OMD6072 Case Analysis--Congestion ISSUE1.1

8/13/2019 OMD6072 Case Analysis--Congestion ISSUE1.1

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OMD6072Case AnalysisCongestion

ISSUE1.1

Wireless Curriculum

Development Section


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Summary

TCH Congestion RatioBasic Principle

Cause and Locating the Cause

Cases analyze

SDCCH Congestion RatioCause and Locating the Cause

Cases analyze


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TCH congestion ratio

Basic principle

Cause and locating method

Cases analyze

TCH congestion ratio


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TCH Congestion Ratio

Basic Principle of TCH congestion ratio

Definition of TCH congestion ratio

Traffic statistics measurement point of TCHcongestion ratio and analysis


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Basic Principle of TCH Congestion Ratio

Definition of TCH congestion ratio

TCH congestion ratio (not including handover)

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

times (not including handover)*100%

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

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

request times)*100%.


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Definition of TCH Congestion Ratio

TCH congestion ratio (including handover)

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

(including handover)*100%

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

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 call occupation request times + early assigned TCH

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

TCH congestion ratio (congestion on all busy)


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TrafficM

easureme

ntPoint

ofTCHCo

ngestionR

atio

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 CMP

Assignment_CMPAlerting

Connect

Connect Ack

communication

Disconnect

Release

Release Complete

Clear_CMD

Clear_CMP

CM Service Accepted

Channel_Active

Channel_Active_Ack

UA

SDCCH

SDCCH

SACCH(TCH)

SACCH(TCH)

MS call flow as the caller


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Request Times Statistic Point of TCH Congestion Ratio

TCH call occupation request times

(1) Receive the MSC assignment request message

Early assigned TCH occupation request times:

(1) When there is no resource for SDCCH allocation and

instant assignment is permitted

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

TCH

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

(1) When in-cell handover request message between cells

intra- BSC is received (non-SDCCH handover).

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

(1) When incoming handover request message is received

(handover type is non-SDCCH)


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Failure Statistic Points of TCH Congestion Ratio

TCH call occupation failure times:

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

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

(9) When assignment failure message is sent.

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

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


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Failure Statistic Point of TCH Congestion Ratio

TCH Occupation Failure Times for in-cell handover

intra-BSC (due to congestion):

Allocation to TCH channel fails at in-cell handover

between cells intra-BSC

TCH Occupation Failure Times for in-cell handover

inter-BSC (due to congestion):

When in-cell handover inter-BSC occurs,

handover failure message is sent because it is not

allocated to TCH channel.


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Analysis of failure statistic point of TCH congestion ratio

A interface

After MSC sends Assignment_req, If trunk circuit at Ainterface is fault, BSC will return Assignment_refuse directly.

In this case, the usually cause is incorrect CIC data

configuration of trunk circuit.


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Analysis of failure statistic point of TCH congestion ratio

ABIS interface and UM interface

1. TRX board is faulty or performance unstable

2. Unbalance of uplink/downlink level in BTS

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

4. SDCCH and TCH do not belong to the same TRX board,

i.e. the two TRX boards cover different areas or TCH TRX

board is faulty.


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The Cause of High TCH Congestion Ratio andLocating Method

The cause of high TCH congestion ratio

How to locate the cause of TCH congestionratio


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Cause of High TCH Congestion Ratio and Locating

Method

Causes of High TCH Congestion Ratio

Incorrect configuration of trunk circuit data at A interface

Co-frequency and co-BSIC results in TCH assignment failure in handover

Board fault or unstable performance causes the high congestion ratio

BTS hardware is not properly installed, which causes uplink/downlink

unbalance and TCH congestion.

The cell is attached with a repeater. After the cell expansion, the repeater is not

expanded.

The transmitting power of BCCH TRX is 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 ratio


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Cause of High TCH Congestion Ratio and

Locating Method

How to Locate the Causes of High TCH Congestion Ratio

Analyze the cause of congestion remotely

1. Preliminary analysis through traffic measurement

2. Check alarms

3. BTS remote maintenance console

4. Test and analyze ABIS interface message with a

signaling analyzer.

Check the BTS locally


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Locating Method

Remote analysis 1: Preliminary Analysis Through Traffic Statistics

Through the traffic statistic CellTCH Performance Measurement,check whether TCH

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

the equipment buyer to expand the capacity.

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

drop ratio will be high.

Register ReceivingPerformance Measurementtraffic statistic task:

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

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

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


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Locating Method

Remote analysis 2: View alarm

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

ratio. Check whether there is any abnormal alarm, such asstanding wave ratio alarm, PCM OOF alarm and uplink data bus

alarm. Judge whether the congestion ratio is associated with

alarms with traffic measurement .


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Locating Method

Remote analysis 3: BTS remote maintenance console

On the BTS remote maintenance console, block TCH channels

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

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


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Locating Method

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

signaling analyzer

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.

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

1) TRX board faulty or performance unstable

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.

