Subject: [Sip] ID: Guidelines for Implementing the GRUU Support in User Agents

From: "Dale R. Worley" <[email-masked]>
Date: Fri, 24 Feb 2006 23:31:40 -0500

I have just submitted an Internet-Draft that gives a concise summary of
how to implement GRUU support in user agents:

      Guidelines for Implementing the GRUU Support in User Agents
                   draft-worley-sip-gruu-implement-01

   Several applications of the Session Initiation Protocol (SIP) require
   a user agent (UA) to construct and distribute a URI which can be used
   by anyone on the Internet to route a call to that specific UA
   instance.  A URI which routes to a specific UA instance is called a
   Globally Routable UA URI (GRUU).  An Internet-Draft is progressing
   toward standardization that gives a method by which proxies can
   construct and delver GRUUs to UAs that request them.  This document
   distills that Internet-Draft into a guide for UA implementors.

This I-D is based on the -06 version of the GRUU I-D and on comments
from the I-D's authors about the forthcoming -07 version.

I would like feedback on this draft, especially from UA implementors.

Until it shows up in the usual I-D directories, you can fetch it from:
http://scm.sipfoundry.org/rep/ietf-drafts/worley/draft-worley-sip-gruu-implement-01.txt
http://scm.sipfoundry.org/rep/ietf-drafts/worley/draft-worley-sip-gruu-implement-01.html
http://scm.sipfoundry.org/rep/ietf-drafts/worley/draft-worley-sip-gruu-implement-01.xml

Dale

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From: "Jeroen van Bemmel" <[email-masked]>
Date: Sat, 25 Feb 2006 16:14:09 +0100

Dale,

Three questions:

1) Guideline 16: "The UA should add "Supported: gruu" to its requests and 
responses [...]", isn't this too broad?
We had some quite extensive discussions about the meaning of Supported, and 
ended up with some text suggested by you on 9th of November 2005:

"The presence of Supported: gruu suggests a high likelihood that the
Contact is a GRUU, and so a UA using that Contact SHOULD proceed on the
assumption that it is a GRUU, until it has positive information that it
is not.  In particular, the UA should not utilize any mechanisms to work
around that the Contact is not a GRUU until it has determined that
utilizing it as a GRUU does not work."

I'm assuming this is going to be in the next update of the draft. 
"Supported: gruu" would thus only be needed whenever a Contact is provided 
(i.e. in dialog-creating requests and responses, REGISTER, target 
refreshes), and then only iff the Contact is indeed a GRUU. A UAC that 
registered with a registrar which does not support GRUUs should not add it

2) Guideline 12 - shouldn't this be about the From header?

3) On 6th of november 2005 Jonathan made a remark on caching of 
capabilities, and that it would probably be convenient if endpoints were to 
change their instance ID when their firmware / software changed. Would this 
be something to put in a guideline?

Regards,

jeroen

----- Original Message ----- 
From: "Dale R. Worley" <[email-masked]>
To: "Sip" <[email-masked]>; "Sip-Implementors" 
<[email-masked]>
Sent: Saturday, February 25, 2006 5:31 AM
Subject: [Sip-implementors] ID: Guidelines for Implementing the GRUU 
Supportin User Agents

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