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GSM infrastructure MSC, BSC, BTS, VLR, HLR, GSGN, GSSN

GSM infrastructure MSC, BSC, BTS, VLR, HLR, GSGN, GSSN. Johan Montelius j m@sics.se. Compared to a fixed network. Gateway MSC. Transit exchang. Local switches. MSC. BSC. Subscriber stage. Fixed phone. MS. What’s new?. Radio access network Encryption Voice coding

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GSM infrastructure MSC, BSC, BTS, VLR, HLR, GSGN, GSSN

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  1. GSM infrastructureMSC, BSC, BTS, VLR, HLR, GSGN, GSSN Johan Monteliusjm@sics.se

  2. Compared to a fixed network Gateway MSC Transit exchang Local switches MSC BSC Subscriber stage Fixed phone MS

  3. What’s new? • Radio access network • Encryption • Voice coding • Locate a mobile station • Identify and authenticate • Handle mobility during a call

  4. A bird eye’s view GMSC Access Network MSC databases BTS BSC BSC BSC BTS MS BTS

  5. ”Typical” Mobile operator • One to ten MSC per 1 M subscribers • Ten to one hundred BSC per MSC • Thousands of BTS per 1 M subscribers

  6. Base Transceiver Station • Controls the radio link • encryption • error control • signal strength • 1 - 6 duplex carriers, for example: • two layers • 120o sectors • (6+8)*3 = 42 voice calls • Cost ~ 100 – 200 k$

  7. Base Station Controller • communication with the mobile terminal • local hand-over • voice codecs • carrier allocation • paging to terminals • talks to the MSC • serves up to 40 BTSs • could be co-located with MSC

  8. Mobile Swicthing Center • Mobility management • identifies and authenticates • locates • switches between BSCs • Handover to other MSCs • 64 kbps regular voice channels

  9. Radio Access network A carrier is divided into logical channels control channels CCH traffic channels TCH The first carrier holds 2 controll channels and 6 traffic channels. Additional carriers holds only traffic channels.

  10. Control Channels • Broadcast • Frequency correction: to synchronize (FCCH) • Broadcast control: this is me, these are my neighbours (BCCH) • Common control • Paging: to notify a mobile station (PCH) • Random access: for the mobile to request service (RACH) • Access grant: reply with assigned dedicated control channel (AGCH) • Dedicated control • Standalone dedicated control: used during call set-up, SMS etc (SDCCH) • Slow associated control: power, time etc (SACCH) • Fast associated control: handover etc, uses the TCH (FACCH) • Cell broadcast: cell broadcast

  11. Traffic Channels • Duplex • Error control • Forward Error Correction (FEC) • retransmission (ARQ) • Full rate (TCH/F) • 13 Kbps speech • 9,6 or 14,4 Kpbs data • Half rate (TCH/H) • 6,5 Kbps speech • 7,2 or 4,8 Kbps data

  12. Logical channels Hyperframe: 2048 superframes 3h28m Superframe: 26 or 51 multiframes 6.12 s CCH CCH Multiframe: 26 or 51 TDMA frames CCH TCH 8 time-slot TDMA frame 4.143 ms

  13. One TDMA frame 148 b 0.577 ms tail guard 8.25 tail training Normal burst 3 57 b 26 b 57 b 3 user data user data stealing flags Frequency correction burst Synchronization burst Dummy burst Access burst

  14. Keeping track of a mobile station VLRvisiting location register Location area Location area update the VLR with newlocation area

  15. Moving to a new MSC VLRwhich LA which MSC ? Location area Location area update the VLR with newlocation area and new MSC

  16. but also…. HLRhome location register VLR update the home location register!

  17. Home Location Register incomming call PSTN where is the mobile? GMSC HLR MSC How do we reach him? VLR

  18. Mobile station numbers mobile subscriber ISDN number (MSISDN) i.e. the phone number PSTN GMSC HLR Mobile Station Roaming Number (MSRN). MSC VLR Temporary Mobile Subscriber Identity International Mobile Subscriber Identity

  19. GPRS Internet Gateway GPRS Support NodeGGSN Access Network Packet Control Unit BTS BSC UDP/TCP tunnel Serving GPRS Support NodeSGSN BTS MS BTS

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