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  • 注:关键计数器统计点如下—— 1 、 BSC 向目标 BTS 发送“ Channel-Activation” 之前,统计“ BSC 内入小区切换请求次数”和“ BSC 内出小区切换请求次数”。 2 、 BSC 向 MS 发送“ HO-Command” 之后,统计“ BSC 内入小区切换次数”和“ BSC 内出小区切换次数”。 3 、 BSC 收到 MS 发来的“ HO-Complete” 之后,统计“ BSC 内入小区切换成功次数”和“ BSC 内出小区切换成功次数”。
  • Difference between "Internal inter cell handover success rate " and "Cell radio handover success rate " : As viewed from formulas, both numerators are success times of handover, while the denominators are different. While viewed from the measurement points of the counter, Attempted inter cell handovers >= inter cell handovers, so intra BSC handover success rate <= cell radio handover success rate. In practice: If "Internal inter cell handover success rate "="cell radio handover success rate ", this indicates that there is no problem with data, the unsuccessful handovers are caused by radio interfaces, and the radio reasons like interference and coverage should be checked in the first place. If "Internal inter cell handover success rate " < "cell radio handover success rate", this indicates that failures may exist in the process from “Channel_Activate” to "HO-COMD", and there might be data problem or congestion.
  • The key measurement points are as follows, same as those of intra BSC handover: After sending "HO-REQUIRED", the original BSC measures "Attempted outgoing inter BSC inter cell handovers". After receiving "HO-REQUEST", the target BSC measures "Attempted incoming inter BSC handovers". After sending "HO-REQUEST ACK", the target BSC measures "incoming inter BSC handovers". After receiving "HO-Command" , the original BSC measures "outgoing inter BSC handovers". After receiving "HO-Complete", the target BSC measures "Successful incoming inter BSC handover" After receiving "Clear-COM" and the cause value is "HO-Successful", the original BSC measures "Successful outgoing inter BSC inter cell handover". The difference between "handover times" and "handover request times": Handover times - After "HO-COM" is received or "HO-REQ-ACK" is sent Handover request times - After "HO-REQUIRED" is sent or "HO-REQUEST" is received Therefore, inter BSC inter cell radio handover success rate >= inter BSC inter cell handover success rate.
  • Note: Signaling flow of A interface and Abis interface of inter MSC handover is the same as that of intra MSC handover, only the signaling between two MSC is particular for the inter-MSC handover. As shown in above figure the signaling with "MAP" is of the MAP layer, and signaling of A and Abis interfaces are omitted. After receiving "HO-REQUIRED" of BSC-A (the request message includes CGI of the original cell and target cell), if MSC-A finds that LAC of the target cell doesn’t belong to this MSC, MSC-A will query the "REMOT LAC Table“ (including the LAC and route of the adjacent MSC), and send "Prepare-HO" message to MSC-B according to the route. CGI of the target cell and the indicator of whether to allocate the handover number are included in this Prepare-HO message. According to the received "Prepare-HO" message, if the handover number needs allocating, MSC-B will request the local VLR to allocate the handover number. If VLR has the free handover number, the handover number will be sent to MSC-B through "Send-HO-Report". If no handover number is needed, proceed to the next step. After SCCP link between MSC-B and BSC-B is established, MSC-B sends "HO-REQUEST" to BSC-B. After that, BSC-B activates the target cell’s channel, and returns "HO-REQUEST ACK" to MSC-B after receiving the channel activation acknowledgement. According to this message, MSC-B sends "Prepare-HO ACK" to MSC-A. MSC-A establishes the route to MSC-B according to the handover number, and sends "Initialize-Address" (IAI) to MSC-B to help the latter to identify which voice channel is reserved for MS. While MSC-B returns "Address-Complete" (ACM) to MSC-A.
  • Frequent handover: Handover in GSM is hard handover, it is meaning, before handover to the new channel, MS must release the original channel firstly. So frequent handover will result in word-loss in handover and break-make of conversation, thus affecting the conversation quality.
  • In isolated cell coverage area, when MS moves towards the cell edge, the signal becomes weaker and weaker, and since there is no adjacent cell available around, handover cannot be triggered, thus call drop will occur.
  • For BTS clock, BSC clock, and MSC clock, the following standards are used to judge whether they are out of synchronization: MSC: △f/f (frequency deviation) ≤ 1E-8 BSC/BTS: △f/f (frequency deviation) ≤5E-8 Inaccurate clock will cause that MS cannot decode BSIC of the adjacent cell correctly.
