OMD6072 Case Analysis--Congestion ISSUE1.1.ppt

OMD6072Case Analysis—Congestion

ISSUE1.1

OMD6072Case Analysis—Congestion

ISSUE1.1

Wireless Curriculum

Development Section

SummarySummary

TCH Congestion RatioTCH Congestion RatioBasic PrincipleBasic PrincipleCause and Locating the CauseCause and Locating the CauseCases analyzeCases analyzeSDCCH Congestion RatioSDCCH Congestion RatioCause and Locating the CauseCause and Locating the CauseCases analyzeCases analyze

TCH congestion ratioTCH congestion ratio

Basic principleBasic principle

Cause and locating methodCause and locating method

Cases analyzeCases analyze

TCH congestion ratioTCH congestion ratioTCH congestion ratioTCH congestion ratio

TCH Congestion RatioTCH Congestion Ratio

Basic Principle of TCH congestion ratioBasic Principle of TCH congestion ratio

Definition of TCH congestion ratioDefinition of TCH congestion ratioTraffic statistics measurement point of TCH Traffic statistics measurement point of TCH

congestion ratio and analysiscongestion ratio and analysis

Basic Principle of TCH Congestion RatioBasic Principle of TCH Congestion Ratio

Definition of TCH congestion ratioDefinition of TCH congestion ratio

TCH congestion ratio (not including handover)TCH congestion ratio (not including handover)

=TCH occupation failure times (not including handover)/TCH occupation request =TCH occupation failure times (not including handover)/TCH occupation request

times (not including handover)*100%times (not including handover)*100%

=(TCH call occupation failure times+very early assigned TCH occupation failure =(TCH call occupation failure times+very early assigned TCH occupation failure

times)/(TCH call occupation request times+very early assigned TCH occupation times)/(TCH call occupation request times+very early assigned TCH occupation

request times)*100%.request times)*100%.


Definition of TCH Congestion RatioDefinition of TCH Congestion Ratio

TCH congestion ratio (including handover)TCH congestion ratio (including handover)

=TCH occupation failure times (including handover)/TCH occupation request times =TCH occupation failure times (including handover)/TCH occupation request times

(including handover)*100%(including handover)*100%

=(TCH call occupation failure times+very early assigned TCH occupation failure =(TCH call occupation failure times+very early assigned TCH occupation failure

times+TCH occupation failure times for in-cell handover intra-BSC (due to times+TCH occupation failure times for in-cell handover intra-BSC (due to

congestion)+TCH occupation failure times for in-cell handover inter-BSC (due to congestion)+TCH occupation failure times for in-cell handover inter-BSC (due to

congestion)/(TCH call occupation request times + early assigned TCH congestion)/(TCH call occupation request times + early assigned TCH

occupation request times + TCH occupation request times for in-cell handover occupation request times + TCH occupation request times for in-cell handover

intra-BSC + TCH occupation request times for in-cell handover inter-BSC)*100%intra-BSC + TCH occupation request times for in-cell handover inter-BSC)*100%

TCH congestion ratio (congestion on all busy)TCH congestion ratio (congestion on all busy)


Tra

ffic M

ea

su

rem

en

t Po

int

Tra

ffic M

ea

su

rem

en

t Po

int

of T

CH

Co

ng

es

tion

Ra

tio

of T

CH

Co

ng

es

tion

Ra

tio

Channel_Active

Channel_Active_Ack

IMMEDIATE ASSIGN COMMAND

BTS BSC MSCMS

Channel_req

first SABMEstablish_IND( CM Service Req)

CR(Complete_l3_information)

CC

Setup

Call Proceeding

Assignment_Req

ASSIGNMENT COMMAND

first SABMEstablish_IND

ASSIGNMENT CMPAssignment_CMP

Alerting

Connect

Connect Ack

communication

Disconnect

Release

Release CompleteClear_CMD

Clear_CMP

CM Service Accepted

Channel_Active

Channel_Active_Ack

UA

SDCCHSDCCH

SACCH(TCH)

SACCH(TCH)

MS call flow as the caller


Request Times Statistic Point of TCH Congestion RatioRequest Times Statistic Point of TCH Congestion Ratio

TCH call occupation request timesTCH call occupation request times

(1) Receive the MSC assignment request message(1) Receive the MSC assignment request message

Early assigned TCH occupation request times:Early assigned TCH occupation request times:

(1) When there is no resource for SDCCH allocation and (1) When there is no resource for SDCCH allocation and instant assignment is permittedinstant assignment is permitted

(2) When channel request is received and channel type is (2) When channel request is received and channel type is TCHTCH

TCH occupation request times for in-cell handover intra-BSCTCH occupation request times for in-cell handover intra-BSC

(1) When in-cell handover request message between cells (1) When in-cell handover request message between cells intra- BSC is received (non-SDCCH handover).intra- BSC is received (non-SDCCH handover).

TCH occupation request times for in-cell handover inter-BSC:TCH occupation request times for in-cell handover inter-BSC:

(1) When incoming handover request message is received (1) When incoming handover request message is received (handover type is non-SDCCH)(handover type is non-SDCCH)


Failure Statistic Points of TCH Congestion RatioFailure Statistic Points of TCH Congestion Ratio

TCH call occupation failure times:TCH call occupation failure times:

(1) CONN_FAIL message is received in process of assignment.(1) CONN_FAIL message is received in process of assignment.

(2) CLEAR_CMD is received in process of out-BSC handover. The (2) CLEAR_CMD is received in process of out-BSC handover. The

cause of handover is direct retry.cause of handover is direct retry.

(3) CLEAR_CMD is received in process of assignment(3) CLEAR_CMD is received in process of assignment

(4) RR_ABORT_REQ is received in process of out-BSC handover and (4) RR_ABORT_REQ is received in process of out-BSC handover and

the cause of handover is direct retry.the cause of handover is direct retry.

(5) RR_ABORT_REQ is received in process of assignment.(5) RR_ABORT_REQ is received in process of assignment.

(6) MSG_HO_REQ_REJ is received in process of out-BSC handover (6) MSG_HO_REQ_REJ is received in process of out-BSC handover

(direct retry).(direct retry).

(7) HO_FAIL is received in out-BSC handover (direct retry)(7) HO_FAIL is received in out-BSC handover (direct retry)

(8) ERR_IND is received in process of assignment.(8) ERR_IND is received in process of assignment.

(9) When assignment failure message is sent.(9) When assignment failure message is sent.

(10) TN_T7 (direct retry) timeout (out-BSC handover request)(10) TN_T7 (direct retry) timeout (out-BSC handover request)

(11) TN_T8 (direct retry) timeout (out-BSC handover complete)(11) TN_T8 (direct retry) timeout (out-BSC handover complete)


Failure Statistic Point of TCH Congestion RatioFailure Statistic Point of TCH Congestion Ratio

Early assigned TCH occupation failure times:Early assigned TCH occupation failure times:

(1) CH_ACT_NACK is received in the very early assigned process. (1) CH_ACT_NACK is received in the very early assigned process.

