7.4.1 Failure Description
When the RRC access success rate is high, the related signaling procedure shows that the UE does not respond to the RRC CONNECTION SETUP message sent by the RNC or the value of the VS.RRC.FailConnEstab.NoReply counter increases.
7.4.2 Fault Handling Procedure
Step 1 Locate the scope where the RRC access success rate decreases.
1. Check whether the RNC-level RRC access success rate decreases.
− Check whether the values of the RNC-level counters listed in Table 7-1 decrease. If yes, go to Step 2.
− If no, no more operations are required.
Table 7-1 Counters for analyzing the RNC-level RRC access success rate
KPIs Counters
VS.RRC.AttConnEstab.RNC VS.RRC.AttConnEstab.CellDCH.RNC VS.RRC.AttConnEstab.CellFACH.RNC VS.RRC.SuccConnEstab.RNC VS.RRC.SuccConnEstab.CellFACH.RNC
VS.RRC.SuccConnEstab.CellDCH.RNC
2. Check the values of the counters listed in Table 7-2 to determine whether the problem mainly occurs on some CPUSs.
− If yes, fix the exceptions in the problem CPUSs. If the exceptions are fixed, go to step 3. If the exceptions persist, contact Huawei Customer Service Center.
− If no, go to Step 3.
Table 7-2 Counters for analyzing the RRC access success rate on the CPUS side
Counters Description
VS.RRC.AttConnEstab.CPUS Number of RRC Connection Requests for CPUS
VS.RRC.SuccConnEstab.CPUS Number of Successful RRC Connection Establishments for CPUS
3. Check the values of the counters that are listed in Table 7-3 and related to cell-level RRC access success rate. Then, determine whether the problem mainly occurs in a single cell.
− If yes, go to step 2.
− If no, the problem occurs in all the cells. Choose some typical cells to analyze and go to step 2.
Table 7-3 Counters for analyzing the RRC access success rate in the cell
Counters Description
VS.RRC.AttConnEstab.Sum Number of Processed RRC Connection Requests for Cell
RRC.SuccConnEstab.sum Number of Successful RRC Connection Setups for Cell
Step 2 Analyze the trend of the counters one week before and one week after the failure based on the failure scope located in step 1. Check if the fluctuation of the counters is normal.
− If yes, no more operations are required.
− If no, locate the time when the RRC access success rate deteriorates and go to Step 3.
Step 3 Check whether any alarms are generated on the RNC or NodeB when the RRC access success rate decreases.
− If yes, clear the alarms according to the online help. If the alarms are cleared, no more operations are required. If the alarms persist, go to Step 4.
− If no, go to Step 4.
Step 4 Query RNC and NodeB operation logs to check whether any changes are falsely made to parameter settings after the problem occurs.
− If yes, check whether the changes are appropriate. If they are inappropriate, modify them and check whether the counters restore. If the counters restore, no more operations are required. If the counters do not restore, go to Step 5.
− If no, go to Step 5.
Step 5 Analyze the counters listed in Table 7-4 to check if the value of the VS MinRTWP is –106 dBm when no services are going on in the problem cell. (optional)
− If yes, there is no interference, go to step 5.
− If no, interference exists. Check whether the value of the counter is caused by external interferences.
Table 7-4 Counters for checking the value of VS MinRTWP Counters Description
VS.MeanRTWP Average RTWP for Cell VS.MaxRTWP Maximum RTWP for Cell VS.MinRTWP Minimum RTWP for Cell
Step 6 Check whether the failure is caused by poor coverage. (optional)
Issue 01 (2012-06-25) Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd
68 Check whether the value of Ec/N0 in the RRC CONNECT REQUEST message is lower than –13 dB. (If the value is lower than –13 dB, the downlink signal quality is poor.)
− If yes, the downlink coverage is poor. Upgrade the network to improve cell coverage.
If the upgrade succeeds, no more operations are required. If the upgrade fails, go to Step 7.
− If no, the downlink coverage is sound. If the value of the counter is normal, go to Step 7.
The value of Ec/N0 is shown in Figure 7-1.
Figure 7-1 Value of Ec/N0
Step 7 If the access failure persists after the preceding steps are taken, contact Huawei Customer Service Center.
7.4.3 Typical Case 1
Failure Description
The RRC ASR decreases after an RNC is upgraded.
Possible Causes
The problem may be caused by inappropriate changes in parameter settings.
Fault Handling Procedure
Statistics show the increase of the VS.RRC.FainConnEstab.NoReply counter is the main cause for the decrease of the RRC access success rate.
Step 1 Check whether the RRC access success rate shown in Figure 7-2 decreases before the upgrade.
The results show that the RRC access success rate decreased before the upgrade.
Step 2 Analyze RNC and NodeB operation logs when the access failure rate is high. The results show that the SET UCONNMODETIMER command has been run and the N381 value is changed from D3 ms to D1 ms.
Figure 7-2 Results of operation logs
Step 3 Change the N381 value to D0 ms and then check whether the RRC access success rate decreases. Related results show the RRC sends the CONNECTION SETUP message only once after the change. UEs on the cell edge experience RRC access failures, which cause the RRC access success rate to decrease, as shown in Figure 7-3.
T381 is started after the RNC send the RRC CONNECTION SETUP message. If T381 expires and RNC does not receive an RRC CONNECTION SETUP COMPLETE message and the V381 value is smaller than the N381 value, RNC resends the RRC CONNECTION SETUP message and restarts the timer T381 and increases the V381 value. Currently N381 is set to D1 ms.
Issue 01 (2012-06-25) Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd
70 Figure 7-3 RRC access failure rate due to bad signal quality
7.4.4 Typical Case 2
Failure Description
The RRC access success rate fluctuates in a cell.
Possible Causes
Interference causes the sudden rise of the RTWP, leading to the increase of the VS.RRC.FailConnEstab.NoReply counter.
Fault Handling Procedure
Step 1 Analyze the values of cell-level counters.
The results show the RRC success rate fluctuates sharply, as shown in Figure 7-4.
Figure 7-4 Sharp fluctuation of RRC success rate
Step 2 Determine when the value of the VS.MaxRTWP counter fluctuates.
The results show the counter fluctuates sharply when the RTWP abnormally increases, and the counter is stable when the RTWP remains unchanged.
Then, analyze the relationship between the RTWP and the number of UEs camping on the problem cell. The results show the RTWP fluctuates sharply when there is a small number of UEs. It can be inferred that the rise of the RTWP is caused by external interference. Then check whether any external interference exists.
Step 3 Conduct an interference test.
The test results show external interference exists when the RTWP abnormally increases, which leads to the problem of no replies to an RRC connection setup request. After the interference is cleared the RTWP and the preceding counter restore.