Download - OMD6046 Case Analsyis--Handover ISSUE1.1

OMD6046Case Analsyis--Handover

ISSUE1.1

OMD6046Case Analsyis--Handover

ISSUE1.1

Wireless Curriculum

Development Section

Outline of Handover Topic Outline of Handover Topic

Statistics by handover counter

Searching process of handover data

Analysis of causes of handover problem

Handover cases

Statistics of handover counter

Intra-BSC handover

Inter-BSC handover

Statistic Point of Handover CounterStatistic Point of Handover CounterStatistic Point of Handover CounterStatistic Point of Handover Counter

Statistic Point of Handover CounterStatistic Point of Handover Counter －－Intra-BSC HandoverIntra-BSC Handover

Statistic Point of Handover CounterStatistic Point of Handover Counter －－Intra-BSC HandoverIntra-BSC Handover

MS BTS(Source) BSC BTS(Target) MSC

Measurement Report

Measurement Report

Handover algorithm verdict on the cell handover request T09++ (In-cell handover request get to) T12++

Channel Activation Channel Activation ACK

Handover Command (Old FACCH)

Handover Access (New FACCH)

Handover Complete (New FACCH) T10++ T13++

RF Channel Release

Handover Performed

Attempted incoming internal inter cell handovers

Successful incoming internal in-cell handover

Attempted outgoing internal inter cell handovers

Successful outgoing internal in-cell handover

Handover FormulaHandover Formula

Internal inter cell handover Success rate

＝—————————————success inter cell handovers

Attempted inter cell handovers

cell radio handover Success rate

＝—————————————

cell handover Success ratescell handover Success rates >=internal inter cell handover success rates>=internal inter cell handover success rates

Statistic Point of Handover CounterStatistic Point of Handover Counter －－ Intra-BSC HandoverIntra-BSC HandoverStatistic Point of Handover CounterStatistic Point of Handover Counter －－ Intra-BSC HandoverIntra-BSC Handover

success inter cell handovers

Inter cell handovers

Possible causes of failure of intra-BSC handoverPossible causes of failure of intra-BSC handover

No available channel in the destination cellNo available channel in the destination cell

Channel activation negative acknowledgementChannel activation negative acknowledgement －－ CHAN ACK NACCHAN ACK NACKK

Transmitting channel activation message failureTransmitting channel activation message failure

Waiting channel activation timeoutWaiting channel activation timeout

MS access failureMS access failure （（ Radio interface may be the causeRadio interface may be the cause ））

Max repeat time of physical informationMax repeat time of physical information *radio link connected with *radio link connected with the timer < time interval of EST IND~HO DETECT (120~180ms)the timer < time interval of EST IND~HO DETECT (120~180ms)

Waiting to timeout after establish indication (MS has not received Waiting to timeout after establish indication (MS has not received UA frame or has not sent handover complete message)UA frame or has not sent handover complete message)

Statistic Point of Handover CounterStatistic Point of Handover Counter －－ Intra-BSC Intra-BSC HandoverHandover

Statistic Point of Handover CounterStatistic Point of Handover Counter －－ Intra-BSC Intra-BSC HandoverHandover

Th

e same as in

tra-T

he sam

e as intra-

MS

CM

SC

Statistic Point of Handover CounterStatistic Point of Handover Counter －－ Inter-BSC HandoverInter-BSC HandoverStatistic Point of Handover CounterStatistic Point of Handover Counter －－ Inter-BSC HandoverInter-BSC Handover MS BTS(Source) BSC MSC BSC BTS(Target)

Measurement Report

Measurement Report

Handover Required T17++ Handover Request T14++ Channel ACT Channel ACT ACK Handover Request ACK Handover Command Handover Access Handover Detect Handover Complete Handover Complete T15++ Clear Command (HO successful) T18++ RF Channel Release

Clear Complete

Attempted outgoing inter-BSC inter cell handovers

Attempted incoming inter-BSC inter cell handovers

Successful outgoing interBSC inter cell handover

Successful incoming interBSC inter cell handover

Signaling flow between MSCsSignaling flow between MSCs

MSC-BMSC-A VLR-BBSC-A BSC-B

HO-Required MAP_Prepare_HO

MAP_Prepare_HO_ACK

MAP_Allocate_HO_NUM

MAP_Send_HO_Report

MAP_Send_HO_Report_ACK

MS

HO-Request

HO-Request-ACK

HO-Command

MS

HO-AccessMAP_Process_Access_Signalling

HO-CompleteMAP_Send_End_Signal

Clear-Command

Clear-Complete

MAP_Send_End_Signal_ACK

Some intermediate steps are omitted

IAIACM

Statistic Point of Handover CounterStatistic Point of Handover Counter －－ Inter-BSC HandoverInter-BSC HandoverStatistic Point of Handover CounterStatistic Point of Handover Counter －－ Inter-BSC HandoverInter-BSC Handover

Success ratio of

inter-BSC handover＝————————————— --------------×100％Success times of inter-cell handover between BSCs

Request times of inter-cell handover between BSCs

Success ratio of

In-BSC handover＝————————————— ----------------×100％Destination BSC receives HO-COMP from MS

After destination BSC receives HO-REQ

Success ratio of

Out-BSC handover＝—————————————— ------------×100％Source BSC receives Clear-COMD from MSC

After BSC sends HO-Required

Statistic Point of Handover CounterStatistic Point of Handover Counter －－ Inter-BSC HandoverInter-BSC HandoverStatistic Point of Handover CounterStatistic Point of Handover Counter －－ Inter-BSC HandoverInter-BSC Handover




Handover cases


Searching Process of Handover DataSearching Process of Handover DataSearching Process of Handover DataSearching Process of Handover Data

1.1. BCCH of all adjacent cells in BA2 table are sent to MS on system BCCH of all adjacent cells in BA2 table are sent to MS on system message 5.message 5.

