CCM call setup bandwidth

[SEAN NILSEN]

Can anyone tell me what the bandwidth consumed is for CCM to setup a call between an IP Phone and a gateway? I have found all of the references as to what the call will take once setup and active depending on CODEC, but I am trying to determine call setup requirements for a Local CCM and an IP Phone and gateway at the same remote location. They have a fairly small WAN link (56k frac Frame Ckt) so I am trying to determine the requirements for call setup so I can best propose the solution, either a CCM local to the phone and gateway or increase the pipe size, depending on the answer to this Q. Thanks.

[rlyons]

Hello Sean,

I have never figured out the bandwidth necessary for a Skinny call setup but it should not matter. If you take the 56kb link and subtract 25% for overhead (Cisco’s recommendation and standard implementation) you will have 42kb remaining for voice (assuming no data). Running G.729 with a 20msec sample with cRTP and FRF 12 (and no VAD) takes 11.4 kb per call. If you divide 42 by the 11.4 you get about 3.7 calls. Imposing QoS you should reject the fourth call setup. The call setup bandwidth is inconsequential when compared to the voice stream plus you have the extra bandwidth (0.7 calls) available because you could not make that fourth call.

Bob