Subject: RE: [Simple] Expires in MESSAGE

From: [email-masked]
Date: Tue, 13 Nov 2001 20:01:55 +0200

Hi Adam,

> > I'm looking for some extended meaning for the "Expires: 0" in 
> > MESSAGE. Like
> > the "fetch" in SUBSCRIBE, or "remove contact" in REGISTER, it 
> > could have
> > some added value for IM applications as well. 
> > 
> > For example, having zero expiry mean "don't store and forward 
> > me" sounds
> > like something an IM inbox might find useful.
> 
> Please, don't special case zero.

I don't see the harm in doing so. Registrars and PAs handle zero in a
special way. Why not IM servers? 

> I agree 100% with Robert and Jonathan: Expires should be treated
> exactly like it is for e-mail. In other words, the client may
> (or may not) choose to render this content in some special fashion
> to indicate to the user that the message is no longer relevant.
>
> Expires for MESSAGE should not have transport semantics.

I fully agree with this. I'm not trying to reuse the Expires as message TTL
in a  SIP network. It should only have meaning to the UA.

But it feels like a missed opportunity here. If it doesn't have any extended
meaning, the zero expiry will be ambiguous -- after all, if the message has
zero expiry, why send it?

Cheers,
Aki

---

From: Paul Kyzivat <[email-masked]>
Date: Tue, 13 Nov 2001 14:04:19 -0500

Aki,

There really isn't any special semantic for 0 in REGISTER or SUBSCRIBE,
in each case the behavior for 0 is simply the natural degenerate
case for the general semantics of the message in a UAS when it expires.

In the case of MESSAGE, there aren't any semantics in
draft-ietf-simple-im-01 that can be
reduced to a degenerate form. I suppose you could propose changes that
would tell the UAS to suppress display of a MESSAGE if it cannot be
displayed until after it has expired. But I doubt that is a good thing
to mandate.

	Paul Kyzivat
	Cisco Systems

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---

From: [email-masked]
Date: Tue, 13 Nov 2001 13:30:08 -0600

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
> 
> > 

Actually, if you study the behavior, they don't. That's what's so
extremely spiffy about the way that registrars and PAs work. I've
made this point before, but I'll repeat it for your benefit.

If want to unregister, I can send a REGISTER with an "Expires" of
"1" and wait a second. I can send a REGISTER with an "Expires" of
"2" and wait two seconds. Or, I can send a REGISTER with an "Expires"
of "0" and wait zero seconds. It all works. Zero isn't a special
case at all.

This all becomes somewhat more obvious when you go to implement a
registrar or PA.

/a

---

From: Pekka Pessi <[email-masked]>
Date: 14 Nov 2001 09:45:43 +0200

In message <[email-masked]> <[email-masked]> writes:
...
>of "0" and wait zero seconds. It all works. Zero isn't a special

	Zero is not magic when handling SIP URLs. However, if you want
	to (un)register an IM or PRES or TEL URL, not to speak about *,
	the Expires: 0 suddenly has a special magic meaning.

	We would like to specify the lifetime of a SIP instant message
	within a IM gateway. The GSM system allows users to specify how
	long their SMS messages are valid. If, for instance, an SMS
	could not have been delivered within 3 hours, it will be
	dropped.

	We would like to have similar functionality for SIP IM gateways;
	sender can select how long her message is kept stored in the IM
	gateway if it cannot be delivered instantly. If user wants to
	have truly instant delivery, no store-and-forward in any case,
	she could use Expires: 0.

						Pekka