6.Gsm Interfaces

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FUNDAMENTALS OF GSM RGMTTC, CHENNAI-27

GSM INTERFACES

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GSM Interfaces

Introduction

The GSM network is shown in the i!"re with the #$%or inter $&es

in'i&$te' $s U#, A(is $n' A

Um

The $ir inter $&e is "se' or e)&h$n!es (etween $ MS $n' $ *SS+

Abis This is $ *SS intern$ inter $&e inkin! the *SC $n' $ *TS, $n' it h$s not

(een st$n'$r'i e'+ The A (is inter $&e $ ows &ontro o the r$'io e."i/#ent $n'

r$'io re."en&0 $ o&$tion in the *TS+12M ink

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A

A inter $&e is (etween the *SS $n' the MSC+ The A inter $&e #$n$!es

the $ o&$tion o s"it$( e r$'io reso"r&es to the MSs $n' #o(i it0 #$n$!e#ent+

12M ink CCS7

B

The * inter $&e is (etween the MSC $n' 3LR+ Most MSCs $re $sso&i$te'

with $ 3LR, #$kin! the * inter $&e 4intern$ 4+ 5hene6er the MSC nee's $&&ess

to '$t$ re!$r'in! $ MS o&$te' in its $re$, it interro!$tes the 3LR+

C

The C inter $&e is (etween the HLR $n' $ GMSC or $ SMS-G+ E$&h &$ori!in$tin! o"tsi'e o GSM 1i+e+, $ MS ter#in$tin! &$ ro# the STN h$s to !o

thro"!h $ G$tew$0 to o(t$in the ro"tin! in or#$tion re."ire' to &o#/ ete the &$ +

12M ink CCS7

D

The D inter $&e is (etween the 3LR $n' HLR, to e)&h$n!e the '$t$

re $te' to the o&$tion o the MS $n' to the #$n$!e#ent o the s"(s&ri(er+ 12M

ink CCS7

E

The E inter $&e inter&onne&ts two MSCs+ The E inter $&e e)&h$n!es '$t$

re $te' to h$n'o6er (etween the $n&hor $n' re $0 MSCs+12M ink CCS7

F

The F inter $&e &onne&ts the MSC to the EIR, to 6eri 0 the st$t"s o the

IMEI th$t the MSC h$s retrie6e' ro# the MS+12M ink CCS7

G The G inter $&e inter&onne&ts two 3LRs o 'i erent MSCs to tr$ns er

s"(s&ri(er in or#$tion, '"rin! e+!+ $ o&$tion "/'$te /ro&e'"re+ 12M ink CCS7

H

The H inter $&e is (etween the MSC $n' the SMS-G, to s"//ort the

tr$ns er o short #ess$!es+ 12M ink CCS7

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Um Interface

It is the $ir inter $&e (etween #o(i e $n' *TS+ There $re "/ ink $n'

'own ink re."en&0 ($n's+ The &$rriers $re s/$&e' $t 2889H + E$&h &$rrier is

/ro6i'in! : ti#es ots+

P !sica" C anne" and #o$ica" C anne"

P !sica" C anne"

The &$rrier n"#(er $n' the re/etiti6e ti#e s ot n"#(er 'eter#ine h0si&$

Ch$nne 1e+!+ ti#e s ot ; on &$rrier n"#(er


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Fre.uenc! Correction C anne"/FCCH

The o!i&$ Ch$nne &ont$ins no in or#$tion 1&ontin"o"s eros ("t /"re

&$rrier is tr$ns#itte' so th$t the #o(i e &$n t"ne itse $n' s0n&hronise with the

re."en&0+ FCCH wi (e tr$ns#itte' in the s$#e (e$&on &$rrier $s *CCH+

S!nc ronisation C anne"/SCH

This o!i&$ &h$nne tr$ns#its in or#$tion $(o"t TDMA r$#e str"&t"re in

$ &e ?se&tor 1 r$#e n"#(er $n' *$se St$tion I'entit0 Co'e whi&h &$n (e

'e&o'e' on 0 i the *TS (e on!s to the network or whi&h the MS h$s s"(s&ri(e'+

SCH wi $ so (e tr$ns#itte' in the s$#e &$rrier o FCCH $n' *CCH+

Ce"" Broadcast C anne"/ CBCH

This o!i&$ &h$nne &ont$ins #ess$!es th$t &$n (e re&ei6e' (0 $#o(i es+ These #ess$!es $re sent (0 "sin! 'e'i&$te' &h$nne s $n' &o#e "n'er

the &$te!or0 o short #ess$!es+ Howe6er, the0 $re &onsi'ere' $s &o##on

&h$nne s sin&e $ #o(i es &$n re&ei6e the#+

Common Contro" C anne"s )CCCH-

The0 o/er$te either in "/ ink or 'own ink 'ire&tions $n' $re /oint-to-/oin t

sim&"e0 c anne"s'

