5.Oma310030 Gsm Bss Communication Flow Issue2

GSM BSSGSM BSS Communication FlowCommunication Flow

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Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.

ForewordForewordCourse Purpose:p

Understand the typical communication flow

Grasp the means of interface trace and trace reviewp

Grasp the method of analyzing communication flow to aid us

for fault handling.

How to learn this course:

With the help of stored tracing files, use tracing review function

in the maintenance console to study.

Attention:

It is strictly forbidden to use the interface tracing function when

the system is under heavy duty.

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Page1

MS-MSC Signaling StackMS-MSC Signaling Stack

MS

CM

MM

MS

CM

MM

MSCBSCBTS

MM

RR

L3

RRBSSMAP

MM

BSSMAP

LAPDmL2

RR BTSM

LAPDm LAPD LAPD

BTSM

SCCP

MTP

BSSMAP

SCCP

SigL1L1 SigL1 SigL1 SigL1 MTP MTP

Um接口 A接口Abis接口Um Abis A


BSSAP Functional StructureBSSAP Functional StructureBSSAP：BSS Application PartBSSAP：BSS Application Part

BSSMAP：BSS Management Application Part

DTAP：Direct Transfer Part

CM

MM

SCCP：Signaling Connection Control Part

BSSAP

SCCPg g

MTP：Message Transfer Part

SCCP

MTP-3

MTP-2

MTP-1


ContentsContents1. Location Update 1. Location Update

2. Call Setup

3. Handover

4. Direct Retry

5. Short Message

6 Release6. Release

7. Case Analysis


Location Update BasisLocation Update Basis

Purpose of location update:

T i f th t th LA i hi h th MS i To inform the system the LA in which the MS is

going to facilitate paging

When does the MS need to perform location update？

Getting into a new location area

Periodical location update timer expire.


Only NotesOnly Notes


Location Update FlowLocation Update FlowMS BTS BSC MSCS S BSC MSC

Channel_req Channel_Required

Channel_Active

Channel_Active_Ack

IMMEDIATE ASSIGN COMMAND

First SABM

Establish_IND(Location Updating Req) CR(Complete_L3_information)

CC

UA

Location Updating Accepted

TMSI Reallocation Complete

CC(NOTE 1)

(NOTE 2)

(NOTE 3)

Clear_CMD

Clear_CMP




NOTE 1: Authentication, Encryption, Identification

After establishing the SCCP connection between BSC and MSC there g

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.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. g p y

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.


Authentication FlowAuthentication Flow

MS BTS BSC MSC

Authentication Request

Authentication Response


NOTE 2NOTE 2

To reallocate TMSI or not during location update is To reallocate TMSI or not during location update is

decided in MSC side configuration.

If MSC chooses “Reallocate TMSI during location

update” to “No”, TMSI will not be refreshed during

location update.


Abnormal OccasionAbnormal OccasionBSC receives “Location Updating Rejected” message BSC receives Location Updating Rejected message

from MSC. The possible reasons are:

The CGI which has been configured in BSC side is not

configured in MSC side.

Communication failure between MSC and VLR.

The MS is not registered in HLR.


ContentsContents1. Location Update1. Location Update

2. Call Setup

3. Handover

4. Direct Retry

5. Short Message

6 Release6. Release

7. Case Analysis


Call Setup Flow (MOC)Call Setup Flow (MOC)MS BTS BSC MSC

Channel_req Channel_Required Channel_Active

Channel_Active_Ack IMMEDIATE ASSIGN COMMAND

Establish_IND(CM Service Req)First SABMCR(Complete L3 information)UA

CM Service Accepted

( p _ _ )CC

(NOTE 1)SetupCall Processing

Channel Active （NOTE 2) Assignment Req

UA

ASSIGNMENT COMMANDFirst SABM Establish_IND

Channel_ActiveChannel_Active_Ack

（NOTE 2) Assignment_Req

Assignment_CMPASSIGNMENT CMPUA g _AlertingConnect

Connect Ack

DisconnectConversation

DisconnectRelease

Release Complete

(NOTE 3)Clear_CMDClear_CMP






Call Setup Flow (MTC)Call Setup Flow (MTC)MS BTS BSC MSC

Channel req Channel Required

PagingPaging CMDPaging CMD_ q Channel_Required


IMMEDIATE ASSIGN COMMANDEstablish_IND(Paging RESP)First SABM

CR(Complete L3 information)

