gsm signalling concepts
TRANSCRIPT
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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