2.2. MS reports service cell and six adjacent cell where level is the most MS reports service cell and six adjacent cell where level is the most powerful (through measurement report) to BSS, including the powerful (through measurement report) to BSS, including the BCCH , BSIC and signal level of the adjacent cells and service BCCH , BSIC and signal level of the adjacent cells and service cells.cells.

3.3. When the measurement report is pre-processed, BSC determines When the measurement report is pre-processed, BSC determines the module ID, cell ID and CGI of all adjacent cells through BCCH the module ID, cell ID and CGI of all adjacent cells through BCCH frequency and BSIC in Cell Adjacency Relation Table and Cell frequency and BSIC in Cell Adjacency Relation Table and Cell Description Data Table (or External Cell Description Data Table).Description Data Table (or External Cell Description Data Table).

4.4. BSC executes handover verdict flow such as basic cell sorting (on BSC executes handover verdict flow such as basic cell sorting (on LAPD board). Once a proper destination is found, the handover LAPD board). Once a proper destination is found, the handover request message of the destination cell CGI will be sent to MPU of request message of the destination cell CGI will be sent to MPU of BSC host, and then MPU will confirm the module ID of the cell in BSC host, and then MPU will confirm the module ID of the cell in Cell Module Information Table based on the CGI.Cell Module Information Table based on the CGI.

5.5. MPU sends handover request message to the module and makes MPU sends handover request message to the module and makes statistics of “Out-cell handover request”.statistics of “Out-cell handover request”.

6. 6. If the destination cell triggered by BSC is an external cell, the If the destination cell triggered by BSC is an external cell, the CGI of the destination cell and service cell is sent to MSC with the CGI of the destination cell and service cell is sent to MSC with the handover request.handover request.

7. MSC first goes to “Location Area Cell Table” to search the cell 7. MSC first goes to “Location Area Cell Table” to search the cell that matches the CGI of the destination cell. Once the cell is that matches the CGI of the destination cell. Once the cell is found, confirm which BSC is belong to. Send the handover request found, confirm which BSC is belong to. Send the handover request message to this BSC.message to this BSC.

8. If there is no CGI of the destination cell in “Location Area Cell 8. If there is no CGI of the destination cell in “Location Area Cell Table”, go to “adjacent MSC table” and find the destination MSC, Table”, go to “adjacent MSC table” and find the destination MSC, then send the handover request message to this MSC.then send the handover request message to this MSC.

Searching Processing of Handover DataSearching Processing of Handover DataSearching Processing of Handover DataSearching Processing of Handover Data





Handover cases

Analysis of Handover Problem

Analysis of Handover Problem

Types of Handover Problems

Locating problem

Causes of Handover Problem

Type of Handover ProblemType of Handover Problem Type of Handover ProblemType of Handover Problem

No handoverNo handover －－ Dropout occursDropout occurs

Handover failureHandover failure －－ Affect the communication quality, heAffect the communication quality, hence the dropout.nce the dropout.

Frequent handoverFrequent handover －－ Affect the communication quality Affect the communication quality and increase the system loadand increase the system load

Locating Handover Locating Handover ProblemProblem

Locating Handover Locating Handover ProblemProblem

Analyze traffic statisticsAnalyze traffic statistics

Measurement of BSC overall performanceMeasurement of BSC overall performance

Measurement of inter-cell handover performanceMeasurement of inter-cell handover performance

Measurement of out-cell/in-cell handover performanceMeasurement of out-cell/in-cell handover performance

Measurement of performance of undefined adjacent cellsMeasurement of performance of undefined adjacent cells

View alarm: View alarm: Board fault, transmission, clock, etc.Board fault, transmission, clock, etc.

Drive test Drive test

Analyze signaling: Analyze signaling: A interface, E interface, Abis interfaceA interface, E interface, Abis interface

Coverage and interference at radio interface

Antenna & feeder system

BS software/hardware

Transmission

BSC software/hardware/ Data Configuration

A interface problem

Destination cell is busy

Interconnection with equipment of other manufacturers

Analysis of Handover ProblemAnalysis of Handover ProblemAnalysis of Handover ProblemAnalysis of Handover Problem

I. I. Coverage and interference at radio interfaceCoverage and interference at radio interface

1. 1. CoverageCoverage::

Poor coverage: forest, complicated topography, Poor coverage: forest, complicated topography, building direction and indoor coverage building direction and indoor coverage

Isolated site: no-neighbor cellIsolated site: no-neighbor cell

Over coverage: island effect result in a no-neighbor Over coverage: island effect result in a no-neighbor cellcell

2. Interference: consequently, MS uplink can not be 2. Interference: consequently, MS uplink can not be accessed or the downlink can not receive any signal.accessed or the downlink can not receive any signal.

