Details of GSM system architecture and subsystems

1. IT 802DMobile CommunicationsPart 3 Debasis Das

2. GSM GSM 900 890-915 uplink, 935-960 downlink GSM 1800 (DCS 1800) 1700-1785 uplink, 1805-1880 downlink GSM 1900 (PCS 1900) 1850-1910 uplink, 1930-1990 downlink GSM 400 450.4-457.6/478.8-486 uplink, 460.4-467.6/488.8-496 for downlink GSM Rail 3/13/2011 Debasis Das Mallabhum Institute of Technology 2

3. Mobile Services Bearer Services Tele services Supplementary Services 3/13/2011 Debasis Das Mallabhum Institute of Technology 3

4. Services 3/13/2011 Debasis Das Mallabhum Institute of Technology 4 Bearer Services MS GSM PLMN Transit network Source/ Destination Network TE MT TE R,S Um U,S,R Tele Services

5. Services Stacks 3/13/2011 Debasis Das Mallabhum Institute of Technology 5 Application Presentation Tele services End to end Session Transport Network Bearer Services All services that Enable Transparent Transmission of Data(connection Oriented, circuit Switched. DLC Physical

6. Bearer Services Transparent Uses functions of the physical layer only. Data transmission has constant delay and throughput if no errors occur. FEC is possible. Depending on FEC 2.4, 4.8 or 9.6 kbps speeds are supported, no lost data recovery due to shadowing or handover Non-transparent Uses protocols of layer 2 & 3 to implement error correction & flow control, A radio link protocol or RLP(similar to HDLC) is used, error rates 10^-7 is possible, but delays could be variable 3/13/2011 Debasis Das Mallabhum Institute of Technology 6

7. Bear Services Several bearer services are specified that use transparent and non transparent services PSTN, ISDN and PSPDN (X.25) are used for internetworking Data transmission can be full duplex 1.2, 2.4, 4.8 and 9.6 kbps and asynchronous full duplex 300 to 9.6 kbps 3/13/2011 Debasis Das Mallabhum Institute of Technology 7

8. Tele Services Mainly voice oriented Encrypted voice, message services, Emergency number, highest priority, to nearest emergency center SMS, up to 160 characters, uses unused capacity of the signaling channels, all kinds of content, updating of software EMS(760 characters) and MMS(video clips, images) Group 3 Fax 3/13/2011 Debasis Das Mallabhum Institute of Technology 8

9. Supplementary Services May vary with provider User id, call redirection, call forwarding Closed user group, multi party communication 3/13/2011 Debasis Das Mallabhum Institute of Technology 9

10. System Architecture Radio subsystem(RSS) Network and switching subsystem(NSS) Operation subsystem(OSS) 3/13/2011 Debasis Das Mallabhum Institute of Technology 10

11. System Architecture 3/13/2011 Debasis Das Mallabhum Institute of Technology 11 EIR OMC AUC OSS MSC VLR MSC VLR NSS ISDN PSTN HLR GMSC Signaling BSC BSC IWF MS BSS PDN BTS RSS BTS

12. Radio Subsystem(RSS) Radio specific entities Mobile station Base station subsystem(BSS) “A” interface connects the RSS to NSS “O” interface for connection to OSS A interface is circuit switched, PCM 30 systems 30x 64 kbps connections O interface is SS7, management data to/fro RSS 3/13/2011 Debasis Das Mallabhum Institute of Technology 12

13. Base Station Subsystem A base station controller controls(BSC) multiple base station subsystems(BSS) BSS contains several base transceiver stations(BTS) All functions required to maintain radio communication to MS is carried out by BSS Coding/decoding of voice, rate adaptation to/fro wireless network part, etc. 3/13/2011 Debasis Das Mallabhum Institute of Technology 13

14. Base Transceiver Stations BTS contains all radio equipment Antenna, signal processing, amplifiers Connects to MS through a Um interface. The ISDN U interface for mobile use Connects to BSC through Abis interface Um contains all the mechanisms for wireless transmission such as TDMA, FDMA etc. The Abis interface contains 16 or 64 kbps connections 3/13/2011 Debasis Das Mallabhum Institute of Technology 14

15. BTS & BSC Functions 3/13/2011 Debasis Das Mallabhum Institute of Technology 15

16. Mobile Station(MS) All user equipment and software needed for communication Hardware, software , subscriber identity module(SIM), stores user specific data relevant to GSM SIM contains an International mobile equipment identity(IMEI) Usually contains card type, serial number, ,subscribed services, PIN, PIN unblocking key, authentication key ki, international mobile subscriber identity(IMSI) Dynamic information when logged into GSM system, such as cipher key Kc and TMSI or temporary mobile subscriber identity(TMSI) and location area identification(LAI) are stored The MS can have many other interfaces and vendor specific features. 3/13/2011 Debasis Das Mallabhum Institute of Technology 16

17. Network & Switching Subsystem(NSS) Connects RSS with standard public networks Performs handovers between different BSSs Has functions for localization of users Supports charging, accounting, and roaming of users between different providers in different countries Subsystems include Mobile services switching center(MSC) Home location register(HLR) Visitor location register(VLR) 3/13/2011 Debasis Das Mallabhum Institute of Technology 17

18. MSC The fixed backbone network nodes. Connections to other MSCs and BSCs are set up through these Manages several BSC in a particular geographic location A gateway MSC(GMSC) has connections to other public networks such as PSTN, ISDN Can also connect to public data networks(PDN) through inter working functions (IWF) 3/13/2011 Debasis Das Mallabhum Institute of Technology 18

19. More on MSC Uses the standard signaling system 7 or the SS7 for all aspects of control signaling for digital networks that includes Reliable routing and delivery of control messages for establishing and monitoring of calls SS7 provides Number portability, free phone, tool/collect calls, credit calls, call forwarding, 3-way calling etc. MSC also provides functionality for supplementary services like call forwarding, multi-party calls, reverse charging etc. 3/13/2011 Debasis Das Mallabhum Institute of Technology 19

20. Home Location register(HLR) Database for all user relevant data Static information like mobile subscriber ISDN number(MSISDN), services subscribed and IMSI Dynamic information like current location area(LA), mobile subscriber roaming number(MSRN), current VLR and MSC, when a MS leaves LA, the info is updated Only one set of user home information is maintained in for any user for any user worldwide Some information may need to meet real time criteria 3/13/2011 Debasis Das Mallabhum Institute of Technology 20

21. Visitor Location Register(VLR) Dynamic database for relevant information for the MS user in LA associated with the MSC Typically, MSISDN, IMSI, HLR address etc. VLR copies the information from the HLR 3/13/2011 Debasis Das Mallabhum Institute of Technology 21

22. Operation Subsystem(OSS) Consists of the following subsystems Operation and maintenance center(OMC) Authentication center (AuC) Equipment identity center(EIR) 3/13/2011 Debasis Das Mallabhum Institute of Technology 22

23. OMC Monitors and controls all other entities via O interface (SS7 & X.25). Typical functions include Traffic monitoring, status reports, subscriber and security management, accounting and billing Uses “telecommunication management network” as standardized by ITU-T 3/13/2011 Debasis Das Mallabhum Institute of Technology 23

24. Authentication center(AuC) Contains algorithms for authentication, as well as keys for encryption and generates the values needed for user authentication in HLR AuC may actually be located in a special protected part of HLR 3/13/2011 Debasis Das Mallabhum Institute of Technology 24