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

reports. The causes may be the following:

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

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


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Locating Method


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Locating Method

Check BTS locally

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

yes, process it promptly.

Check whether there is any hardware problem in uplink/downlink

antenna/feeder tributary, such as loose connector,etc.

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

whether the assignment failure always occurs in one frequency or is randomly

distributed.

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

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

Search the interference source with a spectrum analyzer.

Observe whether the topography in the cell coverage is complex.


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Cases of TCH Congestion Ratio


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Cases of TCH Congestion Ratio Problem

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

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

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

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

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

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

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


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Fault description: 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 was not changed). TCH congestion ratio of the whole network (not

including handover) is 4%(the congestion ratio on all busy is very low). In

addition, many cells but not a few cells are highly congested.

Case 1


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Case 1

Analysis:

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

problem is ruled out.

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

search in a smaller range to see whether the congestion

problem is related to module or data modification.

3. Analyze the main cause of TCH occupation failure

through traffic statistic and finally locate the problem as

data or hardware fault.


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Troubleshooting:

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

related to BSC loading.

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

Then the problem should be with module 1.

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

terrestrial resources. It shows that unavailability of terrestrial resource is the main cause of high

congestion ratio in module 1.

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

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

interface is faulty 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

is ruled out.

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

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

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

Case 1


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Conclusion:

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

correct, otherwise, TCH assignment will fail and the congestion

ratio will be high.

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

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

Case 1


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

been running normally. One day, the result of traffic statistics shows thatTCH channel in cell 1 (6 TRX) overflows very seriously and the congestion

ratio comes to 20%.

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.

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

Case 2


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Case 2

Analysis:

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

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

interface interference or data problem.

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

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

assignment failure.

3. Find out whether there is hardware fault in the TRX for assignmentfailure. Check them one by one by means of resetting and replacing.


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Troubleshooting:

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

possibility 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

no 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

arise again.

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

the 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),

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

Case 2


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Case 2

Conclusion:

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

high congestion ratio.

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

maintenance console . The problem can be confirmed by

blocking in turn.


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Fault description: A specific BTS is configured as S6/6/6. Sincethe BTS in service, the congestion ratio of the 3 cells is high. Check

and confirm that there is no interference.

Case 3


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Analysis: 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

of the BTS.

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

fault in the hardware of every cell.

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

check the hardware connection of the uplink or the downlink.

Case 3


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Troubleshooting:

1. Register traffic statistics Receiving Level Measurement Function and

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

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

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

incorrect. After correction, the problem is solved.

Case 3


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Case 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 18-3-2001Module ID 1, Cell ID 5, TRX

No. 12

Module ID 1, Cell ID 5, TRX

No. 13Module ID 1, Cell ID 5, TRX

No. 14

Module ID 1, Cell ID 5, TRX



No. 17


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Case 3

Conclusion:

Incorrect hardware connection will cause TCH assignmentfailure. The problem can be located accurately by analyzing

different traffic statistics tasks.

In this case, uplink hardware receiver problem is located

through Receiving Level Performance Measurement.


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

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

Case 4


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

therefore attention should be focused on the hardware, to see

whether there is any fault or alarm.

Case 4


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Troubleshooting:

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

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

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%.

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

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

problem is solved.

Case 4


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Conclusion: Antenna VSWR alarm results in large loss, small

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

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

congestion ratio in the cell goes up as a result.

Case 4


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Fault description: When a BTS O2 is expanded to O4, high

congestion ratio occurs, with the peak of 40%.

Case 6


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Case 6

Analysis: Since congestion ratio is abnormal after expansion,

we can

1. Check whether the congestion occurs to all TRX. If yes, re-check the connection of newly added hardware of the BTS to

see whether there is any fault.

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

hardware of these TRX.

3. When hardware problem is ruled out, consider external

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

results in assignment failure.


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Troubleshooting:

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.

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

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

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

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

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.

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

solved, the congestion problem is also solved.

Case 6


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Conclusion:

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

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

which results in the assignment failure.

Case 6


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

(including handover) on busy hours of the two cells is as high as 10%.

TCH seizure Excluding Handover and TCH block rate(meeting a TCH

block state on attempt TCH seizures) are normal. Here, TCH seizure

failure (all) is very high, 89 times and 61 times respectively. But TCH

seizure failure for MOC is 0.

The traffic is a little lower than that before optimization.

The interference band is normal.

Congestion ratio was normal before optimization.

Case 8


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Case 8

Analysis: When the network planning parameters are optimized and

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

congestion ratio including handover is higher, therefore, radiointerference or hardware fault can be ruled out. Analyze whether the

handover is abnormal.


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Troubleshooting:

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

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

cause of congestion.

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

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

TCH channel is assigned.

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

recovered and congestion ratio is normal.

Case 8


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Case 8

Conclusion:

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

also high TCH congestion ratio (including handover).

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

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


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Case 9

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

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

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

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

normal.


