Subject: [Sipping] Conferencing for UAs

From: Gonzalo Camarillo <[email-masked]>
Date: Tue, 24 Feb 2004 14:06:13 +0200

Hello,

some comments on the following draft:
http://www.ietf.org/internet-drafts/draft-ietf-sipping-cc-conferencing-03.txt

The focus of a conference returns the conference URI in the contact 
header field of the 200 OK for the INVITE. The UAC uses this URI to 
SUBSCRIBE to the conf package (using a new dialog)...

Why are we forcing the focus to use the same URI for receiving the 
INVITEs from all the users and for receiving the SUBSCRIBEs? I believe 
the solution would be cleaner if we defined a new header field (e.g., 
Associated-Conf-State) that carried a globally routable URI. The 200 OK 
for the initial INVITE (or the INVITE in a dial-out case) would carry 
this header field. This would keep separate the URI used for joining the 
conference and the URI used for subscribing to the state of the conference.

This is actually the approach that the draft below follows:
http://www.ietf.org/internet-drafts/draft-camarillo-sipping-transac-package-00.txt

We define the Associated-Transactions-State to be returned, for example, 
in the 200 OK of a MESSAGE sent to an exploder. Note that we had to 
create this new header because MESSAGE does not carry a Contact 
header... following the same approach in both, the conferencing work and 
the exploders work would be good, in my opinion.

Comments?

Thanks,

Gonzalo

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---

From: Alan Johnston <[email-masked]>
Date: Tue, 24 Feb 2004 08:14:33 -0600

At 02:06 PM 2/24/2004 +0200, Gonzalo Camarillo wrote:
>The focus of a conference returns the conference URI in the contact header 
>field of the 200 OK for the INVITE. The UAC uses this URI to SUBSCRIBE to 
>the conf package (using a new dialog)...
>
>Why are we forcing the focus to use the same URI for receiving the INVITEs 
>from all the users and for receiving the SUBSCRIBEs? I believe the 
>solution would be cleaner if we defined a new header field (e.g., 
>for the initial INVITE (or the INVITE in a dial-out case) would carry this 
>header field. This would keep separate the URI used for joining the 

Gonzalo,

This is a fundamental design decision made in SIP conferencing nearly two 
years ago, and I believe it is a good one.  A requirement for conferencing 
is that a UA must be able to find out information about a conference (by 
subscribing to the conference package, for example) by only knowing the 
conference URI.

Why is this very useful property a problem?

>in the 200 OK of a MESSAGE sent to an exploder. Note that we had to create 
>this new header because MESSAGE does not carry a Contact header... 
>following the same approach in both, the conferencing work and the 
>exploders work would be good, in my opinion.

With all due respect, the exploders work should follow the approaches 
described in the conferencing work.  Note that the exploders work should 
not also contradict the XCON work in related areas, as well...

Thanks,
Alan Johnston
MCI
sip:[email-masked]

>Comments?
>
>Thanks,
>
>Gonzalo
>
>
>This communication is confidential and intended solely for the 
>addressee(s). Any unauthorized review, use, disclosure or distribution is 
>prohibited. If you believe this message has been sent to you in error, 
>please notify the sender by replying to this transmission and delete the 
>message without disclosing it. Thank you.
>
>E-mail including attachments is susceptible to data corruption, 
>interruption, unauthorized amendment, tampering and viruses, and we only 
>send and receive e-mails on the basis that we are not liable for any such 
>corruption, interception, amendment, tampering or viruses or any 
>consequences thereof.
>
>

---

From: Paul Kyzivat <[email-masked]>
Date: Tue, 24 Feb 2004 12:38:49 -0500

Gonzalo Camarillo wrote:
> INVITEs from all the users and for receiving the SUBSCRIBEs?

Why? Because that URI identifies the entity that I want information 
about. It is the same reason that you might send a subscription for the 
dialog package, or the presence package to the same address you send an 
INVITE or MESSAGE to.

One of the advantages of sip is that it simplifies addressing.

 > I believe

Why complicate life for users by introducing more addresses to deal with?

If the conference server wants to decompose the service, it can always 
return an AOR as its contact address, with a proxy routing subscribe 
requests one way, invite requests a different way, etc.

	Paul