves into another LA (detected by monitoring LAI transmitted on the BCCH) it must perform a LU. • LAI = MCC + MNC + LAC • MCC= Mobile Country Code(3 digits), identifies the country • MNC= Mobile Network Code(1-2 digits), identifies the GSM-PLMN • 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.

  44. TOPICS • GSM CONCEPTS • GSM SYSTEM ARCHITECTURE • IDENTITIES USED IN GSM • GSM CHANNELS • GSM RADIO LINK • MOBILITY MANAGEMENT • CALL MANAGEMENT • RADIO RESOURCE MANAGEMENT

  45. 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.

  46. 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.

  47. Logical Channels on Air interface LOGICAL CHANNELS COMMON CHANNELS DEDICATED CHANNELS BROADCAST CHANNELS COMMON CONTROL CHANNELS DEDICATED CONTROL CHANNELS TRAFFIC CHANNELS FCCH SCH BCCH SDCCH SACCH FACCH PCH RACH AGCH TCH/F TCH/H TCH/EFR

  48. Frequency plan and importance of BCCH Sectored antennas B5 B6 B4 BPL frequency plan: Broadcast frequencies : 15 Broadcast channels = 48-62 15 Hopping channels = 32-46 B3 B7 B1 B8 B2 B12 MS ( monitoring the broadcast radio B1 in ‘idle mode’ ) B9 B10 B11 F0 F1 F2 F3 F4 F5 F10 F11 F50 • F,S,B exist in time slot 0 of each frame

  49. Broadcast channels BCH • Broadcast Channel-BCH • Alloted one ARFCN & is ON all the time in every cell. Present in TS0 and other 7 TS used by TCH. • Frequency correction channel-FCCH • To make sure this is the BCCH carrier. • Allow the MS to synchronize to the frequency. • Carries a 142 bit zero sequence and repeats once in every 10 frames on the BCH. • Synchronization Channel-SCH • This is used by the MS to synchronize to the TDMA frame structure within the particular cell. • Listening to the SCH the MS receives the TDMA frame number and also the BSIC ( in the coded part- 39 bits). • Repeats once in every 10 frames.

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