mobile mangment
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GSM Mobility Management
Originals by: Rashmi Nigalye, Mouloud Rahmani, Aruna Vegesana, Garima Mittal, Fall 2001
ro!" M" Veeraragha#an, olyte$hni$ %ni#ersity, Ne& 'or(
) GSM ar$hite$ture o#er#ie&* Net&or( layout
* roto$ols* Addresses + identi!iers
) o$ation management* -all deli#ery . lo$ation u/date* Se$urity
) ando#er management
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GSM net&or( layout
GSM Network
(PLMN)
MSC region
MSC region
MSC region
Location area
BSCBSC
Location
area
BTS BTS
PLMN: Public Land Mobile Network
MSC: Mobile Switching Center
BTS: Base Transceiver Station
BSC: Base Station Controller
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GSM net&or( layout
BSC
MSC
BSC
BTS
EIRLR
!"C#LR
BTS
BTS
"$
!!bisE
B%C
&MC
'MSC
PSTN
ISDN
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GSM MA /roto$ol
) GSM MA similar to S1 MA) MA uses 3ransa$tions -a/abilities
art 43-A5 o! the SS6 sta$() MA !un$tions:* %/dating o! lo$ation in!ormation in VRs* Storing routing in!ormation in Rs
* %/dating and su//lementing user /ro!ilesin Rs
* ando!! o! $onne$tions bet&een MS-s
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7hat is a lo$ation area 4A58
) A /o&ered9on mobile is in!ormed o! an in$oming$all by a /aging message sent o#er the AG-$hannel o! a $ell
) One etreme is to /age e#ery $ell in the net&or(!or ea$h $all 9 a &aste o! radio band&idth
) Other etreme is to ha#e a mobile send lo$ationu/dates at the $ell le#el" aging $ut to 1 $ell, but
large number o! lo$ation u/dating messages") en$e, in GSM, $ells are grou/ed into o$ationAreas * u/dates sent only &hen A is $hanged;/aging message sent to all $ells in last (no&n A
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Addresses and denti!iers
) nternational Mobile Station MS- !rom the MS"
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Addresses and denti!iers
) Mobile Subs$riber S?N 4MSS?N5* 3he @real tele/hone number: assigned to
the SM
* 3he SM $an ha#e se#eral MSS?Nnumbers !or sele$tion o! di!!erentser#i$es li(e #oi$e, data, !a
CC N(C SN
N?-: National ?estination -ode 4N?- identi!ies o/erator5;SN: Subs$riber Number; --: -ountry -ode;?igits !ollo&ing N?- identi!ies the R
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Addresses and denti!iers
) Mobile Station Roaming Number4MSRN5
* t is tem/orary lo$ation de/endentS?N number
* t is assigned by lo$al VR to ea$h MS inits area"
CC N(C SN
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Addresses and identi!iers
) 3em/orary Mobile Subs$riberdentity 43MS5* t is an alias o! the MS and is used in its /la$e !or
/ri#a$y"* t is used to a#oid sending MS on the radio /ath"
* t is an tem/orary identity that is allo$ated to an MS bythe VR at inter9VR registration, and $an be $hanged bythe VR
* 3MS is stored in MS SM $ard and in VR"
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3MS, MS, MSRN and MSS?N
) %nli(e MSS?N, MS is not (no&n to the GSM user" 3he-- o! MSS?N translates to an M-- o! MS as !ollo&s,e"g, ?enmar( --: B M--: 2CD
) 3MS is used instead o! MS during lo$ation u/date to/rote$t /ri#a$y" As user mo#es, 3MS is used to sendlo$ation u/date" 3hus a third /arty snoo/ing on the &irelesslin( $annot tra$( a user as he>she mo#es"
) MSRN is the routing number that identi!ies the $urrentlo$ation o! the $alled MS"* MSRN is tem/orary net&or( identity assigned to a
mobile subs$riber"* MSRN identi!ies the ser#ing MS->VR"* MSRN is used !or $all deli#ery 4$alls in$oming to an MS5"
) MSS?N is the dialed number to rea$h a GSM user
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Addresses and denti!iers
) o$ation Area ? 4A5* --: -ountry -ode, MN-:Mobile Net&or(
-ode, A-: o$ation Area -ode
* A is broad$ast regularly by EaseStation on E--
*
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o$ation management
) Set o! /ro$edures to:* tra$( a mobile user
* !ind the mobile user to deli#er it $alls) -urrent lo$ation o! MS maintained by
29le#el hierar$hi$al strategy &ith
Rs and VRs"
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7ays to obtain MSRN
1" Obtaining at lo$ation u/date * MSRN !or the MSis assigned at the time o! ea$h lo$ation u/date,and is stored in the R" 3his &ay the R is in a/osition to immediately su//ly the routing in!o
4MSRN5 needed to s&it$h a $all through to thelo$al MS-"
2" Obtaining on a /er $all basis * 3his $ase re=uiresthat the R has at least an identi!i$ation !orthe $urrently res/onsible VR" 7hen routing in!ois re=uested !rom the R, it !irst has to obtainthe MSRN !rom the VR" 3his MSRN is assignedon a /er $all basis, i"e" ea$h $all in#ol#es a ne&MSRN assignment
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Routing in!ormation: $ase &hen MSRNis sele$ted /er $all by VR>MS-
) ! MSRN is allo$ated to ea$h subs$riber #isiting at an MS-, then thenumber o! MSRNs re=uired is large" ! instead, an MSRN is allo$atedonly &hen a $all is to be established, then the number o! MSRNs isroughly e=ual to number o! $ir$uits at MS- * a mu$h smaller number *
hen$e MSRNs ty/i$ally allo$ated /er $all by VR>MS-
MSIS(N
'MSC
LR
MSIS(N
MSC)#LR
MSR
N
IMSI
MSRN
MSIS(NIMSI% #LR nu$ber
MSRN
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-all routing to a mobile station:$ase &hen R returns MSRN
'MSC
BSC
BSC
EIR
LR
!"C#LR
MSCBTS
BTS
BTS
L! *
L! +
IS(N
*
MS
*
MSIS(N
,
TMSI
-
MSRN
.
