Microsoft Power Point - 10 OMF001003 GSM BSS Communication Flow ISSUE2
Transcript of 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
Page2Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page3Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Um½Ó¿ Ú A½Ó¿ ÚAbi s½Ó¿ ÚUm Abis A
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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
Page5Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page6Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
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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
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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.
Page9Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page10Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
NOTE3
� In this flow we have simplified the release flow. To know
more detailed refer to the BSC Normal Release Flow.
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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.
Page12Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page13Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Call Setup Flow (Originating)MS BTS BSC MSC
Channel_req Channel_RequiredChannel_Active
Channel_Active_AckIMMEDIATE 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(NOTE 3)
DisconnectRelease
Release Complete
(NOTE 4)Clear_CMDClear_CMP
Conversation
UA
UA
Page14Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
NOTE 1: Class Mark Update Flow
1. Authentication, encrytion, identification are optional. See Note 1 in Location Update Flow.
2. Class mark update flow:
For dual-band MS, after the SCCP connection is established and before receiving message "CM Service Accepted" there will be a class mark update flow.
CR message reports the information of class mark 2. And in the class mark update flow, MS will report class mark 3 information which is related to the dual-band capabilty.
Page15Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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 Assignment
MSC sends “Assignment_Req” before “Alerting”.
� Late Assignment
MSC sends “Assignment_Req” after ”Alerting”.Very Early Assignment
Page16Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Abnormal Situation
� Abnormal Occasion 1: MSC has sent “Assignment_Req”
and BSC does not send “ASSIGNMENT CMD” but sends a
“Assignment_Fail” message. Possible reasons:
� A. BSC has not available TCH.
� B. The CIC assigned by the MSC is not idle in BSC.
� Abnormal Occasion2: BSC has sent “ASSIGNMENT CMD
message but MS sends “ASSIGNMENT FAIL”. Possible
reason:
� Downlink bit error rate is too high.
Page17Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page18Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Intra-BSC HandoverMS BTS1 BSC BTS2 MS MSC
Channel_Active
Channel_Active_Ack
Measure Report from MS
HANDOVER COMMAND
Handover AccessHandover_Detect
PHYINFOPHYINFO
First SABM
Establish_IND
HANDOVER COMPLETE
Handover_Performed
(NOTE 2)
(NOTE 1)
UA
Page19Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
NOTE1:Asynchronous Handover and Synchronous Handover
� Intra-BSC asynchronous handover:
� BTS1 and BTS2 do not belong to the same BTS. Thus the
target BTS shall send PHY INFO message.
� Intra-BSC synchronous handover:
� BTS1 and BTS2 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.
Page20Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
NOTE2
� After reporting “Handover_Performed” message to MSC,
BSC will start the local-end release flow for the previous
channel (in BTS 2).
Page21Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page22Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page23Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Inter-BSC Handover
MS 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 SABM
Establish_INO
HANDOVER COMPLETEHandover_Cmp
Clear_CMD
Clear_CMP(NOTE 2)
UA
Page24Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page25Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
NOTE2
� When BSC1 receives Clear_CMD message from MSC, it
will start local-end release flow for the previously occupied
channel in BTS1.
Page26Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page27Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
BSC Normal Release Flow
MS BTS BSC MSC
(NOTE 1) Disconnect
Release
Release Complete
CHANNEL RELEASE
Clear_CMD
Clear_CMP
First DISC
Deactive_SACCH
Release_IND
RF_Release_Req
RF_Release_Req_ACK
UA
Page28Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page29Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page30Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Local-end Release Flow
MS BTS BSC MSC
Deactive_SACCH
Release_Confirm
RF_Release_Req
RF_Release_Req_ACK
Release_Req(LOCAL END) (NOTE 1)
Page31Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page32Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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.
Page33Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Case Analysis
� By analyzing the messages we can find that MS has
reported several EST IND messages before ASSIGNMENT
FAIL 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
that the BTS reports many EST IND messages.
Page34Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
Case Analysis
� Conclusion:
� In the practical field, when many ASSIGNMENT FAIL messages appear, the main reason might be the pure downlink receiving power level or receiving quality.
� Connection between TRX and SCU (CDU).
� 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”.
Page35Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
Page36Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
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
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