  • For service cell: Outgoing inter cell handover will fail. For illusory target cell: Incoming inter-cell handover will fail, and successful rate of handover = successful rate of radio handover. Notes: CI can not configure as "FFFF". "Transmitting BS/MS Power Level": If the measurement report preprocess is enabled, this parameter must be set to "Yes".
  • The cause value of the handover failure message: Invalid message content.
  • "Address Indicator" differs from the normal "HO-REQUEST".
  • Signaling tracing is very helpful if there are problems in cooperation with other manufacturers’ equipment.
  • After BSC-HW sends "HO-REQUIRED" to MSC-HW, MSC-HW sends "Prepare-HO" to the peer, however MSC-B directly returns abort message, causing that BSC-HW receives "HO-Reject" from MSC-HW. The handover fails.
  • Failure signaling: MSC receives "HO-REQUEST-ACK" sent by Huawei BSC, and sends "HO-COMD" to N vender BSC. While MS doesn’t perform "HO-ACCESS", so Huawei BSC do not send "HO-Detect" to MSC, and MSC sends "Clear" command to N vender BSC, with the reason "Radio interface error, return to the original channel".
  • Transcript

    • 1. Internal OMF000401Case Analysis -- Handover ISSUE 2.0 www.huawei.comHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved
    • 2. References 31160978-BSC Traffic Statistic Manual Volume I 31033203-BSS Troubleshooting Manual HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 2
    • 3. Upon completion of this course, you are supposed to be able to:  Understand the principles of handover  Analyze and solve handover problemsHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 3
    • 4. Chapter 1 Measurement Points of Handover Chapter 2 Handover Data Process Chapter 3 Analysis of Handover Problem Chapter 4 Handover CasesHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 4
    • 5. Measurement Points of Intra BSC HandoverMS BTS(Source) BSC BTS(Target) MSC Measurement Report Measurement Report Attempted internal inter cell H.O Handover decision Channel Activation Channel Activation ACK Internal inter cell H.O Handover Command (Old FACCH) Handover Access (New FACCH) Handover Complete (New FACCH) Successful internal inter cell H.O RF Channel Release Handover PerformedHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 5
    • 6. Measurement Points of Intra BSC Handover  Handover formula definition  Inter cell radio handover success rate  =(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Incoming internal inter cell handovers + Outgoing internal inter cell handovers )  Internal inter cell handover success rate  =(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Attempted incoming internal inter cell handovers + Attempted outgoing internal inter cell handovers)  Inter cell radio handover success rate >= Internal inter cell handover success rateHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 6
    • 7. Measurement Points of Inter-BSC Handover MS BTS(Source) BSC MSC BSC BTS(Target) Attempted outgoing inter BSC inter cell H.O Measurement Report Attempted incoming inter BSC inter cell H.O Handover Required Handover Request Channel ACT Channel ACT ACK Handover Request ACK Handover Command Handover Access Handover Detect Handover Complete Successful incoming inter BSC H.O Handover Complete Clear Command (HO successful) Successful outgoing inter BSC H.OHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 7
    • 8. Measurement Points of Inter-BSC HandoverMS BSC-A MSC-A MSC-B VLR-B BSC-B MS HO-Required Prepare_HO Allocate_HO_NUM Send_HO_Report Send_HO_Report_ACK HO-Request Prepare_HO_ACK HO-Request-ACK IAI HO-Command ACM HO-Access Process_Access_Signalling Some intermediate steps are omitted HO-Complete Send_End_Signal Clear-Command Clear-Complete Send_End_Signal_ACKHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 8
    • 9. Measurement Points of Inter-BSC Handover Inter BSC handover Success rate =(Successful incoming inter BSC inter cell handovers + Successful outgoing inter BSC inter cell handovers) / (Attempted incoming inter BSC inter cell handovers + Attempted outgoing inter BSC inter cell handovers ) Incoming BSC handover Success rate =(Successful incoming inter BSC inter cell handovers) / (Attempted incoming inter BSC inter cell handovers) Outgoing BSC handover Success rate =(Successful outgoing inter BSC inter cell handovers ) / (Attempted outgoing inter BSC inter cell handovers)HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 9
    • 10. Chapter 1 Measurement Points of Handover Chapter 2 Handover Data Process Chapter 3 Analysis of Handover Problem Chapter 4 Handover CasesHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 10
    • 11. Handover Data Process Search MSC2 Handover target cell judgement ( 4 (7) MSC1 ) Inter-MSC BSC1 CGI ( 6 ) H.O ( 8 ) H.O request ( 7 ) BTS1 Channel BSC2 active ( 5 ) Preprocessed BTS2 BA table ( 1 ) MR ( 3 ) MS MR ( 2 )HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 11
