[Asterisk-Users] GSM codec bandwidth

[Rich Adamson]

> > > 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.
> 
> Yes, I understand about overhead, but this is 4x the bandwidth usage.  Even if
> that is 13kbps for each stream of audio (23kbps total), that is doubled by
> (TCP/UDP)/IP overhead.  That struck me as a lot of overhead.  I guess, though,
> that since the packets need to be sent quite frequently, that could happen.

Just a guess here and I've not use gkrellm at all, but is it possible
gkrellm is adding incoming & outgoing traffic together?

If I take your numbers, divide by two, the result is roughly 
equivalent to the actual codec bandwidth plus the pkt overhead for
data moving in each direction.