Subject: RE: [Simple] Contact header in MESSAGE request

From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 22 Oct 2001 21:13:50 -0400

> -----Original Message-----
> From: Brazier Lachlan [mailto:[email-masked]]
> Sent: Tuesday, October 16, 2001 3:48 AM
> To: [email-masked]
> Subject: [Simple] Contact header in MESSAGE request
> 
> 
> Hello,
>  
> I've been reading draft-ietf-simple-im-01, and at the end I 
> read Appendix A.
> Requirements Evaluation.
>  
>    "Requirement 4.1.3. The common message format MUST include a return
>       address for the receiver to reply to the sender with another
>       INSTANT MESSAGE." This is done through the Contact headers
>       defined in SIP. 
>  
> Does this mean that the Contact header is mandatory in an 
> MESSAGE request?
> It's not according to the table of header fields.

This is something that has changed a bit as the session model has evolved
into a separate entity. The initial model was that MESSAGE itself set up a
session, but this was discarded as we didn't want multiple ways to establish
an interaction communicastions session, and certainly voice/video could be
part of that. In this initial model, since MESSAGE was like INVITE, it had a
Contact header that was used for sending subsequent messages within the
session. 

Then, with the paging model, MESSAGE became a "one-shot" kind of thing.
There is no session or context for the messages. Since Contact is meant to
provide an endpoint address, its not very useful for paging mode. In these
cases, you can't really provide a a host address, since these things change,
and the duration during which that address would remain useful is unknown.
Providing a direct host address is only useful where there is a session, and
we can change it if the host moves (SIP provides this ability). So, Contact
doesn't make sense anymore. Thats why its not in the table.

However, one might want to provide a reply address that isn't a host IP or
hostname. Rather, we want to provide a logical address to send messages in
reply. Normally, the From is used for this kind of thing, but certainly the
address for sending a response could be something else.

Right now, there is no Reply-To header in SIP. It would be a useful thing to
have, as it makes sense for initiating calls as well (If I call you, and
you're not there, I can provide a logical address to use to call me back at
any point later on). In fact, this is a current open issue in the bis
specification itself (whether or not to add a Reply-To address). Oddly, bis
does have an In-Reply-To header that identifies the specific call that a new
call is in reply to.

Since we have multiple cases where it is needed, sounds like its something
that should be added.

-Jonathan R.

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

From: "Drage, Keith (Keith)" <[email-masked]>
Date: Wed, 24 Oct 2001 18:16:31 +0100

Jonathan states that there is no Reply-To header in SIP.

I would note that one of the forms of the Remote-Party-ID header (privacy
draft) is to provide an address for returning a call to, rather than this is
the address that made the call.

Current definition as follows:

   Return session identity (rpi-id-type="return")

     This identifies the point to which the party wishes return
     sessions to be addressed. For example a business may wish to
     provide a 'freephone' identity to encourage return calls. If
     absent, this is assumed to be the same as the subscriber identity.

From the discussion I have read, surely this would fulfil the function
rather than inventing a new header. It would of course mean extenting the
usage of the Remote-Party-ID to another method.

Keith

Keith Drage
Lucent Technologies
Tel: +44 1793 776249
Email: [email-masked]

> ----------
> From: 	Jonathan Rosenberg[SMTP:[email-masked]]
> Sent: 	23 October 2001 2:13
> To: 	Brazier Lachlan; [email-masked]
> Subject: 	RE: [Simple] Contact header in MESSAGE request
> 
> 
> 
>  
>