OMF000405 Case Analysis-Congestion ISSUE1.4

OMF000405 Case Study -Congestion ISSUE1.4

OMF000405 Case Study OMF000405 Case Study --Congestion ISSUE1.4Congestion ISSUE1.4

Wireless Training Department

TCH congestion

SDCCH congestion

Course ContentsCourse Contents

TCH congestionTCH congestion

! TCH congestion" Basic principle

" Causes for high TCH congestion

" Case study of TCH congestion


! Basic principle of TCH congestion

" Definition of TCH congestion rate

" Measurement point for TCH congestion and analysis


! Definition of TCH congestion rate

" TCH congestion rate (excluding handover)

=(TCH seizure failures for call + TCH seizure failures for very early assignment) / (Attempted TCH seizures + Attempted TCH seizures for very early assignment) *100%


! Definition of TCH Congestion rate

" TCH congestion rate (including handover)

=(TCH seizure failures for call + TCH seizure failures for very early assignment + TCH seizure failures for intra BSC incoming cell handover (no radio resource) + TCH seizure failures for inter BSC incoming cell handover (no radio resource) ) / (Attempted TCH seizures (all) + Attempted TCH seizures for very early assignment + Attempted TCH seizures for intra BSC incoming cell handover + Attempted TCH seizures for inter BSC incoming cell handover)


Traffic Measurem

ent Point of Traffic M

easurement Point of

TCH

Congestion rate

TCH

Congestion rate

Channel_ActiveChannel_Active_Ack

IMMEDIATE ASSIGN COMMAND

BTS BSC MSCMSChannel_Req

first SABM Establish_IND( CM Service Req)CR(Complete_l3_information)

CC

SetupCall Proceeding

Assignment_Req

ASSIGNMENT COMMANDfirst SABM Establish_IND

ASSIGNMENT CMP Assignment_CMPAlerting

ConnectConnect AckCommunication

DisconnectRelease

Release CompleteClear_CMDClear_CMP

CM Service Accepted

Channel_Active

Channel_Active_Ack

UA

SDCCHSDCCH

SACCH(TCH)SACCH(TCH)

MS call flow as the caller


! Attempted TCH seizures measurement point

" Attempted TCH seizures for call

# Receive the MSC assignment request message

" Attempted TCH seizures for very early assignment

# When there is no resource for SDCCH allocation and very early assignment is permitted

# When channel required is received and channel type is TCH

" Attempted TCH seizures for intraBSC incoming cell handover

# When intraBSC incoming cell handover request message is received (non-SDCCH handover request).

" Attempted TCH seizures for interBSC incoming cell handover

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

! TCH seizure failures:

" TCH seizure failures for call,

" TCH seizure failures for very early assignment,

" TCH seizure failures for interBSC incoming cell handover,

" TCH seizure failures for intraBSC incoming cell handover,

" TCH seizure failures for intracell handover.


! TCH seizure failures for call measurement point:

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

" (2)CLEAR_CMD is received in process of outgoing BSC handover. The cause of handover is direct retry.

" (3)CLEAR_CMD is received in process of assignment

" (4)RR_ABORT_REQ is received in process of outgoing BSC handover and the cause of handover is direct retry.

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

" (6)MSG_HO_REQ_REJ is received in process of outgoing BSC handover (direct retry).


! TCH seizure failures for call measurement point:

" (7) HO_FAIL is received in outgoing BSC handover (direct retry)

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

" (9) When assignment failure message is sent.

" (10)TN_T7 (direct retry) timeout (outgoing BSC handover request)

" (11)TN_T8 (direct retry) timeout (outgoing BSC handover complete)


! TCH seizure failures for very early assignment measurement point:

" (1)CH_ACT_NACK is received in the very early TCH assignment process. (CH_ACT_NACK is received in WAIT_RR_EST status in satellite transmission BTS)

" (2)In very early TCH assignment process, the returned cause is (internal error) CVI_INTERNAL_ERR when channel is being allocated.

" (3)In very early TCH assignment process, the returned cause is (channel request illegal) CVI_NO_ACCEPT when channel is being allocated.

" (4)In very early TCH assignment process, no channel is allocated.

" (5)TN_WAIT_CH_ACT timeout in very early TCH assignment process.



