gsm interfaces and protocols.docx

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GSM Interfaces and Protocols (Global System forMobile Communication (GSM)) Part 1

The GSM specifications define the interaction between system components through

well-defined interfaces and protocols !igure "-11 shows the interfaces between the

GSM functional entities #able "-" lists the GSM interfaces

Figure 3-12 shows the protocol architecture used for the e$change of signaling

messages on each interface #he protocols are layered according to the %SI &eference

Model It consists of the Physical 'ayer ata 'in* 'ayer and 'ayer " #his 'ayer " is

not the same as defined in %SI 'ayer " In GSM the 'ayer " functions include call

mobility and radio resource management In the %SI model these functions are

pro+ided by the higher layers GSM reuses a few established protocols such as CCS,

M#P #CP SCCP IS.P and IS/ 'P protocols #he MP and 0SSP are newprotocols to support GSM specific needs

Air interface

The air interface between the MS and the 0#S is called .m Most of the

implementations use a freuency band of 233 M45 #he other deri+ati+e of GSM is

called igital cellular system 1633 (CM1633)

Figure 3-11 GSM interfaces.

TABLE 3-3 GSM nterfaces


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Interface Description

Um

Abis

A

B

C

D

E

F

G

H

It uses a freuency band of 1633 M45 #able "-7 lists the GSM freuency bands

The use! fre"uenc# ban! is di+ided into 833-*45 carriers or &! channels in both the

uplin* and downlin* direction 9ach &! channel is then further subdi+ided into eight

different timeslots ie 3 to , by #M techniues set of these eight timeslots is

referred as a #M frame 9ach frame lasts 7:1; ms #he physical channels are

further mapped to +arious logical channels carrying user traffic and control information

between the MS and the 0#S #able "-; describes the logical channels and their

usages

#he following section describes the .m interface protocols used at the MS and the 0#S

side

$h#sica% %a#er 'ayer 1 which is a radio interface pro+ides the functionality reuired to

transfer the bit streams o+er the physical channels on the radio medium #he Physical

'ayer itself does the frame delimitation #he ser+ices pro+ided by this layer to those

abo+e include


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& 'hanne% (apping )%ogica% to ph#sica%*

& 'hanne% co!ing an! ciphering

& +igita% (o!u%ation

& Fre"uenc# hopping

& Ti(ing a!,ance an! power contro%

+ata %in %a#er. Signaling 'ayer 8 is based on the 'Pm protocol to pro+ide a reliable

signaling lin* between the networ* and the mobile station 'Pm uses no flags for

frame delimitation #his way scarce radio resources are not spent on flag bits the bit

Figure 3-12 GSM protoco% stac.

TABLE 3- GSM Fre"uenc# Ban!sSystem Direction Frequency band (MHz)

GSM 900 Uplink 890-815

Downlink 935-960

GSM/DCS1800 Uplink 110-185


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Downlink 1805-1880

/etwor %a#er. Signaling 'ayer " ta*es care of signaling procedures between an MS

and the networ* It consists of three sublayers with distinct signaling procedures

& 0a!io resource (anage(ent )00*

& Mobi%it# (anage(ent )MM*

& 'onnection (anage(ent )'M*

0a!io resource (anage(ent &adio resource management (&&) comprises

procedures reuired to establish maintain and release the dedicated radio

connections #he && sublayer functions include<

& 'hanne% assign(ent an! re%ease

& 'iphering

& Mo!ification of channe% (o!es e.g. ,oice an! !ata

& an!o,er between ce%%s

& Fre"uenc# re!efinition to enab%e fre"uenc# hopping

& MS (easure(ent reports

& $ower contro% an! ti(ing a!,ance

& $aging

& 0a!io channe% access

The (obi%e station a%wa#s initiates an 00 session. !or e$ample the && procedures

are in+o*ed to establish an && session in response to a paging message or to establish

an outgoing call s shown in !igure "-1" the && messages are transferred to 0SC

transparently through the 0#S #able "-: lists && messages

Mobi%it# (anage(ent. #he mobility management (MM) sublayer handles functions and

procedures related to mobility of the mobile user #his includes procedures for<

& Authentication

& Location registration an! perio!ic up!ating

TABLE 3- Logica% Traffic an! 'ontro% 'hanne%sTraffic

channels

(TCH)


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!CH/F "#$$i%s

s&bs"$ib%$

in'o$m#(ion)sp%%"*/+#(#,

#( # $#(% o'

.8 bpswi(* # sp%%"*

"o+in #(

#$o&n+ 13

bps.

!CH/F "#$$i%s

s&bs"$ib%$in'o$m#(ion #(

# $#(% o' 11.

bps wi(* #sp%%"* "o+in

#( #$o&n+

bps.

B$o#+"#s(

"on($ol

"*#nn%ls)BCH,

!*is "*#nn%l is

b$o#+"#s( b2(*% B!S #n+

"#$$i%s

in'o$m#(ion'o$ (*%

'$%&%n"2

"o$$%"(ion o'(*% MS. 4( is

&s%+ in

+ownlink

+i$%"(ion onl2.


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!*is "*#nn%l is

b$o#+"#s( b2

(*% B!S #n+"#$$i%s

in'o$m#(ion

'o$ '$#m%s2n"*$oni#(io

n o' (*% MS.

4n #++i(ion i(

#lso "#$$i%s (*% b#s% s(#(ion

i+%n(i(2 "o+%

)BS4C,. 4( is&s%+ in

+ownlink

+i$%"(ion onl2.

