Subject: RE: [SIP] Tag in From Field

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 21 Mar 2001 01:49:46 -0500

> -----Original Message-----
> From: Christer Holmberg [mailto:[email-masked]]
> Sent: Tuesday, March 20, 2001 10:53 AM
> To: Alexandre Charest
> Cc: [email-masked]
> Subject: Re: [SIP] Tag in From Field
> 
> 
> 
> Hi,
> 
> >Hi,
> > 
> >Isn't it fixed if the From tags become mandatory?
> 
> Yes. 
> 
> The reason I raised the question was because I am confused how the
> re-INVITE is build if the called UA sends the refreshes, 
> since the text
> I referred to was written before this mandatory-From-tag proposal came
> up...
>  
> >Anyway, a UA that want to detect that the re-INVITE is for 
> an existing call
> >just has to include a tag in its From header.
> 
> True, but then it shall be added to the session-timer draft.

The issue has nothing to do with session timer at all, in fact. There can be
re-INVITEs not related to session timers, and then this problem can happen.
Making From tags mandatory solves that. If all clients implemented bis,
there would be no need for text on this in the session timer draft. But,
process wise, since session timer will go to rfc before bis does, we have
the opportunity to prevent the problem in usage of session timer with
rfc2543. THis is probably not a bad idea.

Also, the text in section 4 about responding with a Session-Expires:0 isn't
needed anymore. One of the things we agreed to at IETF49 was that a 481 for
a request within a call leg ends that call leg. So, if I get a new invite
for a call, and that invite already has a to tag in it, I'll reject that
request with a 481, which will terminate the call at the UAC. There is no
need for the explicit Sesion-Expires:0 to accomplish this.

-Jonathan R.
---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (973) 952-5000
http://www.dynamicsoft.com

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---

From: Christer Holmberg <[email-masked]>
Date: Wed, 21 Mar 2001 09:14:42 +0200

Hi,

>there would be no need for text on this in the session timer draft.

True. 

I would still, however, want to add to the session timer draft how the
re-INVITE is defined if it's sent from the called UA. For example, I
guess the called UA would not use the same SDP that it received in the
initial INVITE. Instead it would use the SDP it sent in the 200 OK. Or?

This actually brings up another question, which I HOPE is because I
don't know how to use SDP correctly :)

If the UAC doesn't send an SDP in the INVITE, but in the ACK, the
session-timer refreshes sent by it will then also be without an SDP.
However, if I want to use the re-INVITE to terminate my media stream,
wouldn't that re-INVITE also be without an SDP? How will the UAS know
the difference?

>But, process wise, since session timer will go to rfc before bis does, we have

Again, I think this is a very good idea.

Regards,

Christer Holmberg
Ericsson Finland