! TCH seizure failures for intraBSC incoming cell handover measurement point:

" TCH channel allocation fails at intraBSC incoming cell handover

! TCH seizure failure for interBSC incoming cell handover measurement point:

" When interBSC incoming cell handover failure message is sent because there is no TCH channel


! TCH seizure failure for intracell handover measurement point:

" In the new TCH activation procedure, this item is measured when the serving cell receives the CHANNEL ACTIVATION NEGATIVE ACKNOWLEDGE message from the BTS.

" This item is measured if the implementation of intracell handover procedure fails because the encryption algorithm in Intracell Handover Request message does not support.

" No response after the timer (internal timer, 5 seconds) timeout when the serving cell activates the new TCH.

" In intracell handover procedure, When TCH requested but there is no TCH available in the serving cell, and this leads to the

handover failure. In this case, this item is measured.

! TCH seizure failures due to A-interface failures measurement point:

" A interface

# After MSC sends Assignment_Req, if trunk circuit at A-interface is fault, BSC will return Assignment_Failure directly.

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


! TCH seizure failures due to Abis interface and Um interface failures

" Abis interface and Um interface

# 1. TRX board is faulty or performance unstable

# 2. Unbalance of uplink/downlink level for BTS

# 3. Poor quality of uplink/downlink signal caused by interference

# 4. SDCCH and TCH belong to different TRX board which have different coverage.


! Causes for high TCH congestion

! Troubleshooting for high TCH congestion

Causes for High TCH CongestionCauses for High TCH Congestion

Causes for High TCH CongestionCauses for High TCH Congestion

! Causes of high TCH congestion rate

" Incorrect configuration of trunk circuit data at A interface

" Co-frequency and co-BSIC lead to TCH assignment failure in handover

" Board fault or unstable performance causes the high congestion rate

" BTS hardware is not properly installed, which causes uplink/downlink signal level unbalance and TCH congestion.

" The transmitting power of BCCH TRX is too much higher than that of TCH TRX in the same cell.

" Interference causes the congestion

" TCH assignment failure due to isolated site and complicated topography result in the high congestion rate

TCH CongestionTCH Congestion

! How to locate the causes of high TCH congestion rate

" Analyze the causes of congestion remotely

# 1. Traffic statistics

# 2. Alarm information

# 3. BTS remote maintenance on OMC

# 4. Abis interface message analysis

" Check BTS on-site


! Remote analysis 1: traffic statistics

" In “TCH Measurement Function”, check the channels are all busy or not

# If yes, perform load handover or suggest capacity expansion.

# If not, check interference bands 1~5. if the cause is interference, the call drop rate of the cell will also be high.

" Register “Receiving Level Measurement Function”

# 1. Check the result by object to see whether the numbers of uplink and downlink reports on the same TRX board are balanced. So we can know the uplink and downlink are balanced or not.

# 2. Check the result by time to see whether TRX measurement reports are excessive. So we can know the congestion is related to TRX board or not .

! Remote analysis 2: alarm information

" Check alarms of the site which has high congestion rate.

" Check whether there is any abnormal alarm, such as voltage standing wave rate alarm, PCM out of frame alarm and uplink data bus alarm. Judge whether the congestion rate is associated with alarms in traffic statistics .


! Remote analysis 3: BTS remote maintenance on OMC

" On the BTS remote maintenance console, block TCH board in turn. Observe whether the congestion rate is related to the TRX board.


! Remote analysis 4: Abis interface message analysis.

" Trace Abis interface message of the congested BTS, analyze Assignment CMD sent on SDCCH

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

– TRX board faulty or performance unstable.

– Uplink/downlink unbalance, hardware problem in uplink or downlink.

– Bad quality of uplink or downlink signal. Analyze TA value of MS to locate interference.

# If the assignment fails on the boards of the whole cell randomly, analyze the measurement reports. The causes may be the following:

– The topography in the cell coverage is quite complicated.

– There is interference in the whole cell, such as interference from repeater.



! Check BTS on-site

" Check antenna and feeder for any problem of uplink or downlink.

" Dial test at the same place to see whether the assignment failure always occurs in a certain TRX or in the cell randomly.

" Make driving test to see whether there is abnormal handover relationship and downlink interference, so as to find the cause of the congestion rate.

" Search the interference source with a spectrum analyzer.

