Question about VOIP Compression over a WAN Link

[Neuromancer]

Hypothetical situation:

I have a Call Manager and VOIP phones at my HQ site. I have a WAN link to a remote branch with limited bandwidth. The edge router at the branch does not have a voice enabled image. The users at the branch are requesting VOIP phones. I want to deploy VOIP phones at the branch site using G.729 compression (32k) to call over the WAN. The VOIP phone calls made within HQ are compressed using G.711 (64k).

My question is this, if a user at the branch makes a call to a user @ HQ, I want the call to be compressed to G.729. Is this compression negotiated when the signaling is done between the remote VOIP phone and the Call Manager?

Any advice or tips would be appreciated!

[msulieman]

cico ip phones support both g711 and g729 so there is no need for compression, they will negotiate within call setup on either g711 or g729.

[Chris Deren]

It's configured within CallManager by using "Regions" and then referencing regions within Device Pool, which off course I used by phones.

So in your scenario you would have to create 2 regions: SiteA, and SiteB, define them to use g729 between each other , and g711 within themselves. The create 2 device pools and reference these regions.

As stated eariler the phones as well as voice GW will negotiate the approrpiate codec, so even if you make an outbound call from this remote site to PSTN via the HQ this call will negotiate g729, as long as the GW is assigied to the correct device pool (region).

Chris

[Neuromancer]

Thank you very much, this is exactly what I was looking for!

One additional question, since there is no voice enabled image on the remote branch router, and no PSTN access, will the VOIP phones @ the remote branch be able to directly negotiate with the CCM at HQ for the proper codec to use?

The network at the remote site was not built with any regard to VOIP. Can I still put the VOIP phones in it with IP addresses, and they should work right?

[Chris Deren]

What type of a router do you have at the remote site?

Phone will work fine, except you may not be able to utilize SRST if you loose WAN connection.

The voice compression is negotiated between the voice endopoints and as long as there is network L3 connectivity to the remote site voice will traverse the WAN just fine.

Another limitation you may expereince is QoS, again depending on the router and IOS version, you may not be able to prioritize voice over data.

HTH, please rate all posts!

Chris