T0/es o Co##on Contro Ch$nne s

CH- $!in! Ch$nne

AGCH-A&&ess Gr$ntCh$nne

RACH- R$n'o# A&&ess Ch$nne

Pa$in$ C anne"/ PCH It is o!i&$ &h$nne in the 'own ink 'ire&tion $n' it is /oint-to-/oint t0/e+ It&o#/rises o $ &a$in$ messa$e to indicate an incomin$ ca"" or s ortmessa$e' T e &a$in$ messa$e consists of t e identit! of mobi"e t enet(or1 (ants to contact'

Access Grant C anne"/AGCH It is $ /oint-to-/oint o!i&$ &h$nne in the 'own ink 'ire&tion+ It in or#s the#o(i e $(o"t the $ssi!n#ent o si!n$ in! &h$nne or &$ set-"/ i+e+ SDCCH+

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Random Access C anne" )RACH- It is $ /oint-to-/oint o!i&$ &h$nne in the "/ ink 'ire&tion+ It is sent (0 the#o(i e $s $ re."est or #$kin! $ &$ or $s $ res/onse to $ /$!in! to the #o(i e+It &onsists o the i'entit0 o the #o(i e $n' o&$tion $re$ 'et$i s $s $6$i $( e in

SIM+Dedicated Contro" C anne" )DCCH-

These $re the o!i&$ &h$nne s, whi&h $re /oint-to-/oint, '"/ e) $n'

$6$i $( e in "/ ink $n' 'own ink 'ire&tions+

T!&es of DCCH

SDCCH-St$n'$ one De'i&$te' Contro Ch$nne

SACCH-S ow Asso&i$te' Contro Ch$nne

FACCH-F$st Asso&i$te' Contro Ch$nne

SDCCH/Standa"one Dedicated Contro" C anne"

It is the o!i&$ &h$nne or e)&h$n!e o in or#$tion (etween *TS $n' MS

when n o TCH is a""otted' It a"so used to send SMS )S ort Messa$e

Ser2ice-'It is used for ser2ices "i1e

S"(s&ri(er $"thenti&$tion

Ci/herin! Initi$tion

E."i/#ent 6$ i'$tion

Assi!n#ent o $ TCH

C$ Set"/

Lo&$tion U/'$tes

SACCH/S"o( Associ ated Contro" C anne"

This o!i&$ &h$nne is "se' or non-"r!ent in or#$tion e)&h$n!e (etween

#o(i e $n' *TS+ It &$n (e $sso&i$te' either with SDCCH or TCH+

In the "/ ink 'ire&tion it is "se' to sen' $6er$!e' #e$s"re#ent o si!n$stren!th $n' ."$ it0 o the /resent ser6in! *TS $n' nei!h(o"rin! *TSs+

In the 'own ink 'ire&tion it is "se' to tr$ns#it /ower &ontro $n' ti#in!

$'6$n&e '$t$ to the #o(i e+

SACCH is "se' e6en when &$ s $re in /ro!ress

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GSM Frame Structure and Burst T!&es3

GSM, one ti#e s ot '"r$tion is 8+=77#s1>=?2@#s + One TDMA r$#e

&$rries : ti#es ots $n' hen&e '"r$tion o one r$#e is 2#s+ Se/$r$te #" ti r$#es $re 'e ine' or tr$ i& $n' &ontro si!n$ s+ A 2@- r$#e TDMA #" ti r$#e is 'e ine' or &$rr0in! TCH, SACCH $n' FACCH+D"r$tion o this #" ti r$#e is 2)2@ >28#s1>=?2@):)2@ +

A =>- r$#e TDMA #" ti r$#e is 'e ine' or &ontro #" ti r$#e or &$rr0in! *CCH,CCCH, SDCCH $n' its $sso&i$te' SACCH+ The '"r$tion o s"&h #" ti r$#e is2)=> 2;=#s+

A s"/er r$#e is 'e ine' whi&h &onsists o => tr$ i& #" ti r$#es or 2@&ontro #" ti r$#es $n' '"r$tion o s"/er r$#e is @+;>2s+It re/resents s#$ est&0& e or whi&h the or!$ni $tion o $ &h$nne s is re/e$te'+

A h0/er r$#e is 'e ine' whi&h &onsists o 28


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Traffic Mu"tiframe

Tr$ i& M" ti r$#e is 'e ine' with 2@ r$#es+ The en!th o $ 2@-M" ti r$#eis >28 #s+ O the 2@ r$#es, 2< $re "se' or tr$ i&, > is "se' or the S ow

Asso&i$te' Contro Ch$nne 1SACCH , $n' > is "n"se' in &$se o " r$te&h$nne 'e/ o0#ent+In &$se h$ r$te &h$nne s $re "se' the r$#e 2= is "se' orSACCH or the se&on' set o &$ s+

I FACCH is to (e sent then /re-e#/tion o tr$ i& &h$nne is e#/ o0e'+

Hen&e the o!i&$ &h$nne &o#(in$tions th$t $re $ owe' &$n (e either

TCH?F SACCH?F FACCH?F or TCH?H SACCH?H FACCH?H+

Traffic Mu"tiframe

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Contro" Mu"tiframe

The0 $re 'e ine' or => TDMA r$#es+ The &o#(in$tions &$n (e $s o ows+

FCCH SCH *CCH CCCH FCCH SCH *CCH CCCH SDCCH?< SACCH?< CCCH *CCH SDCCH?: SACCH?:

