gsm-call-flow

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Ericsson Confidential EIL/PY/XM Surender Mohan Panchal 2008-07-18

Location Update (LU)


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Introduction (LU)

There are three different types of Location updating. The difference inSignaling between these three types is a parameter in the Location UpdatingRequest Message.

The three types are: Normal: used when an MS reaches a new location area; also called

Forced Registration Periodic: used to prevent mobiles from becoming accidentally detached

from the system Attach: used when a mobile is switched on

The steps involve in a location update are RR connection establishment,service request, Authentication (except for periodic registration), cipheringmode setting, location updating and RR connection release.


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RR Connection Establishment (LU)MS BTS BSC

Channel Required

Channel Activation Acknowledge

Channel Activation

Imm Ass Command

Imm AssignmentRR(AGCH)

Channel RequestRR(RACH)

Click on Imm AssignmentFor more information


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Service Request (LU)MS BTS BSC MSC

SABM

Est Ind(CM_Ser_Req)

UA

Conn Request

Conn Confirmed

Click on Conn ConfirmedFor more information


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Authentication (LU)

Click on Auth ResponseFor more information

MS BTS BSC MSC

Auth Request

Auth ReqMM(SDCCH)

DR (Auth Req)

DI (Auth Resp)

Auth Response

Auth RespMM(SDCCH)


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Ciphering (LU)

Click on Ciph Mode ComFor more information

MS BTS BSC MSC

Ciph Mode Cmd

Ciph Mode Command

RR(SDCCH)

Encryption Cmd

DI (Ciph Mode Com)

Ciph Mode Com

Ciph Mode Complete

RR(SDCCH)


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Update Location (LU)

Click on TMSI Real ComFor more information

MS BTS BSC MSC

Loc Upd Acc

Loc Upd AccMM(SDCCH)

DR (Loc Upd Acc)

DI (TMSI Real Com)

TMSI Real Com

TMSI Real CompleteMM(SDCCH)


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RR Connection Release (LU)

Click on Clear CompleteFor more information

MS BTS BSC MSC

Clear Command

Ch ReleaseRR(SDCCH)

DR (Ch Release)

Clear Complete

Disc

UARel Ind

Deact SDCCH

Rf Ch Release

Rf Ch Rel Ack


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SCCP, Connection Oriented, Release (LU)

Click on RLCFor more information

BSC MSC

RLSD Release

RLC (Release Complete)


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Location Updating Reject (LU)

If location updating cannot be accepted, the network sends a Location Updating Reject message to the MS. This message contains the cause for rejection. For example, IMSI unknown in HLR, illegal MS, congestion, etc.

The RR connection is then released, and if the reject cause is either number 2 "IMSI unknown in HLR" or number 3 "Illegal MS", the MS deletes any TMSI, stored LAI, cipher key and ciphering key sequence number. The MS then enters the "IDLE no IMSI" state. In this state, the MS acts in the following way:

• No starting any normal location updating attempt• No performing periodic updating• No performing IMSI detach if powered down• Only allows emergency calls• No responding to paging


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Signaling Diagram Location Update


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Call Set-up in GSM


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IntroductionCall set-up within GSM consists of the following main steps:

RR connection establishment

Service request

Authentication

Ciphering mode setting

IMEI Check

TMSI-Reallocation

Call initiation

Assignment of a traffic channel

User alerting

Call accepted

Note: The above steps are taken for both mobile originating and mobile terminating calls. However, for mobile terminating call they must be preceded by an interrogation phase.


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Overview of Call Set-up in GSM


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Mobile Terminating (MT)


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Messages Overview Between MS and Network (MT)


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Interrogation Phase (MT)

MSC/VLR HLR GMSC PSTN/ISDN

IAM

Send Routing Information

Provide Roaming Number

Send Routing Information

IAM

Provide Roaming Number

Click on IAMFor more information


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RR Connection Establishment (MT)MS BTS BSC

Channel Required

Channel Activation Acknowledge

Channel Activation

Imm Ass Command

Imm AssignmentRR(AGCH)

Channel RequestRR(RACH)

Click on Imm AssignmentFor more information

MSCPaging

Paging CommandPaging Command

RR(PCH)


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Service Request (MT)MS BTS BSC MSC

SABM(Paging Resp)

Est Ind(Paging Resp)

UA(Paging Resp)

CR(Paging Resp)

Conn Confirmed

CM Service Request

Click on Conn ConfirmedFor more information


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Authentication (MT)Ciphering (MT)

Authentication and Ciphering process remains same as in LU


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IMEI Check (MT)MS BTS BSC MSC

Identity Request

DR (Id Req)

DI (Id Resp)

Identity Response

Identity ResponseMM(SDCCH)

Click on Identity ResponseFor more information

Identity RequestMM(SDCCH)


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TMSI Reallocation (MT)MS BTS BSC MSC

TMSI reallocation Cmd

DR(TMSI reallocation)

DI(TMSI reallocation)

MM(SDCCH)

TMSI reallocation Cmd

MM(SDCCH)

TMSI reallocation Com

TMSI reallocation Com

Click on TMSI Rel ComFor more information


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Call Initiation (MT)MS BTS BSC MSC

Setup

SetupCM(SDCCH)

DR(Setup)

DI(Call Confirmed)

Call Confirmed

Call ConfirmedCM(SDCCH)

Click on Call ConfirmedFor more information


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Assignment of a Traffic Channel (MT)MS BTS BSC MSC

Assignment Req

DR(Ass Cmd)

DI(Ass Com)

RR(SDCCH) Assign Command

SABM

Ass Complete

Channel Activation

Ch Act Ack

UAEst Ind

RR(FACCH)Assign Complete

Rf Ch Rel Ack

Rf Ch Release

Click on Ass CompleteFor more information


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Call Confirmation and Call Accept (MT)MS BTS BSC MSC

AlertingCM(FACCH)

DI (Connect)

DI(Alerting)

Alerting

Connect Ack

Connect

DR(Connect Ack)

ConnectCM(FACCH)

Connect AckCM(FACCH)

Click on Connect AckFor more information


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Call Release MTMS BTS BSC MSC

DR(Release)

DI(Release Complete)

CM(FACCH) Release

Clear Complete

DI(Disconnect)Disconnect

Release

CM(FACCH) Release Complete

Release Complete

Clear CommandDR (Ch Release)

Deact SACCH

UA

Disc

Rel Ind

Rf Ch ReleaseRf Ch Rel Ack

DisconnectCM(FACCH)

Ch ReleaseRR(FACCH)

Click on Clear CompleteFor more information


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Signaling Diagram MT


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Mobile Originating (MO)


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Messages Overview Between MS and Network (MO)


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Signaling Diagram MO


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Timers for RR Connection Establishment & Service Request (ALOHA)

Above figure shows timers used at RR connection establishment on the MS and on the network side.


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gsm-call-flow

Technology

normal location

different types of location

reject luif location

connection oriented

new location area

illegal ms

mobile terminating calls

ciph mode comfor