GSM BSS Communication Flow.ppt
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Transcript of GSM BSS Communication Flow.ppt
www.huawei.com
Copyright © 2015 Huawei Technologies Co., Ltd. All rights reserved.
英文标题 :40-47pt
副标题 :26-30pt
字体颜色 : 反白内部使用字体 :
FrutigerNext LT Medium
外部使用字体 : Arial
中文标题 :35-47pt
字体 : 黑体 副标题 :24-28pt
字体颜色 : 反白字体 : 细黑体
GSM BSS Communication Flow
Page2
Foreword• Course Purpose:
– Understand the typical communication flow– Grasp the means of interface trace and trace review– 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 traffic.
Page3
MS-MSC Signaling Stack
CM
MM
RR
LAPDm
SigL1
L3
L2
L1
MS
RR BTSM
LAPDm
SigL1
LAPD
SigL1
LAPD
SigL1
BTSM
RR
SCCPMTP
BSSMAP
CM
MM
BSSMAP
SCCPMTP
MSCBSCBTS
Um接口 A接口Abis接口Um Abis A
Page4
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
BSSAP
SCCP
MTP-3
MTP-2
MTP-1
Page5
Contents1. Location Update 2. Call Setup 3. Handover 4. Direct Retry 5. Short Message6. Release7. Case Analysis
Page6
Location Update Basis
• Purpose of location update:– 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.
Page8
Location Update FlowMS 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
CC
(NOTE 1)
(NOTE 3)
Clear_CMD
Clear_CMP
First SABM
UA
(NOTE 2)
Page10
NOTE 1: Authentication, Encryption, Identification
• 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.
Page11
Authentication Flow
MS BTS BSC MSC
Authentication Request
Authentication Response
Page12
NOTE 2
• 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.
Page13
Abnormal Occasion• 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.(wrong CGI)– Communication failure between MSC and VLR.– The MS is not registered in HLR.
Page14
Contents1. Location Update 2. Call Setup 3. Handover 4. Direct Retry 5. Short Message6. Release7. Case Analysis
Page15
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 SABM
CM Service Accepted
CR(Complete_L3_information)CC
(NOTE 1)SetupCall Processing
ASSIGNMENT COMMANDFirst SABM Establish_IND
Channel_ActiveChannel_Active_Ack
( NOTE 2) Assignment_Req
Assignment_CMPASSIGNMENT CMPAlertingConnect
Connect Ack
DisconnectRelease
Release Complete
(NOTE 3)Clear_CMDClear_CMP
Conversation
UA
UA
Page18
Call Setup Flow (MTC)MS BTS BSC MSC
Channel_req Channel_Required Channel_Active
Channel_Active_Ack IMMEDIATE ASSIGN COMMAND
Establish_IND(Paging RESP)First SABM
CM Service Accepted
CR(Complete_L3_information)CC
(NOTE 1)
SetupCall Confirmed
ASSIGNMENT COMMANDFirst SABM Establish_IND
Channel_ActiveChannel_Active_Ack
(NOTE 2) Assignment_Req
Assignment_CMPASSIGNMENT CMPAlertingConnect
Connect Ack
DisconnectRelease
Release CompleteClear_CMDClear_CMP
Conversation
UA
UA
PagingPaging CMDPaging CMD
Page19
NOTE 1: Class Mark Update Flow
Page20
NOTE 2: Assignment Method• Very Early Assignment
In “IMMEDIATE ASSIGN COMMAND ” ,TCH is directly assigned. When 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 AssignmentMSC sends “Assignment_Req” before “Alerting”.
• Late AssignmentMSC sends “Assignment_Req” after ”Alerting”.
