when use transcoding

[borovac]

Can anyone explain all cases with examples

when transcoding must be used ?

Are remote site with g729 codec configured must be transcoded during local call to central site if

central site use g711 codec ?

[Chris Deren]

You need transcoder anytime call is being setup between endpoint with different codecs. For example phone at branch office using g729 and HQ phone using g711.

If you search in CCO there is great amount of literature on this topic. Also I would recomment IP Telephony Troubleshooting Cisco Press Book.

[borovac]

Can CCM negotiate codec on the moment when call is started on both locations on the fly without transcoding or not ? My local support say transcoding is not necessary.

[Chris Deren]

No. You need a transcoder. Transcoding resources are only available in hardware because they require high speed DSPs to convert the media stream from one codec to another in real time. Check the following link:

http://www.cisco.com/univercd/cc/td/doc/product/voice/c_callmg/4_0/sys_ad/4_0_1/ccmsys/a05trans.htm#23882

[Sascha Monteiro · Accepted solution]

You don't need transcoding for calls between ipphones.

In your region, you state the codec between sites and within the sites. (g729 and g711 resp.)

Only if both endpoints cannot negotiate the required codec, a transcoder is needed. If you i.e. have a (j)tapi application (CRA) that only supports g711, and you call it from your remote site, it will use the transcoder to transcode between g711 and g729