[Asterisk-Users] IAX2 codecs used asymmetric ?!!

[tim panton]

On 9 Nov 2005, at 19:12, Branko Samardzic wrote:

> Hi,
> I am trying to make following setup
>
> PSTN --> Asterisk_1 ------- IAX2 stream over Internet ----->  
> Asterisk_2 -->
> PSTN
>              ^
>              |
>           AGI control App
>
> Basically this is calling card solution that accepts calls from  
> PSTN of one
> country
> checks user credentials (PIN and access rights), collects  
> destination number
> and
> establishes IAX2 connection with another Asterix server in  
> different country
> that
> is used to terminate call on another PSTN.
> So far I made everything working nice except one VERY important thing:
>
> IAX2 stream over Internet is at least in one direction bearing 16  
> bit Signed
> Linear PCM
> data although I insisted on GSM codec. As link has limited bandwith  
> (64kpbs)
> it becomes
> congested with single call.
> My iax.conf files contain disallow=all and allow=gsm in general  
> section on
> both servers
> but it is of no help.
> Is there any chance to tweak IAX2 stream to be symetric (i.e. to  
> bring GSM
> encoded audio
> in both directions) and how to achieve that.
> Any help is appreciated.

I am amazed that you are seeing asymmetric codecs on IAX. I _really_  
didn't
think the protocol could do that.

Try turning on IAX2 debug (or capturing the packets with ethereal)  
and send us
the relevant logs and configs.

Once you have this fixed, you will need to look at getting IAX  
trunking working
between the two hosts, this will reduce the overhead per stream.

20ms of gsm data is 33bytes, but the combined IP, UDP and IAX headers  
are 32 bytes
So almost half your traffic is headers ! IAX trunking puts multiple  
streams
within 1 header. Without trunking you will only get 2 calls (at most)  
down a 64k
link. With trunking you might just get 4.

Tim.