G711 bandwidth when use gatekeeper

[ciscoforum]

One of the document says when CCM requests bandwidth from gatekeeper during an admission request(ARQ) or bandwidth request(BRQ) it requests the maxium tranmits and receive, therefore for G711 and g729, it will use 128kbps and 20kbps respectively. Could anybody tell me how they get the figure 128?

[rbradfield]

I don't know its always been like that ! might be something to do with DS0 so might say one 64k channel is not enough so need two which is 128k

but really I have no idea.

[jpinkus]

Per the H.323 specs an ARQ will request bw in a bidirectional manner, thus 128K per G711 call.

[pbarman]

The bandwidth requested in ARQ or BRQ is only used for CAC (Call Admission Control). It is NOT an actual link bandwidth allocated for the call, it is just used for calculation by the gatekeeper(s) only.

Suppose you are using CAC and limiting interzone bandwidth to say 256kbps. Gatekeeper will allow only 2 g711 calls, but the actual bandwidth being used between the two endpoint gateways is actually ~160kbps.

So, it is just a way of calculating the bandwidth for CAC only, and 128kbps was probably picked up by someone who thought a bidirectional call with take 64+64=128kbps, so it makes sense to pick 128.

[gbrome]

If I wanted to have WAN calls from one independent CCM cluster to another use G.729, what's the best way to do that? For example, I have one cluster in California and one in Philadelphia. I am using a gatekeeper for CAC. It appears all my calls are G.711 instead of G.729 if I look at the BW measurement being used per call. My CCM in CA is 4.0, and only in one physical location, and therefore, I only have one region. How do I get calls that go out the H.225 trunk to be G.729? Thanks!

[pbarman]

Create a new region and device pool, say GKPR. Between the GKPR region and CA region use g729 codec (you need to configure that in CCM). Assign the h225 trunk to the GKPR device pool, and phones in CA to CA device pool. That way any calls from IP Phones in CA through the h225 trunks would be forced to use g729.

Do the same for the Philadelphia site !!