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Case 9

Analysis:

1. Since the congestion ratio 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 dropout ratio into

consideration and analyze the receiving performance of uplink/downlink,

including level, quality.


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Case 9

Troubleshooting:

1. 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.

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

measurement reports of low level grades.

3. Analyze ABIS signaling to find that the uplink level is very low (about98dbm)

when the assignment fails.

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 kilometersaway from the BTS, it can receive90dbm downlink signal. But the uplink signal

is not enough, so TCH assignment fails.


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Case 9

Conclusion:

1. Poor uplink coverage causes the high congestion ratio.

Adding BTS can help form a continuous coverage.

Change the omni-directional site into a directional site

by adjusting the antenna angle. Intensify the transmitting

level and BTS receiver sensitivity. Avoid over coverage.

2. Trace Abis port message on the BTS maintenance

console to analyze the assignment status.


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SDCCH Congestion Ratio

SDCCH congestion ratio

Basic principle

Cause and locating method

Cases analyze

B i P i i l f SDCCH C i R i


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Basic Principle of SDCCH Congestion Ratio

Calculation formula:

SDCCH congestion ratio=SDCCH occupation

on all busy times/SDCCH occupation request

times

SDCCH occupation on all busy times:

SDCCH occupation failure due to all busy

The cause of SDCCH occupation:

1) The caller assignment command is sent to channels

2) The called paging response is sent reported to channels

3) Location updating

4) Short message

5) IMSI detachment and attachment process

Basic Principle of SDCCH Congestion


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Basic Principle of SDCCH Congestion

RatioMS BTS BSC MSC

BSC random accessimmediate 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


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Cause of SDCCH Congestion and Locating the

Cause

Location area boundary results in excessiveSDCCH location updatingPolicy: Modify location area selection

Modify CRH (Cell Reelect Hysteresis)

Modify the parameters of periodical area updating.

Modify the frequent handover problem of the dual-frequencynetwork.

Excessive short messages

Policy: Add SDCCH channel

Cause of SDCCH Congestion and Locating


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Cause of SDCCH Congestion and Locating

the Cause

Insufficient system capacity: more SDCCH should be

configured

Policy: expansion

Improper setting of system parameters,RACH system

parameter. Actually multiple SDCCH are assigned.

Policy: Increase RACH access threshold (for coping with

interference).

Decrease MAX re-transmitting times and increase extended

transmission timeslots appropriately

Dynamic SDCCH allocation

Board (TRX) fault and transmission fault result in SDCCH

congestion

Cases of SDCCH Congestion Ratio


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Problem

SDCCH Congestion Cases



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g

Problem

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

the traffic statistics to find that SDCCH congestion only

occurs to a few sites.

Case 1:



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g

Problem

Analysis: Since only a few BTS are congested,please register SDCCH Measurement Function and

analyze the shares of respective causes for SDCCH

occupation. Solve the problems accordingly.

Case 1



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g

Problem

Troubleshooting: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 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.

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

updating results in SDCCH congestion.

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

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

results in the congestion.

4. Add SDCCH or enable SDCCH dynamic allocation function.

Case 1



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g

Problem

Conclusion:For SDCCH congestion due to location updating, check

whether it is caused by improper setting of location area.This case is a special one. Add SD or enable dynamic

allocation function to solve the problem.

Case 1



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g

Problem

Fault descriptionDeploy 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

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

statistics and find that the SDCCH assignment of traffic statistics fails

about 1000 times (in busy hours).

Case 3



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g

Problem

Analysis:1. Since SDCCH is congested after the BTS deployment, but TCH and

communication are normal. First check data and hardware. The whole site

suffers from congestion problem. Swap ports with other sites of the same

type to confirm whether there is data problem or hardware problem underAbis interface.

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

focused on the transmission problem.

Case 3



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g

Problem

Troubleshooting1. Check alarm: LAPD link fault alarm and recovery alarm (within one second). The alarm

appears once per ten minutes.

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

and BSC side hardware problem are ruled out.

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

SDCCH traffic measurement remains abnormal.

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

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

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

Case 3


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g

Problem

Fault descriptionA 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

maintenance console.

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

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

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

line with BTS-A.

Case 4



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Problem

AnalysisThe 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 the4 BTS. The transmission lines of the 4 BTS are related, therefore, check

the transmission carefully.

Case 4



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Problem

Troubleshooting1. 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

abnormal indication is found.

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.

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, and find no data modification has been done in a few days in the past.

Therefore data problem is ruled out.

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

that the transmission is normal.

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

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 problem.

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Problem

Troubleshooting6. The only transmission equipment in doubt after the resetting --- primary

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

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

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

CHAN_ACTIV_ACK or IMMEDIATE_ASSIGN_COMMAND message appears.

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

normally.

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

BTS have been running normally.

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Problem

Conclusion:

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

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

finally locate the problem with the exclusive method.

Case 4


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Documents

OMD6072 Case Analysis--Congestion ISSUE1.1