Page21
NOTE 2: Assignment Method• Very Early Assignment
MS BTS BSC MSCChannel_req Channel_Required
Channel_Active
Channel_Active_Ack IMMEDIATE ASSIGN COMMAND (TCH)
Establish_IND(CM Service Req)First SABM
CM Service Accepted
CR(Complete_L3_information)
CC
Setup
Call Processing
Channel Mode Modify
Mode_Modify
Mode_Modify_Ack
Assignment_Req
Assignment_CMPChannel Mode Modify ACKAlerting
UA
Page22
NOTE 2: Assignment Method• Late Assignment (MOC)
MS BTS BSC MSCChannel_req Channel_Required
Channel_ActiveChannel_Active_Ack
IMMEDIATE ASSIGN COMMANDEstablish_IND(CM Service Req)First SABM
CM Service Accepted
CR(Complete_L3_information)CC
SetupCall Processing
ASSIGNMENT COMMANDFirst SABM Establish_IND
Channel_ActiveChannel_Active_Ack
Assignment_Req
Assignment_CMPASSIGNMENT CMP
Alerting
ConnectConnect Ack
Conversation
UA
UA
Page23
NOTE 2: Assignment Method• Late Assignment (MTC)
MS BTS BSC MSC
Channel_req Channel_Required Channel_Active
Channel_Active_Ack IMMEDIATE ASSIGN COMMAND
Establish_IND(Paging RESP)First SABM
CM Service Accepted
CR(Complete_L3_information)CC
SetupCall Confirmed
ASSIGNMENT COMMANDFirst SABM Establish_IND
Channel_ActiveChannel_Active_Ack
Assignment_Req
Assignment_CMPASSIGNMENT CMP
AlertingConnect
Connect AckConversation
UA
UA
PagingPaging CMDPaging CMD
Page24
Abnormal SituationMS BTS BSC MSC
Call Processing
Assignment_Req
Assignment_Fail
ASSIGNMENT COMMAND
Channel_Active_Ack
ASSIGNMENT FAIL
Page25
Contents1. Location Update 2. Call Setup 3. Handover 4. Direct Retry 5. Short Message6. Release7. Case Analysis
Page26
Intra-BSC HandoverMS BTS1 BSC BTS2 MS MSC
Channel_Active
Channel_Active_Ack
Measure Report from MS
HANDOVER COMMAND
Handover AccessHandover_Detect
PHYINFO
PHYINFO
First SABM
Establish_IND
HANDOVER COMPLETEHandover_Performed
(NOTE 2)
(NOTE 1)
UA
Page28
NOTE1:Asynchronous/Synchronous Handover
• Intra-BSC asynchronous handover:– cell1 and cell2 do not belong to the same BTS.
Thus the 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.
Page29
Abnormal Occasion• 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, 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.
Page30
Inter-BSC HandoverMS BTS1 BSC1 BTS2 MSMSC
Measure Report from MS
BSC2
(NOTE 1)
Handover_Required Handover_RequestChannel_Active
Channel_Active_AckHandover_Request_Ack
Handover_CMD
Handover_Detect
Handover_Detect
HANDOVER COMMAND Handover Access
PHY INFO
PHY INFO
First SABMEstablish_IND
HANDOVER COMPLETEHandover_CmpClear_CMD
Clear_CMP(NOTE 2)
UA
Page32
NOTE1: Two Different Handover Occasions of 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.– The A-interface messages are the same for
the two occasions above.
Page33
Contents1. Location Update 2. Call Setup 3. Handover 4. Direct Retry 5. Short Message6. Release7. Case Analysis
Page34
Direct Retry – Intra-BSCMS BTS1 BSC MSC
Channel_req Channel_Required
Channel_Active
Channel_Act_Ack
IMMEDIATE ASSIGN CMD
Est_IND
First SABM
CM Service Accepted
CR(CMP_L3_info)
CC
Setup
Call Processing
Handover CMD
PHY INFO
Establish_IND
Channel_Active
Channel_Active_Ack
Assignment_Req
Assignment_CMP
Handover CMP
UA
BTS2 MS
Handover AccessHandover Detect
First SABM
UA
Page35
Direct Retry – Inter-BSCMS BTS1 BSC1 MSC
CM Service Accepted
Setup
Call Processing
Handover CMD
PHY INFO
Channel_Active
Channel_Act_Ack
Assignment_Req
Handover RQD
Handover CMP
BSC2 BTS2
Handover Access
First SABM
MS
Clear CMP
Handover REQ
Handover REQ AckHandover CMD
Handover DetectHandover Detect
EST_IND
Handover CMPClear CMD
UA
Page36