(CH_ACT_NACK is received in WAIT_RR_EST status in satellite (CH_ACT_NACK is received in WAIT_RR_EST status in satellite

transmission)transmission)

(2) In very early assigned process, the returned cause is (internal (2) In very early assigned process, the returned cause is (internal

error) CVI_INTERNAL_ERR when channel is being allocated.error) CVI_INTERNAL_ERR when channel is being allocated.

(3) In very early assigned process, the returned cause is (channel (3) In very early assigned process, the returned cause is (channel

request illegal) CVI_NO_ACCEPT when channel is being request illegal) CVI_NO_ACCEPT when channel is being

allocated.allocated.

(4) In very early assigned process, no channel is allocated.(4) In very early assigned process, no channel is allocated.

(5) TN_WAIT_CH_ACT timeout in very early assigned process.(5) TN_WAIT_CH_ACT timeout in very early assigned process.


Failure Statistic Point of TCH Congestion RatioFailure Statistic Point of TCH Congestion Ratio

TCH Occupation Failure Times for in-cell handover TCH Occupation Failure Times for in-cell handover intra-BSC (due to congestion):intra-BSC (due to congestion):

Allocation to TCH channel fails at in-cell handover Allocation to TCH channel fails at in-cell handover between cells intra-BSCbetween cells intra-BSC

TCH Occupation Failure Times for in-cell handover TCH Occupation Failure Times for in-cell handover inter-BSC (due to congestion):inter-BSC (due to congestion):

When in-cell handover inter-BSC occurs, When in-cell handover inter-BSC occurs,

handover failure message is sent because it is not handover failure message is sent because it is not

allocated to TCH channel.allocated to TCH channel.


Analysis of failure statistic point of TCH congestion ratioAnalysis of failure statistic point of TCH congestion ratio

A interfaceA interface

After MSC sends Assignment_req, After MSC sends Assignment_req, If trunk circuit at A interfaIf trunk circuit at A interface is fault, BSC will return Assignment_refuse directly.ce is fault, BSC will return Assignment_refuse directly.

In this case, the usually cause is incorrect CIC data configuraIn this case, the usually cause is incorrect CIC data configuration of trunk circuit.tion of trunk circuit.


Analysis of failure statistic point of TCH congestion ratio Analysis of failure statistic point of TCH congestion ratio

ABIS interface and UM interfaceABIS interface and UM interface

1. TRX board is faulty or performance unstable1. TRX board is faulty or performance unstable

2. Unbalance of uplink/downlink level in BTS2. Unbalance of uplink/downlink level in BTS

3. Poor quality of uplink/downlink signal due to interference3. Poor quality of uplink/downlink signal due to interference

4. SDCCH and TCH do not belong to the same TRX board, 4. SDCCH and TCH do not belong to the same TRX board, i.e. the two TRX boards cover different areas or TCH TRX i.e. the two TRX boards cover different areas or TCH TRX board is faulty.board is faulty.


The Cause of High TCH Congestion Ratio and The Cause of High TCH Congestion Ratio and Locating MethodLocating Method

The cause of high TCH congestion ratioThe cause of high TCH congestion ratioHow to locate the cause of TCH congestion How to locate the cause of TCH congestion

ratioratio

Cause of High TCH Congestion Ratio and Locating Method


Causes of High TCH Congestion RatioCauses of High TCH Congestion Ratio

Incorrect configuration of trunk circuit data at A interfaceIncorrect configuration of trunk circuit data at A interfaceCo-frequency and co-BSIC results in TCH assignment failure in handoverCo-frequency and co-BSIC results in TCH assignment failure in handoverBoard fault or unstable performance causes the high congestion ratioBoard fault or unstable performance causes the high congestion ratioBTS hardware is not properly installed, which causes uplink/downlink BTS hardware is not properly installed, which causes uplink/downlink

unbalance and TCH congestion.unbalance and TCH congestion.The cell is attached with a The cell is attached with a repeater. After the cell expansion, the repeater is not . After the cell expansion, the repeater is not

expanded.expanded.The transmitting power of BCCH TRX is higher than that of TCH TRX in the The transmitting power of BCCH TRX is higher than that of TCH TRX in the

same cell.same cell.Interference causes the congestionInterference causes the congestionTCH assignment failure due to Isolated site and complicated topography result TCH assignment failure due to Isolated site and complicated topography result

in the high congestion ratioin the high congestion ratio



How to Locate the Causes of High TCH Congestion RatioHow to Locate the Causes of High TCH Congestion Ratio

Analyze the cause of congestion remotelyAnalyze the cause of congestion remotely

1. Preliminary analysis through traffic measurement 1. Preliminary analysis through traffic measurement

2. Check alarms2. Check alarms

3. BTS remote maintenance console3. BTS remote maintenance console

4. Test and analyze ABIS interface message with a 4. Test and analyze ABIS interface message with a signaling analyzer.signaling analyzer.

Check the BTS locallyCheck the BTS locally



Remote analysis 1: Remote analysis 1: Preliminary Analysis Through Traffic StatisticsPreliminary Analysis Through Traffic Statistics

Through the traffic statistic “Cell TCH Performance Measurement”, check whether Through the traffic statistic “Cell TCH Performance Measurement”, check whether

TCH congestion is attributed to all busy status. If yes, perform traffic equalization or TCH congestion is attributed to all busy status. If yes, perform traffic equalization or

suggest the equipment buyer to expand the capacity.suggest the equipment buyer to expand the capacity.

If the congestion is not due to all busy status, analyze whether it is caused by If the congestion is not due to all busy status, analyze whether it is caused by

interference. Check interference bands 1~5. In the cell affected by interference, the interference. Check interference bands 1~5. In the cell affected by interference, the

drop ratio will be high.drop ratio will be high.

Register “Receiving Performance Measurement” traffic statistic task:Register “Receiving Performance Measurement” traffic statistic task:

1. Check the measurement result by object to see whether the numbers of 1. Check the measurement result by object to see whether the numbers of

uplink/downlink reports on the same TRX board are balanced. Thus you can know uplink/downlink reports on the same TRX board are balanced. Thus you can know

whether the uplink/downlink hardware tributaries on the board are balanced.whether the uplink/downlink hardware tributaries on the board are balanced.

2. Check the measurement result by time to see whether TRX measurement reports are 2. Check the measurement result by time to see whether TRX measurement reports are

excessive in a cell. Thus you can know whether the congestion is related to the board.excessive in a cell. Thus you can know whether the congestion is related to the board.



Remote analysis 2: Remote analysis 2: View alarm View alarm

Check alarms of the site in the cell where there is high congestion Check alarms of the site in the cell where there is high congestion

ratio. Check whether there is any abnormal alarm, such as ratio. Check whether there is any abnormal alarm, such as

standing wave ratio alarm, PCM OOF alarm and uplink data bus standing wave ratio alarm, PCM OOF alarm and uplink data bus

alarm. Judge whether the congestion ratio is associated with alarm. Judge whether the congestion ratio is associated with

alarms with traffic measurement .alarms with traffic measurement .



