by tbenson » Fri Aug 17, 2007 2:40 am
Here are some links to pages that help you calculate Codecs and Bandwidth consumed.
http://www.voip-info.org/wiki/index.php?page=Asterisk+bandwidth+iax2
http://www.voip-info.org/wiki-Bandwidth+consumption
One thing people tend to overlook when using VoIP is that its realtime communication. So once you do the math in these pages consider EVERY packet of traffic not for VoIP is going to reduce your numbers and/or call quality. Don't forget to consider the inbound calls and adapt level, as calls ringing into or out of the server before terminating to a conference room will also consume bandwidth.
If the circuit is Asymetric (DSL, Cable, etc.) then you should expect even less as simultanious upstream exponentially reduces available downstream. IE a good rule of thumb is if you have a 6Mbps Downstream and a 784Kbps Upstream do your math as if the circuit is a 784K Symetric Circuit instead.
Thus even if you change your codec today, and reduce the amount of NA's your getting, If ANYONE in the building uses the same circuit for Internet access while your around 40-60% utilization then you can expect call quality to go down and NA's to rise at the drop of a hat.
Trevor Benson
dCAP, LPIC-1, Network+, MCP
A1 Network Solutions - VoIP Business phone systems, Call Centers, Failover and Load Balanced network design.