[Asterisk-Users] GSM codec bandwidth

[steve at daviesfam.org]

On Thu, 2 Sep 2004, Michael George wrote:

> I've a question about the bandwidth consumed by IAX2/GSM.
> 
> According to the wiki page, the GSM codec should run about 13 kilo-bits/sec
> for a voice encoding.
> 
> However, watching gkrellm when I initiate a call to Digium, it looks like the
> channel is taking a consistent 5-6 kilo-bytes/sec.  That's a lot more
> bandwidth than it should take.  Is there perhaps a setting I have wrong
> somethere in the conf files?
> 
> I have:
> bandwidth=low
> disallow=all
> allow=gsm
> 
> so it's surely using GSM and it should be gearing itself for a low-bandwidth
> situation.


The codec itself takes 13kbps, but by the time the codec frames are 
wrapped in all the IP overhead it is a lot more.

If you are sending several concurrent calls to the same place, you can 
reduce the overhead by using trunking - which shares the IP overhead over 
the concurrent calls.

Steve