microsoft power point - 10 omf001003 gsm bss communication flow issue2

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Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

GSM BSS Communication Flow


Foreword

� Course Purpose:

� Grasp the means of interface trace and the method of analyzing it to

aid us for fault handling.

� How to learn this course:

� Copy the interface trace result files.

� Use the maintenance console’s interface trace review function to

study,

� Attention:

� It is strictly forbidden to use the interface tracing function when the

system is busy or the system is under heavy duty.


MS-MSC Signaling Stack

CM

MM

RR

LAPDm

Si gL1

L3

L2

L1

MS

RR BTSM

LAPDm

Si gL1

LAPD

Si gL1

LAPD

Si gL1

BTSM

RR

SCCPMTP

BSSMAP

CM

MM

BSSMAP

SCCPMTP

MSCBSCBTS

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BSSAP Functional Structure

� BSSAP：BSS Application Part

� BSSMAP：BSS Management Application Part

� DTAP：Direct Transfer Part

� CM

� MM

� SCCP：Signaling Connection Control Part

� MTP：Message Transfer Part

MTP-1

MTP-2

MTP-3

SCCP

BSSAP


Contents

1. Location Update Flow

2. Call Setup (Originating)

3. Intra-BSC Handover

4. Inter-BSC Handover

5. BSC Normal Release

6. BSC Local-end Release

7. Case Analysis


Location Update Flow

� Purpose of location update:

� To inform the system the LA in which the MS is to

facilitate paging

� When need the MS perform location update？

� Getting into a new LA

� Periodical location update


Location Update Flow

� SABM: Set asynchronous balanced

mode command——initial access frame

� UA: Unnumbered acknowledgement

response

MS BTS BSC MSC

Channel_req Channel_Required

Channel_Active

Channel_Active_Ack

IMMEDIATE ASSIGN COMMAND

Establish_IND(Location Updating Req)

CR(Complete_L3_information)

Location Updating Accepted

TMSI Reallocation Complete(NOTE 2)

CC

(NOTE 1)

(NOTE 3) Clear_CMD

Clear_CMP

First SABM

UA


NOTE 1: Authentication, Encryption, Identity

� After establishing the SCCP connection between BSC and MSC there

might be authentication and encryption in an intact location update flow.

� For Huawei MSC, authentication and encryption are all optional. And normally

authentication is mandatory and encryption is optional in practical situation.

� Huawei BSS system supports encryption algorithm A5/1 and A5/2.

� Identification: The ID in Est_IND message reported by the MS is TMSI.

When VLR cannot identify the TMSI or TMSI authentication fails, MSC

will start Identification flow. That means MSC will send transparent

transfer message “Identity Request” to MS and MS will report “Identity

Response” message which involves IMSI.


NOTE 2

� To reallocate TMSI or not during location update is

optional in MSC.

� If MSC chooses “Reallocate TMSI during location update”

to “No”, MS will not report “TMSI Reallocation Complete”

message.


NOTE3

� In this flow we have simplified the release flow. To know

more detailed refer to the BSC Normal Release Flow.


Abnormal Occasion

� BSC receives “Location Updating Rejected” message

from MSC. The possible reason is listed below:

� MSC has not configured the CGI which has been

configured in BSC.

� Communication failed between MSC and VLR.

� MS has not been registered in HLR.