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

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GSM infrastructureMSC, BSC, BTS, VLR, HLR, GSGN,
GSSN

• Johan Monteliusjm_at_sics.se

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

• Radio access network
• Encryption
• Voice coding
• Locate a mobile station
• Identify and authenticate
• Handle mobility during a call

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

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Base Transceiver Station

• Controls the radio link
• encryption
• error control
• signal strength
• 1 - 6 duplex carriers, for example
• two layers
• 120o sectors
• (68)3 42 voice calls
• Cost 100 200 k

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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

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Mobile Swicthing Center

• Mobility management
• identifies and authenticates
• locates
• switches between BSCs
• Handover to other MSCs
• 64 kbps regular voice channels

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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.
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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

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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

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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
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One TDMA frame
148 b 0.577 ms
tail
guard
8.25
tail
training
Normal burst
57 b
57 b
26 b
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3
user data
user data
stealing flags
Frequency correction burst
Synchronization burst
Dummy burst
Access burst
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Keeping track of a mobile station
VLRvisiting location register
Location area
Location area
update the VLR with newlocation area
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Moving to a new MSC
VLRwhich LA which MSC ?
Location area
Location area
update the VLR with newlocation area and new MSC
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but also.
HLRhome location register
VLR
update the home location register!
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Home Location Register
incomming call
PSTN
where is the mobile?
GMSC
HLR
MSC
How do we reach him?
VLR
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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
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GPRS
Internet
Gateway GPRS Support NodeGGSN
Access Network
Packet Control Unit
BTS
BSC
UDP/TCP tunnel
Serving GPRS Support NodeSGSN
BTS
MS
BTS