Analysis of Causes of Handover ProblemAnalysis of Causes of Handover Problem

Island effect results in handover failureIsland effect results in handover failure

Adjacent

Cell N3

Adjacent

Cell N2

Adjacent

cell N1

Non-adjacent

cell

Non-adjacent

cell

Non-adjacent

cell

Service cell

There is no There is no adjacent cells, adjacent cells, so handover so handover become become impossible.impossible.

Isolated island Isolated island resulting from resulting from cross-cell cross-cell coveragecoverage


II. Antenna & Feeder SystemII. Antenna & Feeder System

1. High voltage standing wave ratio(VSWR)1. High voltage standing wave ratio(VSWR)

2. Antennae are not properly installed2. Antennae are not properly installed

3. Antennae are not parallel3. Antennae are not parallel

4. The azimuth and obliquity are not correct4. The azimuth and obliquity are not correct

5. Poor antenna isolation5. Poor antenna isolation

6. RF cables ,connection are loose or incorrect 6. RF cables ,connection are loose or incorrect

connectionconnection


III. BTS software/hardwareIII. BTS software/hardware

1. CDU, splitter/combiner failure1. CDU, splitter/combiner failure

2. TRX, RC board failure2. TRX, RC board failure

3. TMU failure3. TMU failure

4. FPU failure4. FPU failure

5. Clock failure5. Clock failure

6. Internal communication cable6. Internal communication cable

7. BTS software7. BTS software


IV. TransmissionIV. Transmission1. Transmission is not stable1. Transmission is not stable

2. Serious BER in transmission2. Serious BER in transmission

V. Fault BSC Software/HardwareV. Fault BSC Software/Hardware

Example for:Clock board: the defective clock board causExample for:Clock board: the defective clock board caus

es clock inconsistency between BSs.es clock inconsistency between BSs.


Data Configuration －－ Cause handover failure, delay, frequent handovCause handover failure, delay, frequent handover, no handover, unreasonable in/out handover ratioer, no handover, unreasonable in/out handover ratio

Improper setting of handover threshold (higher, lower, the edge handover thrImproper setting of handover threshold (higher, lower, the edge handover threshold is higher than the power control threshold.)eshold is higher than the power control threshold.)

Improper setting of hysteresis handover and priority handoverImproper setting of hysteresis handover and priority handover

Improper setting of P, N value of statistic timeImproper setting of P, N value of statistic time

Incomplete frequency and adjacency relation configured in BA2 tableIncomplete frequency and adjacency relation configured in BA2 table

There are adjacent cells with the same frequency and the same BSICThere are adjacent cells with the same frequency and the same BSIC

CGI and module ID in “Cell Description Data Table” are different from those iCGI and module ID in “Cell Description Data Table” are different from those in “Cell Module Information Table”.n “Cell Module Information Table”.

CGI, BCCH and BSIC in “External Cell Description Table” are different from tCGI, BCCH and BSIC in “External Cell Description Table” are different from those in the opposite BSC. hose in the opposite BSC.

The Destination signaling point of BSC in MSC “Location Area Cell Table” is iThe Destination signaling point of BSC in MSC “Location Area Cell Table” is incorrect.ncorrect.


Precautions:Precautions:

“ “Frequency of Preprocess Measurement Report”: when “Measurement Frequency of Preprocess Measurement Report”: when “Measurement

Report Preprocess” is enable , if the link configuration is 15:1, the Report Preprocess” is enable , if the link configuration is 15:1, the

setting is once per second. At this time, for the handovers that needs P/N setting is once per second. At this time, for the handovers that needs P/N

verdict, such as boundary handover, layer handover, PBGT handover verdict, such as boundary handover, layer handover, PBGT handover

and concentric handover, the P/N verdict time should be shortened.and concentric handover, the P/N verdict time should be shortened.

BSC can not process the CGI in lower case. Therefore it must be input BSC can not process the CGI in lower case. Therefore it must be input

in upper case, otherwise the handover would fail.in upper case, otherwise the handover would fail.

BSC does not recognize CI as FFFF cell, otherwise the handover BSC does not recognize CI as FFFF cell, otherwise the handover

would not happenwould not happen

“ “Transmitting BS/MS Power Level”: If the measurement report Transmitting BS/MS Power Level”: If the measurement report

preprocess is enabled, this parameter must be set to “Yes”.preprocess is enabled, this parameter must be set to “Yes”.


VI. A interface ProblemVI. A interface Problem

Basically the insufficient link resource results in the abnormal handover, Basically the insufficient link resource results in the abnormal handover, as well as abnormal communication.as well as abnormal communication.

VII. Destination Cell BusyVII. Destination Cell Busy

The destination cell is busy and there is no available channel, which The destination cell is busy and there is no available channel, which

causes the handover failure. Then the destination cell should be causes the handover failure. Then the destination cell should be

expanded or reduce its traffic .expanded or reduce its traffic .

