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There is no audio after calls are established between the CallManager and Nortel PBX when using a 2621XM router with an AIM-voice-30/E1 interface as the IOS gateway to the Nortel PBX. Signaling protocol is E1 QSIG, and the MGCP backhauls to CallManager

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.

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