Remote analysis 3: Remote analysis 3: BTS remote maintenance consoleBTS remote maintenance console

On the BTS remote maintenance console, block TCH channels On the BTS remote maintenance console, block TCH channels

of cell TRX board with high congestion ratio in turn. Observe of cell TRX board with high congestion ratio in turn. Observe

whether the congestion ratio is related to the cell TRX board.whether the congestion ratio is related to the cell TRX board.



Remote analysis 4: Remote analysis 4: Test and analyze ABIS interface message with a Test and analyze ABIS interface message with a

signaling analyzersignaling analyzer

Trace ABIS message of the congested BTS, analyze Assignment CMD sent by SDCCH and judge Trace ABIS message of the congested BTS, analyze Assignment CMD sent by SDCCH and judge

whether the assignment always fails on a specific TRX board.whether the assignment always fails on a specific TRX board.

If the assignment always fails on a specific TRX board, the cause may be one of the following:If the assignment always fails on a specific TRX board, the cause may be one of the following:

1) TRX board faulty or performance unstable1) TRX board faulty or performance unstable

2) Uplink/downlink level difference, hardware problem in uplink tributary or downlink tributary.2) Uplink/downlink level difference, hardware problem in uplink tributary or downlink tributary.

3) Low quality of uplink/downlink signal. Analyze TA value of the MS to locate interference.3) Low quality of uplink/downlink signal. Analyze TA value of the MS to locate interference.

If the assignment fails on the RC boards of the whole cell randomly, analyze the measurement If the assignment fails on the RC boards of the whole cell randomly, analyze the measurement

reports. The causes may be the following:reports. The causes may be the following:

1) The topography in the cell coverage is quite complicated.1) The topography in the cell coverage is quite complicated.

2) There is band interference in the whole cell, such as repeater interference.2) There is band interference in the whole cell, such as repeater interference.





Check BTS locallyCheck BTS locally

Perform local maintenance and check to see if there are abnormal alarms. If Perform local maintenance and check to see if there are abnormal alarms. If

yes, process it promptly.yes, process it promptly.

Check whether there is any hardware problem in uplink/downlink antenna/feCheck whether there is any hardware problem in uplink/downlink antenna/fe

eder tributary, such as loose connector,etc.eder tributary, such as loose connector,etc.

Perform a dial test with the test mobile phone in the same place to see whetPerform a dial test with the test mobile phone in the same place to see whet

her the assignment failure always occurs in one frequency or is randomly disther the assignment failure always occurs in one frequency or is randomly dist

ributed.ributed.

Make driving test to see whether there is abnormal handover relation and doMake driving test to see whether there is abnormal handover relation and do

wnlink interference, so as to find the real cause of the congestion ratio.wnlink interference, so as to find the real cause of the congestion ratio.

Search the interference source with a spectrum analyzer.Search the interference source with a spectrum analyzer.

Observe whether the topography in the cell coverage is complex.Observe whether the topography in the cell coverage is complex.


Cases of TCH Congestion RatioCases of TCH Congestion Ratio

Cases of TCH Congestion Ratio ProblemCases of TCH Congestion Ratio Problem

Data configuration problem at A interface ----------------------- Case 1Data configuration problem at A interface ----------------------- Case 1

TRX board faulty , causing high congestion ratio ------------ Case 2TRX board faulty , causing high congestion ratio ------------ Case 2

Uplink hardware problem --------------------------------- Cases 3, Uplink hardware problem --------------------------------- Cases 3,

Downlink hardware problem ------------------------------------ Cases 4,5Downlink hardware problem ------------------------------------ Cases 4,5

Effect from booster attached to the cell -------------------------- Case 6Effect from booster attached to the cell -------------------------- Case 6

Other data configuration ------------------- Cases 7, 8Other data configuration ------------------- Cases 7, 8

Isolated site and complicated topography ----------- Case 9Isolated site and complicated topography ----------- Case 9


Fault description: Fault description: There is one BSC in the local network. And from one day on, There is one BSC in the local network. And from one day on,

TCH congestion ratio of the whole network begins to rise (frequency planning TCH congestion ratio of the whole network begins to rise (frequency planning

was not changed). TCH congestion ratio of the whole network (not including hwas not changed). TCH congestion ratio of the whole network (not including h

andover) is 4%(the congestion ratio on all busy is very low). In addition, many andover) is 4%(the congestion ratio on all busy is very low). In addition, many

cells but not a few cells are highly congested.cells but not a few cells are highly congested.

Case 1Case 1


Case 1Case 1

Analysis: Analysis:

1. Since the frequency plan is not adjusted, radio interface 1. Since the frequency plan is not adjusted, radio interface

problem is ruled out.problem is ruled out.

2. Congestion ratio is abnormal in most BTS. In this case, 2. Congestion ratio is abnormal in most BTS. In this case,

search in a smaller range to see whether the congestion search in a smaller range to see whether the congestion

problem is related to module or data modification.problem is related to module or data modification.

3. Analyze the main cause of TCH occupation failure 3. Analyze the main cause of TCH occupation failure

through traffic statistic and finally locate the problem as through traffic statistic and finally locate the problem as

data or hardware fault.data or hardware fault.


Troubleshooting: Troubleshooting:

1. View the traffic statistics . The problem occurs after BSC data are modified and loaded. Maybe it is rel1. View the traffic statistics . The problem occurs after BSC data are modified and loaded. Maybe it is rel

ated to BSC loading.ated to BSC loading.

2. Analyze traffic statistics to find that the highly congested cells are focused on module 1 of BSC. The2. Analyze traffic statistics to find that the highly congested cells are focused on module 1 of BSC. The

n the problem should be with module 1.n the problem should be with module 1.

3. Check the module to find that TCH occupation failure is mainly attributed to unavailability of terrestri3. Check the module to find that TCH occupation failure is mainly attributed to unavailability of terrestri

al resources. It shows that unavailability of terrestrial resource is the main cause of high congestion ratal resources. It shows that unavailability of terrestrial resource is the main cause of high congestion rat

io in module 1.io in module 1.

4. The cause of terrestrial resources unavailability is mainly on the circuit of Abis interface or A interfa4. The cause of terrestrial resources unavailability is mainly on the circuit of Abis interface or A interfa

ce. This problem occurs to many cells in module 1. However, it is quite unlikely that Abis interface is face. This problem occurs to many cells in module 1. However, it is quite unlikely that Abis interface is fa

ulty in many cells at the same time. Therefore, the cause should be the hardware or data at A interface.ulty in many cells at the same time. Therefore, the cause should be the hardware or data at A interface.

5. Check the hardware of A interface to find that the hardware is normal. A interface hardware problem i5. Check the hardware of A interface to find that the hardware is normal. A interface hardware problem i

s ruled out.s ruled out.

6. Check the data configuration of the trunk circuit of A interface to find that the CIC code of the first 32 6. Check the data configuration of the trunk circuit of A interface to find that the CIC code of the first 32

timeslots of group 0, module 1 is 65535. But group 0 of module 1 in the trunk group table corresponds ttimeslots of group 0, module 1 is 65535. But group 0 of module 1 in the trunk group table corresponds t

o the circuit from BSC to MSC. Obviously this CIC number is wrong. Change it to 0~31 and set dynamico the circuit from BSC to MSC. Obviously this CIC number is wrong. Change it to 0~31 and set dynamic

ally, and then the congestion ratio is lowered to normal.ally, and then the congestion ratio is lowered to normal.

