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IAX vs SIP

ronsterchan
Posts: 7
 Member Since:
2007-12-11
Submitted by ronsterchan on Wed, 12/12/2007 - 8:31am.

googling "IAX vs SIP" gives me a number a good articles on relative technical merits

the summary I come to is IAX is developed for VOIP and developed for Asterisk, therefore 'should' be technically superior, the bandwidth requirements should be lower and the network support requirements should be lower because it goes through single port

However, I would like to hear from people who have had real world experience of both, especially with regards to
1. bandwidth requirements
2. call quality

Thanks
Ron

‹ VoIPStreet problems AGAIN? [RESOLVED] SIP Provider for Small Business (that's not Vonage) ›

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drmessano
Posts: 208
 Member Since:
2006-10-10
IAX is better.. 1000%
Wed, 12/12/2007 - 9:23am

IAX is better.. 1000% better.... but don't go nuts based on that.

Use IAX for your inter-office trunks, ITSP trunks, and a device here and there. If you have someone that needs to work at home, setting up an IAXy is easier than a SIP device sometimes. Beyond that, SIP works.


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ronsterchan
Posts: 7
 Member Since:
2007-12-11
better call quality? or
Wed, 12/12/2007 - 9:34am

better call quality? or better because it is easier to support?
or both?

Thanks
Ron


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drmessano
Posts: 208
 Member Since:
2006-10-10
Easier to support and less
Wed, 12/12/2007 - 9:44am

Easier to support and less bandwidth.. Call quality is based on Codec for the most part.

IAX also has some jitter buffering in place which helps, but if you put them side by side on a 100MB connection, you wouldn't notice a difference.


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vijayaa
Posts: 75
 Member Since:
2006-06-14
IAX/SIP Comparison (Endpoint or Trunk)
Wed, 12/12/2007 - 10:57am

A comparison of IAX & SIP is complex because you need to define the scope. For example, do you want to compare SIP endpoint (e.g X-lite) with an IAX endpoint (e.g. IDEFISK). Or do you want to compare a SIP Trunk with an IAX Trunk.

SIP endpoints are open standards so can work with non-Asterisk servers (e.g. SER - SIP Express Router).

IAX Endpoints use a single UDP port so is easier to get working with NAT and through Firewalls.

The fact that IAX uses a single UDP port/socket can be an advantage. However, this does limit the scalability of an IAX Trunk. I heard somewhere that most TCP/IP stacks can only handle up to 30 concurrent connectons on a single UDP socket/port. i.e. a IAX trunk between 2 Asterisk Servers can only handle 30 simultaneos calls. However, SIP uses 10,000+ UDP ports, so there is no such limits on a SIP Trunk, between 2 Asterisk Servers.

I don't think one is better than the other, they are just different and each has it's own pros & cons, and your choice of what to use depends on your requirements/circumstances.


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16again
Posts: 370
 Member Since:
2007-03-04
vijayaa, An IAX trunk
Wed, 12/12/2007 - 12:35pm

vijayaa,

An IAX trunk between 2 asterisk servers only uses a single port for multiple calls, so there's no connections based limit for number of calls on the trunk.

afaik, 64000 connections are possible on a single port

Better call quality? Same codecs are used!

Less bandwidth? Only when having multiple calls on an IAX trunk


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ronsterchan
Posts: 7
 Member Since:
2007-12-11
I can understand that call
Wed, 12/12/2007 - 1:31pm

I can understand that call quality is largely down to codecs.

However, in a limited bandwidth environment, eg a small office on a DSL shared with internet traffic, if the line gets busy during a call, does that not impact the call quality?


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peteradtel
Posts: 48
 Member Since:
2007-07-23
not so clear cut as it seamed.
Wed, 12/12/2007 - 4:47pm

I was using IAX2 to interconnect an old Asterisk @ home 1.2 system and a current 2.2.8 system.

Call quality was in-consistent until i swapped over to SIP
(OK at first but during the day it would degrade and sometimes go into a deadlock where no calls would go through - with no channels active - a restart of the old server was the only fix - amportal restart did nothing)

i believe it was due to the 1.2 system running an SVN edition of asterisk, but
because the system was running an EICON BRI card which was compiled into asterisk.
Re-compiling / upgrading asterisk on that system was not an option as it took a month to get the card to work properly in the first place.

but after i switched over to SIP, no more problems.

i guess this might be a unique senario
but don't forget SIP was designed by Cisco & Iax was open source
(to my understanding, so please don't take this as gospel as i may be wrong)


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drmessano
Posts: 208
 Member Since:
2006-10-10
Call Quality isn't just
Wed, 12/12/2007 - 7:19pm

Call Quality isn't just about codecs. I get so sick of hearing this one. IAX performs much better on the wire than SIP/RTP does. It's not an audio issue, it's the overall experience of the call.

While the benefits of IAX in regard to bandwidth are realized from call N+1 not 1, an IAX call will perform better under the varying conditions of a network. To question it's bandwidth use based on one call makes no sense to me, when anyone would know the clear benefit is how it handles N+1 and above.

Everyone is an expert.

dm


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asiby
Posts: 1
 Member Since:
2007-04-17
SIP was *NOT* designed by Cisco
Tue, 09/02/2008 - 9:26am

To my knowledge, SIP has been designed by two fellows, one was from Columbia University and the other one was from University College London.


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