Root Cause ***ysis for Mute Call Issue

                     BSC6900

                     V900R015ENGC00SPH536

There were so many mute calls reported on only one cell. The issue appeared was unknown.

CDIG logs were extracted and ***yzed. From the CDIG logs, it was observed that almost all the mute calls were happened on channel 6 of TRX 360:

Figure 3-1 CDIG logs showing problematic TRX and Channel No.

3.2 Abis timeslots were checked by executing DSP ABISTS command. It was found that ABIS TSs were allocated confusedly:

Figure 3-2 Result of DSP ABISTS

The channel with issue was assigned with idle TSs, the Sub TS No is 134:

Figure 3-3 TS of the channel with issue

For E1 TS, one TS is 64K, and one Sub TX in the result of DSP ABISTS is 8K, so one E1 TS includes 8 Sub TS.

Sub TS No. 134 means the E1 TS is 16.

It was confirmed from the TXN team that there was only 1M bandwidth used for that site, it means that only TS0 to TS15 were used on that site, and that TS16 was not used.

Therefore the channel assigned on E1 TS16 was on fault. This is the root cause of mute calls on Channel 6 of TRX360.

There isn’t enough ABIS TS to support channel 6, so we removed the idle TS, and then we try to DEA & ACT the BTS so that the ABIS TS can be re-allocated.

After the operation, the TS distribution were as following:

Figure 3-4 ABIS TS Distribution after DEA&ACT the BTS

After this, the issue was resolved.

Figure 3-5 No mute all after the operation

There was only 1M of bandwidth used for that site, which means the TS-0 to TS-15 were used on that site. The TS-16 was not used, so the channel assigned on E1 TS-16 was on fault. Channel No. 6 of TRX360 was assigned to E1’s TS-16, so the mute call issue happened on that GTRX.