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

why am I getting one way audio problem ?


I have stranges problems with a 1751 router with VIC with IOS 12.2(11)T. When I try to establish a call between Netmeeting and the router, it completely fail. It's probably because of the H.323 version that is quite more recent on 12.2.

However, I have other H.323 devices that support H.323 v4. When the call is established from the PSTN to the IP phone, everything works fine. When I tried to establish the call from the IP phone out to the PSTN, I have one way audio problem. The PSTN user can't hear the IP user.

IP routing is enable, voice rtp send-rcv, h323-gateway bind src addr on a loopback... My default gateway is set, I don't understand and I also think that the TAC doesn't also. If anyone has problem, please reply I think it's a bug...

New Member

Re: why am I getting one way audio problem ?

trace, trace, trace

there could be some IOS related issues, but if TAC can't understand your problem, you will have to use all means necessary to get them to see that the problem is on their side. I am referring to taking some sniffer traces. you want to analyze all h323 signals to insure that the media IP and ports offered form this purpose are being used by the remote end for RTP exchange. Most likely, one of the devices might be flipping these around in an unfamiliar way for the ohter end, or maybe the other end choses to ignore it and sends it to the wrong place. evidence of that could be some ICMPs floating around.

you can get a free VoIP sniffer at and also get the plugins at together you will be ready to confront tac about what standards the device is violating, or what config parameter you missconfigured.

one other remotely related cause of one-way voice is the presence of some ACLs or any type of firewalling in that category that may bloc the RTP path one way or the other. Just FYI :)


New Member

Re: why am I getting one way audio problem ?


Since you are using the IP phone, check the default router on the Ip phone, check where the Packets from the Ip phone are going "debug ip packet". Sniffer trace will tell you more details. If you are using NAT on the router check the "voice-class source interface " under dial-peer voip.



New Member

Re: why am I getting one way audio problem ?

We had occasional (random) one-way audio problems using AS5400 as IP to PSTN gateway. We solved them by upgrading to 122-11.T1

Cisco Employee

Re: why am I getting one way audio problem ?

This image had a problem with NAT causing one way audio. Are you running NAT?

CreatePlease to create content