On Oct 11, 2007, at 11:55 AM, Francois Audet wrote:
Hi Dean,
Can you tell me what is the difference between "contextually-adapted
INFO", and a "subscription embedded in the INVITE, with the NOTIFY
using the same dialog"? I don't see any advantage to the INFO
approach.
One might argue that the second is a means of implementing the first.
INFO, as written, lacks contextual negotiation. You're proposing to
replace the method name with NOTIFY and use the event-package
framework for content and context expression, using a header-field in
the INVITE request to engage context negotiation. It seems to me like
that would work. There's nothing "implicit" about it, and it is no
worse for overhead than using Supported or Allow. It also has the
advantage of letting us reuse an existing registration framework,
IANA process, and specification review process under RFC 3427. Very
tidy, I think I like it.
I would argue that it would be nice to have an extension mechanism
that allows a UA to be asked "Do you support this specific
extension?" without the UA having to encode every extension it
supports in every request it sends, but that's a different issue.
It seems to me we already have a mechanism for asking for asynchroous
information with subscriptions. Why not use that?
As you pointed out, the current mechanism adds a dialog overhead. It
also raises issues with event-stream correlation that can be a bit of
a challenge depending on the application's API and threading model.
Your suggested workaround for in-dialog notification relieves these
issues, so it may be better than the existing mechanism for a number
of use cases. More importantly, it is no worse than NOTIFY for those
use cases (barring the small increase in request size for context
negotiation).
--
Dean
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