VIII. Handover between Equipment of Different VIII. Handover between Equipment of Different

ManufacturersManufacturers

The signalings at A interface, E interface of the opposite end are not The signalings at A interface, E interface of the opposite end are not

matching to our equipment and they can not be recognized or support, matching to our equipment and they can not be recognized or support,

which causes the handover failure, such as voice version, handover which causes the handover failure, such as voice version, handover

number, TUP circuit, addressing mode (CGI or LAI).number, TUP circuit, addressing mode (CGI or LAI).






Handover cases

Case 1Case 1

Fault Description: Fault Description: a 1800 cell of a dual-band network a 1800 cell of a dual-band network

(all the cells of this are 1800), the success ratio of in-BS(all the cells of this are 1800), the success ratio of in-BS

C handover and in-cell handover in BSC are low from thC handover and in-cell handover in BSC are low from th

e beginning of the service, while out-cell handovers inse beginning of the service, while out-cell handovers ins

ide BSC and between BSCs are normal.ide BSC and between BSCs are normal.

Typical Handover Cases

Case 1Case 1

Typical Handover

Case

Tips for troubleshooting:Tips for troubleshooting:

1. Register the traffic statistics and analyze whether the low 1. Register the traffic statistics and analyze whether the low

handover ratio is due to the failure of handover from all cells to this handover ratio is due to the failure of handover from all cells to this

cell or from some few cells to this cell.cell or from some few cells to this cell.

2. If handover fails from some few cells to this cell, check the 2. If handover fails from some few cells to this cell, check the

handover data and see whether there is co-channel or same BSIC handover data and see whether there is co-channel or same BSIC

problem.problem.

3. If handover fails from all other cells to this cell, check the data of 3. If handover fails from all other cells to this cell, check the data of

this cell.this cell.

4. If data cause is ruled out, check the hardware carefully. Check 4. If data cause is ruled out, check the hardware carefully. Check

the alarm or perform drive test to locate uplink fault or downlink the alarm or perform drive test to locate uplink fault or downlink

fault. Check step by step and find out the cause.fault. Check step by step and find out the cause.

Typical Handover Case

Solution:Solution:

1. Register the in-cell handover performance measurement and find that 1. Register the in-cell handover performance measurement and find that

the success ratio of handover from all other cells to this cell is low, the success ratio of handover from all other cells to this cell is low,

although it is not always 0 percent. Check the data and the data are although it is not always 0 percent. Check the data and the data are

correct.correct.

2. Perform drive test and find that the downlink signal is normal but 2. Perform drive test and find that the downlink signal is normal but

almost all handovers to this cell fail. In the BS, the handover is almost all handovers to this cell fail. In the BS, the handover is

successful occasionally.——Perhaps the problem is with the uplink successful occasionally.——Perhaps the problem is with the uplink

signal.signal.

3. Check the uplink, antenna, CDU are no problem. Change the TRX and 3. Check the uplink, antenna, CDU are no problem. Change the TRX and

everything is normal. everything is normal.

Conclusion: Conclusion: The symptom is that the uplink and downlink at The symptom is that the uplink and downlink at UM port are not balanced so the opposite hears low quality UM port are not balanced so the opposite hears low quality voice.voice.


Fault Description: Fault Description: in a cell of a 900M mono-in a cell of a 900M mono-frequency network, the success ratio of in-cell frequency network, the success ratio of in-cell wireless handover in BSC is low (10wireless handover in BSC is low (10 ％～％～ 3030 ％％ ), ), which is the same as handover success ratio.which is the same as handover success ratio.

Case 2Case 2


Case 2Case 2

Analysis:Analysis:

Since the wireless handover ratio is low, check Since the wireless handover ratio is low, check

data, coverage and interference.data, coverage and interference.

Data: co-frequency of BCCH and co-BSICData: co-frequency of BCCH and co-BSIC

Coverage: signal is weak, uplink and downlink are Coverage: signal is weak, uplink and downlink are

not balanced.not balanced.

Interference: high BER, MS can not be accessed or Interference: high BER, MS can not be accessed or

can not receive signals correctly.can not receive signals correctly.

Typical Handover CasesSolution:Solution:

1. Check data: register “In-cell Handover Performance Measurement” and 1. Check data: register “In-cell Handover Performance Measurement” and

find that the success ratio of handover into all adjacent cells is low, but is not find that the success ratio of handover into all adjacent cells is low, but is not

0. Check the data to find that there is no co-frequency 0f BCCH and co-BSIC 0. Check the data to find that there is no co-frequency 0f BCCH and co-BSIC

problem. Data cause is ruled out.problem. Data cause is ruled out.

2. Check coverage:2. Check coverage: The traffic in this cell is relatively low. Check “BS Maintenance” to find that The traffic in this cell is relatively low. Check “BS Maintenance” to find that

TCH channel can be occupied, but occupation times are few.TCH channel can be occupied, but occupation times are few. Perform a drive test. In a place 2 km from the BS, the downlink receiving Perform a drive test. In a place 2 km from the BS, the downlink receiving

signal is signal is －－ 85dbm, but in-cell handovers always fail or dropout always 85dbm, but in-cell handovers always fail or dropout always

occurs at handover.occurs at handover. Make dial test in this cell by locking frequency, the caller can not be Make dial test in this cell by locking frequency, the caller can not be

created. The called can be created but can not call out. A rough conclusion is created. The called can be created but can not call out. A rough conclusion is

that poor uplink causes the problem.that poor uplink causes the problem.