Case 1Case 1


Conclusion: Conclusion:

1. In trunk circuit data configuration at A interface, CIC must be 1. In trunk circuit data configuration at A interface, CIC must be

correct, otherwise, TCH assignment will fail and the congestion correct, otherwise, TCH assignment will fail and the congestion

ratio will be high.ratio will be high.

2. In the meantime, if the CIC of two FTC boards (multiple trunk 2. In the meantime, if the CIC of two FTC boards (multiple trunk

circuits) are the same, this problem will also happen.circuits) are the same, this problem will also happen.

Case 1Case 1


Fault description: Fault description: The configuration of a specific BTS is S6/4/2 and it had The configuration of a specific BTS is S6/4/2 and it had

been running normally. One day, the result of traffic statistics shows that been running normally. One day, the result of traffic statistics shows that

TCH channel in cell 1 (6 TRX) overflows very seriously and the congestion TCH channel in cell 1 (6 TRX) overflows very seriously and the congestion

ratio comes to 20%.ratio comes to 20%.

1. The traffic of the cell is very low, which is about 0.8Erl in busy hours.1. The traffic of the cell is very low, which is about 0.8Erl in busy hours.

2. At the same time, the times of TCH occupation on all busy is 0.2. At the same time, the times of TCH occupation on all busy is 0.

3. Observe the channel status of all base bands in cell 1. It is all “Idle”.3. Observe the channel status of all base bands in cell 1. It is all “Idle”.

Case 2Case 2


Case 2Case 2

Analysis: Analysis:

1. No data have been adjusted and there is no hopping in the cell. 6 1. No data have been adjusted and there is no hopping in the cell. 6

TRX use different bands. It is unlikely that they are subject to TRX use different bands. It is unlikely that they are subject to

external interference at the same time. Therefore, it can not be Um external interference at the same time. Therefore, it can not be Um

interface interference or data problem.interface interference or data problem.

2. Check hardware specifically. Since the problem only occurs to 2. Check hardware specifically. Since the problem only occurs to

cell 1, we can block TRX in turn to determine which TRX causes the cell 1, we can block TRX in turn to determine which TRX causes the

assignment failure.assignment failure.

3. Find out whether there is hardware fault in the TRX for 3. Find out whether there is hardware fault in the TRX for

assignment failure. Check them one by one by means of resetting assignment failure. Check them one by one by means of resetting

and replacing.and replacing.



1. Check BT channel status through remote maintenance and find that there is possibil1. Check BT channel status through remote maintenance and find that there is possibil

ity of TCH occupation failure in BT4, BT5 in cell 1.ity of TCH occupation failure in BT4, BT5 in cell 1.

2. Block BT4 and BT5 as well as RC4 and RC5 at the same time and find that there is n2. Block BT4 and BT5 as well as RC4 and RC5 at the same time and find that there is n

o TCH congestion all the day. It indicates that the problem is on RC4 and RC5.o TCH congestion all the day. It indicates that the problem is on RC4 and RC5.

3. Unblock BT4, BT5, RC4, RC5, and reset RC4(TRX4), RC5(TRX5) and high congestion 3. Unblock BT4, BT5, RC4, RC5, and reset RC4(TRX4), RC5(TRX5) and high congestion

arise again.arise again.

4. Go to the BTS site and make a dial test with the frequency locked (on TRX4, TRX5), 4. Go to the BTS site and make a dial test with the frequency locked (on TRX4, TRX5),

TCH occupation failure still occurs. Exchange the slots of TRX4 and TRX5 and make thTCH occupation failure still occurs. Exchange the slots of TRX4 and TRX5 and make th

e dial test again (TRX4, TRX5). The TCH occupation failure persists. e dial test again (TRX4, TRX5). The TCH occupation failure persists.

5. Replace TRX4, TRX5 and make dial test with the frequency locked (on TRX4, TRX5), 5. Replace TRX4, TRX5 and make dial test with the frequency locked (on TRX4, TRX5),

TCH occupation is successful and there is no TCH congestion. The problem is solved.TCH occupation is successful and there is no TCH congestion. The problem is solved.

Case 2Case 2


Case 2Case 2


1. The faulty TCH TRX board causes TCH assignment failure and 1. The faulty TCH TRX board causes TCH assignment failure and

high congestion ratio.high congestion ratio.

2. Usually, the fault of TRX board can not be found on the BTS 2. Usually, the fault of TRX board can not be found on the BTS

maintenance console . The problem can be confirmed by blocking maintenance console . The problem can be confirmed by blocking

in turn.in turn.


Fault description: Fault description: A specific BTS is configured as S6/6/6. Since A specific BTS is configured as S6/6/6. Since

the BTS in service, the congestion ratio of the 3 cells is high. Check the BTS in service, the congestion ratio of the 3 cells is high. Check

and confirm that there is no interference.and confirm that there is no interference.

Case 3Case 3


Analysis: Analysis: There is no interference but congestion always exists after the BTS is in There is no interference but congestion always exists after the BTS is in

service, in every cell. But other BTS has no such problem, therefore, check hardware service, in every cell. But other BTS has no such problem, therefore, check hardware

of the BTS.of the BTS.

1. Hardware fault: communication is normal in every cell, so it is unlikely that there is 1. Hardware fault: communication is normal in every cell, so it is unlikely that there is

fault in the hardware of every cell.fault in the hardware of every cell.

2. Hardware connection: Check hardware connection carefully. Analyze the traffic 2. Hardware connection: Check hardware connection carefully. Analyze the traffic

measurement to locate whether the fault is in the uplink or the downlink and then measurement to locate whether the fault is in the uplink or the downlink and then

check the hardware connection of the uplink or the downlink.check the hardware connection of the uplink or the downlink.

Case 3Case 3



1. Register traffic statistics “Receiving Level Measurement Function” and 1. Register traffic statistics “Receiving Level Measurement Function” and

query the result of traffic statistics by time. It is found that when the receiving query the result of traffic statistics by time. It is found that when the receiving

level and receiving quality of different TRX boards in the same cell are the level and receiving quality of different TRX boards in the same cell are the

same, the number of downlink measurement reports is balanced but the same, the number of downlink measurement reports is balanced but the

number of uplink measurement reports is not, regularly unbalanced.number of uplink measurement reports is not, regularly unbalanced.

2. Check and find that the connection of TRX and CDU in the same cell is 2. Check and find that the connection of TRX and CDU in the same cell is

incorrect. After correction, the problem is solved.incorrect. After correction, the problem is solved.

Case 3Case 3


Case 3Case 3

14258222

16646294

293105655

501

303

702

Times of uplink receiving level grade 0 and receiving quality level 0

Times of uplink receiving level grade 0 and receiving quality level 1

Times of Uplink receiving level grade 0 and receiving quality level 2

30 minutes starting from 11:00 18-3-2001 Module ID 1, Cell ID 5, TRX No. 12Module ID 1, Cell ID 5, TRX No. 13Module ID 1, Cell ID 5, TRX No. 14Module ID 1, Cell ID 5, TRX No. 15Module ID 1, Cell ID 5, TRX No. 16Module ID 1, Cell ID 5, TRX No. 17


Case 3Case 3


Incorrect hardware connection will cause TCH assignment Incorrect hardware connection will cause TCH assignment

failure. The problem can be located accurately by analyzing failure. The problem can be located accurately by analyzing

different traffic statistics tasks.different traffic statistics tasks.