    • 12. Handover Data Process  BCCH frequencies of all adjacent cells in BA2 table are sent to MS on system message 5.  MS reports measurement report to BSS. It includes the BCCH , BSIC and signal level of the adjacent cells and serving cells.  When the measurement report is preprocessed, BSC determines the CGI of all adjacent cells through BCCH frequency and BSIC .  BSC executes handover judgment flow such as basic cell ranking . Once a proper target cell is found, the handover request message which includes the target cell CGI will be sent to MPU of BSC , and then MPU will confirm the module ID of the cell based on the CGI.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 12
    • 13. Handover Data Process  MPU sends handover request message to the module and makes statistics of "outgoing inter cell handover request". At the same time BSC send the “channel active” to the BTS.  If the target cell triggered by BSC is an external cell, the CGI of the target cell and service cell is sent to MSC on the handover required.  By matching the CGI of the target cell, MSC searches target cell . Once the cell is found, MSC will confirm which BSC is belonged to, and send the handover request message to this BSC.  If there is no CGI of the target cell , MSC will check “Adjacent MSC Table" and find the target MSC, then send the handover request message to that MSC.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 13
    • 14. Chapter 1 Measurement Points of Handover Chapter 2 Searching Process of Handover Data Chapter 3 Analysis of Handover Problem Chapter 4 Handover CasesHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 14
    • 15. Analysis of Handover Problem  Types of handover problems  Locating handover problem  Causes of handover problemHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 15
    • 16. Types of Handover Problems  Types - Possible Results  No handover - Cause call drop  Handover failure - Affect the conversation quality, and call drop.  Frequent handover - Affect the conversation quality and increase load of the systemHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 16
    • 17. Locating Handover Problem  Traffic statistics analysis  Measurement of BSC overall performance  Measurement of inter cell handover performance  Measurement of outgoing/incoming inter cell handover performance  Measurement of performance of undefined adjacent cell  View alarm  Board fault, transmission, clock, etc.  Drive test  Signaling analysis  A interface, E interface, Abis interfaceHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 17
    • 18. Causes of Handover Problem  Coverage  Interference  Antenna and feeder system  Base station hardware  Transmission  BSC hardware  Data Configuration  A interface  Target cell congestion  Cooperation with equipment of other manufacturersHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 18
    • 19. Causes of Handover Problemcauses Types No H.O H.O failure Frequent H.O Coverage √ √ √ Interference √ Antenna and feeder √ system BTS hardware √ transmission √ BSC hardware √ Data configuration √ √ √ A interface √ √ √ Target cell congestion √ √H.O between equipment of √ different manufacturesHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 19
    • 20. Coverage and interference at radio interface  Coverage: − Poor coverage: forest, complicated topography, building direction and indoor coverage − Isolated site: no adjacent cell − Over shooting: island effect result in no adjacent cell  Interference: MS can not access network or receive any signal.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 20
    • 21. Island effect results in handover failure There is no adjacent cell, so handover becomes Non-adjacent impossible. Adjacent cell cell N1 Service cell Non-adjacent cell Adjacent Cell N2 Non-adjacent Adjacent cell Cell N3 Isolated island resulting from over shootingHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 21
    • 22. Antenna and Feeder System  High Voltage Standing Wave Ratio (VSWR)  Antenna is not properly installed  Antenna is not parallel  The azimuth and downtilt are not correct  Poor antenna isolation value  RF cables, connection are loose or incorrectHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 22
    • 23. BTS hardware  CDU, splitter/combiner failure  TRX failure  TMU failure  Clock failure  Internal communication cableHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 23
    • 24. Analysis of Handover Problem  Transmission  Transmission is not stable  Serious BER in transmission  Fault of BSC Hardware  Clock board: the faulty clock board causes clock inconsistency between base stations.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 24
    • 25. Data configuration  Unsuitable setting of handover hysteresis and handover priority.  Unsuitable setting of P, N value of statistic time  Unsuitable frequency and adjacency relation configured in BA1/BA2 table  CGI, BCCH and BSIC in "External Cell Description Table" are different from those in the opposite BSC.  The DPC of BSC in MSC "LAI and GCI Table" is incorrect.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 25
    • 26. Analysis of Handover Problem A interface problem  Basically, the insufficient link resource results in the abnormal handover, as well as abnormal communication.  Circuit pool numbers are different ,causing the handover failure. Target cell congestion  The target cell is congested, which causes the handover failure. Then the target cell should be expanded or reduce its traffic .HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 26
