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New Member

One way voice transmission issues

I have two 3640's connected via a serial HDLC point to point circuit. Both routers can ping and telnet each other and have full data connectivity. However, the problem is when router A calls Router B, the calls connects, but the voice can only be heard inbound, no outbound voice is heard at the remote end. When Router B calls Router A, the calls are perfect in both directions. In addition both sites can communicate with 3 other VoIP enabled sites without any problems, they just can communicate with each other (in one direction). Router A has an E1 and uses ISDN QSIG Router B has a T1 and uses E&M signalling. Any light on this very strange problem would be much appreciated

Both routers are running IOS 12.1(5)T10


Re: One way voice transmission issues

Sounds like the answer supervision is not sent back to A correctly. Check on that.

Also you can try putting the following command in:

voice rtp send-recv

New Member

Re: One way voice transmission issues

I had a similar problem between a 3745 in Mexico and a 2600 in the US. Turned out the issue was missing network-clock-participate commands on the 3745. We were using an AIM module on the 3745, but I believe the command is needed when using a NM-HDV module as well.

network-clock-participate wic 0

network-clock-participate aim 0

network-clock-select 1 E1 0/0


Re: One way voice transmission issues

Without seeing your configs to confirm, but chances are you have pointed the dial peer session target to remote ehternet addresses on the routers. By default , IOS will use the IP address of the interface that the packet leaves the router from as the source address of the rtp stream, but if the remote router is configured to use a different address under the VOIP dial peer you will see excatly what you have reported - the signalling works fine but there is no audio.

Change the session targets of the VOIP dial peers to be the addresses of the serial interfaces and give it another try.

The network-clock-participate commands mentioned in an earlier post won't help here as the the 3640 is not a TDM capable device and does not support AIM-VOICE-30 modules.

New Member

Re: One way voice transmission issues

I stand corrected on the 3640 capabilities.

Wouldn't a loopback address serve as a better anchor point for the VOIP dial peer than any physical interface?