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

GSM infrastructure
MSC, BSC, BTS, VLR, HLR, GSGN, GSSN
Johan Montelius
[email protected]
Compared to a fixed network
Transit exchang
Gateway MSC
Local switches
MSC
BSC
Subscriber stage
Fixed phone
MS
What’s new?
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Radio access network
Encryption
Voice coding
Locate a mobile station
Identify and authenticate
Handle mobility during a call
A bird eye’s view
Access Network
BTS
MSC
GMSC
databases
BSC
BSC
MS
BTS
BSC
BTS
”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
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$
Base Station Controller
• communication with the mobile
terminal
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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
Mobile Swicthing Center
• Mobility management
– identifies and authenticates
– locates
– switches between BSCs
– Handover to other MSCs
• 64 kbps regular voice channels
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.
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
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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
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
Logical channels
Hyperframe: 2048 superframes
3h28m
Superframe: 26 or 51 multiframes
CCH
6.12 s
CCH
Multiframe: 26 or 51 TDMA frames
CCH
TCH
8 time-slot TDMA frame
4.143 ms
One TDMA frame
148 b 0.577 ms
tail
Normal burst
3
tail
training
57 b
26 b
user data
57 b
user data
stealing flags
Frequency correction burst
Synchronization burst
Dummy burst
Access burst
3
guard 8.25
Keeping track of a mobile
station
Location area
VLR
visiting location register
Location area
update the VLR with new
location area
Moving to a new MSC
VLR
which LA which MSC ?
Location area
Location area
update the VLR with new
location area and new MSC
but also….
HLR
home location register
VLR
update the home location register!
Home Location Register
PSTN
incomming call
where is the mobile?
GMSC
HLR
MSC
VLR
How do we reach him?
Mobile station numbers
PSTN
mobile subscriber ISDN number
(MSISDN) i.e. the phone number
GMSC
Mobile Station Roaming
Number (MSRN).
MSC
VLR
International Mobile
Subscriber Identity
HLR
Temporary Mobile
Subscriber Identity
GPRS
Internet
Gateway GPRS Support Node
GGSN
Access Network
Packet Control Unit
BTS
BSC
UDP/TCP tunnel
Serving GPRS Support Node
SGSN
MS
BTS
BTS