MSRN
+
MSIS(N
/
TMSI
/TMSI
/
TMSI
0
TMSI
1
MSRN
MSC
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Messages e$hanged: $all deli#ery
PSTN'MSC
LR#LR
Target
MSC
Originating
Switch
GMSC HLRVLR
Target
MSC
*2 IS"P I!M+2 M!P3SEN(3R&"TIN'3IN4&
.2 M!P3PRI(E3R&!MIN'3N"MBER
-2 M!P3PRI(E3R&!MIN'3N"MBER3ack
12 M!P3SEN(3R&"TIN'3IN4&3ack
,2 IS"P I!M
*
+ .
-1
,
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Find o/eration in GSM
) S?N s&it$h re$ognies !rom the MSS?N that the$all subs$riber is a mobile subs$riber" 3here!ore,!or&ard the $all to the GMS- o! the home MN4ubli$ and Mobile Net&or(5
) GMS- re=uests the $urrent routing address 4MSRN5!rom the R using MA
) Ey &ay o! MSRN the $all is !or&arded to the lo$alMS-
) o$al MS- determines the 3MS o! the MS 4by=uerying VR5 and initiates the /aging /ro$edure inthe rele#ant A
) A!ter MS res/onds to the /age the $onne$tion $anbe s&it$hed through"
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GSM se$urity
) Authenti$ation) 7hat signed res/onse 4SR
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GSM se$urity
)
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ey management
) -i/hering (ey $ is generated using algorithm AD in the samemanner as SR
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o$ation registration
) MS has to register &ith the MN to get $ommuni$ation ser#i$es) Registration is re=uired !or a $hange o! MN) MS has to re/ort to $urrent MN &ith its MS and re$ei#e ne&
3MS by ee$uting o$ation Registration /ro$ess") 3he 3MS is stored in SM, so that e#en a!ter /o&er on or o!!,
there is only normal o$ation %/date") ! the MS re$ognies by reading the A broad$ast on E-- that
it is in ne& A, it /er!orms o$ation %/date to u/date the Rre$ords"
) o$ation u/date /ro$edure $ould also be /er!ormed /eriodi$ally,inde/endent o! the MS mo#ement"
) 3he di!!eren$e in o$ation Registration and o$ation %/date isthat in lo$ation u/date the MS has already been assigned a 3MS"
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o$ation registrationMS BSS)MSC #LR LR !"C
IMSI 9i
!. < !0
=
'enerate
TMSI
Loc2";d2Re57IMSI%L!I8
";d Loc2!rea
7IMSI%L!I8!ut2Par2Re5 !uth2Ino2Re5
7IMSI8
7R!N(8
!uthenticate7IMSI%9c%
R!N(%SRES8
!ut2 Ino2
7IMSI8
7R!N(8
!uthentic2 Re5 7IMSI%9c%
R!N(%SRES8
!uth2Ino
!uth2Res;27SRES8
7SRES8
!uth2Res;
";date
Location
7IMSI%MSRN8
SRES
R!N(9i
9c SRES
Contd222
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4I$ontd5 o$ation registration"
MS BSS)MSC #LR LR !"C
!1
'enerateTMSI
79c8
Start Ci;h2
Ci;h2Mod2Co$2
Message M9c
9c7M8
Ins2Subsc2(ata
7IMSI8
4orw2 New TMSI
7TMSI8
Subs2(at2Ins2!ck
Loc2";d2!cce;t
7IMSI8Loc2";d2!cce;t
Ci;h2Mod29c7M8
!19c7M89c
M
TMSI Realloc2!ck
TMSI Realloc2C$d2
TMSI2!ck
Loc2";d2!cce;t can be co$bined
New TMSI is receie! "# MS
(TMSI Reallocation) in ci$hering %o!e&
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o$ation u/dateMS BSS)MSC #LR LR !"C
IMSI% TMSI
9i% 9c% L!I
Start ci;hering2
!uthentication
Loc2";d2Re5
7TMSI%L!I8";date Loc2!rea
7TMSI%L!I8
";date Location
7IMSI%MSRN8
'enerate
TMSI
Start ci;hering
79c8 IMSI
Insert Subscriber2 data
Subs2 (ata Insert !ck7contd228
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4""$ontd5 o$ation u/date"
MS BSS)MSC #LR LR !"C
7IMSI8
!uth2Ino2Re5