3. Check the installation of uplink hardware, nothing abnormal is identified. 3. Check the installation of uplink hardware, nothing abnormal is identified.

Maybe a fault has occurred to the uplink path of TRX or CDU. Replace CDU, Maybe a fault has occurred to the uplink path of TRX or CDU. Replace CDU,

the problem is solved.the problem is solved.

Conclusion: hardware fault results in poor signal, Conclusion: hardware fault results in poor signal, and the success ratio of wireless handover is low.and the success ratio of wireless handover is low.

Fault Description: Fault Description: After a dual-band network was LAPD updated on After a dual-band network was LAPD updated on

September 19, it was found that some cells in module 4 under 1800M are September 19, it was found that some cells in module 4 under 1800M are

seriously congested (40seriously congested (40 ％～％～ 5050 ％％ ), and overall handover index of BSC ), and overall handover index of BSC

(success ratio of out/in-BSC handovers and inter-cell handover inside (success ratio of out/in-BSC handovers and inter-cell handover inside

BSC) is lowered, from 95BSC) is lowered, from 95 ％％ to about 90to about 90 ％％ . From “Inter-cell handover . From “Inter-cell handover

performance measurement, it was found that beside module 4, some performance measurement, it was found that beside module 4, some

cells of other modules also suffer from the problem that inter-cell cells of other modules also suffer from the problem that inter-cell

handover success ratio is lowered. After September 19, the situation was handover success ratio is lowered. After September 19, the situation was

worsened.worsened.

Case 3Case 3


Case 3Case 3


Analysis:Analysis:

1. Check whether it is attributed to LAPD 1. Check whether it is attributed to LAPD

updating;updating;

2. Analyze traffic statistics, the main causes of 2. Analyze traffic statistics, the main causes of

the failure and locate the problem.the failure and locate the problem.

Solution:Solution:

1. Check whether it is attributed to LAPD updating: after the upgdating, 1. Check whether it is attributed to LAPD updating: after the upgdating,

not all cells under module 4 are congested and the handover indexes of not all cells under module 4 are congested and the handover indexes of

some indexes are not lowered. Upgrading is not the cause.some indexes are not lowered. Upgrading is not the cause.

2. Analyze traffic statistics:2. Analyze traffic statistics: Congested cells are mostly at Site A and Site B. Their traffics are lowerCongested cells are mostly at Site A and Site B. Their traffics are lower

ed than those before the upgrading. It is a pseudo congestion.ed than those before the upgrading. It is a pseudo congestion. The cells where handover success ratio is lowered are mostly at Site A,The cells where handover success ratio is lowered are mostly at Site A,

B, C, D and E and the main cause of the failure is timer timeout. B, C, D and E and the main cause of the failure is timer timeout.

3. Check alarm:3. Check alarm:

At 19:31 of September 18, the clock systems of Site A and Site B gave alAt 19:31 of September 18, the clock systems of Site A and Site B gave al

arms. It was found that 13M loses lock.arms. It was found that 13M loses lock.

the clock problem lowers the handover success ratio of the two sites. Sthe clock problem lowers the handover success ratio of the two sites. S

uch impact is spread to the adjacent cells of these two cells and even to tuch impact is spread to the adjacent cells of these two cells and even to t

he whole network.he whole network.


Solution:Solution:

4. Analyze handover data and traffic statistics:4. Analyze handover data and traffic statistics:

All cells where handover success ratio is lowered are adjacent All cells where handover success ratio is lowered are adjacent

to A and B except A and B themselves.to A and B except A and B themselves.

5. Reset Site A and Site B, the clock system is recovered, and 5. Reset Site A and Site B, the clock system is recovered, and

the handover success ratio inter/intra-BSC goes up to 93the handover success ratio inter/intra-BSC goes up to 93 ％％ . The . The

problem is solved.problem is solved.

Conclusion: the problem in clock system Conclusion: the problem in clock system will lower the handover success ratio. Pay will lower the handover success ratio. Pay attention to the alarm console and the attention to the alarm console and the slow switchover of the clock system.slow switchover of the clock system.


Case 4Case 4

Fault Description: Fault Description: Huawei BSC and the another manufacturer’BHuawei BSC and the another manufacturer’B

SC(for short S BSC) are connected to the same MSC. After the cSC(for short S BSC) are connected to the same MSC. After the c

utover, S BSC’BS can not handover into Huawei BS but Huawei utover, S BSC’BS can not handover into Huawei BS but Huawei

BS can handover into S’BSC BS. In other words, “In-BSC handoBS can handover into S’BSC BS. In other words, “In-BSC hando

ver request times” of Huawei BSC is 0.ver request times” of Huawei BSC is 0.


Case 4Case 4

Analysis: Analysis: Since in-BSC handover request Since in-BSC handover request

times is 0 but the out handover is normal. times is 0 but the out handover is normal.

