Core Issue
Since the setup has Cisco WAN Q Interface Signaling Protocol (QSIG) running as the signaling protocol, the problem could be due to the way Nortel numbers B channels above TS 16. Such issues were reported in the past and caused by the PBX using TS1-30, including TS 16 while we count 1-15, 17-31.
Resolution
In order to resolve this issue, try these steps:
- Add the network-clock-select 1 e1 0/0 command in order to ensure correct synchronization between the AIM voice card and the E1 interface.
- Remove the POTS dial peer that has the application mgcpapp command configured because it is not needed for the Media Gateway Control Protocol (MGCP) ISDN operation.
- Add the isdn contiguous-bchan command on router's D channel configuration and set the Cisco CallManager Gateway Configuration Channel IE to continuous.
- If companding is set to ulaw on the Cisco CallManager gateway, attempt to change this setting to a-law. Also, change the PBX companding to a-law.
Ideally, the audio quality should now be fine.