In this case, uplink hardware receiver problem is located In this case, uplink hardware receiver problem is located

through “Receiving Level Performance Measurement”.through “Receiving Level Performance Measurement”.


Fault description: Fault description: In a BTS S6/6/5, one cell has high congestion In a BTS S6/6/5, one cell has high congestion

one day. No adjustment has been made in this period.one day. No adjustment has been made in this period.

Case 4Case 4


Analysis: Analysis: There is no parameter adjustment before/after the fault, There is no parameter adjustment before/after the fault,

therefore attention should be focused on the hardware, to see therefore attention should be focused on the hardware, to see

whether there is any fault or alarm.whether there is any fault or alarm.

Case 4Case 4



1. Trace ABIS interface message of the BTS with a signaling analyzer MA10 and analyze the 1. Trace ABIS interface message of the BTS with a signaling analyzer MA10 and analyze the

signaling to find that in process of TCH assignment failure, the uplink signal in the signaling to find that in process of TCH assignment failure, the uplink signal in the

measurement report from the MS is of high quality after BSC sends ASSIGNMENT CMD, but measurement report from the MS is of high quality after BSC sends ASSIGNMENT CMD, but

the downlink signal level can not be resolved, i.e. the levels of uplink/downlink signals are the downlink signal level can not be resolved, i.e. the levels of uplink/downlink signals are

not balanced. Then ASSI FAILURE message is returned. It is also found that the assignment not balanced. Then ASSI FAILURE message is returned. It is also found that the assignment

is directed to the last TRX board in the cell.is directed to the last TRX board in the cell.

2. Block the TRX board channel temporarily and congestion ratio of the cell is lowered to 1%. 2. Block the TRX board channel temporarily and congestion ratio of the cell is lowered to 1%.

Perhaps there is problem in TRX board and the downlink hardware.Perhaps there is problem in TRX board and the downlink hardware.

3. Check and find that the Transmitting antenna&feeder VSWR is over 2.5 alarm on the 3. Check and find that the Transmitting antenna&feeder VSWR is over 2.5 alarm on the

combiner connected with TRX board. Process the antenna&feeder VSWR alarm and the combiner connected with TRX board. Process the antenna&feeder VSWR alarm and the

problem is solved.problem is solved.

Case 4Case 4


Conclusion: Conclusion: Antenna VSWR alarm results in large loss, small Antenna VSWR alarm results in large loss, small

coverage and assignment failure. When the MS is in the cell BCCH coverage and assignment failure. When the MS is in the cell BCCH

coverage, but not in the coverage area of the board where VSWR alarm coverage, but not in the coverage area of the board where VSWR alarm

occurs, assignment to this TRX board is easy to fail and the congestion occurs, assignment to this TRX board is easy to fail and the congestion

ratio in the cell goes up as a result.ratio in the cell goes up as a result.

Case 4Case 4


Fault description: Fault description: When a BTS O2 is expanded to O4, high When a BTS O2 is expanded to O4, high congestion ratio occurs, with the peak of 40%.congestion ratio occurs, with the peak of 40%.

Case 6Case 6


Case 6Case 6

Analysis: Analysis: Since congestion ratio is abnormal after Since congestion ratio is abnormal after

expansion, we canexpansion, we can

1. Check whether the congestion occurs to all TRX. If yes, 1. Check whether the congestion occurs to all TRX. If yes,

re-check the connection of newly added hardware of the re-check the connection of newly added hardware of the

BTS to see whether there is any fault.BTS to see whether there is any fault.

2. If congestion occurs to one or a few TRX, check the 2. If congestion occurs to one or a few TRX, check the

hardware of these TRX.hardware of these TRX.

3. When hardware problem is ruled out, consider external 3. When hardware problem is ruled out, consider external

cause. For example, the booster is not expanded, which cause. For example, the booster is not expanded, which

results in assignment failure.results in assignment failure.



1. Block TRX of the last two newly added TRX on the remote BTS maintenance console to find that 1. Block TRX of the last two newly added TRX on the remote BTS maintenance console to find that

the congestion ratio is lowered to normal status. Perhaps, the problem is related to the two boards.the congestion ratio is lowered to normal status. Perhaps, the problem is related to the two boards.

2. Trace and analyze ABIS interface signaling to find that the assignment failure occurs to the two 2. Trace and analyze ABIS interface signaling to find that the assignment failure occurs to the two

newly added TRX. When the assignment fails, SDCCH measurement report analysis shows that the newly added TRX. When the assignment fails, SDCCH measurement report analysis shows that the

level on SDCCH is normal and TA value is large and the assignment takes place in a distant area. level on SDCCH is normal and TA value is large and the assignment takes place in a distant area.

However, there is no measurement report on SACCH (TCH). Perhaps the two boards have hardware However, there is no measurement report on SACCH (TCH). Perhaps the two boards have hardware

problem in uplink/downlink tributaries. Sometimes the assignment of the two boards succeeds, so problem in uplink/downlink tributaries. Sometimes the assignment of the two boards succeeds, so

the boards could not be faulty.the boards could not be faulty.

3. A 4 in 1 combiner and a splitter are used in the cell, the antenna & feeder part can not have a 3. A 4 in 1 combiner and a splitter are used in the cell, the antenna & feeder part can not have a

hardware fault. Check the cable from TRX board to the combiner/splitter and no hardware problem is hardware fault. Check the cable from TRX board to the combiner/splitter and no hardware problem is

found. Basically it can not be a hardware problem.found. Basically it can not be a hardware problem.

4. It is told that this cell is attached with a repeater. After the expansion, the repeater did not lock the 4. It is told that this cell is attached with a repeater. After the expansion, the repeater did not lock the

two newly added TRX, which causes the assignment failure. When the repeater band problem is two newly added TRX, which causes the assignment failure. When the repeater band problem is

solved, the congestion problem is also solved.solved, the congestion problem is also solved.

Case 6Case 6



Because of the repeater, the coverage areas of the first two Because of the repeater, the coverage areas of the first two

TRX and the last two TRX in the same area are different, TRX and the last two TRX in the same area are different,

which results in the assignment failure.which results in the assignment failure.

Case 6Case 6


Fault description: In the optimization of a network, the congestion ratio (incFault description: In the optimization of a network, the congestion ratio (inc

luding handover) on busy hours of the two cells is as high as 10%. “TCH seiluding handover) on busy hours of the two cells is as high as 10%. “TCH sei

zure Excluding Handover” and “TCH block rate(meeting a TCH block state ozure Excluding Handover” and “TCH block rate(meeting a TCH block state o

n attempt TCH seizures)” are normal. Here, “TCH seizure failure (all)” is vern attempt TCH seizures)” are normal. Here, “TCH seizure failure (all)” is ver

y high, 89 times and 61 times respectively. But “TCH seizure failure for MOy high, 89 times and 61 times respectively. But “TCH seizure failure for MO

C” is 0”.C” is 0”.

