[asterisk-biz] SIP , SIP-I and SIP-T

[Trixter aka Bret McDanel]

On Fri, 2008-05-23 at 16:33 +0700, Dome Charoenyost wrote:
> Dear All,
> 
> Can someone explain about SIP,SIP-T and SIP-T ?
> and Asterisk support SIP-I,SIP-T or not ?
> 

they are basically variants of sip.  While they are generally similar
there are differences that can arise and mean that generally they arent
compatible with each other.  

To understand the differences you need to know a little history about
SIP.  In a nutshell there was the PSTN, then data networks came about
and people started streaming voice over it.  Eventually the ITU came up
with H.323 which more or less is a "pstn over data networks" type thing.
It has fields for most if not all informational elements that exist on
the pstn.  Some argued that it was too complex of a protocol, and that
stripping it down to only the base information needed was a good thing.
They came up with SIP.  Then it was realized that the pstn isnt going
away and some put the stripped out stuff from H.323 back and you had
SIP-T.  SIP-I has the isup elements in it.

Remember these are all signalling standards and not ways to carry voice,
voice is generally carried by RTP with these protocols.  Not that they
are limited to voice.

AFAIK asterisk only does part of SIP and does not do SIP-T or SIP-I (and
before anyone says anything its not RFC compliant on SIP fix it or deal
with it but dont attack me for pointing it out).


-- 
Trixter http://www.0xdecafbad.com     Bret McDanel
Belfast +44 28 9099 6461        US +1 516 687 5200
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