How to solve the problem that the assignment success rate is low due to improper BSC configuration?

A large number of assignment failures occur during peak hours. The cause value is equipment failure or requested terrestrial resource unavailable and the values of ZTA312L:Failed Assignments per BSC (Equipment Failure) and A3129B:Failed Assignments (First Assignment, Terrestrial Resource Request Failed) increases.

Background Information

Location Procedure

Figure 1 shows the procedure for locating low assignment success rates due to inappropriate BSC configuration

Figure 1 Procedure for locating low assignment success rates due to inappropriate BSC configuration

Troubleshooting Procedure

1. Check whether the value of A3129T:Failed Assignments (No Ater Resource Available) increases.

• If yes, Ater interface resources are insufficient. Check whether the Ater interface resources are blocked or faulty by referring to Maintaining Ater Interface Resources. If any Ater interface resources are blocked, unblock them. If any Ater interface resources are faulty, replace the transmission cables for the faulty Ater timeslots. If the problem persists, run the MML command ADD ATERCONPATH to add Ater interface resources. If the problem is resolved, no further action is required. If the problem persists, go to Step 2.

• If no, go to Step 2.

Check whether the number of CICs over the A interface exceeds the number of calls that all DPUs support.

• If yes, reduce the number of CICs over the A interface or add DPUs. Then, check whether the problem is resolved. If yes, no further action is required. If no, go to Step 3.

• If no, go to Step 3.

If Abis over IP is used, go to Step 4.

If Abis over time division multiplexing (TDM) is used, go to Step 6.

In Abis over IP mode, run the MML command LST IPPATH to check whether an IPPATH with IP path type being EF is configured.

• If yes, go to Step 5.

• If no, run the MML command ADD IPPATH to add an IPPATH with IP path type being EF(EF). Then, check whether the problem is resolved. If yes, no further action is required. If no, go to Step 5.

In Abis over IP mode, if the problem occurs only during peak hours and the value of A312F:Number of Assignment Failures (No Abis Resource Available) increases significantly, run the MML command LST IPLOGICPORT to check whether the problem BTS is configured with logical ports.

• If yes, go to Step 6.

• If no, run the MML command ADD IPLOGICPORT to add a logical port. Then, check whether the problem is resolved. If yes, no further action is required. If no, go to Step 6.

Run the MML command LST SRCONPATH to check whether inter-subrack connections are configured.

• If yes, go to Step 7.

• If no, run the MML command ADD SRCONPATH to add inter-subrack connections. Then, check whether the problem is resolved. If yes, no further action is required. If no, go to Step 7.

Check whether the numbers of resources configured for some BSC boards exceed the processing capacity of these BSC boards.

• If yes, add BSC boards accordingly and configure resources for the new BSC boards. Ensure that the numbers of resources configured for the new BSC boards do not exceed the processing capacity of these BSC boards. Then, check whether the problem is resolved. If yes, no further action is required. If no, Contact Huawei Customer Service Center.

• If no, Contact Huawei Customer Service Center.

Typical Case

Symptom

A BSC uses one POUc as the A interface board and the POUc is configured with more than 7000 CICs. When the traffic volume exceeds 4000 Erl, the assignment success rate decreases and the value of ZTA312L:Failed Assignments per BSC (Equipment Failure) increases sharply.

Cause Analysis

When the traffic volume exceeds 4000 Erl, the assignment success rate decreases and most assignment failures are due to equipment faults. Therefore, this problem is mostly probably caused by inappropriate BSC configuration.

Troubleshooting Procedure

1. Check the traffic statistics collected during the period this problem occurs. The value of A3129T:Failed Assignments (No Ater Resource Available) is 0 and therefore the problem is not caused by insufficient Ater interface resources.

2. Check the number of DPUs. DPUs are sufficient.

3. Check inter-subrack connections. Inter-subrack connections are configured.

4. Check data configuration. A POUc is used as the A interface board and is configured with more than 7000 CICs. The POUc, however, can process a maximum of 3906 CICs. When 3906 CICs over the A interface are occupied, a new call can apply for a CIC over the A interface successfully but fails to request low voltage differential signal (LVDS) resources because the LVDS resources are used together with the CICs and the POUc supports a maximum of 3906 LVDS resources. As a result, the assignment success rate decreases.

5. Reduce the number of CICs configured for the POUc. The problem is resolved.