Why does an H.323 gatekeeper subtract 128k for a G.711 call when it only actually uses 80K of bandwidth?

[PETER NEGUS]

I'm confused why a H.323 gatekeeper deducts 128kbps from the bandwidth pool for each G.711 call, which only consumes 80k, and then only deducts 16k for a G.729a call, which actually consumes 24k. Does it mean that a H.323 gatekeeper is useless for environment where you have different bandwidth codecs?

Can anyone explain the reasoning as to how these weird values got into the standard?

[clileikis]

Hi Peter,

H323 Gatekeepers use twice the codec bandwidth without UDP/IP header bandwidth which is 64 X 2 = 128 for G711 a single G711 call  and 8 X 2 = 16 for G729 for a single G729 call.

HTH,

Chris 

[PETER NEGUS]

Hi Chris

That doesn't make sense. The codec rate of G711 is 64kbps, which means an IP bandwidth of 80kbps @ 50 packets per second including the IP headers. The codec rate of G729a is 8k, which has an IP bandwidth of 24kbps @ 50pps. So if you were using that model and doubling the bandwidth (for some unknown reason), you would have G711 = 160k and G729 = 48k in the gatekeeper calculations.

[clileikis]

Hi Peter,

I updated my previous post, the G711 bandwidth calculation without the IP headers calculated by a Gatekeeper is 128 for a single call is 128, not 160.  Therefore a single G711 call uses 128 and a single G729 call uses 16.

HTH,

Chris