CODEC Negotiation Question

Unanswered Question
Sep 8th, 2010
User Badges:

We need to use G.729 for users checking voicemail with Unity Connection.   See attached diagram, which should make the scenario more clear.  The CUBE config only allows for explicit config of G.729a or G.729ab, but not G.729:

! G.729ab

codec preference 1 g729br8 bytes 30

! G.729a

codec preference 2 g729r8 bytes 30

While Unity Connection is only using G.729 (not G.729a or G.729ab), as specified in the Unity Connection Design Guide:

Supported Line Codecs (Advertised Codecs)

·         G.711 mu-law

·         G.711 a-law

·         G.722

·         G.729

·         iLBC

What will happen when users call in remotely to check their messages if the CUBE cannot negotiate G.729 with Unity Connection?


  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3.3 (3 ratings)
dksingh Mon, 09/13/2010 - 13:47
User Badges:
  • Cisco Employee,

Hello Aaron,

Don't think there will be an issue as from IOS standpoint, g729 and g729-AnnexA

codecs are completely interoperable and IOS will use the right variant based on

codec complexity.

Hope this helps.


Aaron Dhiman Wed, 09/15/2010 - 14:26
User Badges:

So, are you suggesting that by setting the CODEC Complexity to High that we can force the router to use G.729 instead of G.729a?


Aaron Dhiman Wed, 09/15/2010 - 15:27
User Badges:

This is a great link, and it leads me to believe that G.729 can be selected by the router by setting CODEC Complexity to High.  However, it doesn't explicitly state this.  Is that your understanding?  I cannot test this at the moment b/c I don't have the CUBE or Unity Connection servers to test with...


dksingh Wed, 09/15/2010 - 20:22
User Badges:
  • Cisco Employee,

Yes, your understanding is correct wrt to codec complexity. Doc does mention....

On Cisco IOS gateways, the variant to use (G.729 or G.729A) is related to the  codec complexity configuration on the voice card. It does not show up explicitly  in the Cisco IOS command line interface (CLI) codec choice. For example, the CLI  does not show g729ar8 ("a" code) as a codec option. However, if the voice-card  is defined as medium-complexity, then the g729r8 option is the G.729A  codec.

But since you are using CUBE here, no DSP would be engaged (unless u r xcoding) but since IOS treats G.729 and G.729A variants as interoperable,

I don't expect any issues.

If you are using voice class codec on CUBE dialpeers, I would suggest to use IOS 15.1(2)T or later where support for voice class codec supp service was introduced.

Hope this helps,



This Discussion

Related Content