Subject: [Sip] GRUU issue 2: Callee caps param or not

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 12 Mar 2004 17:20:30 -0500

Currently, the instance attribute in the Contact header field is a 
callee capabilities parameter. This is "flagged" by the presence of 
+sip. as a prefix. So, a REGISTER would look like this:

REGISTER sip:example.com
To: sip:[email-masked]
Contact: sip:[email-masked];+sip.instance="hasdasdsadiasdasida"

The alternative would be to use a new, non-callee-caps parameter:

REGISTER sip:example.com
To: sip:[email-masked]
Contact: sip:[email-masked];instance="hasdasdsadiasdasida"

The only difference in these two approaches is that in the former case, 
you can use caller preferences with the tag. That means one could 
construct an INVITE request an ask for preferential routing to a device 
with that instance ID. For example:

INVITE sip:[email-masked]
Accept-Contact *;+sip.instance="hasdasdsadiasdasida"

This would prefer that the INVITE be routed to a device with that 
instance ID. Its important to note that this is NOT AN ALTERNATIVE for 
the gruu, which would guarantee routing to the device with that instance:

INVITE sip:hhs777asd==[email-masked]

Indeed, one of the reasons we specified gruu was that caller-prefs based 
routing was unreliable:

1. there was no guarantee it was honored by a proxy
2. it would only work in cases where routing decisions were made by a 
single proxy - the one that the users registered too
3. it depended on knowledge of downstream routing behaviors

That said, there may be cases where the desired behavior is "I want to 
reach this user at this aor, but would prefer this instance id". Having 
the instance ID as a callee-cap parameter would allow that.

So, the question is, what to do in the spec? callee cap or not? There 
was consensus at the meeting to keep it as a callee-cap, and document 
the above issues so that people would be clear when to use caller prefs, 
and when to use the gruu.

Does anyone object to this decision?

Thanks,
Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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---

From: "Chris Boulton" <[email-masked]>
Date: Mon, 15 Mar 2004 09:59:06 -0000

<<in-line>>

>-----Original Message-----
>From: Jonathan Rosenberg [mailto:[email-masked]]
>Sent: 12 March 2004 22:21
>To: [email-masked]
>Subject: [Sip] GRUU issue 2: Callee caps param or not
>

[Chris Boulton] I can't think where this would be used BUT see no harm.
I would leave it as a callee cap.

Chris.

>Jonathan R.

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