Dean Willis wrote:
We had a large, long, and lengthy thread of discussion that I will try
to summarize.
So far, almost everybody who has voiced an opinions says we need to fix,
rather than deprecate, INFO.
Opinions on fixing it vary.
Most people seem to think we need a registry of INFO usages that will,
at the very least, give us a table of the existing usages and the RFCs
or other specs that define them.
The sticky point of discussion is a negotiation and discovery mechanism.
We've had on-list proposals for a strong mechanism based on the mode
used in RFC 3265.
Some folks think we need to do this, and others thing there's no reason
to bother since it is not likely to get implemented because just
inventing a non-standard INFO use is easier.
Is there a middle ground?
What if we were to:
1) Establish an INFO registry and register our existing usages, policy
either "first come, first served" or "Specification required".
Its probably a little different from either of these existing policies.
Thats because it should only be applicable to *preexisting* usages.
We don't want new, yet to be deployed, usages registered in this way.
(We will probably have to use the honor system for determining which
usages qualify.)
2) Define an Info-type header field and register (in the regoistry of
#1) a value for each known Info usage. Fully-compliant implementations
would send an Info-type header field with the appropriate value in every
INFO message.
I think either this is a different registry, or else it is the same
registry but a different class of entry.
I'm inclined to think it is a different registry because it is a
different namespace. The namespace for (1) is mime-types, while for (2)
it is a unique namespace of Info-types.
3) Require registration of an Info-type for each future usage into the
registry of #1 above.
4) Define an "Info-type not supported" error response message. This
handles the use case of a UAS that receives an INFO with an Info-type it
does not understand.
5) For Info-types for which discovery is required, use a standards-track
RFC to define a SIP extension and option tag, and use the usual
OPTIONS/Require negotiation mechanism for discovery. We might consider
revising each INFO-using RFC to define an appropriate option tag.
Revising the old usages is IMO counterproductive. They are what they are.
This lets people easily register INFO usages and a corresponding
Info-type tag. It lets nodes that don't understand an Info-type usage
reject the message (at the expense of whacking the dialog, which
arguably was already in need of whacking).
Its not even that bad. It only whacks the dialog if you put Requires in
the dialog-establishing request. If you simply put it in the INFO
itself, then the dialog doesn't get whacked.
And it provides a standard
(although heavy) mechanism for discovery and negotiation when those are
required.
I think the above addresses the major concerns, is reasonably
implementable, is reasonably operable, and requires the smallest
possible effort to document. It's also pretty much backward compatible.
Works for me. Its pretty much what I had in mind.
Thanks,
Paul
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