    • 27. Analysis of Handover Problem  Handover between equipment of different manufacturers  The signaling at A interface, E interface of the opposite equipment are not matched to our equipment and can not be recognized or supported, which causes the handover failure, such as voice version, handover number, TUP circuit, addressing mode (CGI or LAI).HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 27
    • 28. Chapter 1 Measurement Points of Handover Chapter 2 Searching Process of Handover Data Chapter 3 Analysis of Handover Problem Chapter 4 Handover CasesHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 28
    • 29. Handover Case 1 Fault Description A 1800 cell of a dual-band network (all the 1800 cells belong to one BSC), the incoming handover success rate of incoming BSC and intra BSC are low from the beginning of the service, while the outgoing handover success rate of intra-BSC and inter-BSC are normal.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 29
    • 30. Handover Case 1 Analysis:  Register the traffic statistics and analyze whether the low handover success rate is due to the failure of handover from all cells to this cell or from some few cells.  If handover fails from some few cells to this cell, check the handover data and see whether there is co-channel and co-BSIC problem.  If handover fails from all other cells to this cell, check the data of this cell.  If data cause is ruled out, check the hardware carefully. Check the alarm or perform drive test to locate uplink fault or downlink fault. Check step by step and find out the cause.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 30
    • 31. Handover Case 1 Solution:  Register the incoming inter cell handover measurement function and find that the successful rate of handover from all other cells to this cell is low, although it is not always 0 percent. Based on careful data checking, the data of this cell is correct.  Perform drive test and find that the downlink signal is normal but almost all handovers to this cell are failure. Near the BTS, the handover is successful occasionally. Perhaps the problem is with the uplink signal.  Check the uplink channel, antenna, CDU, they are no problem. Change the TRX , everything is normal. Conclusion:  The symptom is that the uplink and downlink at UM interface are unbalanced so uplink voice quality is bad.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 31
    • 32. Handover Case 2 Fault Description: After LAPD software upgrade of a dual-band network on 19th September, it was found that some cells in module 4 under 1800 network are seriously congested (40 % ~ 50 % ), and overall handover indices of BSC come down from 95 % to 90 % . From "Inter -cell Hanover Measurement Function, it was found that besides module 4, some cells of other modules also suffer from the problem that inter cell handover success rate is low. After 19th September, the situation became worse.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 32
    • 33. Handover Case 2 Analysis:  Check whether it is attributed to LAPD software upgrade.  Analyze traffic statistics and the main causes of the failure to locate the problem.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 33
    • 34. Handover Case 2 Solution:  Check whether it is attributed to LAPD software upgrade. After the upgrade, not all cells under module 4 are congested and the handover indices of some cells are not low. Upgrade isn’t the cause.  Analyze traffic statistics: − Congested cells are mostly at site A and site B. Their traffics are lower than before the upgrade. It is a pseudo congestion. − The cells where handover success rate is low are mostly at site A, B, C, D and E , the main cause of the failure is timer timeout.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 34
    • 35. Handover Cases 2 Solution:  Check alarm: At 19:31 of 18th September, the clock system alarms of site A and site B occurred. It is found that 13M clock isn’t synchronous. The clock problem result in low handover success rate of the two sites. Such impact spread to the adjacent cells of these two cells and even affected the whole network.  Analyze handover data and traffic statistics: All cells where handover success rate is low are adjacent to A and B except A and B themselves.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 35
    • 36. Handover Cases 2 Solution: Reset site A and site B, the clock system is recovered, and the handover success rate inter/intra BSC goes up to 93 % . The problem is solved. Conclusion: The problem in clock system will result in low handover success rate. Pay attention to the alarm console and the excursion of the clock system.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 36
    • 37. Handover Cases 3 Fault Description: Huawei BSC and another manufacturer’s BSC (S vender) are connected to the same MSC. After cutover, MS can not handover from S BSC to Huawei BSC but opposite is normal.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 37
    • 38. Handover Cases 3 Analysis: Since incoming BSC handover request times is 0 but the outgoing handover is normal. Carefully check the outgoing inter-cell handover signaling and handover data at S BSC.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 38
