Subject: [Sip] Clarification for multipart/alternative handling

From: "Eric Tremblay" <[email-masked]>
Date: Mon, 18 Feb 2008 11:08:24 -0500

Hi Gonzalo,

I have been going through draft-ietf-sip-body-handling-01 and noticed
something that is either en error or counter-intuitive.

Section 5.1 states:
   The body parts are
   ordered so that the last one is the richest representation of the
   information.  This way, the recipient of a 'multipart/alternative'
   body chooses the last body part it understands.

Section 6.2 states:
   If the handling of a 'multipart/alternative' body is required, the UA
   MUST set the 'handling' parameter of the 'multipart/alternative' body
   to 'required'.  The UA MUST also set the 'handling' parameter of the
   last body part within the 'multipart/alternative' to 'required'.

Why the last body part? Somehow, I would have expected that the
'handling' parameter of first body part to be set to 'required', not the
last one, as the last one should hold the richest representation of the
information, and possibly the one most difficult to
understand/implement...

And thinking about it a little bit more, I think that an application
should always set the 'handling' parameter in the internal parts of a
'multipart/alternative' to 'optional', as this is pretty much what
'multipart/alternative' is. If 'multipart/alternative' itself is has its
'handling' set to 'required', then it means at least one of its internal
part must be understood and handled. The sender cannot really decide
which one has to be understood.

Maybe my suggestion is going against things already defined in MIME or
somewhere else. If this is the case, I think a simple clarification in
the draft would do, something in the line:

Even though the last part of the 'multipart/alternative' has its
'handling' parameter set to 'required', the receiving UA (or UAS) does
not necessarly have to be able to handle this specific body part, it
only has to be able to handle any body part within the
'multipart/alternative' body parts.

Best Regards,

EricT
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