The traffic is a little lower than that before optimization.The traffic is a little lower than that before optimization.

The interference band is normal.The interference band is normal.

Congestion ratio was normal before optimization.Congestion ratio was normal before optimization.

Case 8Case 8


Case 8Case 8

Analysis: Analysis: When the network planning parameters are optimized and When the network planning parameters are optimized and

modified, the congestion ratio of the two cells is higher and only the modified, the congestion ratio of the two cells is higher and only the

congestion ratio including handover is higher, therefore, radio congestion ratio including handover is higher, therefore, radio

interference or hardware fault can be ruled out. Analyze whether the interference or hardware fault can be ruled out. Analyze whether the

handover is abnormal.handover is abnormal.



1. Register “Incoming Inter cell Handover Measurement Function” for 15 minutes 1. Register “Incoming Inter cell Handover Measurement Function” for 15 minutes

in the two cells to find that all the handovers from a specific cell in the two cells to find that all the handovers from a specific cell

(CGI=*********1768) to these two cells fail, and the handover is not the actual cause (CGI=*********1768) to these two cells fail, and the handover is not the actual cause

of congestion.of congestion.

2. Failure of all handovers means that there is problem with the handover data. 2. Failure of all handovers means that there is problem with the handover data.

Check the handover data of the two cells to find that there is co-frequency and Check the handover data of the two cells to find that there is co-frequency and

co-BSIC as expected. The two cells are adjacent to the specific cell, therefore the co-BSIC as expected. The two cells are adjacent to the specific cell, therefore the

handover from the specific cell to any other cell will fail. The failure occurs when handover from the specific cell to any other cell will fail. The failure occurs when

TCH channel is assigned.TCH channel is assigned.

3. Modify the BCCH and BSIC of the two cells, and then the handover is recovered 3. Modify the BCCH and BSIC of the two cells, and then the handover is recovered

and congestion ratio is normal.and congestion ratio is normal.

Case 8Case 8


Case 8Case 8


1. Two cells (both adjacent to a specific cell) with co-frequency and 1. Two cells (both adjacent to a specific cell) with co-frequency and

co-BSIC will not only result in low in-cell handover success ratio, but co-BSIC will not only result in low in-cell handover success ratio, but

also high TCH congestion ratio (including handover).also high TCH congestion ratio (including handover).

2. The case indicates that TCH congestion ratio (including handover) 2. The case indicates that TCH congestion ratio (including handover)

and TCH congestion ratio (not including handover) are different.and TCH congestion ratio (not including handover) are different.


Case 9Case 9

Fault description: Fault description: Site O2 of a suburban county has suffered from high Site O2 of a suburban county has suffered from high

congestion ratio (not including handover), from 3% to 10% (in proportion to congestion ratio (not including handover), from 3% to 10% (in proportion to

traffic). But the congestion ratio on all busy is 0%.traffic). But the congestion ratio on all busy is 0%.

1. Block 2 TRX in turn, the congestion ratio remains serious as before.1. Block 2 TRX in turn, the congestion ratio remains serious as before.

2. Other indexes: dropout ratio is high (about 5%). Interference band is 2. Other indexes: dropout ratio is high (about 5%). Interference band is

normal.normal.


Case 9Case 9

Analysis: Analysis:

1. Since the congestion ratio is not very high, the problem may not be 1. Since the congestion ratio is not very high, the problem may not be

on the data or hardware.on the data or hardware.

2. The interference band is normal, so the interference at the Um 2. The interference band is normal, so the interference at the Um

interface is unlikely.interface is unlikely.

3. Analyze the cause of assignment failure. Take dropout ratio into 3. Analyze the cause of assignment failure. Take dropout ratio into

consideration and analyze the receiving performance of consideration and analyze the receiving performance of

uplink/downlink, including level, quality.uplink/downlink, including level, quality.


Case 9Case 9


1. View “Dropout Performance Measurement” to find that TA value is large upon View “Dropout Performance Measurement” to find that TA value is large upon

dropout, at a distance of 25.6km~31.1km away from the BTS.dropout, at a distance of 25.6km~31.1km away from the BTS.

2. View “Receiving Level Performance Measurement” to find that there are many 2. View “Receiving Level Performance Measurement” to find that there are many

measurement reports of low level grades.measurement reports of low level grades.

3. Analyze ABIS signaling to find that the uplink level is very low (about –98dbm) 3. Analyze ABIS signaling to find that the uplink level is very low (about –98dbm)

when the assignment fails.when the assignment fails.

4. Make a driving test on the site to find that the site is isolated, with large 4. Make a driving test on the site to find that the site is isolated, with large

coverage and complicated topography. When the MS is more than 25 kilometers coverage and complicated topography. When the MS is more than 25 kilometers

away from the BTS, it can receive –90dbm downlink signal. But the uplink signal away from the BTS, it can receive –90dbm downlink signal. But the uplink signal

is not enough, so TCH assignment fails.is not enough, so TCH assignment fails.


Case 9Case 9


1. Poor uplink coverage causes the high congestion ratio.1. Poor uplink coverage causes the high congestion ratio.

Adding BTS can help form a continuous coverage. Chan Adding BTS can help form a continuous coverage. Chan

ge the omni-directional site into a directional site by adjuge the omni-directional site into a directional site by adju

sting the antenna angle. Intensify the transmitting level asting the antenna angle. Intensify the transmitting level a

nd BTS receiver sensitivity. Avoid over coverage.nd BTS receiver sensitivity. Avoid over coverage.

2. Trace Abis port message on the BTS maintenance con2. Trace Abis port message on the BTS maintenance con

sole to analyze the assignment status.sole to analyze the assignment status.

SDCCH Congestion RatioSDCCH Congestion Ratio

SDCCH congestion ratioSDCCH congestion ratio

Basic principleBasic principle

Cause and locating methodCause and locating method

Cases analyzeCases analyze

Basic Principle of SDCCH Congestion RatioBasic Principle of SDCCH Congestion Ratio

Calculation formula:Calculation formula:

SDCCH congestion ratio=SDCCH occupation SDCCH congestion ratio=SDCCH occupation

on all busy times/SDCCH occupation request on all busy times/SDCCH occupation request

timestimesSDCCH occupation on all busy times:SDCCH occupation on all busy times:

SDCCH occupation failure due to all busySDCCH occupation failure due to all busy

The cause of SDCCH occupationThe cause of SDCCH occupation: :

1) The caller assignment command is sent to channels1) The caller assignment command is sent to channels

2) The called paging response is sent reported to channels2) The called paging response is sent reported to channels

3) Location updating3) Location updating

4) Short message4) Short message

5) IMSI detachment and attachment process5) IMSI detachment and attachment process

Basic Principle of SDCCH Congestion Ratio

Basic Principle of SDCCH Congestion Ratio

MS BTS BSC MSC

BSC random access – immediate assignment

Cell SDCCH occupation request times

Channel Required

Channel Request (RACH)

Cell immediate assignment request times

Cell SDCCH occupation failure BTSS008015

SDCCH Channel No Resource

Cell SDCCH occupation on all busy 008014

Immediate Assignment Command

Immediate Assignment Reject

Cause of SDCCH Congestion and Locating the Cause


Location area boundary results in excessive SDCCLocation area boundary results in excessive SDCCH location updatingH location updatingPolicy: Modify location area selectionPolicy: Modify location area selectionModify CRH (Cell Reelect Hysteresis)Modify CRH (Cell Reelect Hysteresis)Modify the parameters of periodical area updating.Modify the parameters of periodical area updating.Modify the frequent handover problem of the dual-frequency netModify the frequent handover problem of the dual-frequency network.work.

