Carrier vs. 2811 vs. CUCM Codecs/Transcoding

[Martin Koch]

Hi!

Does anyone have a good example how to use a 2811 router as a media termination / transcoding resource as a GW to a h323 VoIP Provider. Faststart is enabled with alaw.

What we get signalized from the carrier is either g711a+g711u, g711a or g711u.

First we had a voice class codec list on the

carrier site with g711alaw and g711ulaw and

a fixed alaw codec on the internal site, but then calls failed which were signalized as a

combi of alaw and ulaw.

We thought that using codec transparent and then using the communications manager to decide

if transcoding resources are needed would solve

the problem, but the users then complained that

forwarded calls had one way audio and that it

added issues on the fax transmission via the atas.

Also I did not find anything to define in

call manager that a region has to use

g711alaw, it seems that you can define g711ulaw.

How can I define the preference of the

specific g711 type on the region or the

sccp phone itself?

So again in short setup:

Carrier (h323) <-> 2811 <-> (h323) CUCM 7.0 <-> cisco phones

How shall the config of the codecs,

dial peers, mtp/transcoding/gw and

phone codec / regions look like?

Any help and commments is highly appreciated!

[douhanm]

you definatly want to stay away from MTP unless you really need them, because they hairpin calls through the MTP in ways that will be non optimal.

For the codec type there is no way in the region settings to define a ir u law it is done on the dial-peers in the GW when you use H.323

your setup shold be solvable without fast start and MTP, simply assigna voice class codec XX on the dial-peer and be done with it.

We have seen issues when G.711 u and a has been in the voice class so if you dont need u then remove it from the voice class codec.