GSM Signalling concepts

7/23/2019 GSM Signalling concepts

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GSM Signalling


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Objective

The Trainee will be able to understand:

Signalling between MSC/VLR and SS

Conce!t o" #T$%

Conce!t o" SSM$%

Signalling between SC and TS

&unctions o" L$%#'

&unctions o" L$%#

&ra'e structure o" L$%#' $nd L$%#


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(ntroduction

There are two di""erent t)!es o" co''unication channels:

Tra""ic channel at *+ ,b!s- carr)ing s!eech or data "orradio channels.

Signalling channels at *+,b!s- carr)ing signallingin"or'ation.

(n %CM one ti'e slot is reserved "or signalling and re'aining

are used "or trans'itting s!eech or data. $s the entiresiganlling is done on *+,b!s - there should be s!ecial"unction converting the in"or'ation to *+,b!s "or'at and

bac at the receiving end.


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%rotocols in GSM 0etwors

VLR

VLR

MSC

$1C

2LR 3(R

SC

TS

SS$%

L$%#

M$% M$%

M$% M$%M$%

(S#0

GMSC

MSC

%ST0

(S1%

(S1%

M$%

T1%

MSL$%#'

Switching S)ste'

ase

Station

S)ste'


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GSM Signalling Matri4

L$%#'

MS TS MSC

#T$%

RR

R(L5

R(L5 RSM

L$%#' L$%#

SC

RSM

SSM$%

SS$%

L$%#

SCC%

MT%6 75

MT%8 MT%8

MT%6 7 5

SCC%

SS$%

#T$%SS

M$%

M$%

TC$%

(S1%

#atabase


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MSC uses (S1%/T1% !rotocols "or %ST0 signalling.

M$% siganlling "or database a!!lications lie 2LR- VLR-3(R- $1C- SMS9SC- GMSC.

GSM s!eci"ic !rotocol as SS$%- which co'!rises o"

#T$% and SSM$%.

The SC on la)er 6 uses L$%# !rotocol- which is an(S#0.

TS has L$%#' as la)er 6 !rotocol.

Mobile has #T$% "or MSC and RR "or Radio Resource

signalling.


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M$% Mobile $!!lication %art;

M$% is a !rotocol s!eciall) designed "or GSM re


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SS $!!lication %art SS$%;

SS$% is used "or signalling between MSC/VLR and SS.

Three grou!s o" signals belong to SS$%

8. #T$%

6. SSM$%

5. (nitial MS 'essages


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M

SC

M

S

SC/TS

#T$%

(nitial MS Message

SSM$% L$%#'

Trans!arent to SS


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#irect Trans"er $!!lication %art

#T$%;

#T$% is a 'essages between the MSC and MS- !asses

through the SS trans!arentl). These are call control and

'obilit) 'anage'ent 'essages directed towards a s!eci"ic'obile.

5 'ain t)!e o" #T$% 'essages are:

Messages "or 'obilit) 'anage'ent lie location u!date-

authentication- identit) re


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SSM$%

SS 'anage'ent 'essages SSM$%; between MSC and

SS SC/ TS;- which are necessar) "or resource

'anage'ent- handover control- !aging order etc. The

SSM$% 'essages can either be connection less or

connection oriented.


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(nitial MS Messages

These 'essages are !assed unchanged through SS- but SSanal)ses !art o" the 'essages and is not trans!arent lie#T$% 'essages.

etween SS and MSC- the initial MS 'essage is trans"erredin the la)er 5 in"or'ation in the SSM$%.

The (nitial MS 'essages are:

CM Re


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L$%#'

Lin $ccess %rocedures on the #' channel L$%#'; is thela)er 6 !rotocol used to conve) signaling in"or'ation

between la)er 5 entities across the radio inter"ace- using

the #' channel. #' channel re"ers to the controlchannels- inde!endent o" the t)!e. This includes broadcast-co''on or dedicated control channels.

L$%#' is based on the (S#0 !rotocol L$%#- which is usedon the $bis inter"ace. #ue to the radio environ'ent- the

L$%# !rotocol can not be used in its original "or'.There"ore- L$%#' seg'ents the 'essage into a nu'bero" shorter 'essages.


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#ata e4changed between the data lin la)er and the !h)sicalla)er is 65 octets "or CC2- CCC2- S#CC2 and &$CC2.

&or S$CC2 onl)- 68octets are sent "ro' la)er 6 to la)er 8.

L$%#' "unctions include:

L$%#' !rovides one or 'ore data lin connections on a

#' channel. #ata Lin Connection (denti"ier #LC(; isused "or discri'inating between data lin connections.

(t allows la)er 5 'essage units be delivered trans!arentl)between la)er 5 entities.

(t !rovides se


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L$%#' &ra'e Structure

in"o length co''and address

0R; %/& 0S; = = = 8 S$%( CR 8


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Se = "or nor'al signalling o" #T$% 7 RR

S$%( > 5 "or short 'essage services


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L$%#' has no error detection and correction. (t is used intwo 'odes:

$cnowledge 7

1nacnowledged

and having a di""erent structure "or both.


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L$%#

$ll signaling 'essages on the $bis inter"ace use the Lin

$ccess %rocedures on the #9channel. L$%# !rotocol;.

L$%# !rovides two inds o" signaling:

unacnowledged in"or'ation acnowledged in"or'ation

L$%# lin handling is a basic "unction to !rovide data lins

on the *+ b!s !h)sical connections between SC andTS.


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Lins are !rovided "or o!eration and 'aintenance O7M; o"

the lins- "or O7M o" the TS e


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L$%# has three sub signalling channels

8. RSL Radio Signalling Lin;- deals with tra""ic

'anage'ent- TR? signalling.

6. OML O!eration 7 Maintenance Lin;- serves "or

'aintenance related in"o and trans'ission o" tra""icstatistics.

5. L6M La)er 6 Manage'ent;- used "or 'anage'ent o"

the di""erent siganlling on the sa'e ti'e slot.


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L$%# &ra'e Structure

&lag &CS in"o length co''and address &lag

0R ; %/& 0S; = T3( 8 S$%( CR =


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L$%# &ra'e structure is 'ade u! o":

&lag: (ndicates the beginning and end o" each "ra'e unit. &laghas a !attern o" =888888=.

&CS: &ra'e Chec Se


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C/R: This bit indicates whether it is co''and or res!onse.

%/&: (n co''and "ra'es- the %/& bit is re"erred to as the % bit

and the other end trans'its the res!onse b) setting this bit

to &.

T3(: Ter'inal 3nd!oint (denti"ier- is a uni


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S$%(: Service $ccess %oint (denti"ier- used to identi") the

t)!e o" lin.

S$%( > = "or RSL

S$%( > *6 "or OMLS$%( > *5 "or L6ML

3ach L$%# lin is identi") b) S$%(/T3( !air.


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34ercise

@8. 0a'e the !rotocol which is trans!arent to SS and what

in"or'ation is used to trans"er on this !rotocolA

@6. 0a'e the !rotocols used betweenMobile and TS

TS and SC

SC to MSC

MSC to %ST0

GSM Signalling concepts

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