[Sip] update-01 comments

["Bob Penfield" <bpenfield@acmepacket.com>]

Section 4 says the UPDATE may contain an offer any time after a dialog is
established. Although section 5.3 says it must follow the offer/answer rules
you may want to point out in section 4 that the UPDATE can only contain an
offer if allowed under the offer/answer rules.

Section 5.3 talks about the Supported header in the response, but section
5.2.1 mandates the response contain the Require header. This should be made
consistent. Otherwise it is not clear why the Require:update is needed.
Also, the language in 5.3 implies that the fact that it is a 155 response is
sufficient.

Since we have changed the strength of the UAS requirement for generating a
155 from MAY to SHOULD, I suggest that we change the addition of
Require:update in the proxy from a SHOULD to a MAY. If the UAS does not
support update, you'll end up with 3 exchanges if there is a repairable
error in the INVITE instead of 2. I don't see any great advantage in the
proxy requiring update.

cheers,
(-:bob

Robert F. Penfield
Chief Software Architect
Acme Packet, Inc.
130 New Boston Street
Woburn, MA 01801
bpenfield@acmepacket.com




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