Subject: [Sip] UPDATE and Expires

From: "Rosen, Brian" <[email-masked]>
Date: Fri, 10 May 2002 08:25:37 -0400

This morning, I arrived to find an experimental SIP implementation 
was "ringing" all night.  It's experimental.  The UAC that called
me died in the middle of the transaction.  Still, my end should
have given up the call at some point.  I go looking for the
codesmith.

The programmer says "That's correct behavior.  Just because the 
caller died, the UAS got an INVITE, and is waiting for the user to 
answer before it sends the 200 OK.  Since this is user time, 
there is no good time after which it is okay to abandon the call"

I protest "But the UAC died!"

And the programmer says "The UAS doesn't know that, as far as it knows,
the user at the UAS wants it to keep ringing"

And I reach for my copy of bis-09 and say "Ah Ha, why don't we put
an Expire header on the Invite, and send 487 if it expires.  And
CANCEL to boot?"

And he says "Sure, but what if the user at the UAC WANTS to wait
longer than whatever the Expires says"

And I reach for my copy of update-02, ready to say "Send an UPDATE
and extend the Expire", but, alas, Expire is not legal on
Update.

And so I wrote this email

Brian

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From: "Prabhas Sinha" <[email-masked]>
Date: Fri, 10 May 2002 11:17:38 -0400

I would second Brian's suggestion in this case. We should make use of a
timer (which can be configured by the user in the UAC -- very much like
number of rings in a PSTN phone beforethe control goes to the answering
machine) so that the phone doesnt keep ringing all night or for that matter
whole month if Brian is vacationing :-)

> longer than whatever the Expires says"

this doesnt make sense. In a PSTN line you know that if the call is not
picked up in 5 rings, then it goes to the answering machine. If the UAC
wants to wait longer then he should adjust the timer of the UAC accordingly.

> and extend the Expire", but, alas, Expire is not legal on

is it really neccessary to do this ? think of the overheads in real time
scenario. Most of the time this will happen when the user is not on his
seat, a very few times he would want to wait longer so why to complicate the
matter ?

I still feel that a use of a simple counter at the UAC should suffice.

Any further thoughts ?

Thanx,
Prabhas.

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From: "Bert Culpepper" <[email-masked]>
Date: Fri, 10 May 2002 12:08:33 -0400

comment inline...

> wants to wait longer then he should adjust the timer of the

I agree, see below.

> seat, a very few times he would want to wait longer so why to

I would think the caller will have an idea of how long he/she wants to wait
for answer, and set the value of the Expires header accordingly in the
INVITE request.  However, if the caller's UA doesn't support this and it
crashes, then I believe it's an implementation issue for the UAS.  Or when
the callee answers the call, current defined protocol behavior (no ACK
received) will suffice here.

Regards,
Bert

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From: "Prabhas Sinha" <[email-masked]>
Date: Fri, 10 May 2002 13:05:49 -0400

> received) will suffice here.

on the contrary, why dont dont we support it from the callee end like PSTN ?
If the callee is not at his seat, then why to hold up the resources until
caller's "Expire" header?
Think of the performance when there are millions of users hitting this bend
and blocking the resources for more than actually needed.
If I know that I am not available then I can configure my UAC somehow to
inform the caller on the very first ring that
I am not able to pick up the phone. I am just thinking it on the lines of
PSTN operation -- its not the caller who decides how long the call should be
presented
but its the callee's phone which handles it. If the current bis doesnt
support it then we might wanna bring in a minor extension to handle this.

Does it sound ok ?

Prabhas