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One way audio between Avaya PBX, Cisco GW and Service provider


I have a one way audio issue while calling the PSTN from the Avaya PBX. I have the following topology:

Avaya PBX --- Cisco GW --- CPE Service Provider : Router Cisco (Gateway) : Avaya Extreme (Switch) : Media GW Avaya : PBX Avaya IP Phone : IP Address for Signaling of CPE SP : IP Address for Media of CPE SP

So the main problem is we can ONLY receive the service of the SP on our Cisco GW since Avaya does not support that interface. Since the Cisco GW loopback0 ( is the one registered with the Service Provider, they only accept calls from that IP Address.

I made a NAT to announce everything with the loopback, the call is completed since the h.323 signaling is done with the loopback but the media is connected using the IP address of the avaya, so there is no audio.

Is there something that can be done on the Cisco GW to announce only the Loopback and avoid that one way audio? I'm not quite a Routing guru so any help will be appreciated.

Attached are the Sh run of the Cisco GW, a trace on the Service Provider CPE and a sniffer trace on the phone (eventhouhg is saved as a txt it needs to be open with ethereal or any other sniffer program)



1 Reply 1


From the avaya trace, I see:

Media Channel Address:

Since Avaya I assume is sending under H245 OR channel ack an IP address not reachable, Cisco GW is not the one that originates this signalling| recognizing H.323 packets, it simply forwards the message.

Our Cisco GWs support this through NAT

NAT/PAT will change the IP headers but unless it is aware of H.323, SIP or SCCP signaling will not modify the embedded addresses in

the UDP or TCP payload used for signaling the media addresses resulting in one way or no way audio.

You may double check the PAT configuration or try using IPIP GW feature.

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