Carefully check the out-cell handover Carefully check the out-cell handover

signaling and handover data at S BSC sidesignaling and handover data at S BSC side


Case 4Case 4

Solution:Solution:

1. Trace interface message. After receiving 1. Trace interface message. After receiving HO-REQUEST HO-REQUEST

message, Huawei BSC returns HO-FAILURE message message, Huawei BSC returns HO-FAILURE message

immediately but Huawei BSC should have returned HO-immediately but Huawei BSC should have returned HO-

REQ-ACK message as in normal conditions.REQ-ACK message as in normal conditions.

Carefully analyze HO-REQ message and HO-FAILURE Carefully analyze HO-REQ message and HO-FAILURE

messagemessage


HO-REQUESTHO-REQUEST


解决方法：解决方法：

SolutionSolution ：：2. HO-FALUER: The cause of the failure is 2. HO-FALUER: The cause of the failure is invalid message continvalid message cont

entent

3. HO-REQ3. HO-REQ ：： the difference is basically the Address Indicator in cthe difference is basically the Address Indicator in c

omparison with the normal handover request message. HUAWEI Bomparison with the normal handover request message. HUAWEI B

SC does not recognize case 41. The system thinks that Address InSC does not recognize case 41. The system thinks that Address In

dicator must be 0x43. inform the owner of network, modify the reldicator must be 0x43. inform the owner of network, modify the rel

ation parameter,and this problem is solved.ation parameter,and this problem is solved.

Case 4Case 4


解决方法：解决方法：Conclusion:Conclusion:

In interworking with equipment of other manufacturers, faults In interworking with equipment of other manufacturers, faults

can be located by analyzing the signaling.can be located by analyzing the signaling.

Case 4Case 4


解决方法：解决方法：Fault Description: Fault Description: Huawei MSC interworks with MSC of N Huawei MSC interworks with MSC of N

(manufacturer) with N’s BSC attached. The communication is (manufacturer) with N’s BSC attached. The communication is

normal. The handovers inside Huawei BSC and in-BSC are normal. The handovers inside Huawei BSC and in-BSC are

normal, but out-BSC handover success ratio is about 25%. normal, but out-BSC handover success ratio is about 25%.

The handover from the BSC of N to Huawei BSC is successful The handover from the BSC of N to Huawei BSC is successful

and the subsequent handover is also successful (In the same and the subsequent handover is also successful (In the same

communication, the handover goes back to BSC of N).communication, the handover goes back to BSC of N).

Case 5Case 5


解决方法：解决方法：Analysis: Analysis: Check handover data, including the Check handover data, including the

external cell description table, BA2 table, cell external cell description table, BA2 table, cell

adjacency relation table inside Huawei BSC adjacency relation table inside Huawei BSC

and opposite BSC and CGI at MSC side. If the and opposite BSC and CGI at MSC side. If the

data are correct, check out-BSC handover data are correct, check out-BSC handover

signaling.signaling.

Case 5Case 5


解决方法：解决方法：

Solution:Solution:

1. Check data: BSC and MSC of Huawei and N. No problem is found.1. Check data: BSC and MSC of Huawei and N. No problem is found.

2. Check alarm: BS maintenance console, No.7 link and A interface circuit are all nor2. Check alarm: BS maintenance console, No.7 link and A interface circuit are all nor

mal.mal.

3. Trace Huawei A interface signaling. After “HO-Required” message is received, “H3. Trace Huawei A interface signaling. After “HO-Required” message is received, “H

O-COMD” command is not received from MSC.O-COMD” command is not received from MSC.

4. Trace MAP message at E interface (inter-MSC) with a signaling meter. It is found t4. Trace MAP message at E interface (inter-MSC) with a signaling meter. It is found t

hat after receiving HO-Number, Huawei MSC never sends IAI (Initial Address Informahat after receiving HO-Number, Huawei MSC never sends IAI (Initial Address Informa

tion).tion).

5. Check HO-Number message from the opposite end to find that the handover code 5. Check HO-Number message from the opposite end to find that the handover code

format is 130********(only a number of mobile telephone, no any prefix). But this mobiformat is 130********(only a number of mobile telephone, no any prefix). But this mobi

le company requires that roaming/handover between exchanges should be in the forle company requires that roaming/handover between exchanges should be in the for

mat: 00+country code+roaming/handover number. In addition, Huawei equipment domat: 00+country code+roaming/handover number. In addition, Huawei equipment do

es not recognize the handover number without 00+country code. Therefore the signaes not recognize the handover number without 00+country code. Therefore the signa

ling is halted.ling is halted.

6. Coordinate with N, asking them to add “00+country code” before the handover nu6. Coordinate with N, asking them to add “00+country code” before the handover nu

mber. Then out-BSC handover is normal.mber. Then out-BSC handover is normal.

Case 5Case 5


解决方法：解决方法：Conclusion:Conclusion: Problems can be located quickly and accurately Problems can be located quickly and accurately

if you are familiar with the signaling flow of handovers.if you are familiar with the signaling flow of handovers.