7IMSI%9c% R!N(%SRES8
!uth2Ino
Start ci;hering2
4orward new TMSI
!uth2 Para2 Re5
Loc2 ";d2 !ce;t
Loc2 ";d2 !ce;t
TMSI !ckTMSI Reallocation
Co$;lete
TMSI Realloc2 C$d2
7TMSI8
!uth2 Ino2
7IMSI%9c% R!N(%SRES8
7IMSI8
7IMSI8
Loc2 ";d2 !ce;t
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3y/es o! hando#er4same as @hando!!5
) 3here are !our di!!erent ty/es o!hando#er in the GSM system" ando#erin#ol#es trans!erring a $all bet&een:
* -hannels 4time slots5 in the same $ell* -ells 4Ease 3rans$ei#er Stations5 under the
$ontrol o! the same Ease Station -ontroller4ES-5,
* -ells under the $ontrol o! di!!erent ES-s, butbelonging to the same Mobile ser#i$esS&it$hing -enter 4MS-5, and
* -ells under the $ontrol o! di!!erent MS-s"
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Attributes o! radio9lin( hando#er
) ard hando#er
) MAO
) Ea$(&ard) -OS sele$tion s$heme: stati$
* -ross9o#er s&it$h: an$hor s&it$h
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ando#er 4MAO5
) ando#ers are initiated by the ESS>MS-4as a means o! tra!!i$ load balan$ing5"
) ?uring its idle time slots, the mobile s$ans
the Eroad$ast -ontrol -hannel o! u/ to 1Jneighboring $ells, and !orms a list o! thesi best $andidates !or /ossible hando#er,based on the re$ei#ed signal strength"
) 3his in!ormation is /assed to the ES- andMS-, at least on$e /er se$ond, and is usedby the hando#er algorithm"
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ando#er /ro$edures in GSM
BSC
MSC>!
BSC
MSC>B
BTS *
BTS .
BTS +
BSC
MSC>C
BTS .
Connection route
*
+
.-
1
,
/
0
0
?
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nter MS- basi$ hando#erMS)BSS * MSC>!
andover re5uired
! Indication
MSC>B #LR>B
Radio chan2 !ckandover re;ort
MS)BSS +
!llocate andover nu$ber
RLC
!NS
REL
End Signal
B Indication
B Conir$
andover re;ort
Peror$ andover
I!M
!CM
Send End Signal
End o Call
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Subse=uent hando#er !rom MS-9E to MS-9A
MS)BSS * MSC>!
B Indication
B Conir$
MSC>B
#LR>B
Subse52 andover
!cknowledge
MS)BSS +
RLC
REL
End Signal
! Re5uired
! Indication
andover re;ort
Peror$ subse5uent
andover
End o Call
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Subse=uent hando#er !rom MS-9E to MS-9-
MSC>!
MSC>C
Peror$ andover
Radio chan2 !ck2
MSC>B
!llocate andover
Nu$ber
MS
I!M
!CM
! Re5uestPeror$ subse5uent
andover
#LR>C
Send andover re;ort
B Indication
7Contd@8
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4I$ontd5 Subse=uent hando#er !rom MS-9E to MS-9-
MSC>!
MSC>C
Send End Signal
ando Re;ort
MSC>B MS
REL
RLC
! IndicationPeror$ subse5uent
!cknowledge
B Conir$
!NS
MSC>B #LR>B
End Signal
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Abbre#iations
) S-: nternational s&it$hing $enter) OM-: O/erations and maintenan$e $enter) GMS-: Gate&ay s&it$hing $enter) MS-: Mobile s&it$hing $enter
) VR: Visitor lo$ation register) R: ome o$ation register)
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Re!eren$es
) 3he GSM Sytem !or Mobile$ommuni$ations by Mouly + autet
) 7ireless and Mobile Net&or(
Ar$hite$tures by 'i9Eing in + mri$h-hlamta$
) 7ireless ersonal -ommuni$ations Systems
by ?r" Goodman) GSM S&it$hing, Ser#i$es and roto$ols byKorg
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