GSM BSS GSM BSS Communication Flow Communication Flow www.huawei.com Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Oct 30, 2014
GSM BSSGSM BSS Communication FlowCommunication Flow
www.huawei.com
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.
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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
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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
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ContentsContents1. Location Update 1. Location Update
2. Call Setup
3. Handover
4. Direct Retry
5. Short Message
6 Release6. Release
7. Case Analysis
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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.
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Only NotesOnly Notes
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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
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Only NotesOnly Notes
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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.
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Authentication FlowAuthentication Flow
MS BTS BSC MSC
Authentication Request
Authentication Response
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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.
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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.
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ContentsContents1. Location Update1. Location Update
2. Call Setup
3. Handover
4. Direct Retry
5. Short Message
6 Release6. Release
7. Case Analysis
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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
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Only NotesOnly Notes
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Only NotesOnly Notes
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Call Setup Flow (MTC)Call Setup Flow (MTC)MS BTS BSC MSC
Channel req Channel Required
PagingPaging CMDPaging CMD_ q Channel_Required
Channel_ActiveChannel_Active_Ack
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
ASSIGNMENT COMMANDFirst SABM Establish_IND
Channel_ActiveChannel_Active_Ack
(NOTE 2) Assignment_Req
UA Assignment_CMPASSIGNMENT CMPAlertingConnect
Connect AckConversation
UA
DisconnectRelease
Release CompleteClear_CMDClear CMP
Conversation
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Clear_CMP
NOTE 1: Class Mark Update FlowNOTE 1: Class Mark Update Flow
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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 .
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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
CR(Complete_L3_information)CC
UA
CM Service AcceptedCC
SetupCall Processing
Mode Modify Assignment Req
Channel Mode Modify
Mode_ModifyMode_Modify_Ack
Assignment_Req
Assignment_CMPChannel Mode Modify ACKAlertingAlerting
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NOTE 2: Assignment MethodNOTE 2: Assignment MethodLate Assignment (MOC)
MS BTS BSC MSCChannel_req Channel_Required
Channel_ActiveChannel_Active_Ack
IMMEDIATE ASSIGN COMMANDIMMEDIATE ASSIGN COMMANDEstablish_IND(CM Service Req)First SABM
CM Service Accepted
CR(Complete_L3_information)CC
UA
SetupCall Processing
Channel_Active Assignment_Req Alerting
ASSIGNMENT COMMANDFirst SABM Establish_IND
Channel_Active_Ack
Assignment_CMPASSIGNMENT CMPConnect
UA
ConnectConnect Ack
Conversation
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NOTE 2: Assignment MethodNOTE 2: Assignment MethodLate Assignment (MTC)
MS BTS BSC MSC
Channel_req Channel_Required Channel_Active
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
CR(Complete_L3_information)CC
UA
CM Service AcceptedSetup
Call ConfirmedAlertingConnect
ASSIGNMENT COMMANDFirst SABM Establish_IND
Channel_ActiveChannel_Active_Ack
Assignment_Req
A i t CMPASSIGNMENT CMPUA Assignment_CMPASSIGNMENT CMPConnect AckConversation
UA
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Abnormal SituationAbnormal SituationMS BTS BSC MSC
Call Processing
Assignment ReqAssignment_Req
Assignment_Fail
Channel_Active_Ack
ASSIGNMENT COMMAND
ASSIGNMENT FAIL
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ContentsContents1. Location Update1. Location Update
2. Call Setup
3. Handover
4. Direct Retry
5. Short Message
6 Release6. Release
7. Case Analysis
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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)
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Only NotesOnly Notes
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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
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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.
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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)
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Only NotesOnly Notes
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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.
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ContentsContents1. Location Update1. Location Update
2. Call Setup
3. Handover
4. Direct Retry
5. Short Message
6 Release6. Release
7. Case Analysis
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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
SetupCall Processing
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
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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
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ContentsContents1. Location Update1. Location Update
2. Call Setup
3. Handover
4. Direct Retry
5. Short Message
6 Release6. Release
7. Case Analysis
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Short Message – MO on SDCCHMS BTS BSC MSCChannel_req Channel_Required
Channel_ActiveChannel_Active_Ack
IMMEDIATE ASSIGN COMMANDIMMEDIATE ASSIGN COMMAND
EST_IND(CM Service Req)First SABM
CR(Complete_L3_information)CC
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
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RLSD CMP
Short Message MT on SDCCHShort Message – MT on SDCCHMS BTS BSC MSC
Paging CMDPaging CMD F SC
Channel_req Channel_Required Channel_Active
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
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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
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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
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ContentsContents1. Location Update1. Location Update
2. Call Setup
3. Handover
4. Direct Retry
5. Short Message
6 Release6. Release
7. Case Analysis
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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
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Only NotesOnly Notes
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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
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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
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ContentsContents1. Location Update1. Location Update
2. Call Setup
3. Handover
4. Direct Retry
5. Short Message
6 Release6. Release
7. Case Analysis
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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.
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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.
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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).
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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
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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
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15-28 0 5 6
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