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


Case Study of TCH CongestionCase Study of TCH Congestion

! Cases of TCH congestion

" Case 1: A interface data configuration mistake

" Case 2: TRX board fault

" Case 3: Uplink hardware problem

" Case 4: Downlink hardware problem

" Case 5: Effect from repeater in the cell

" Case 6: Other data configuration mistake

" Case 7: Isolated site and complicated topography

! Case 1 fault description :

" There is one BSC in the local network. From one day, TCH congestion rate (excluding handover) of the whole network increase to 4%, and most of cells are highly congested.

A-interface Data Configuration MistakeA-interface Data Configuration Mistake

! Case 1 analysis:

" Since the frequency had not been changed, Um interface problem is excluded.

" Congestion rate is abnormal for most BTS. In this case, we can search in a smaller range to see whether the congestion problem is related to a certain module or data modification.

" Analyze the main cause of TCH seizure failure through traffic statistic and finally locate the problem caused by data or hardware.

A-interface Data Configuration MistakeA-interface Data Configuration Mistake

! Case 1 Troubleshooting:

" 1.Analyze traffic statistics. The problem occurs after BSC data modified and reloaded. Maybe it is related to BSC reloading.

# Analyze traffic statistics and find that the highly congested cells are all on module 1 of BSC, so the problem should related to module 1.

# Check TCH seizure failures (requested terrestrial resource unavailable), It shows that unavailability of terrestrial resource is the main cause of high congestion rate in module 1.

# The cause of terrestrial resources unavailability is mainly on Abisinterface or A interface. It is quite unlikely that Abis interface is faulty for many cells in module 1 at the same time. Therefore, the cause should be the hardware or data at A interface.


! Case 1 Troubleshooting:

" 2.Check the hardware of A interface and find that the hardware is normal. A interface hardware problem is excluded.

" 3. Check the data configuration of A interface trunk circuit andfind 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 to the circuit from BSC to MSC. Obviously this CIC number is wrong. Change it to “0~31”, and then the congestion rate becomes normal.


! Case 1 conclusion:

" 1. In trunk circuit data configuration at A interface, CIC must be correct, otherwise, TCH assignment will fail and the congestion rate will be high.

" 2. In the meantime, if the CIC of two FTC boards (multiple trunkcircuits) are the same, this problem will also happen.


! Case 2 fault description :

" The configuration of a BTS is S6/4/2 and it had been on service successfully. One day, the result of traffic statistics shows that TCH channel in cell 1 (6 TRX) congestion rate comes to 20%.

" The traffic volume of the cell is very low, it is about 0.8Erl in busy hour.

" At the same time, the times of “TCH seizure failures for call (no radio resource)” is 0.

" Observe the channel status in cell 1, all of channels are “Idle”.

TRX Board FaultTRX Board Fault


! Case 2 analysis:

" 1. No data has been adjusted and there is no hopping in the celland 6 TRXs use different frequencies, it is unlikely that they are subject to external interference at the same time. Therefore, itcan not be Um interface interference or data problem.

" 2. Check hardware specifically. Since the problem only occurs to cell 1, we can block TRX one by one to determine which TRX causes the assignment failure.

" 3.Find whether there is hardware fault in the TRX for assignment failure. Confirm the fault TRX by means of resetting and replacing.


! Case 2 troubleshooting:

" 1. Check BT channel status on OMC and find that there is possibility of TCH seizure failure in BT4 of cell 1.

" 2. Block TRX4, there is no TCH congestion all the day. It indicate problem is on TRX4.

" 3. Unblock TRX4 and reset them, congestion appear again.

" 4. Go to BTS site and make a dial test on TRX4, TCH seizure failure still occurs. Interchange the slots of TRX4 and TRX5, make the dial test again on TRX5. The TCH seizure failure persists.

" 5. Replace TRX4 and make dial test, there is no TCH congestion.



" 1.Faulty TCH TRX board causes TCH seizure failures and high congestion rate.

" 2. Usually, the fault of TRX board can not be found on the BTS maintenance console. The problem can be confirmed by blocking TRXs in turn.

! Case 3 fault description:

" A certain BTS configuration is S6/6/6, the congestion rate of the 3 cells are all high since the BTS on service. Having checked and confirmed that there is no interference.

Uplink Hardware ProblemUplink Hardware Problem

! Case 3 analysis:

" There is no interference but congestion always exists after the BTS on service in every cell. Check hardware of the BTS first.

# Hardware fault: communication is normal for every cell, so it isunlikely that there is fault in the hardware of every cell.

# Hardware connection: Analyze the traffic statistics for uplink or downlink and then check the hardware connection of uplink or downlink.



