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

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

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 Common control Dedicated control
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 Full rate (TCH/F)
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 ms

13. One TDMA frame Normal burst Frequency correction burst
148 b 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
VLR visiting location register
Location area
Location area
update the VLR with new location area

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

16. but also…. HLR home 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 Access Network BTS BSC BTS MS BTS Internet
Gateway GPRS Support Node GGSN
Access Network
Packet Control Unit
BTS
BSC
UDP/TCP tunnel
Serving GPRS Support Node SGSN
BTS MS
BTS