Codec confusion

Unanswered Question
Nov 10th, 2008

Hello Everyone,

I'm hoping somebody out there can help shed some light on the different Codecs that are out there and which ones the CallManager supports. Most specifically with G729.

In the Regions in CallManager I configure G729 and that's it. I don't have any options for G729A or G729B or G729AB. So which one does it use? In router dial-peers you specify g729r8 or g729br8 so how do those match up with the different G729s that are out there?

The main thing that brought this up is I'm trying to use the DSP Calculator tool and it's asking me if I want to use G711, G729A or G729B and I'm not sure what to pick.

Can anyone please shed some light on the different flavors of the G729 codec.

Thanks in advance!

I have this problem too.
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Jaime Valencia Mon, 11/10/2008 - 08:31

Q. What codecs are supported by Cisco CallManager 4.x?

A. Cisco CallManager 4.x supports these codecs:

* G.711 a-law and u-law.

* G.723 (only supported by the IP phones VIP30 and SP12+).

* Automated bandwidth selection.

* G.723.1.

* G.729 Annex A and Annex B.

* Global System for Mobile Communications (GSM)-Enhanced Full Rate (EFR) and Full Rate (FR).

* Wideband audio - proprietary 16-bit resolution and 16 kHz sampled audio.

about Annex A and B the difference is complexity, VAD and CNG.

more info can be found here:

Understanding Codecs: Complexity, Hardware Support, MOS, and Negotiation



if this helps, please rate

xipccguyx Mon, 11/10/2008 - 08:51

Thanks a lot for the information Java.

So for example if I have two IP Phones registered to CallManager and they are both in the same device pool and the region associated to that device pool is set to use G729, then what codec is used when the phones are connected on an active call to each other? Is that G729A or G729B?

Thanks a lot!

aalejo Thu, 02/26/2009 - 09:47

Hi Java

But looking to some h245 debugs looks like the CCM only sends G729 capabilities and never G279AnnexA?

Unity Support G729A and CallManager sents G729. Same thing with the IP Phone.

The problem is that for newer GW and flex conplexity configured, the GW always choose G729 because the CCM only sents G729. (This means more DSP resources being used on the GW)

On the other hand if I configured the codec complexity to medium, the numbers of calls gets reduced for G711 calls because G711 is trated as a medium complexity.

Any ideas how to overcome this? (whithout adding more DSPs)


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