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[Sip] Re: [Simple] -05 MESSAGE and Expires header
Ben Campbell wrote:
> It seems to me that if the UAC cares about intermediaries seeing the
> expires header, it would put an expires header in the outer message.
It could; but really, why duplicate the information?
RFC 2076 (Common Internet Message Headers) says that 'Priority' can
"influence transmission speed and delivery". Which seems to fit exactly
with what we want to do.
In fact, the more I think of it, the more I am convinced that
overloading 'Expires: 0' to mean something completely different in
MESSAGE is not a good idea; especially after a precedent has been
established by REGISTER and SUBSCRIBE to use 'Expires: 0' to mean
'no longer valid'.
It's been pointed out that Priority is not the right header, but I just
don't see why not. Expires is deemed to be an end-to-end header; as
such, why use it for routing purposes by relays? Whereas, Priority
appears to be exactly for this purpose.
Adam has proposed the 'Urgency' header; but I don't think we need
to make up yet another new header for this and update deployed parsers;
Priority handles many shades of urgencies and emergencies.
IMHO, giving 'Expires: 0' an overloaded meaning, while having a header
('Priority') that can be used for expedited delivery is what leads to
problems of the kind Jonathan alluded to:
> A message can be for immediate delivery, and be either urgent ("my
> house is on fire") or not ("leaving now for lunch"). A message can be
> OK for storage (some non-zero expires) and be urgent ("I need that
> business presentation by 10pm!") or non-urgent ("Did you see that
> movie").
If, on the other hand, we simply specify 'Priority: Urgent' (or
'Priority: Emergency'), both the UA and the relays should act
immediately on that message. No need to add new semantics to 'Expires:
0'.
In the final analysis, what is the harm if we can make the MESSAGE PDU
self explanatory? I would think that almost everyone will agree that
'Priority: Urgent' is more self-documenting than 'Expires: 0'. As I
suggested earlier, the MESSAGE I-D can mandate that 'Priority: Urgent'
or 'Priority: Emergency' be only used when, as 3261 says, "life, limb,
or property are in imminent danger."
Regards,
- vijay
--
Vijay K. Gurbani vkg@{lucent.com,research.bell-labs.com,acm.org}
Wireless Networks Group/Internet Software and Services
Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
Naperville, Illinois 60566 Voice: +1 630 224 0216
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