Discussion: IAX versus SIP

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Interestingly enough, while SIP is covered under CALEA in the US (required to be monitored), IAX is currently NOT covered under CALEA. This means that, in theory, if your VoIP traffic is all IAX-based, you're not required to make it available for recording by the US government as you are if you were SIP-based. Of course, there are other court orders they could use (Title 18, etc) to get around the CALEA limitations if they really wanted to press the issue.

One assumes that, with the increasing popularity of IAX, this will be remedied in a later version of CALEA (CALEA 2.0?). however, it could now save you hundreds of thousands in implementation costs — especially with the CALEA deadline approaching.

by eneref, Friday 04 of May, 2007 (02:09:36 UTC)
SIP vs IAX Summary

Someone has tried to resume the advantages and disadvantages.

I think it can be useful.


by jtamasaf, Tuesday 20 of February, 2007 (17:44:28 UTC)
IAX DTMF inband or out of band

This page says
<blockquote>"9) IAX always sends DTMF out of band so there is never any confusion about</blockquote>
what method is used. "
but the <a href="http://www.voip-info.org/wiki/view/IAX">IAX page</a> says
<blockquote>"IAX always sends DTMF inline, eliminating the confusion often found with SIP."</blockquote>

My confusion is not eliminated ;-) Does IAX2 send DTMF inband or out-of-band? One of these pages needs to be corrected.

by splante, Friday 26 of January, 2007 (16:44:39 UTC)

Well one MAJOR point Mark did not touch on.

Audio always goes through the IAX server. With SIP, the RTP stream can redirect on a transfer.

You have a calling card application. Someone calls your PBX and enters the code. You then transfer them to the number they entered. SIP keeps accounting the call, but the audio stream is sent from provider to provider (So, you don't have to deal with the audio bandwidth).

You must set up Reinvites in my experience to get this to work. But, it saves us a ton of bandwidth.

If you are using a provider that supports sip, but uses a major telco backbone with good network pipes, this could improve your sound quality depending on how your provider coded it. Using IAX with voipjet for instance, the call has to go to New Jersey.. then off to Washington and then who knows where else. Voxee is the same way.

Anyone, correct me if I am wrong here. But, I have this setup working for me.

- Chris

by cdyne, Thursday 08 of June, 2006 (21:34:55 UTC)
Objective comparison

Maybe I can help you. I do not say that I'm a guru, so please tell me if there is something wrong...

  • SIP is implemented in nearly every IP-Phone, IAX2 is just found in some.
  • SIP is able to transport neary everything, IAX just carries phone and obviously videocalls. SIP, as the name says, initiates a session, what you carry depends on which protocols like RTP or whatever you want to transport. With SIP you can create your own messenger. IMHO this will never be possible with IAX (and is never intended to..).
  • SIP needs a port for control information and one for each RTP stream, so at minimum 3 ports, IAX uses just one port regardless of how many calls you pass through.
  • IAX is ways better with handling NAT/PAT
  • SIP may need a STUN-Server
  • I'm sure I forgot something...

I decided to use SIP as the protocol for the customers because all the phones out there are compatible with SIP, just some are capable of IAX. Maybe this changes in future and we use IAX2, too. For trunking, means carrying all the data to the big local carriers, we use IAX2 if possible.

Rolf (rowi.net)

by rowitech, Thursday 27 of April, 2006 (18:12:49 UTC)
Re: very biased!!

What do you expect... Mark wrote it :). Besides, its all true!

by cydonia, Sunday 04 of September, 2005 (12:14:37 UTC)
Need objective review of SIP & IAX

I would like someone who is very competent in the area of IAX and SIP implementation and application to submit an article that compares and contrasts IAX and SIP, objectively. I am looking into this at the organization where I work and I am interested in the following particular topics regarding IAX and SIP:

1. Encoding and decoding

2. Information verfication

3. Layer 2 and Layer 3 separation

4. Transparent NAT navigation

5. Authentication mechanism

You may contact me directly if you have substantial information.



by osioke, Wednesday 10 of August, 2005 (18:21:20 UTC)
very biased!!

This is not a comparison of AIX and SIP - instead it is just why AIX is better than SIP in the opinion of the author.

by , Wednesday 26 of January, 2005 (13:10:37 UTC)