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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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Basic Principle of TCH Congestion Ratio
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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Basic Principle of TCH Congestion Ratio
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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Basic Principle of TCH Congestion Ratio
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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Basic Principle of TCH Congestion Ratio
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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Basic Principle of TCH Congestion Ratio
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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Basic Principle of TCH Congestion Ratio
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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Basic Principle of TCH Congestion Ratio
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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TCH Congestion Ratio
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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Cause of High TCH Congestion Ratio and
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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Cause of High TCH Congestion Ratio and
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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Cause of High TCH Congestion Ratio and
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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Cause of High TCH Congestion Ratio and
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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Cause of High TCH Congestion Ratio and
Locating Method
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Cause of High TCH Congestion Ratio and
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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TCH Congestion Ratio
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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. 15Module ID 1, Cell ID 5, TRX
No. 16Module ID 1, Cell ID 5, TRX
No. 17
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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of TCH Congestion Ratio Problem
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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Cases of SDCCH Congestion Ratio
Problem
SDCCH Congestion Cases
Cases of SDCCH Congestion Ratio
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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:
Cases of SDCCH Congestion Ratio
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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
Cases of SDCCH Congestion Ratio
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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
Cases of SDCCH Congestion Ratio
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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
Cases of SDCCH Congestion Ratio
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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
Cases of SDCCH Congestion Ratio
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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
Cases of SDCCH Congestion Ratio
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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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Cases of SDCCH Congestion Ratio
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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
Cases of SDCCH Congestion Ratio
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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
Cases of SDCCH Congestion Ratio
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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.
Case 4
Cases of SDCCH Congestion Ratio
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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.
Case 4
Cases of SDCCH Congestion Ratio
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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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