Case 5Case 5


解决方法：解决方法：Fault Description: Fault Description: In the independent MSC networking of a In the independent MSC networking of a

dual frequency network, Huawei 1800M coordinates with dual frequency network, Huawei 1800M coordinates with

900M of manufacturer A . After the cutover, the success ratio 900M of manufacturer A . After the cutover, the success ratio

of handover from M1800 to M900 is low (about 60of handover from M1800 to M900 is low (about 60 ％％ ), while ), while

the handover from M900 to M1800 are normal and the the handover from M900 to M1800 are normal and the

handover data are correct.handover data are correct.

Case 6Case 6


Analysis 1: Analysis 1: Trace the signalings at A interface and E Trace the signalings at A interface and E

interface. Normally:interface. Normally:

MSC-BMSC-HW VLR-BBSC-HW BSC-B


MAP_Prepare_HO_ACK

MAP_Allocate_HO_NUM

MAP_Send_HO_Report

MAP_Send_HO_Report_ACK

MS

HO-Request

HO-Request-ACK

HO-Command

MS

HO-AccessMAP_Process_Access_Signaling

HO-CompleteMAP_Send_End_Signal

Clear-Command

Clear-Complete

MAP_Send_End_Signal_ACK

Intermediate steps are omitted.

IAIACM


Analysis 2: Analysis 2: Abnormally:Abnormally:

MSC-BMSC-HW VLR-BBSC-HW BSC-B


MS

HO-REJECT

MS

MAP_Abort


Analysis 2:Analysis 2:

1. Analyze the Prepare-HO message sent from Huawei MSC to the opposite 1. Analyze the Prepare-HO message sent from Huawei MSC to the opposite

end. The voice version is full rate version 1, 2 and half-rate version 1. It is a end. 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 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 sent from M900 to Huawei M1800. It turns out that the opposite does not

support half-rate version, so the handover fails.support half-rate version, so the handover fails.

2. Modify A interface circuit pool table of Huawei MSC data, only using full-rate 2. Modify A interface circuit pool table of Huawei MSC data, only using full-rate

version 1.version 1.

3. Then the out-BSC handover is normal.3. Then the out-BSC handover is normal.

Case 6Case 6

Conclusion: Conclusion: There are often many problems in coordination There are often many problems in coordination

between the equipment of different manufacturers. However, between the equipment of different manufacturers. However,

problems can be located accurately by tracing signaling.problems can be located accurately by tracing signaling.


Case 7Case 7

Fault Description: Fault Description: A specific GSM network, where one MSC is attached with tA specific GSM network, where one MSC is attached with t

wo BSC, is all configured with Huawei equipment. When the two BSCs are cuwo BSC, is all configured with Huawei equipment. When the two BSCs are cu

t over one after another, the success ratio of handover from BSC1 to BSC2 it over one after another, the success ratio of handover from BSC1 to BSC2 i

s very low, but the success ratio of handover from BSC2 to BSC1 is normal. Is very low, but the success ratio of handover from BSC2 to BSC1 is normal. I

ntra-BSC handover inside BSC1 and BSC2 is normal.ntra-BSC handover inside BSC1 and BSC2 is normal.


Case 7Case 7

Analysis: Analysis: check handover data and trace signaling.check handover data and trace signaling.

Solution:Solution:

1. Check all data of inter-BSC handover: external cell description data table, 1. Check all data of inter-BSC handover: external cell description data table,

BA2 table, CGI of MSC. No problem is found.BA2 table, CGI of MSC. No problem is found.

2. Trace A interface message of BSC1 and BSC2. After BSC1 sends “HO-2. Trace A interface message of BSC1 and BSC2. After BSC1 sends “HO-

Required”, BSC2 has not received “HO-Request” message, but BSC1 has.Required”, BSC2 has not received “HO-Request” message, but BSC1 has.

3. The path of data search: MSC goes to “Location Area Cell Table” according 3. The path of data search: MSC goes to “Location Area Cell Table” according

to the CGI of the destination cell in “HO-Required” message, refers to the to the CGI of the destination cell in “HO-Required” message, refers to the

description of the DSP of the cell given in the table and sends HO request to description of the DSP of the cell given in the table and sends HO request to

the correct BSC.the correct BSC.

4. The Ho-request message, which should have been sent to BSC2, is sent to 4. The Ho-request message, which should have been sent to BSC2, is sent to

BSC1, so it is DSP error. After correction, the problem is solved.BSC1, so it is DSP error. After correction, the problem is solved.


Case 7Case 7

Conclusion:Conclusion:

For the data of inter-BSC handover, besides checking For the data of inter-BSC handover, besides checking

whether CGI at MSC side is consistent with that at the whether CGI at MSC side is consistent with that at the

opposite and at BSC, check whether the DSP is correct. MSC opposite and at BSC, check whether the DSP is correct. MSC

indexes to the CGI of the destination cell with the existing indexes to the CGI of the destination cell with the existing

CGI.. When the DSP is incorrect, “HO-Request” will be sent to CGI.. When the DSP is incorrect, “HO-Request” will be sent to

wrong BSC.wrong BSC.


