[Freeswitch-users] Simple IAX2 setup - help with converting from asterisk to freeswitch

[Derek Smithies]

On Fri, 5 Feb 2010, Matthew Law wrote:

> Why is that? - a lot of web pages I have read claim that IAX is more
> secure and efficient.  I have no problem with using SIP whatsoever and it
> certainly appears to be ubiquitous.  I am a complete newcomer to VoIP and
> I am trying to do this as securely as possible since I want to run
> freeswitch on a Xen VPS which will be visible on the internet.
>

Sigh.
  the web pages are wrong.

I have implemented the earlier version of IAX2 inside the opal library. At 
one stage, I could make a voip call using IAX2 to digiums test server.

The standard IAX2 codebase did not (at one stage) support silence 
suppression. With silence suppression, the bandwidth usage is halved. 
Using efficient packing of audio makes a few percent of difference. Doing 
silence suppression makes 50% of difference to bandwidth.

IAX2 is more efficient? Most(>90%) of the cpu work when doing voip is in 
the codec. By using a non standard approach (iax2 audio packets) for 
carrying audio, you will have a minimal gain in effiency (or cpu usage). 
Remember that iax2 uses the same codecs as in H.323/SIP. Oh - you are 
right, g711 is a codec, and has trivial cpu cost. However, with g711 any 
bandwidth you save on the header is negligible compared to the size of the 
encoded audio block.

Secure? Security protocols (HIP, ZRTP, etc) take years of careful 
development to get something that works well. I do not recall seeing 
evidence of years of development going into IAX2 security. Either the 
author of the security in IAX2 is a pure genius, able to do in 
days/weeks what other do in years,,,, or the iax2 security is 
average (at best).

Yes, all the iax2 packets go to the same port. This has huge advantages 
for getting through firewalls, and setting up firewalls to accept incoming 
calls. It does (slightly) increase the complexity inside the iax2 code.

===================================

if you want iax2 inside freeswitch, my suggestion is that the opal library 
needs to have the iax2 code there brought up to spec, and then used (in 
the same way as the H.323 component of the opal library).

Derek.
-- 
Derek Smithies Ph.D.
IndraNet Technologies Ltd.
Email: derek at indranet.co.nz
ph +64 3 365 6485
Web: http://www.indranet-technologies.com/