    • 39. Handover Cases 3 Solution: Trace interface message. After receiving HO-REQUEST message, Huawei BSC returns HO-FAILURE message immediately. In normal conditions Huawei BSC should return HO-REQ-ACK message. Carefully analyze HO-REQ message and HO-FAILURE message.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 39
    • 40. Handover Cases 3 Handover failureHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 40
    • 41. Handover Cases 3 HO-REQUESTHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 41
    • 42. Handover Cases 3 Solution :  HO-FALUER: The cause of the failure is invalid message content  HO-REQUEST: The difference is basically the Address Indicator in comparison with the normal handover request message. HUAWEI BSC does not recognize case 41. The system thinks that Address Indicator must be 0x43. Inform the owner of network, modify the relation parameter, and this problem is solved.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 42
    • 43. Handover Cases 3 Conclusion: In cooperation with equipment of other manufacturers, faults can be located by analyzing the signaling.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 43
    • 44. Handover Cases 4 Fault Description: Huawei MSC cooperate with MSC of N (vender). The communication is normal. The Huawei intra BSC handover and incoming BSC handover are normal, but outgoing BSC handover success rate is about 25%. The handover from the N BSC to Huawei BSC is successful, but opposite is failure sometimes.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 44
    • 45. Handover Cases 4 Analysis: Check handover data, including the external cell description table, BA2 table, cell adjacency relation table inside Huawei BSC and N BSC and CGI at N MSC. If the data are correct, check outgoing BSC handover signaling.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 45
    • 46. Handover Cases 4 Solution:  Check data: There is no fault in BSC and MSC of the two venders.  Check alarm: BTS maintenance console, No.7 link and A interface circuit are all normal.  Trace Huawei A interface signaling. After "HO-REQUIRED" message is sent, "HO-COMD" command is not received from MSC.  Trace MAP message at E interface (inter-MSC) with a signaling meter. It is found that after receiving HO-Number, Huawei MSC never sends IAI (Initial Address Information).HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 46
    • 47. Handover Cases 4 Solution:  Check HO-Number message from the opposite and find that the handover code format is 130********(only a number of mobile telephone, no any prefix). But this mobile company requires that roaming/handover between exchanges should be in the format: 00+country code + roaming/handover number. In addition, Huawei equipment does not recognize the handover number without 00+country code. Therefore the signaling is halted.  Discuss with N, asking them to add "00+country code" before the handover number. Then outgoing BSC handover is normal.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 47
    • 48. Handover Cases 4 Conclusion: Problems can be located quickly and accurately if you are familiar with the signaling flow of handovers.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 48
    • 49. Handover Cases 5 Fault Description: In the independent MSC networking of a dual band network, Huawei 1800 network cooperate with 900 network of vender A . After cutover, the successful rate of handover from M1800 to M900 is low (about 60 % ), while the handover from M900 to M1800 are normal and the handover data are correct.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 49
    • 50. Handover Cases 5 Analysis 1: Trace the signalings at A interface and E interface. Normal signaling is as follow:MS BSC-HW MSC-HW MSC-B VLR-B BSC-B MS HO-REQUIRED MAP_Prepare_HO MAP_Allocate_HO_NUM MAP_Send_HO_Report MAP_Send_HO_Report_ACK HO-REQUEST HO-REQUEST-ACK MAP_Prepare_HO_ACK IAI HO-Command ACM HO-Access MAP_Process_Access_Signaling Intermediate steps HO-Complete are omitted. MAP_Send_End_Signal Clear-Command Clear-Complete MAP_Send_End_Signal_ACKHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 50
    • 51. Handover Cases 5 Analysis 2: Abnormally signaling is as follow: MS BSC-HW MSC-HW MSC-B VLR-B BSC-B MS HO-REQUIRED MAP_Prepare_HO MAP_Abort HO-REJECTHUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 51
    • 52. Handover Cases 5 Solution:  Analyze the Prepare-HO message sent from Huawei MSC to the opposite. The voice version is full-rate version 1, 2 and half-rate version 1. It is a PHASE 2+ version. However there is only full-rate version 1 in the message sent from M900 to Huawei M1800. It turns out that the opposite does not support half-rate version, so the handover fails.  Modify A interface circuit pool table of Huawei MSC data, only using full-rate version 1.  Then the outgoing BSC handover is normal.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 52
    • 53. Handover Cases 5 Conclusion: There are often many problems in coordination between the equipment of different manufacturers. However, problems can be located accurately by tracing signaling.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 53