Contents1. Location Update 2. Call Setup 3. Handover 4. Direct Retry 5. Short Message6. Release7. Case Analysis
Page37
Short Message – MO on SDCCHMS BTS BSC MSCChannel_req Channel_Required
Channel_Active
Channel_Active_Ack IMMEDIATE ASSIGN COMMAND
EST_IND(CM Service Req)
First SABM
CP DATA
CR(Complete_L3_information)CC
CP ACK
Disconnect
Release Complete
UA
First SABM(SAPI 3)UA EST_IND(SAPI 3)
Release
Clear CMDChannel Release
Disconnect
From SC (Service Centre )
Deactive SACCH Release IND
RF Channel REL RF Channel REL ACK Clear CMP
RLSDRLSD CMP
CP DATACP ACK
To SC (Service Centre )
Page38
Short Message – MT on SDCCHMS BTS BSC MSC
Channel_req Channel_Required
Channel_ActiveChannel_Active_Ack
IMMEDIATE ASSIGN COMMAND
EST_IND (Paging Response)
First SABM
CP DATA
CR(Complete_L3_infor)CC
CP ACK
Disconnect
Release Complete
UA
First SABMUA
EST_REQ(SAPI 3)
Release
Clear CMD
Paging CMDPaging CMD
EST_CNF(SAPI 3)
Clear CMP
CP DATA
From SC
To SCCP DATACP ACK
Page39
Short Message – MO on SACCHMS BTS BSC MSC
ACTIVE CALL
CP DATA
CP ACK
First SABM(SAPI 3)UA EST_IND(SAPI 3)
CM Service ACC (FACCH)
CM Service REQ (FACCH)
CP DATA
CP ACK
From SC
To SC
ACTIVE CALL
Page40
Short Message – MT on SACCHMS BTS BSC MSC
ACTIVE CALL
CP DATA
CP ACK
First SABM(SAPI 3)UA
EST_IND(SAPI 3) CP DATA
CP DATA
CP ACK
EST_CNF(SAPI 3)
From SC
To SC
ACTIVE CALL
Page41
Contents1. Location Update 2. Call Setup 3. Handover 4. Direct Retry 5. Short Message6. Call Release7. Case Analysis
Page42
BSC Normal Release FlowMS BTS BSC MSC
(NOTE 1) Disconnect
Release
Release Complete
CHANNEL RELEASEClear_CMD
Clear_CMP
First DISC Deactive_SACCH
Release_IND
RF_Release_Req
RF_Release_Req_ACK
UA
RLSD
RLSD CMP
Page44
NOTE1 : Two Occasions of 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.
Page45
Local-end Release FlowMS BTS BSC MSC
Deactive_SACCH
Release_Confirm
RF_Release_Req
RF_Release_Req_ACK
Release_Req(LOCAL END) (NOTE 1)
Page46
Contents1. Location Update 2. Call Setup 3. Handover 4. Direct Retry 5. Short Message6. Release7. Case Analysis
Page47
Case Description
• 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 Protocol error unspecified.
Page48
Case Analysis• By analyzing the messages we can find that MS has
reported several EST IND messages before ASSIGNMENT FAIL message.
• When BTS receives an 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 caused the BTS to report many EST IND messages.
Page49
Case Analysis
• Conclusion:
– In the practical field, when many ASSIGNMENT FAIL messages appear, the main reason might be the poor downlink receiving power level or receiving quality.
– Connection between TRX and (CDU).(ie duplexer in case of BTS30X….series)
Case 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 TCH but can’t succeed. And
then MS sends ASSIGNMENT FAIL via the previous SDCCH and the causing
value is “Protocol error unspecified”.
Page50
Appendix: Power Class• 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 2.5
5 0.8W(29dBm) 2 2.5
Page51
Power Control Level
Phase 2 MS Power control level and the exact power relations.
power control level
output power (dBm)
Tolerance_normal
(dB)
Tolerance _extreme
(dB)
Power control level
output power (dBm)
Tolerance_normal
(dB)
Tolerance _extreme
(dB)
0-2 39 2 2.5 29 36 2 2.5
3 37 3 4 30 34 3 4
4 35 3 4 31 32 3 4
5 33 3 4 0 30 3 4
6 31 3 4 1 28 3 4
7 29 3 4 2 26 3 4
8 27 3 4 3 24 3 4
9 25 3 4 4 22 3 4
10 23 3 4 5 20 3 4
11 21 3 4 6 18 3 4
12 19 3 4 7 16 3 4
13 17 3 4 8 14 3 4
14 15 3 4 9 12 4 5
15 13 3 4 10 10 4 5
16 11 5 6 11 8 4 5
17 9 5 6 12 6 4 5
18 7 5 6 13 4 4 5
19-31 5 5 6 14 2 5 6
15-28 0 5 6