" Register traffic statistics “Receiving Level Measurement Function” and query the result by time. It is found that when the receiving level and quality of different TRX boards in the same cell are the same, the number of downlink measurement reports is equivalent, but the number of uplink measurement reports is not equivalent.

" Check hardware and find that the connection of TRX and CDU in the same cell is incorrect. After correction, the problem is solved.


Case 3Case 3

14258222

16646294

293105655

501

303

702

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

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

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

30 minutes starting from

11:00 18-3-2001

Module ID 1, Cell ID 5, TRX No. 12








" Incorrect hardware connection will cause TCH seizure failure. The problem can be located accurately by analyzing traffic statistics. In this case, uplink hardware receiver problem is located through “Receiving Level Measurement Function”.



" In a S6/6/5 BTS, one cell has high congestion rate one day. No adjustment has been performed in this period.

Downlink Hardware ProblemDownlink Hardware Problem

! Case 4 analysis:

" There is no parameter adjustment before the fault, so we should focus on the hardware, to see whether there is any fault or alarm.



" Trace Abis interface message of the BTS and analyze the signaling and find that in process of TCH seizure failure, the uplink signal in the measurement report from MS is good, after BSC sends ASSIGNMENT CMD, the downlink channel can not be seized. So the signal levels of uplink and downlink are not balanced, then ASSI FAILURE message is appeared. It is also found that the failure related to the last TRX board of the cell.

" Block TRX board and congestion rate of the cell is less than 1%.There is problem in TRX board of downlink hardware.

" Check and find that the VSWR of TX antenna and feeder connected with this TRX board is higher than 2.5. Process the antenna& feeder VSWR alarm, problem solved.



" Antenna VSWR alarm results in larger loss, less coverage and assignment failure. When MS is in BCCH TRX coverage, signal level is good enough, but after assignment a TCH in the board where VSWR alarm occurs, MS TCH seizure fails and the congestion rate is increased.



" When an O2 BTS is expanded to O4, high congestion rate occurs. The peak value of congestion rate is as high as 40%.

Effect from Repeater in the CellEffect from Repeater in the Cell

! Case 5 analysis:

" Since congestion rate is abnormal after expansion

# Check whether the congestion occurs to all TRX. If yes, re-check the connection of newly added hardware of the BTS to see whetherthere is any fault.

# If congestion occurs to one or a few TRXs, check the hardware ofthese TRXs.

# When hardware problem is excluded, consider external causes. Forexample, the repeater is not expanded, which results in assignment failure.



" Block TRX of the last two newly added TRX on OMC and find that the congestion rate is lowered to normal status. Perhaps, the problem is related to newly added boards.

" � Analyze Abis interface signaling, the assignment failure occurs on the two newly added TRXs. And SDCCH measurement report analysis shows that the level on SDCCH is normal and TA value islarge. However, there is no measurement report on SACCH (TCH). Because sometimes the assignment of the two TRXs succeed, so it is impossible that these tow newly added TRXs are both faulty.

" � Operator told that there is a repeater in the cell. When expansion, the repeater did not lock on the two newly added TRXs. Confirm and reconfigure repeater, problem solved.



" Because of the repeater, the actual coverage areas of the existing two TRX and the expanded two TRX are different, which results in the assignment failure.



" In network optimization, the congestion rate (including handover) on busy hours of the two cells is as high as 10%. “TCH seizure failures excluding handover” and “TCH seizure failures for call (no radio resource)” are normal. Here, “TCH seizure failures (all)” is very high, 89 times and 61 times respectively, but “TCH seizure failures for MOC” is 0”.

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

" The interference band is normal.

" Congestion rate is normal before optimization.

Other Data Configuration MistakeOther Data Configuration Mistake

! Case 6 analysis:

" When the network parameters are modified, the congestion rate of the two cells is higher and only the congestion rate (including handover) is higher, therefore, radio interference or hardware fault can be excluded. Mainly analyze whether the handover is abnormal or not.



" Register “Incoming Inter Cell Handover Measurement Function”for 15 minutes, and find that all the handovers from cell A (CGI=*********1768) to these two cells all fail, and the handover failure cause is not congestion.

" Failures of all handovers mean that there is problem with the handover data. Check the handover data of the two cells and find that there is co-frequency and co-BSIC as supposed, the two cells are adjacent cell of cell A, therefore the handover from the cell A to the two cells will fail.

