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Transcoding Sessions using CM7 MTP for SIP Trunk

We are setting up a SIP trunk from Callmanager 7 to a external 3rd party conference bridge and have our SIP trunk set up to use MTP and use the 2 callmanager servers as the MTP which looks like it is doing transcoding from external calls at G.729 to G.711 to the Conference bringe.

My question is, what is the impact of using callmanager as the MTP and how many transcoding sessions can we realisticly expect the callmanager servers to be able to handle.

On another note what exact version of G.729 do ip phones/callmanager use? My conference bridge is supposed to support G.729 but it is only accepting SIP requests for G.711, and the vendor is thinking it is a compatibility issue with the type of G.729.

Cisco Employee

Re: Transcoding Sessions using CM7 MTP for SIP Trunk

A big clarification, an MTP cannot work as an XCODER. An XCODER can work as an MTP. The MTP cannot be changing from G711 to G729 magically. Specially when you're using SW MTP on the server. Any XCODER are external DSPs to the server.

When MTP is running in software on Cisco Unified Communications Manager, the resource supports 48 MTP sessions. When MTP is running on a separate Cisco Unified Communications Manager appliance (server), the resource supports up to 128 MTP sessions. In addition, Cisco Voice Gateway Routers also can provide MTP services.

To understand exactly what an MTP can do read this

Media Termination Point (MTP)

Most phones use G.729a and G.729ab. If you have a model in mind just search the model on CCO and look at the datasheet.



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