Excessive short messagesExcessive short messages

Policy: Add SDCCH channelPolicy: Add SDCCH channel



Insufficient system capacity: more SDCCH should be configureInsufficient system capacity: more SDCCH should be configuredd

Policy: expansionPolicy: expansion

Improper setting of system parameters,RACH system parameteImproper setting of system parameters,RACH system parameter. Actually multiple SDCCH are assigned.r. Actually multiple SDCCH are assigned.

Policy: Increase RACH access threshold (for coping with interferPolicy: Increase RACH access threshold (for coping with interference).ence).Decrease MAX re-transmitting times and increase extended tranDecrease MAX re-transmitting times and increase extended transmission timeslots appropriatelysmission timeslots appropriately

Dynamic SDCCH allocationDynamic SDCCH allocation

Board (TRX) fault and transmission fault result in SDCCH congBoard (TRX) fault and transmission fault result in SDCCH congestionestion

Cases of SDCCH Congestion Ratio Problem


SDCCH Congestion CasesSDCCH Congestion Cases



In a network, the radio call complete ratio is low. Analyze In a network, the radio call complete ratio is low. Analyze

the traffic statistics to find that SDCCH congestion only the traffic statistics to find that SDCCH congestion only

occurs to a few sites.occurs to a few sites.

Case 1: Case 1:



【【 AnalysisAnalysis 】】 : : Since only a few BTS are congested, Since only a few BTS are congested,

please register “SDCCH Measurement Function” and please register “SDCCH Measurement Function” and

analyze the shares of respective causes for SDCCH analyze the shares of respective causes for SDCCH

occupation. Solve the problems accordingly.occupation. Solve the problems accordingly.

Case 1 Case 1



【【 TroubleshootingTroubleshooting】】 : :

1. Analyze traffic measurement : in the congested cell, SDCCH is occupied for 300-400 times in 1. Analyze traffic measurement : in the congested cell, SDCCH is occupied for 300-400 times in

busy hours. They are all S1/1/1 BTS. Each cell is configured with SDCCH/8 channels. Normally, they busy hours. They are all S1/1/1 BTS. Each cell is configured with SDCCH/8 channels. Normally, they

are capable of supporting with 300-400 SDCCH occupations. But it is strange enough that there are are capable of supporting with 300-400 SDCCH occupations. But it is strange enough that there are

only dozens of SDCCH congestion in each cell on busy hours.only dozens of SDCCH congestion in each cell on busy hours.

2. Register “SDCCH Measurement Function” to find that most SDCCH occupations are attributed to 2. Register “SDCCH Measurement Function” to find that most SDCCH occupations are attributed to

location updating. Analyze the cell locations and find that the above congested BTS are at the cross location updating. Analyze the cell locations and find that the above congested BTS are at the cross

points of two location area on railway lines. This gives us a hint that maybe sudden location points of two location area on railway lines. This gives us a hint that maybe sudden location

updating results in SDCCH congestion.updating results in SDCCH congestion.

3. Register “SDCCH Measurement Function” for five minutes to find that locations are always 3. Register “SDCCH Measurement Function” for five minutes to find that locations are always

updated in a specific 5 minutes. Query the train timetable to find that 4 or 5 trains pass by the point updated in a specific 5 minutes. Query the train timetable to find that 4 or 5 trains pass by the point

in this period. When the trains pass by, a large amount of location updating occur in a short, which in this period. When the trains pass by, a large amount of location updating occur in a short, which

results in the congestion.results in the congestion.

4. Add SDCCH or enable SDCCH dynamic allocation function.4. Add SDCCH or enable SDCCH dynamic allocation function.

Case 1Case 1



【【 ConclusionConclusion 】】 : :

For SDCCH congestion due to location updating, check For SDCCH congestion due to location updating, check

whether it is caused by improper setting of location area. whether it is caused by improper setting of location area.

This case is a special one. Add SD or enable dynamic This case is a special one. Add SD or enable dynamic

allocation function to solve the problem.allocation function to solve the problem.

Case 1 Case 1



【【 Fault descriptionFault description 】】Deploy a BTS30 base station. After the deployment, SDCCH channel is Deploy a BTS30 base station. After the deployment, SDCCH channel is

always in all busy status (A). TCH channel is in (I) or (A) status. When always in all busy status (A). TCH channel is in (I) or (A) status. When

the call is connected, the communication is normal. Observe the traffic the call is connected, the communication is normal. Observe the traffic

statistics and find that the SDCCH assignment of traffic statistics fails statistics and find that the SDCCH assignment of traffic statistics fails

about 1000 times (in busy hours).about 1000 times (in busy hours).

Case 3Case 3



【【 AnalysisAnalysis 】】 : :

1. Since SDCCH is congested after the BTS deployment, but TCH and com1. Since SDCCH is congested after the BTS deployment, but TCH and com

munication are normal. First check data and hardware. The whole site suffmunication are normal. First check data and hardware. The whole site suff

ers from congestion problem. Swap ports with other sites of the same typers from congestion problem. Swap ports with other sites of the same typ

e to confirm whether there is data problem or hardware problem under Abe to confirm whether there is data problem or hardware problem under Ab

is interface.is interface.

2. If data problem and hardware problem are ruled out, attention should b2. If data problem and hardware problem are ruled out, attention should b

e focused on the transmission problem.e focused on the transmission problem.

Case 3Case 3



【【 TroubleshootingTroubleshooting 】】1. Check alarm: LAPD link fault alarm and recovery alarm (within one second). The 1. Check alarm: LAPD link fault alarm and recovery alarm (within one second). The

alarm appears once per ten minutes.alarm appears once per ten minutes.

2. Check the data to find no problem. At night, exchange with BIE port of other BTS of 2. Check the data to find no problem. At night, exchange with BIE port of other BTS of

the same type, other sites work normally but problem of this site persists. Data problem the same type, other sites work normally but problem of this site persists. Data problem

and BSC side hardware problem are ruled out.and BSC side hardware problem are ruled out.

3. Since the BTS is far from the city , first register the transmission related traffic 3. Since the BTS is far from the city , first register the transmission related traffic

measurement . Observe the result (related to transmission) and find no problem, but measurement . Observe the result (related to transmission) and find no problem, but

SDCCH traffic measurement remains abnormal.SDCCH traffic measurement remains abnormal.

4. Replace TMU and TRX board in the BTS and the problem persists.4. Replace TMU and TRX board in the BTS and the problem persists.

