asterisk users - Sep 2004 - GSM codec bandwidth

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.

Am I missing something, or are my expectations wrong?

-- 
-M

There are 10 kinds of people in this world:
	Those who can count in binary and those who cannot.

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