!*is "*#nn%l

"#$$i%s

b$o#+"#s(in'o$m#(ion

$%l#(%+ (o (*%

B!S #n+ (*%n%(wo$k. !*%

in'o$m#(ion

in"l&+%s"on'i&$#(ion

+%(#ils o'"ommon

"on($ol"*#nn%ls

)CCH,

+%s"$ib%+ b%low.

4( is &s%+ in+ownlink

+i$%"(ion onl2.

Common"on($ol

"*#nn%ls

)CCH,


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!*is is &s%+ (o

p#% #n MS. 4(is &s%+ in

+ownlink

+i$%"(ion onl2.

!*% MS &s%s(*is "*#nn%l (o

$%&%s( (*%

#llo"#(ion o' #SDCCH. 4( is

&s%+ in &plink

+i$%"(ion onl2.

!*% B!S

#llo"#(%s #

SDCCH o$!CH in

$%spons% (o (*%

#llo"#(ion$%&%s( b2 (*%

MS &sin (*is

"*#nn%l. 4( is&s%+ in

+ownlink

+i$%"(ion onl2.

D%+i"#(%+

"on($ol

"*#nn%ls)DCH,


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!*is "*#nn%l is

&s%+ 'o$

"#$$2insin#lin

in'o$m#(ion

b%(w%%n (*%B!S #n+ # MS

b%'o$%

#llo"#(ion o' #

!CH. Fo$%#mpl%7

SDCCH is

&s%+ 'o$"#$$2in

sin#lin

m%ss#%s

$%l#(%+ (o&p+#(%

lo"#(ion #n+

"#ll%s(#blis*m%n(.

!*is is #

bi+i$%"(ion#l"*#nn%l.

!*is "*#nn%l is#lw#2s &s%+ in

"on&n"(ionwi(* # !CH o$

# SDCCH. !*%MS #n+ (*%

B!S &s% i( (o

m#in(#in #nSDCCH o$ #

!CH. 4n (*%

&plink7 (*% MSs%n+s

m%#s&$%m%n(

$%po$(s (o (*%B!S &sin (*is

"*#nn%l. 4n (*%

+ownlink7 (*%

B!S ($#nsmi(sin'o$m#(ion (o

k%%p (*%

mobil%


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&p+#(%+ on

$%"%n( "*#n%s

in s2s(%m"on'i&$#(ion.

!*is "*#nn%l is

#lw#2s#sso"i#(%+ (o #

!CH #n+ is

&s%+ (o($#ns'%$

sin#lin

m%ss#%sw*%n # mobil%

is #l$%#+2

inol%+ in #"#ll.


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Figure 3-13 Air interface signa%ing protoco%s.

& Securit#

& TMS rea%%ocation

& MS !etach4attach

As shown in Figure 3-13 the CM layer from the transmitting side uses the MM layer to

establish && connection and then transfers messages transparently across to the

recei+ing side that is MSC #able "-: lists MM messages

'onnection (anage(ent. #he connection management (CM ) sublayer contains thefunctions and procedures for call control #his includes procedures to establish release

and access ser+ices and facilities #he CM consists of three sublayers namely call

control (CC) supplementary ser+ices (SS) and short message ser+ices (SMS)

The ca%% contro% sub%a#er pro+ides procedures for IS/ call control #hese procedures

are based on IS/ call control procedures defined in the I#.-# =2"1 specification

4owe+er the minor modifications are done to adopt these to mobile en+ironment


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#he supplementary ser+ice sublayer pro+ides the procedures to support non-call-related

supplementary ser+ices such as call forwarding and call waiting

TABLE 3-5 La#er 3 Messages

messa!es MM messa!es CM messa!es

C*#nn%l %s(#blis*m%n( m%ss#%s :%is($#(ion m%ss#%s C#ll %s(#blis*m%n( m%ss#%s

ADDi(ion#l ASSinm%n(

4MS4 DE!#"* A;E:!in

4D#(in C=#in m%ss#%s

Conn%"(ion C=

>AGin :E&%s( !2p% CM SE:i"% :E@%"( EME:G%n"2 SE!U>

>AGin :E&%s( !2p% 3 CM SE:i"% :E&%s( >:=G:ESS

>AGin :%S>ons% CM SE:i"% AB=$( C#ll p*#s% m%ss#%s

H#n+o%$ m%ss#%s CM :E%S(#blis*m%n( M=Di'2


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:E&%s(

ASSinm%n( CoMm#nD S%"&$i(2 m%ss#%s M=Di'2 :E@%"(

ASSinm%n( C=Mpl%(% AU!H%n(i"#(ion :E@%"( M=Di'2 C=M>l%(%

ASSinm%n( FA4;&$% AU!H%n(i"#(ion USE: 4

HA

>Hsi"#l 4


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>A:!i#l :E;%#s% :E;%#s% C=Mpl%(%

>A:!i#l :E;%#s% C=Mpl%(% =(*%$ m%ss#%s

S2s(%m in'o$m#(ion m%ss#%s C=SS(%m 4


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=(*%$ m%ss#%s

CHA # P % S # < GSM Interfaces and Protocols (Global System for Mobile Communication

(GSM)) Part 8

P & 9 ? I % . S P % S # < System rchitecture (Global System for Mobile Communication (GSM))

Part 8

• R E L AT E D L I N K S

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