    • 54. Handover Cases 6 Fault Description: A GSM network, where one MSC is attached with two BSC, is all configured with Huawei equipment. When the two BSC are cutover, the successful rate of handover from BSC1 to BSC2 is 0, but opposite is normal. Intra BSC handover of BSC1 and BSC2 are normal.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 54
    • 55. Handover Cases 6 Analysis:  Register “outgoing inter-cell handover measurement function” of BSC1 and “incoming inter-cell handover measurement function” of BSC2.  Check the data related to handover of BSC1 and BSC2.  Analyze signaling of handover failure.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 55
    • 56. Handover Cases 6 Solution:  Check all data of inter-BSC handover: external cell description data table, BA2 table, CGI of MSC. No problem is found.  Trace A interface message of BSC1 and BSC2. After BSC1 sends "HO-REQUIRED", BSC2 has not received "HO- REQUEST" message, but opposite is normal.  The path of data search: MSC goes to "LAI and GCI Table" according to the CGI of the target cell in "HO-REQUIRED" message, and sends HO request to the correct BSC base on the description of the DPC of the cell given in the table.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 56
    • 57. Handover Cases 6 Solution: The HO-REQUEST message, which should have been sent to BSC2, is sent to BSC1. It is DPC error. After correction, the problem is solved.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 57
    • 58. Handover Cases 6 Conclusion: For the data of inter-BSC handover, besides checking whether CGI at MSC side is consistent with that of opposite and BSC, check whether the DPC is correct. MSC look up target DPC based on the CGI of the target cell. When the DPC is incorrect, "HO-REQUEST" will be sent to wrong BSC.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 58
    • 59. Handover Cases 7 Fault Description: A dual band network is a mixed networking of Huawei BSC (M1800) and vender N BSC (M900), attached to MSC of vender S. After the cutover, the successful rate of Huawei incoming BSC handover is always 88 %~ 92 % , while outgoing BSC and intra-BSC handovers are normal (above 92 % ). Furthermore, the cells with low successful rate of incoming BSC handover are randomly distributed.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 59
    • 60. Handover Cases 7 Analysis: Since the handover success rate is not very low and the low ratio is not in some few cells, data problem is excluded. Perhaps it is due to some interference at the radio interface coverage hole. So, trace the signaling.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 60
    • 61. Handover Cases 7 Solution:  Perform forced handover with a test mobile between several cells where handover success rate is low. The forced handovers are all successful. Data problem is excluded.  The interference band of cells is ideal, call drop and congestion rate are normal. It is unlikely that the coverage and interference at the radio interface causes the problem.  Trace A interface signaling and compare the failure signaling with success signaling:HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 61
    • 62. Handover Cases 7 A interface signaling analysis of inter-BSC handover in MSC: Failure signaling: Success signaling:HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 62
    • 63. Handover Cases 7 Solution:  The comparison result is that Huawei BTS has not detected any MS access information (No HO DETECT signaling occurs). It shows that there is problem when the MS is accessing M1800 cells.  Reconfirm that there is no problem with the handover data, otherwise the handover success rate will be very low.  Re-trace large number of handover signaling to find that all failures are attributed to the same cause. In addition, the problem is the same: there are several handover requests in a call duration but all requests fail.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 63
    • 64. Handover Cases 7 Solution:  Analyze other similarities of the failed message, to find that the first 6 digits of IMEI numbers of these MS are all 449684. It shows that the handover problem is related to the MS.  Find the MS owners with the IMSI numbers and find that all MS with handover problem are F MS. Not long ago it was proved that this MS has poor insulation performance between M900 and M1800, so it can not access M1800 network. Now the cause is found.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 64
    • 65. Handover Cases 7 Conclusion: MS problem will also causes handover failure.  In this case the handover success rate is not very low, therefore coordination problem is unlikely.  Trace the signaling to find the cause of the handover failure: BTS has not received handover access message from MS.  Find the similarity of these MS through large amount of signaling tracing: IMEI numbers are the same. Then it is found that the problem is on F MS.  The coverage of M900 is very good, F MS is always under M900 in idle status. Therefore in a call, TCH assignment seldom fail, which will not result in high congestion rate. But in handover, problem is very likely to happen.HUAW I T CH E E NOL OGIE CO., L D. S T All rights reserved Page 65
    • 66. Thank Youwww.huawei.com

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