Re: [Sip] SIP backward compatibility issue

[Rohan Mahy <rohan@cisco.com>]

On Tuesday, December 24, 2002, at 09:45 AM, Steve Levy wrote:

> At 11:46 AM 12/24/2002 -0500, Jonathan Rosenberg wrote:
> > Early media was not specified in rfc2543. It did say that you should 
> > be prepared to receive media before receiving the answer, which is 
> > still the case for 3264. Another issue was that people used to put 
> > SDP in non-reliable 1xx responses, and then put the same thing in 
> > 2xx. That case is explicitly allowed for in 3261, so it should 
> > interoperate as well.
> >
> > Perhaps you could identify the specific problem you are concerned 
> > about?
> my concern was SDP in a 18x followed by another 18x/2xx with different 
> SDP. Wouldnt the SDP in the subsequent 18x/2xx be treated differently 
> by 3264 compliant UAs as opposed to earlier 2543 compliant UAs ?
Because offers and answers need to be sent reliably, you can't put an 
answer in a non-reliable 18x and an offer in a 2xx.  This is spelled 
out in 3261 section 13 as quoted below...

> If the initial offer is in an INVITE, the answer MUST be in a reliable 
> non-failure message from UAS back to UAC which is correlated to that 
> INVITE. For this specification, that is only the final 2xx response to 
> that INVITE. That same exact answer MAY also be placed in any 
> provisional responses sent prior to the answer. The UAC MUST treat the 
> first session description it receives as the answer, and MUST ignore 
> any session descriptions in subsequent responses to the initial > INVITE.
thanks,
-rohan



> thx,
> steve
>
>
>
> > -Jonathan R.
> >
> > Steve Levy wrote:
> > > > <snip>
> > > > rfc3261 is sufficiently backwards compatible with rfc2543. There is 
> > > > no need to detect versions or anything. Any backwards compatibility 
> > > > functions are built into specific features of rfc3261 that needed 
> > > > to support backwards compatibility. If you just implement rfc3261 
> > > > you will be backwards compatible.
> > > <snip>
> > > broadening the discussion to rfc 3264 (offer/answer), isn't there a 
> > > potential for backward compatibility issues with rfc 2543 
> > > implementations wrt early media ?
> > > thx,
> > > steve
> > --
> > Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
> > Chief Scientist                             First Floor
> > dynamicsoft                                 East Hanover, NJ 07936
> > jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
> > http://www.jdrosen.net                      PHONE: (973) 952-5000
> > http://www.dynamicsoft.com
> >
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_______________________________________________
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Use sipping@ietf.org for new developments on the application of sip