Unity Connection advertise G729a

Unanswered Question
Feb 20th, 2009

Hi Connection does not advertise G729a - only G729 (amongst others). Is this a major overhead on Connection? Is there anything in the roadmap for G729a?

I have this problem too.
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Rob Huffman Fri, 02/20/2009 - 06:11

Hi Jag,

Good question!

There is no significant difference in overhead when using g.729. Here is a good clip that describes these relationships;

Because transcoding is inherent in every connection, there is little difference in system impact when the

line codec differs from the recording codec. The exception to this is when using the iLBC or G.722

codecs, which require more computation to transcode, and therefore have a greater system impact. The

G.722 and iLBC codecs use approximately twice the server resources that the G.711 mu-law codec uses.

Consequently, a Connection system can support only half as many G.722 or iLBC connections as it can

G.711 mu-law connections.

Supported Line Codecs (Advertised Codecs)

• G.711 mu-law

• G.711 a-law

• G.722

• G.729

• iLBC

Supported Recording Codecs (System-Level Recording Audio Codecs)

• PCM linear (default)

• G.711 mu-law

• G.711 a-law

• G.729a

• G.726

Sizing and Scaling Cisco Unity Connection



G.729 is a high complexity algorithm, and G.729A (also known as G.729 Annex-A) is a medium complexity variant of G.729 with slightly lower voice quality. All platforms that support G.729 also support G.729A.

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


Hope this helps!


askq2forum Fri, 02/20/2009 - 07:46

Hi Rob,

thanks for the reply.

We had a fault recently where we had the recording format as G729a and the advertising codec as G729 which was causing garbled messages. The only quick fix was to change the recording codec to G711 - this obviously must be less intensive than transcoding from G729 to G729a and vice versa - although G711 uses up roughly 2.5 times more disk space.


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