Codec problem

Unanswered Question
Jun 8th, 2007

I have two routers configured with CCME, when i set in the main router the codec g729br8 and the branch router the codec g729br8,,the communication failed. Busy tone. But when is set in the both router the codec g711ulaw, it does work. How can i configured to use g729br8.

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Paolo Bevilacqua Fri, 06/08/2007 - 14:10


With CCME (and CCM) you will be limited exclusively to the codecs supported by the phones. These are G.711u and G.729a. This is because the RTP stream flows between the phones and the router normally doesn't touch it.

If you want to use G.729 between phones located on different CCMEs, you have two choices:

1. Configure the phone for G.729. This is done in configuration under "ephone". The side effect is that the phone will try to use G.729 all the time, even for local calls, with a small decrease in voice quality.

2. Configure transcoding. I will not go over the details as there is a lot of material, but basically, the router will support transcoding only between G.711 and G.729. No other codecs are supported.

Now, if you want your CCME systems to communicate with a different codec (eg, a very low bitrate like g723ar53, or one resilient to packet loss like iLBC) the only choice is to go through a telephone interface, preferably a digital one. That means routers back-to-back, or even interfaces connected back-to-back in the same router. This is the only mean to potentially use any of the codecs supported by the platform.

Hope this helps, please rate post if it does!


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