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No Audio on Transfer

CCM 4.1(3)   2851 12.4(25b)

User at remote site tries to transfer a call from the PSTN to another site.

Call arrives at remote phone, but no audio in either direction. (No re-order or anything, just dead air)

Call information appears on destination phone. (Call appears to be active)

Conference works fine, problem is only with transfer.

Gateway is using MGCP, G.729 inter region.

Local DSPs are used for transcoding and they are registered in CCM

I am going to have the customer switch the codec to G.711 and see if the issue remains.  I am leaning towards a transcoding issue, but usually this would result in a fast busy.  I have verified the voice path between endpoints and to the CCM.

Any help is appreciated.


Hello Ahochau,

Can you provide us a complete topology description, also some sniffer captures and traces from the call manager will be great.


Luis Sandi


How did you verified the audio path? And did you mean from two phone to CCM?

You 've said the call flow is call from PSTN to IP Phone. Then IP Phone transfer the call to another IP Phone. So the Audio path should be between PSTN gw to remote Phone. You can use "show voip rtp connection" on gw to check the rtp path. Also you can browse to IP Phone, then select "Stream 1" from the bottom left corner. That should tell you the current rtp path to/from IP Phone.

Wireshark capture from the GW or IP Phone after transfer would be great


-     Abu

We have fixed the problem by applying the workaround number 1 for the caveat described below.  Even though it should have been fixed in the version of IOW we are using.

Resolved Caveats—Cisco IOS Release 12.4(25b)


Symptoms: Calls on an MGCP gateway negotiating the g729br8 codec may fail to have audio in one or both directions.

Conditions: This occurs on MGCP gateways with the fix for CSCsu66759 when the g729br8 codec is being negotiated.

Workaround: Any of the following will be sufficient to get around this issue:

1. Configure the gateway for static payload type using the following commands on the gateway:

mgcp behavior g729-variants static-pt
mgcp behavior dynamically-change-codec-pt disable

2. Disable g729br8 from being negotiated for this call. If CUCM is involved, this is done with the service parameter "Strip G.729 Annex B (Silence Suppression) from Capabilities."

3. Use a Cisco IOS code on the gateway which does not contain the fix for CSCsu66759 (Cisco IOS Release 12.4(22)T and below).

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