5. Measure the transmission and self-loop BIE, then It is found that there is bit error in 5. Measure the transmission and self-loop BIE, then It is found that there is bit error in

the transmission. Test the line section by section and find that in a segment of access the transmission. Test the line section by section and find that in a segment of access

network from a county to the BTS, one 2M transmission board is faulty. Replace the network from a county to the BTS, one 2M transmission board is faulty. Replace the

board and the problem is solved (the two BTS are on the same board).board and the problem is solved (the two BTS are on the same board).

Case 3Case 3



【【 ConclusionConclusion 】】 : :

The causes of SDCCH congestion can be :The causes of SDCCH congestion can be :

1. Data configuration error1. Data configuration error

2. SDCCH channels insufficient2. SDCCH channels insufficient

3. Um interface problem (interference, low level, uplink/downlink unbalance)3. Um interface problem (interference, low level, uplink/downlink unbalance)

4. Hardware fault4. Hardware fault

5. Transmission quality problem5. Transmission quality problem

In this case, the cause is item 5 mentioned above. Due to transmission bit error, large In this case, the cause is item 5 mentioned above. Due to transmission bit error, large

number of data are lost at SDCCH assignment or data are resent many times to number of data are lost at SDCCH assignment or data are resent many times to

timeout after the data loss. This causes the occupation failure and hence the high timeout after the data loss. This causes the occupation failure and hence the high

congestion.congestion.

Case 3Case 3



【【 Fault descriptionFault description】】A complaint is received that mobile subscribers near 4 sites (ABCD) of a local A complaint is received that mobile subscribers near 4 sites (ABCD) of a local

network can not make calls, but there no related alarm information on the alarm network can not make calls, but there no related alarm information on the alarm

maintenance console.maintenance console.

1. Check the 4 BTS, the board status is all normal. Almost no TCH channel is 1. Check the 4 BTS, the board status is all normal. Almost no TCH channel is

occupied. Sometimes one TCH is occupied, it becomes idle in several seconds. All occupied. Sometimes one TCH is occupied, it becomes idle in several seconds. All

SDCCH channels are in A status.SDCCH channels are in A status.

2. It is learnt that .BTS-A is attached under it with BTS-B and BTS-C. BTS-D, using a 2. It is learnt that .BTS-A is attached under it with BTS-B and BTS-C. BTS-D, using a

primary combiner (a transmission timeslot multiplexer), shares a 2M transmission primary combiner (a transmission timeslot multiplexer), shares a 2M transmission

line with BTS-A.line with BTS-A.

Case 4Case 4



【【 AnalysisAnalysis 】】

The symptom can help judge whether the problem is on the hardware or The symptom can help judge whether the problem is on the hardware or

on the transmission. But it is unlikely that faults occur to hardware of the on the transmission. But it is unlikely that faults occur to hardware of the

4 BTS. The transmission lines of the 4 BTS are related, therefore, check 4 BTS. The transmission lines of the 4 BTS are related, therefore, check

the transmission carefully.the transmission carefully.

Case 4Case 4



【【 TroubleshootingTroubleshooting】】1. Carefully observe 32BIE indicator to find that the indicator flashes every 12 seconds. It indicates 1. Carefully observe 32BIE indicator to find that the indicator flashes every 12 seconds. It indicates

that there is bit error in the transmission. Check the microwave and optical transceiver and no that there is bit error in the transmission. Check the microwave and optical transceiver and no

abnormal indication is found.abnormal indication is found.

2. Check ABIS interface signaling to find that a large number of PAGING_CMD messages are 2. Check ABIS interface signaling to find that a large number of PAGING_CMD messages are

generated. Among them, one RF_RESORCE_INDICATION message is generated occasionally. generated. Among them, one RF_RESORCE_INDICATION message is generated occasionally.

There is no CHAN_ACTIV, CHAN_ACTIV_ACK or IMMEDIATE_ASSIGN_COMMAND message. It There is no CHAN_ACTIV, CHAN_ACTIV_ACK or IMMEDIATE_ASSIGN_COMMAND message. It

indicates that SDCCH channel is not activated.indicates that SDCCH channel is not activated.

3. Check data O&M log, and find no data modification has been done in a few days in the past. 3. Check data O&M log, and find no data modification has been done in a few days in the past.

Therefore data problem is ruled out.Therefore data problem is ruled out.

4. Check the indicator of corresponding ports of 32BIE and find that the indicator is off. It seems 4. Check the indicator of corresponding ports of 32BIE and find that the indicator is off. It seems

that the transmission is normal.that the transmission is normal.

5. Reload and activate the board software of BTS-ABCD, and find that the system response is slow, 5. Reload and activate the board software of BTS-ABCD, and find that the system response is slow,

even with communication timeout prompt. When the board is loaded and activated, SDCCH is still even with communication timeout prompt. When the board is loaded and activated, SDCCH is still

congested. Users still complain that they can hardly call out. Since the 4 sites share one 2M congested. Users still complain that they can hardly call out. Since the 4 sites share one 2M

transmission line and SDCCH occupation is abnormal at the same time, it is concluded that it is transmission line and SDCCH occupation is abnormal at the same time, it is concluded that it is

transmission problem.transmission problem.

Case 4Case 4



【【 TroubleshootingTroubleshooting】】6. The only transmission equipment in doubt after the resetting --- primary 6. The only transmission equipment in doubt after the resetting --- primary

combiner (resetting causes the re-initialization of ABCD). After ABCD combiner (resetting causes the re-initialization of ABCD). After ABCD

initialization is complete, and it is found that SDCCH are fully occupied and TCH initialization is complete, and it is found that SDCCH are fully occupied and TCH

can be occupied normally. Trace ABIS interface signaling, CHAN_ACTIV, can be occupied normally. Trace ABIS interface signaling, CHAN_ACTIV,

CHAN_ACTIV_ACK or IMMEDIATE_ASSIGN_COMMAND message appears. CHAN_ACTIV_ACK or IMMEDIATE_ASSIGN_COMMAND message appears.

SDCCH is no longer congested. Users on the site say that they can make calls SDCCH is no longer congested. Users on the site say that they can make calls

normally.normally.

7. The same problem may occur to the primary combiner, therefore the operator 7. The same problem may occur to the primary combiner, therefore the operator

is recommended to use optical transmission circuit. After the modification, the 4 is recommended to use optical transmission circuit. After the modification, the 4

BTS have been running normally.BTS have been running normally.

Case 4Case 4



【【 ConclusionConclusion】】 : :

The transmission problem causes SDCCH congestion. But transmission problem is The transmission problem causes SDCCH congestion. But transmission problem is

attributed to different causes. In this case, the fault on the primary combiner results in the attributed to different causes. In this case, the fault on the primary combiner results in the

transmission problem. All BTS connected with this transmission equipment have the same transmission problem. All BTS connected with this transmission equipment have the same

problem. In handling this type of problems, try to find the similarity of the problem and problem. In handling this type of problems, try to find the similarity of the problem and

finally locate the problem with the exclusive method.finally locate the problem with the exclusive method.

Case 4Case 4

Documents

OMD6072 Case Analysis--Congestion ISSUE1.1.ppt