Subject: Clarification of Expires header in an Invite

From: John Hearty <[email-masked]>
Date: Thu, 22 Apr 1999 08:26 -0500 (CDT)

I need clarification of the Expires header in the Invite method. 
The RFC gives examples that it can limit the validity of an invitation
if a client wants to limit the duration of a search or a conference
invitation.  I take this to mean only the time in which the client
is waiting for a final response, not the duration of the session. 
Is this correct?  If this is the case, a clarified description would
be appreciated explicitly stating the client is waiting for a _final
response_.  One scenario I plan on using this for is to give the callee
a clue how long the caller will ring the device before giving up and
moving on to another address in a serial search.

John Hearty
MCI Worldcom

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From: Henning Schulzrinne <[email-masked]>
Date: Thu, 22 Apr 1999 11:46:30 -0400

> moving on to another address in a serial search.

That's the idea. I've added the following wording to the spec (for the
next revision):

Note that the expiration time does {\em not} affect the duration of the 
actual session that may result from the invitation.  Session description
protocols may offer the ability to express time limits on the session
duration, however.

(SDP does provide the latter functionality.)

-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 22 Apr 1999 12:03:33 -0400

> is waiting for a final response, not the duration of the session.

Yes. Session duration is indicated in SDP, if you want.

> moving on to another address in a serial search.

That is the intended application. The UAS wouldn't continue alerting
past the Expires time. However, the spec doesn't *mandate* that the
called party not send a final response after the Expires time ends.
Thus, its really up to the UAC to decide how long its going to wait
around. Nothing prevents if from waiting more or less than this time.
Expires is really more of a hint.

-Jonathan R. 

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX:   (732) 834-5379                       Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen