Codec selection/usage

[rainee.ortiz]

In an effort to add more DSP resources to our CUBE, we added the offer-all option on the voice-class command in the dial-peer interface.

I need clarification on why the following configuration results in the codecs being used for G711 to G711 calls.

voice class codec 2
 codec preference 1 g711ulaw
 codec preference 2 g729r8

dspfarm profile 4 transcode universal 
 codec g729abr8
 codec g729ar8
 codec g711alaw
 codec g711ulaw
 codec g729br8
 codec g729r8
 maximum sessions 10
 associate application CUBE

What is the best practice for configuring hardware DSPs?  Would it be accurate to believe that because the codec preference in our voice class codec 2 - could force the g711 to g711 calls?

Thanks in advance for your help and guidance.

Rainee

[rainee.ortiz]

I'm confused.  When I make an outbound call (IP Phone -> CUCM -> CUBE -> ITSP), I send the INVITE to the ITSP

sdp includes:

a=rtpmap:0 PCMU/8000
a=rtpmap:18 G729/8000

I received ACK from the ITSP

sdp includes:

a=rtpmap:18 G729/8000

But between the CUBE and CUCM the INVITES and the ACKs

sdp includes:

a=rtpmap:0 PCMU/8000

So that would indicate to me that the CUBE is transcoding, am I wrong?

[John Huthmaker]

Sort of, but not really.

The call control entity is what is actually setting up the call, and gathering the resources to make it happen.  The Call Control entity in this case is CUCM.  The resources may physically be on the same router that is acting as your border element, but they would work just as well on a different router.

Your border element is literally just a mediator between the sip domains.  Your internal sip domain, and your carriers.  You can think of it as being similar to the way a firewall does nat between the internet and your lan.

Look at questions 5 and 12 on this FAQ about border elements.  Now there is an obvious typo in Q12, as it should say "are not required to simply connect to a sip trunk",  but you can tell that if you read the rest of the paragraph.  The paragraph wouldnt make sense any other way. 

https://supportforums.cisco.com/document/69976/frequently-asked-questions-cisco-unified-border-element-cube

[John Huthmaker]

I'm going to take everything I said back.  Your config does an "associate application CUBE".  You are probably right that the CUBE is requesting the resource.  I've always set my media resources to use SCCP and bound the profiles to CUCM.  You have a very different setup than I've come across in the past.  I apologize if I caused any confusion.  It looks like this command was added on the newer ISR G2 routers.

[rainee.ortiz]

Hi John,

  Sorry for not getting back to you sooner, but I was out of the office.  Maybe our setup is not what we should be using.  Yes our carrier does support G711 and G729.  Internally, we only have G711 but in order to make carrier G729 calls we needed to include that in our setup.

  I wished I could understand that one command's (offer-all) purpose.  Thanks for your time and effort.

Rainee

[Terry Cheema]

Run the following command on CUBE (as you have mentioned you have media resources on CUBE):

show sccp connection

It should display any transcoder being invoked. From some of the above posts I get that you are doing both G711 and 729. Does your carrier support both codecs?

-Terry