" Change the BCCH and BSIC of one cell, and then the handover problem disappears and congestion rate become normal.



" Two cells (both adjacent to cell A) with co-frequency and co-BSIC will result in result in low incoming cell handover successful rate, but also high TCH congestion rate (including handover).

" The case indicates that TCH congestion rate (including handover) and TCH congestion rate (excluding handover) are different.



" An O2 site in a suburban county has suffered from high congestion rate (excluding handover), from 3% to 10% (in proportion to traffic volume). But the “TCH seizure failures for call (no radio resource)” is 0%.

# 1. Block 2 TRX in turn, the congestion rate is serious as before.

# 2. Other indexes: call drop rate is high (about 5%). Interference band is normal.

Isolated Site and Complicated TopographyIsolated Site and Complicated Topography


! Case 7 analysis:

" 1. Since the congestion rate is not very high, the problem may not be on the data or hardware.

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

" 3. Analyze the cause of assignment failure. Take call trop rate into consideration and analyze the receiving performance of uplink or downlink, including level and quality.


" Check “Call Drop Measurement” and find that TA value is large when call drop, the distance is about 25.6Km~31.1Km away from the BTS.

" View “Receiving Level Measurement Function” and find that there are many measurement reports of low signal level.

" Analyze Abis signaling and find that the uplink level is very low (about -98dBm) when the assignment fails.

" Drive test on-site and find the site is isolated, with large coverage and complicated topography. When the MS is more than 25 Km away from the BTS, it can receive -90dBm downlink signal. But the uplink signal is not enough, so TCH assignment fails.



" Poor uplink coverage causes the high congestion rate. Adding BTS can help to obtain a continuous coverage. Change the omni site into directional site or add TMA can improve uplink strength and avoid over shooting of downlink.


TCH congestion

SDCCH congestion

Course ContentsCourse Contents

SDCCH Congestion SDCCH Congestion

! SDCCH congestion " Basic principle

" Causes for SDCCH congestion and solutions

" Case study of SDCCH congestion

SDCCH CongestionSDCCH Congestion

! Formula for SDCCH congestion rate:

" SDCCH congestion rate=Attempted SDCCH seizures meeting a SDCCH blocked state /Attempted SDCCH seizures (all)

! Causes of SDCCH seizure:

" SDCCH assignment for MOC

" SDCCH assignment for MTC

" Location update

" SDCCH handover

" Short message

" IMSI attach and detach

SDCCH CongestionSDCCH CongestionMS BTS BSC MSC

BSC random access – immediate assignment

Cell SDCCH seizure request times

Channel RequiredChannel Request (RACH)

Cell immediate assignment request times

Cell SDCCH seizure failure BTSS008015

Attempted SDCCH seizures meeting a SDCCH blocked state (No SDCCH available)

Immediate Assignment Command

Immediate Assignment Reject

! Location area border results in excessive location update and SDCCH attempt

" Optimize for location area design

" Modify CRH (Cell Reselect Hysteresis)

" Modify T3212 for BSC period location update

" Solve frequent handover problem between dual-band network

! Excessive short messages

" Add SDCCH channel

" Enable dynamic SDCCH allocation function

Causes for SDCCH Congestion and SolutionsCauses for SDCCH Congestion and Solutions

! Insufficient system capacity, lack of SDCCH channels

" Expansion for more TCH and SDCCH channels

" More SDCCH should be added

! Improper configuration of system parameters, RACH system parameter.

" Increase RACH access threshold (overcoming interference).

" Decrease maximum re-transmitting times and increase extended transmission timeslots

! Board (TRX) fault and transmission fault result in SDCCH congestion

SDCCH CongestionSDCCH Congestion

Case Study of SDCCH Congestion Case Study of SDCCH Congestion

! SDCCH congestion cases

" Case 1: Too many times of location update

" Case 2: Transmission equipment board fault

" Case 3: Transmission timeslot multiplexer problem


" In a network, the radio link call setup successful rate is low. Analyze the traffic statistics and find that SDCCHs congest in afew sites.

Too Many Times of Location UpdateToo Many Times of Location Update

! Case 1 analysis:

" Since only a few BTS are congested, register “SDCCH Measurement Function” and analyze the ratio of SDCCH seizure for different causes, then we can find the real reason for SDCCHcongestion.


