[Asterisk-Dev] IAX2 Spec?

[Steve Kann]

On Apr 8, 2005, at 10:05 PM, Johnathan Corgan wrote:

> Steve Kann wrote:
>
>> It's fun, especially when the receive side is mostly implemented in 
>> one 1300 line function (socket_read()) :)
>
> Yeah, I was digging through this to try to tease out some of the inner 
> workings of the protocol.
>
> One thing I did notice, and was curious about.  A mini-frame only has 
> the sender conversation number.  This is used to as in index for the 
> connection in iaxs[].  Since this is assigned by the sender and not 
> the receiver, isn't it possible for there to be a collision?  I would 
> think that only the combination of scallno:dcallno would be guaranteed 
> to be unique.
>
> Or am I missing something really simple?

The receiver knows what the sender's callno is, and it _also knows who 
the sender is_, by virtue of where the packet came from.

So, the receiver's call number  gets looked up right here (in 
chan_iax2.c, anyway).

6228         if (!fr.callno)
6229                 fr.callno = find_callno(ntohs(mh->callno) & 
~IAX_FLAG_FULL, dcallno, &sin, new, 1, fd);


Also, you can look at libiax2.c's implementation, which is very 
similar, but somewhat simpler than chan_iax2.

-SteveK