Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

intermittant on way audio

We are having a very frustrating one way audio issue with one phone only. On some inbound calls from the PSTN the user is complaining that she cannot hear the caller, but the call can hear her. The problem usually occurs once every one or two days.

I have replaced her phone and reset the DSP modules on our 2811 PSTN gateways without any success. Any suggestions would be helpful as to what would be causing this issue.



Re: intermittant on way audio


Do you have any security applied in the voice path

Always, silent calls is related to security or routing issues

wish this be helpfull

New Member

Re: intermittant on way audio

No there is not any security between the gateway, site, CCM and phone.

This issue just started up about 3 weeks ago.

Re: intermittant on way audio

Hi There,

This document should help with the troubleshooting steps.

You can also check this document to see if this apply's to your configuration

Hope this helps, please rate if so



New Member

Re: intermittant on way audio

Thanks for the input. I have verified that all the requirements are met for the first two documents. Calls to the extension that is experiencing one way audio are not routed through unity before arriving at the phone, so I don't think the second document applies. Which is why this is very frustrating for us.

I'm going to try and recreate the issue tonight while running an mgcp debug, then send the information to TAC.

I'll let you know how it turns out.

If there are any other suggestions, i'm always thankful for the help.

Re: intermittant on way audio

Watch out for this bug that is going around. kind of like H1N1.

Hi All,

If your gateway is MGCP and your service parameter to advertise G.729 annex-b, which is the default, you will not be able to hear audio on 12.4(24)T.

Becoming kind of a hot bug, thought I would let you know.




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


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


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. Downgrade to IOS code on the gateway which does not contain the fix for CSCsu66759, which would be 12.4(22)T and below.

New Member

Re: intermittant on way audio

Thanks for the heads up. We are currently not utalizing g729, all our codecs are g711

Re: intermittant on way audio

You might want to double check that. Seeing as that it's a single phone causing you the issue, you might have it in different (test) device pool configured with a different region. Just an idea!