! Case 1 troubleshooting :

" 1. Register “SDCCH Measurement Function”

# In congested cell, SDCCH is attempted about 300-400 times in a certain hour. The configuration are all S1/1/1. Each cell is configured with SDCCH/8 channels. Normally, they are enough to support 300-400 times seizure, but there are dozens of SDCCH congestion for each cell in busy hour.

# It is found that most of SDCCH seizures are for location update.Analyze the cell locations and find that the congested BTS are at the border of two location area crossed by railway, most of location update are in a specific 5 minutes. Query the train timetable and find that 4 or 5 trains pass there within this period. When the trains pass by, a large amount of location update requests from MS.

" 2. Add SDCCH or enable SDCCH dynamic allocation function, problem solved.



" For SDCCH congestion due to location update, check whether it is caused by improper setting of location area. Add SDCCH channel or enable dynamic allocation function to solve the problem.



" After a new BTS30 is on service, SDCCH channels are all in status “A”, TCH channels are in “I” or “A”. When the call is connected, the communication is normal. Observe the traffic statistics and find that SDCCH seizure failure times are more than 1000 (in busy hour).

Transmission Equipment Board FaultTransmission Equipment Board Fault

! Case 2 analysis:

" Since SDCCH is congested after BTS is on service, but communication is normal.

# First check data and hardware. Because the whole site suffers from congestion problem, interchange Abis link with another BTS (which has the same site configuration) to confirm whether there is anydata or hardware problem in Abis interface.

# If there is no problem with data or hardware, we should analyze the Abis interface transmission system.



" Check alarm and find there are LAPD link fault alarm and recovery alarm (within one second). The alarms appear once per ten minutes.

" Check the data and then interchange Abis link with another BTS which is in the same configuration, the other site work normally. But problem of this site persists. So data and BSC hardware have no problem.

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

" Measure the transmission and self-loop BIE, then It is found that there is high BER for transmission. Test the line section by section and find that one 2M transmission board is faulty. Replace the board and the problem is solved.



" In this case, due to transmission high BER there is too much SDCCH assignment message but missed, then SDCCH assignment message re-sent, these cause high congestion rate.



" Many complaints from subscribers it is difficult to make a call through 4 sites (ABCD), but there are no related alarm information.

# Check the 4 sites, the board status are all normal. Almost no TCH channel is seized successfully. Sometimes one TCH status is “A”, but return to “I” within several seconds.

# Operator engineer said that BTS-A was attached with BTS-B, BTS-C and BTS-D, these 4 BTSs used a primary combiner (a transmission timeslot multiplexer) and shared one EI .

Transmission Timeslot Multiplexer ProblemTransmission Timeslot Multiplexer Problem

! Case 3 analysis:

" The locate information is helpful to judge that the problem is on the hardware or the transmission. But it is unlikely that faultsoccur to hardware of the 4 BTSs. The transmission lines of the 4BTSs are related, therefore, check the transmission carefully.



" 1. Observe BIE, there is BER indication for transmission. But there are no abnormal indication in microwave and optical transceiver.

" 2. Check Abis interface signaling and find there are a large number of PAGING_CMD messages, but only one RF_RESOURCE_INDICATION message appears occasionally. There is no CHAN_ACTIV, CHAN_ACTIV_ACK or IMMEDIATE_ASSIGN_COMMAND message. It indicates that SDCCH channel is not activated.

" 3. Check data O&M log, no data modified within a few days.

" 4. Reload and activate BTS software, and find that system response is slow even communication timeout. SDCCH is still congested after software reloaded.



" 5. Reset the primary combiner and initialize the 4 BTSs, SDCCH are all seized and TCH can be seized successfully. Trace Abis interface signaling, CHAN_ACTIV, CHAN_ACTIV_ACK or IMMEDIATE_ASSIGN_COMMAND message appears. SDCCH is no longer congested because MS can make a call successfully.

" 6. To avoid the same problem occurring again, it is suggested that the operator remove the combiner for transmission timeslotsmultiplexer.



" The transmission problem causes SDCCH congestion by MS channel request repeatedly. Transmission problem can be caused by different reasons. In this case, the fault on the primary combiner leads SDCCH can not be activated, so 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 finally locate the problem with the exclusive method.


OMF000405 Case Analysis-Congestion ISSUE1.4

Documents

tch seizure

attempted

traffic measurement

tch seizure

interchange

call measurement

newly added

outgoing bsc