Each CODEC has different capabilities for compressing voice, so you'll have
to know which CODEC you want to use first.
The compressed voice is then put into an IP frame, so you will need to take
into account the bandwidth used by headers of the following sizes:
20-byte IP header
8-byte UDP header
12-byte Real-Time Protocol (RTP) header
On point-to-point links those headers can be compressed down to just a few
bytes. Even the IP header can be compressed if it's a point to point link
and IP addressing isn't needed for forwarding to the next hop.
If you use Voice-Activity Detection (which uses no bandwidth during
silence) you can further reduce bandwidth requirements.
Finally, you need to take into account the data-link header, PPP, Frame
Relay, whatever.
According to a chart that I picked up at Networkers a couple years ago,
here are a few examples:
G.729 CODEC on PPP without compressed IP/UDP/RTP and without VAD uses 26.4Kbps.
G.729 CODEC on PPP with compressed IP/UDP/RTP and without VAD uses 11.2 Kbps.
G.729 CODEC on PPP with compressed IP/UDP/RTP and with VAD uses 5.6 Kbps.
G.729 CODEC on Frame Relay without compressed IP/UDP/RTP and without VAD
uses 25.6Kbps.
G.729 CODEC on Frame Relay with compressed IP/UDP/RTP and without VAD uses
10.4Kbps.
G.729 CODEC on Frame Relay with compressed IP/UDP/RTP and with VAD uses
5.2Kbps.
I would copy and paste the whole chart but I only have hard copy. You
should be able to find such a chart somewhere though.....
Priscilla
At 11:47 AM 1/9/01, Ishtiaque Mahbub wrote:
>Hello Group!
>
>A very happy new year to you all!
>
>I was wondering if any one could advise what is the minimum Bandwidth
>required for Voice Over IP installation on Cisco Routers (Router Series will
>be 2600).
>
>Is 64kbps is too steep for 4 simultaneous voice operations?
>
>Suggestion, advices welcome.
>
>Regards
>
>Ishtiaque
>
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