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GSM infrastructure MSC, BSC, BTS, VLR, HLR, GSGN, GSSN. Johan Montelius j [email protected] 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

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

Johan [email protected]


Compared to a fixed network
Compared to a fixed network

Gateway MSC

Transit exchang

Local switches

MSC

BSC

Subscriber stage

Fixed phone

MS


What s new
What’s new?

  • Radio access network

  • Encryption

  • Voice coding

  • Locate a mobile station

  • Identify and authenticate

  • Handle mobility during a call


A bird eye s view
A bird eye’s view

GMSC

Access Network

MSC

databases

BTS

BSC

BSC

BSC

BTS

MS

BTS


Typical mobile operator
”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 trans ce iver station
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
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


Mobile swicthing center
Mobile Swicthing Center

  • Mobility management

    • identifies and authenticates

    • locates

    • switches between BSCs

    • Handover to other MSCs

  • 64 kbps regular voice channels


Radio access network
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
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


Traffic channels
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
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


One tdma frame
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


Keeping track of a mobile station
Keeping track of a mobile station

VLRvisiting location register

Location area

Location area

update the VLR with newlocation area


Moving to a new msc
Moving to a new MSC

VLRwhich LA which MSC ?

Location area

Location area

update the VLR with newlocation area and new MSC


But also
but also….

HLRhome location register

VLR

update the home location register!


Home location register
Home Location Register

incomming call

PSTN

where is the mobile?

GMSC

HLR

MSC

How do we reach him?

VLR


Mobile station numbers
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


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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