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Home > Archive > CCNP > February 2002 > G711, G723, G729?
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| supergoku0 2002-02-19, 4:20 am |
| Hi all,
Refering to a poin-point VOIP application(e.g. with two cisco 1750 routers), can somebody give me a rough idea/link regarding bandwidth consumption per voice call, how is it related to codec standards G711, G723 & G729?
TIA,
Goku | |
| MadChef 2002-02-19, 5:23 am |
| I'm not a voice person, so take this with a grain of salt. Someone else can probably correct me.
VoIP bandwidth per call is a result of the codec you use. The codec takes incoming analog voice and puts out a digital stream, so the manner in which it does this determines the size of the output stream.
G711 is straight Pulse Code Modulation with no compression. It uses 64kbs for a voice call (see Nyquist's theorem for why).
G711a (which I think is the default for VoIP) compresses the stream using some algorithm I can't remember to result in a slightly degredated 8kbs stream. It's degregated, but it's still considered business quality. I believe this is just for the voice stream, though, and the IP header will add to the bandwidth needed. If it's a point to point link and you can turn on rtp header compression, you're down to something like 12kbs per call, if I remember correctly.
MadChef | |
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