Case 7Case 7

Fault Description: Fault Description: A specific dual frequency network is a mixed A specific dual frequency network is a mixed

networking of Huawei BSC (M1800) and manufacturer N BSC (M900), networking of Huawei BSC (M1800) and manufacturer N BSC (M900),

attached to MSC of manufacturer S. After the cutover, the success attached to MSC of manufacturer S. After the cutover, the success

ratio of Huawei in-BSC handover is always 88ratio of Huawei in-BSC handover is always 88 ％～％～ 9292 ％％ , while out-, while out-

BSC and intra-BSC handovers are normal (above 92BSC and intra-BSC handovers are normal (above 92 ％％ ). Furthermore, ). Furthermore,

the cells with low success ratio of in-BSC handover are randomly the cells with low success ratio of in-BSC handover are randomly

distributed. When there is no fixed BM, there is no fixed LAC.distributed. When there is no fixed BM, there is no fixed LAC.


Case 7Case 7

Analysis: Analysis: Since the handover success ratio is not very low Since the handover success ratio is not very low

and the low ratio is not focused in some few cells, data and the low ratio is not focused in some few cells, data

problem is unlikely. Perhaps it is due to some interference at problem is unlikely. Perhaps it is due to some interference at

the radio port or some dead zone. Next, trace the signaling.the radio port or some dead zone. Next, trace the signaling.


Case 7:Case 7:

Solution:Solution:

1. Perform forced handover with a tester between several cells where 1. Perform forced handover with a tester between several cells where

handovers have failed. The forced handovers are all successful. Data handovers have failed. The forced handovers are all successful. Data

problem is ruled out.problem is ruled out.

2. The interference band of cells is ideal, dropout and congestion ratio are 2. The interference band of cells is ideal, dropout and congestion ratio are

normal. It is unlikely that the coverage and interference at the radio port normal. It is unlikely that the coverage and interference at the radio port

causes the problem.causes the problem.

3. Trace A interface signal and compare the failure signaling and success 3. Trace A interface signal and compare the failure signaling and success

signaling:signaling:


A interface signaling analysis of inter-BSC A interface signaling analysis of inter-BSC handover in MSC:handover in MSC:

Failure signaling:Failure signaling:

Success signaling:Success signaling:


Case 7:Case 7:

Solution:Solution:

4. The comparison result is that Huawei BTS has not detected any MS access informat4. The comparison result is that Huawei BTS has not detected any MS access informat

ion (No HO DETECT signaling occurs). It shows that there is problem when the MS is aion (No HO DETECT signaling occurs). It shows that there is problem when the MS is a

ccessing cell M1800 or the MS does not access cell 1800.ccessing cell M1800 or the MS does not access cell 1800.

5. Reconfirm that there is no problem with the handover data, otherwise the handover 5. Reconfirm that there is no problem with the handover data, otherwise the handover

success ratio will be very low.success ratio will be very low.

6. Re-trace large number of handover signalings to find that all failures are attributed t6. Re-trace large number of handover signalings to find that all failures are attributed t

o the same cause. In addition, the problem mode is the same: one MS makes multiple o the same cause. In addition, the problem mode is the same: one MS makes multiple

handover requests in one communication and all requests fail.handover requests in one communication and all requests fail.

7. Analyze other similarities of the failed message, to find that the first 6 digits of IMEI 7. Analyze other similarities of the failed message, to find that the first 6 digits of IMEI

numbers of these MSs are all 449684. It shows that the MSs that have handover problenumbers of these MSs are all 449684. It shows that the MSs that have handover proble

m are of the same model.m are of the same model.

8. Find the MS owners with the IMSI numbers and find that all MSs with handover prob8. Find the MS owners with the IMSI numbers and find that all MSs with handover prob

lem are F-MS. Not long before it was proved that this MS has poor insulation performalem are F-MS. Not long before it was proved that this MS has poor insulation performa

nce between 900 and 1800, so it can not access 1800 network. Now the cause is found. nce between 900 and 1800, so it can not access 1800 network. Now the cause is found.

..


Case 7:Case 7:

Conclusion: Conclusion: MS problem will also causes handover failure.MS problem will also causes handover failure.

1. In this case the handover success ratio is not very low, ther1. In this case the handover success ratio is not very low, ther

efore coordination problem is unlikely.efore coordination problem is unlikely.

2. Trace the signaling to find the cause of the handover failure:2. Trace the signaling to find the cause of the handover failure:

BTS has not received handover access message from MS. BTS has not received handover access message from MS.

3. Find the similarity of these MSs through large amount of si3. Find the similarity of these MSs through large amount of si

gnaling tracing: IMEI numbers are the same. Then it is found tgnaling tracing: IMEI numbers are the same. Then it is found t

hat the problem is on F-MS.hat the problem is on F-MS.

4. In this case, the coverage of M900 is very good, F-MS is al4. In this case, the coverage of M900 is very good, F-MS is al

ways under M900 in idle status. Therefore in a call, TCH assigways under M900 in idle status. Therefore in a call, TCH assig

nment seldom fail, which will not result in high congestion ratnment seldom fail, which will not result in high congestion rat

io. But in handover, problem is very likely to happen.io. But in handover, problem is very likely to happen.


Download - OMD6046 Case Analsyis--Handover ISSUE1.1

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