[asterisk-users] Bandwidth requirements

[Jay R. Ashworth]

On Thu, Oct 05, 2006 at 09:44:56AM +0100, Brian Candler wrote:
> A 20ms packet duration means that 20ms of audio is stuffed into one IP
> packet. Since each packet carries 1/50th of a second of audio, that means
> you're generating 50 packets per second for each channel.
> 
> With g729 your audio is 8000 bits per second.
> 
> The overhead on each packet is 20 bytes (IP) + 8 bytes (UDP) + 12 bytes
> (RTP) = 40 bytes or 320 bits.
> 
> So your bandwidth requirement per channel is:
> - 8000 bits per second for payload
> - 320x50 = 16000 bits per second for overhead
> making a total of 24000 bits per second.
> 
> 20 simultaneous calls is therefore 480,000 bits per second.

A reminder: much equipment, particularly low end/consumer equipment,
chokes *much* faster on high PPS than it does on high BPS.

While short packets are good for latency, they do impose stricter
engineering evaluation requirements on the other links in your chains.

Cheers,
-- jra
-- 
Jay R. Ashworth                                                jra at baylink.com
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