FCCH4SCH4BCCH4CCCH

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SDCCH564SACCH56

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FCCH4SCH4BCCH4CCCH4SDCCH574SACCH57

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GSM Bursts

*"rst is the &ontent o the ti#es ot+ The '"r$tion o ti#es ot is =77 #i&ro

se&s+ It &onsists o "s$( e (its $n' !"$r' /erio'+ The ("rst $re & $ssi ie' into+

Nor#$ *"rst D"##0 *"rst Fre."en&0 Contro *"rst1F-*"rst S0n& *"rst1S-*"rst A&&ess *"rst

F-*"rst is $sso&i$te' with FCCH, S-("rst with SCH $n' A&&ess *"rst with

RACH+ A other o!i&$ &h$nne s "se nor#$ ("rst+ D"##0 *"rst is "se' to ithe e#/t0 /h0si&$ &h$nne in TS8 in *CCH &$rrier, i ne&ess$r0+

Norma" Bursts

It &onsists o >


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Dumm! Bursts

It is tr$ns#itte' in I' e ti#e s ots on the *CCH Crrier,whi&h ens"res th$tthe *CCH C$rrier is $ w$0s /resent $n' MS is $( e to in' it e$si 0 $n' &$rr0 o"t

the $ssess#ent o si!n$ e6e +This he /s in Mo(i e Assiste' H$n' O6er1MAHO

Fre.uenc! Correction Burst F/burst

It is $sso&i$te' with FCCH $n' tr$ns#itte' in TS8 in r$#es8,>8,28,;8,$n'


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S!nc Bursts)S/Burst-

It is $sso&i$te' with SCH $n' is tr$ns#itte' in TS8 o r$#es >,>>,2>,;>$n' th r$#es in $ &ontro #" ti r$#e+ This ("rst &onsists o three t$i (its e$&h$t the st$rt $n' en', !"$r' /erio' o :+2= (its with two ( o&ks o ;B (its o

in or#$tion $n' $ tr$inin! se."en&e o @< (its s$n' wit&he' in (etween the#+This is the irst ("rst in the 'own ink 'ire&tion to (e /ro&esse' (0 the MS+Theon!er tr$inin! se."en&e he /s the MS to e e&ti6e 0 'e#o'" $te the si!n$ ro#

*TS

Access Burst

It is "se' (0 MS or RACH+ It &onsists o ;@ nos o en&r0/te' (its with :t$i (its in the (e!innin!, three t$i (its $t the en' $n' $ tr$inin! se."en&e o (its+ The re#$inin! /erio' is !"$r' /erio'+ This is the Short ("rst "se' (0 MS inthe U/ ink 'ire&tion $t $n initi$ /h$se o $ &$ when the /ro/$!$tion 'e $0(etween MS $n' *TS is not known 0et neither $s the re."en&0 error $n're&e/tion e6e + It /ro6i'es $ on!er (its TSC in or'er to $&i it$te the initi$'e#o'" $tion or the *TS #ore s"&&ess " +

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Different Modes of 8&eration

The 'i erent o!i&$ &h$nne s $re "se' to t$ke MS ro# O #o'e to I' e #o'e$n' then to De'i&$te' #o'e +

8FF M8DE

MS is in the Swit&he' O &on'ition+It &$nnot re&ei6e in&o#in! /$!in! #ess$!esor &$nnot #$ke o"t!oin! &$ $n' No 'e'i&$te' &h$nne is $sso&i$te' with it+

Id"e Mode

MS Swit&he' On $n' it is $tt$&he' to the network $n' &$n re&ei6e in&o#in!/$!in! #ess$!es, &$n #$ke o"t!oin! &$ , ("t there is no 'e'i&$te' &h$nne$sso&i$te' with it

Dedicated Mode

MS is in &on6ers$tion $n' $ 'e'i&$te' &h$nne is $sso&i$te' with it+

Abis Interface

It is &onne&ti6it0 (etween *SC to *TS $n' 2 M(/s ink is est$( ishe' or this/"r/ose+ E6er0 ti#es ot o @@ 9(/s $n' thetr$ i& o >;9(/s ro# *TS with the $sso&i$te' si!n$ in! in or#$tion is#" ti/ e)e' $s >@9(/s $n' inserte' in the ti#es ots+ Hen&e e$&h ti#es ot on

2M(/s A(is &$n $&&o##o'$te o"r /h0si&$ &h$nne s o U#+ For one &$rrier wenee' two s ots+ A''ition$ 0 we re."ire e)& "si6e ti#es ots or si!n$ in! /"r/osesre $te' to the tr$ns&ei6ers o e$&h se&tor 1TR $n' or O $n'M /"r/oses+

Consi'er $ *TS with three se&tors with < C$rriers in e$&h se&tor 1

6.Gsm Interfaces

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