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

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Presentation on theme: "GSM infrastructure MSC, BSC, BTS, VLR, HLR, GSGN, GSSN Johan Montelius"— Presentation transcript:

1 GSM infrastructure MSC, BSC, BTS, VLR, HLR, GSGN, GSSN Johan Montelius

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

3 Whats new? Radio access network Encryption Voice coding Locate a mobile station Identify and authenticate Handle mobility during a call

4 A bird eyes view BTS MS BSC MSC BSC BTS GMSC Access Network databases

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 duplex carriers, for example: –two layers –120 o 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 traffic channels TCH control channels CCH 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 8 time-slot TDMA frame ms Multiframe: 26 or 51 TDMA frames Superframe: 26 or 51 multiframes 6.12 s Hyperframe: 2048 superframes 3h28m CCH TCH

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

14 Keeping track of a mobile station VLR visiting location register Location area update the VLR with new location area

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

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

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

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

19 GPRS BTS MS BSC BTS Access Network Packet Control Unit Gateway GPRS Support Node GGSN UDP/TCP tunnel Serving GPRS Support Node SGSN Internet


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