CM Service Accepted

CR(Complete_L3_information)CC

(NOTE 1)Setup

Call Confirmed

UA



(NOTE 2) Assignment_Req

UA Assignment_CMPASSIGNMENT CMPAlertingConnect

Connect AckConversation

UA

DisconnectRelease

Release CompleteClear_CMDClear CMP

Conversation


Clear_CMP

NOTE 1: Class Mark Update FlowNOTE 1: Class Mark Update Flow


NOTE 2: Assignment MethodNOTE 2: Assignment MethodVery Early AssignmentVery Early Assignment

In “IMMEDIATE ASSIGN COMMAND ” ,TCH is directly assigned. When

MSC sends “Assignment Req” message, BSC will not assign new MSC sends Assignment _Req message, BSC will not assign new

channel but perform “Mode_Modify” flow. After that, MS will report

“Assignment _CMP” message to MSC.

Early Assignment

MSC sends “Assignment Req” before “Alerting”.SC se ds ss g e t_ eq be o e e t g

Late Assignment

MSC sends “Assignment Req” after ”Alerting”MSC sends Assignment_Req after Alerting .


NOTE 2: Assignment MethodNOTE 2: Assignment MethodVery Early Assignment

MS BTS BSC MSCChannel_req Channel_Required

Channel_ActiveChannel Active AckChannel_Active_Ack

IMMEDIATE ASSIGN COMMAND (TCH)Establish_IND(CM Service Req)First SABM


UA

CM Service AcceptedCC

SetupCall Processing

Mode Modify Assignment Req

Channel Mode Modify

Mode_ModifyMode_Modify_Ack

Assignment_Req

Assignment_CMPChannel Mode Modify ACKAlertingAlerting


NOTE 2: Assignment MethodNOTE 2: Assignment MethodLate Assignment (MOC)

MS BTS BSC MSCChannel_req Channel_Required


IMMEDIATE ASSIGN COMMANDIMMEDIATE ASSIGN COMMANDEstablish_IND(CM Service Req)First SABM

CM Service Accepted


UA


Channel_Active Assignment_Req Alerting


Channel_Active_Ack

Assignment_CMPASSIGNMENT CMPConnect

UA

ConnectConnect Ack

Conversation


NOTE 2: Assignment MethodNOTE 2: Assignment MethodLate Assignment (MTC)

MS BTS BSC MSC


Ch l A ti A k

PagingPaging CMDPaging CMD

Channel_Active_Ack IMMEDIATE ASSIGN COMMAND

Establish_IND(Paging RESP)First SABM

CM Ser ice Accepted


UA

CM Service AcceptedSetup

Call ConfirmedAlertingConnect



Assignment_Req

A i t CMPASSIGNMENT CMPUA Assignment_CMPASSIGNMENT CMPConnect AckConversation

UA


Abnormal SituationAbnormal SituationMS BTS BSC MSC

Call Processing

Assignment ReqAssignment_Req

Assignment_Fail

Channel_Active_Ack

ASSIGNMENT COMMAND

ASSIGNMENT FAIL



2. Call Setup

3. Handover

4. Direct Retry

5. Short Message

6 Release6. Release

7. Case Analysis


Intra-BSC HandoverIntra-BSC HandoverMS BTS1 BSC BTS2 MS MSC

Channel_Active

Measure Report from MS

Channel_Active_Ack

HANDOVER COMMAND

Handover AccessHandover_Detect

PHYINFOPHYINFO

First SABM

(NOTE 1)

First SABM

Establish_IND

HANDOVER COMPLETEHandover Performed

UA

Handover_Performed

(NOTE 2)




NOTE1:Asynchronous/Synchronous HandoverNOTE1:Asynchronous/Synchronous Handover

Intra-BSC asynchronous handover:Intra BSC asynchronous handover:

cell1 and cell2 do not belong to the same BTS. Thus the

t t BTS h ll d PHY INFO target BTS shall send PHY INFO message.

Intra-BSC synchronous handover:

cell1 and cell2 belong to the same BTS. Actually they are

two cells of one BTS. In such occasion there will not be PHY

INFO message, After “Handover Access” message, MS will

send SABM directly.y


Abnormal OccasionAbnormal OccasionIn case of intra-BSC asynchronous handover when In case of intra BSC asynchronous handover, when

BTS1 has sent PHY INFO message to the maximum

time but the MS still can’t access the new channel time but the MS still can’t access the new channel,

BTS1 will send CONN FAIL IND message. Its causing

value is “handover access failure”. When BSC receives

this message, it will start local-end release flow to

release the new channel in BTS1.


