Subject: [SIP] is SIP backward compatible?

From: Itamar Gilad <[email-masked]>
Date: Thu, 4 Jan 2001 19:23:17 +0200

Everybody,
I'm looking for some guidance in regard to the backward compatibility of
SIP.  From following the mailing list and relevant events I know that an
effort is made not to break existing implementations, yet a pure RFC2543
might have interop problems with a pure bis-02 implementation because of
some of the changes made.  My questions:
* What are the rules that determine this?  
* Are the compatibility-breaking changes about to stop once bis-02 goes RFC?
Anytime?
* Is there some sort of general IETF guideline to this matter?

Thanks,

Itamar Gilad
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From: "Dean Willis" <[email-masked]>
Date: Thu, 4 Jan 2001 14:53:09 -0600

RFC 2026 says:

"A specification may be (indeed, is likely to be) revised as it  advances
through the standards track.  At each stage, the IESG shall determine the
scope and significance of the revision to the specification, and, if
necessary and appropriate, modify the recommended action.  Minor revisions
are expected, but a significant revision may require that the specification
accumulate more experience at its current maturity level before progressing.
Finally, if the specification has been changed very significantly, the IESG
may recommend that the revision be treated as a new document, reentering the
standards track at the beginning."

In other words: we try not to break compatibility, but sometimes find that a
protocol is already broken and needs fixing. Change is not mandatory.
Neither is survival ;-).

Generally speaking the rate of change declines as a protocol prgresses up
the standards track. There are no absolute rules in this area that I am
aware of.

--
Dean Willis