Audio Codec Preference List - CUCM 10 Question

[voip7372]

Let's say we want Site A to only use G.729 codec for normal conversations over the WAN to Site B, but for the occasional instance when a call needs to go to voice mail (from Site A to Site B) and the voice mail system only supports G.711 codec, we want to allow G.711 to be used.  But again, normally we only want to use the lower bandwidth G.729 codec and ONLY use G.711 when the system determines that the other side simply can't talk with G.729...such as in the case when the voice mail system answers (it can only talk with G.711 codec).  

I think I have this figured out, but please tell me if I'm wrong.  We copy the factory default 'low loss' Audio Codec Preference List and give it a new name.  We move all the G.729 codec entries from the lower position they're in by default all the way up to the top so G.729 is the first option.   We can leave the other entries for G.711, G.722, etc where they are and let the system use those when necessary.  

Next, in the Region settings for Site A, we select the entry for Site B and then change the Audio Codec Preference List to be the new list we created that has G.729 at the top of the list.  Also, we change the Maximum Audio Bit Rate to 64 kbps.  

Is that correct?  

[Vivek Batra · Accepted solution]

Seems Unity Connection is also in SiteB. If yes, then what you are thinking seems correct. 

You need to ensure CUC only offers G.711 codec in 'Codec Advertising' settings (available under Port Group).

To summarize, you will be having two regions viz SiteA and SiteB.

1. Call from SiteA to SiteB (to phones) - G.729 codec will be used because it has higher priority than G.711 as per settings you did.

2. Call from SiteA to SiteB (voice mail) - G.711 codec will be used b/c CUC shall only offer G.711 and your region settings are configured appropriately with 64Kbps.

Thanks

Vivek

[voip7372]

Ok, thanks.  I just wanted to verify my understanding of how this works is correct. 

The voice mail is Microsoft Unified Messaging, not Unity...but it doesn't matter.  Only thing that really matters is the fact that it won't work with G.729, so I had to make sure it would be able to use a 64 kbps codec when it needed it...but still restrict phone to phone and other traffic that is able to use G.729 to use G.729 as the first choice. 

[Vivek Batra]

Yes, it doesn't matter which voice mail system is this, but should ensure that it never offers G.729 codec else call from SiteA to voicemail system in SiteB may select G.729 (although you have already mentioned that your vm system only supports G.711 hence this is not the case).

To use G.711 codec from SiteA to SiteB voice mail, 64Kbps is the minimum requirement which you have already taken care under Region settings.

SiteA to SiteB phones will always use G.729 because of higher priority.

[UrbanPeasant]

Vivek, thanks for this post, it put me onto the fix for my CXN problem. Since we upgraded from CXN 10.5.2 to 11.5.1 we've not been able to use Unity to make notification device calls out to the PSTN, (we use this feature for On Call engineers) and when I saw in the SDL traces that Unity was using a codec we don't use in the INVITE to the CUCM subscriber I couldn't figure out what had changed.

As it happens, the upgrade over-wrote the advertised codecs with ones that must be standard in the USA, but we're in the UK and don't use ulaw, and we don't use 729 anywhere either. Once I saw that and made the change to alaw only, the notifications started working again.

Very pleased.

Best regards

Nathan.