Inter-BSC HandoverInter-BSC HandoverMS BTS1 BSC1 BTS2 MSMSC BSC2BTS1 BSC1 MSC

Measure Report from MS

BSC2(NOTE 1)

Handover Required Handover Request_ q Handover_RequestChannel_Active

Channel_Active_AckHandover_Request_Ack

Handover_CMDHANDOVER COMMAND Handover AccessHandover_Detect

Handover_Detect

HANDOVER COMMAND Handover Access

PHY INFO

PHY INFOFirst SABM

Establish_INO

HANDOVER COMPLETEHandover_CmpClear CMD

UA

_Clear_CMP(NOTE 2)




NOTE1: Two Different Handover Occasions of Inter-BSC Handover

Intra-MSC inter-BSC Handover:Intra MSC inter BSC Handover:

Two BSCs belong to the same MSC.

Inter-MSC Handover:

Two BSCs do not belong to the same MSC.g

The A-interface messages are the same for the two

occasions aboveoccasions above.



2. Call Setup

3. Handover

4. Direct Retry

5. Short Message

6 Release6. Release

7. Case Analysis


Direct Retry Intra-BSCDirect Retry – Intra-BSCMS BTS1 BSC MSC

Channel_req Channel_Required BTS2 MS

Channel_ActiveChannel_Act_Ack

IMMEDIATE ASSIGN CMDFirst SABM

Est_INDFirst SABM

CM Service Accepted

CR(CMP_L3_info)CC

UA


Channel Active

Assignment_Req

Handover CMD

PHY INFO

E t bli h IND

Channel_ActiveChannel_Active_Ack Handover AccessHandover Detect

First SABMEstablish_IND

Assignment_CMPHandover CMP


Direct Retry Inter-BSCDirect Retry – Inter-BSCMS BTS1 BSC1 MSC BSC2 BTS2 MS

CM Service AcceptedSetup

C ll P iCall Processing

Channel_Active

Assignment_Req

Handover RQD Handover REQ

Handover CMD

PHY INFO

Channel_Act_Ack

Handover Access

Handover REQ AckHandover CMD

Handover DetectHandover Detect

Handover CMP

First SABMEST_IND

Handover CMPClear CMD

Clear CMP



2. Call Setup

3. Handover

4. Direct Retry

5. Short Message

6 Release6. Release

7. Case Analysis


Short Message – MO on SDCCHMS BTS BSC MSCChannel_req Channel_Required


IMMEDIATE ASSIGN COMMANDIMMEDIATE ASSIGN COMMAND

EST_IND(CM Service Req)First SABM


UA

First SABM(SAPI 3)

CP DATACP ACK

First SABM(SAPI 3)UA EST_IND(SAPI 3)

From SC (Service Centre )CP DATA

To SC (Service Centre )

Disconnect

Release Complete Release

From SC (Service Centre )CP ACK

Clear CMDChannel Release

Disconnect

Deactive SACCH R l INDRelease IND

RF Channel REL RF Channel REL ACK Clear CMP

RLSD


RLSD CMP

Short Message MT on SDCCHShort Message – MT on SDCCHMS BTS BSC MSC

Paging CMDPaging CMD F SC


Channel_Active_Ack

Paging CMDPaging CMD From SC

IMMEDIATE ASSIGN COMMAND

EST_IND (Paging Response)First SABM

CR(Complete_L3_infor)CC

UA

CP DATA

First SABMUA

EST_REQ(SAPI 3)

EST_CNF(SAPI 3)

CP DATA

CP ACK

Disconnect

To SCCP DATACP ACK

Release Complete Release

Clear CMDClear CMP


Clear CMP

Short Message MO on SACCHShort Message – MO on SACCHMS BTS BSC MSCMS BTS BSC MSC

ACTIVE CALL

CM S i REQ (FACCH)

First SABM(SAPI 3)

CM Service ACC (FACCH)

CM Service REQ (FACCH)

CP DATA

CP ACK

First SABM(SAPI 3)UA EST_IND(SAPI 3)

To SCCP ACK

CP DATA

CP ACKFrom SC

ACTIVE CALL


Short Message MT on SACCHShort Message – MT on SACCHMS BTS BSC MSC

ACTIVE CALL

First SABM(SAPI 3)UA

EST_IND(SAPI 3) CP DATA

EST_CNF(SAPI 3)

From SC

CP DATA

CP ACK

CP DATACP DATA

CP ACKTo SC

ACTIVE CALL



2. Call Setup

3. Handover

4. Direct Retry

5. Short Message

6 Release6. Release

7. Case Analysis


BSC Normal Release FlowBSC Normal Release Flow

MS BTS BSC MSCMS BTS BSC MSC

(NOTE 1) Disconnect

Release

Release Complete

Clear CMDCHANNEL RELEASE

Clear_CMD

First DISCDeactive_SACCH

Release IND

Clear_CMP

_

RF_Release_ReqRF_Release_Req_ACK

UA

RLSDRLSD

RLSD CMP




NOTE1：Two Occasions of ReleaseNOTE1：Two Occasions of Release

NSS originating release NSS originating release

MS originating release

In these two different occasions all the messages are the

same except the direction of the first 3 messages.p g


Local-end Release FlowLocal-end Release FlowMS BTS BSC MSCMS BTS BSC MSC

Deactive_SACCH

Release_Confirm

RF R l R

Release_Req(LOCAL END) (NOTE 1)

RF_Release_Req

RF_Release_Req_ACK



2. Call Setup

3. Handover

4. Direct Retry

5. Short Message

6 Release6. Release

7. Case Analysis


Case DescriptionCase DescriptionBSC’s ASSIGNMENT CMD message has been sent but the BSC s ASSIGNMENT CMD message has been sent but the

BTS sends several EST IND messages. Later MS sends

ASSIGNMENT FAIL message and the causing value is ASSIGNMENT FAIL message and the causing value is

Protocol error unspecified.


Case AnalysisCase AnalysisBy analyzing the messages we can find that MS has By analyzing the messages we can find that MS has

reported several EST IND messages before ASSIGNMENT

FAIL messageFAIL message.

When BTS receives a SABM frame it will report an EST

IND message to BSC. So we know now that the MS must

have sent many SABM frames to the BTS.

BTS can decode the SABM frame sent by MS but MS

cannot decode the UA frame sent by BTS And this causes cannot decode the UA frame sent by BTS. And this causes

that the BTS reports many EST IND messages.


Case AnalysisCase AnalysisCase realize:

In the lab we can simulate. Disconnect the TX antenna to make the

downlink signal pure. Trace the A-bis signaling we can find that

BTS sends several EST IND messages to BSC for the newly assigned BTS sends several EST IND messages to BSC for the newly assigned

TCH but can’t succeed. And then MS sends ASSIGNMENT FAIL via

the previous SDCCH and the causing value is “Protocol error

Conclusion:

p g

unspecified”.

Conclusion:

In the practical field, when many ASSIGNMENT FAIL messages appear, the main reason might be the pure messages appear, the main reason might be the pure downlink receiving power level or receiving quality.

Connection between TRX and SCU (CDU).


Appendix: Power ClassAppendix: Power ClassPhase 2 MS output Power Class and the exact power Phase 2 MS output Power Class and the exact power

relations.

power class

GSM900 Max peak power

DCS1800 Max peak power

Tolerance(dB)_normal

Tolerance(dB)_extreme

1 ------ 1W(30dBm) +/-2 +/-2.5

2 0.25W(24dBm) 2 2.5( )

3 5W(37dBm) 4W(36dBm) 2 2.5

4 2W(33dBm) 2 2 54 2W(33dBm) 2 2.5

5 0.8W(29dBm) 2 2.5


Power Control LevelPower Control Levelpower control

output power

Tolerance_normal

Tolerance _extreme

Power control

output power

Tolerance_normal

Tolerance _extreme

Phase 2 MS

Power control

level (dBm) (dB) (dB) level (dBm) (dB) (dB)0-2 39 2 2.5 29 36 2 2.53 37 3 4 30 34 3 44 35 3 4 31 32 3 4

level and the

exact power

5 33 3 4 0 30 3 46 31 3 4 1 28 3 47 29 3 4 2 26 3 48 27 3 4 3 24 3 4

relations.8 3 3 39 25 3 4 4 22 3 410 23 3 4 5 20 3 411 21 3 4 6 18 3 412 19 3 4 7 16 3 412 19 3 4 7 16 3 413 17 3 4 8 14 3 414 15 3 4 9 12 4 515 13 3 4 10 10 4 516 11 5 6 11 8 4 516 11 5 6 11 8 4 517 9 5 6 12 6 4 518 7 5 6 13 4 4 5

19-31 5 5 6 14 2 5 6


15-28 0 5 6

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5.Oma310030 Gsm Bss Communication Flow Issue2