Re: Policy to register media feature tags

Some issues just never go away. :-(

This seems to be a resurection of issues that first surfaced during the 
initial discussions of extended presence status many years ago. And it 
also harks back to discussions last year or the year before about 
communication service identifiers and application service identifiers.

The problem is one of openness. Specifically, do you have to be "part of 
the club" in order to properly interoperate with a device that uses 
these identifiers to identify its preferences or capabilities.

On one side were those who wanted capabilities and preferences to be 
stated in terms of feature tags that are well known and orthogonal. On 
the other side were those who prefer to associate arbitrary names to 
collections of features and then negotiate on the basis of the names of 
those collections.

Using the latter approach its possible that interoperation will fail 
because the parties don't share a common name for a collection of 
features even though they both possess the necessary features to 
interoperate.

I don't have a problem with independent groups defining new feature 
tags, as long as they are primitive and orthogonal to existing ones. But 
I do have a problem with defining feature tags that identify collections 
of features, especially when the mapping from the identifier to the 
collection of features is not public.

The bottom line is that I think this sort of thing needs to be thrashed 
out within the sip community. So I think the RFC process is the right 
process.

	Thanks,
	Paul

Gonzalo Camarillo wrote:
> Folks,
> 
> as you know, RFC 3840 specifies how to indicate UA's capabilities using
> media feature tags. Section 12.1 of RFC 3840 creates the SIP Media
> Feature Tag Registration Tree. Media feature tags applicable to SIP are
> registered in this tree.
> 
> http://www.ietf.org/rfc/rfc3840.txt
> 
> RFC 2506 defines the global tree to register feature tags. Section 3.1.2
> of RFC 2506 says: "A registration may be proposed for the global tree by
> anyone who has the need to allow for communication on a particular
> capability or preference".
> 
> http://www.ietf.org/rfc/rfc2506.txt
> 
> The currently registered feature tags in both the SIP and the global
> trees can be found at:
> 
> http://www.iana.org/assignments/media-feature-tags
> 
> As you can see, the only three feature tags registered in the global
> tree come from 3GPP.
> 
> The issue we are facing is that the SIP and the global trees have
> different registration policies. The SIP registry requires an RFC
> defining the feature tag while the global tree only requires an expert
> review.
> 
> Now, 3GPP would like to register two new feature tags:  g.3gpp.icsi-ref,
> g.3gpp.iari-ref
> 
> This is the description of how these feature tags will be used:
> 
> "Each value of the Application Reference media feature-tag indicates the
> software applications supported by the agent. The values for this tag
> equal the IMS communication Service Identifier (ICSI) and IMS
> Application Reference Identifier (IARI) values supported by
> the agent. The Application Reference media feature tag is
> defined to fulfil the requirements for forking to an appropriate UE when
> multiple UEs are registered and dispatch to an appropriate application
> within the UE based upon the IMS communication Service Identifier
> (ICSI) and IMS Application Reference Identifier (IARI) values as
> stated in 3GPP TS 23.228.  Multiple tag-values can be included in the
> Application Reference media feature-tag."
> 
> 
> The expert reviewer indicated that this tags will not contain simple
> features but rather more complex services, or feature sets, or
> application logic (pick your favorite term). Therefore, he did not find
> it appropriate to register them in the global tree. He suggested that
> RFC 2506 is amended so that it covers this type of more complex features.
> 
> However, before going down that path, I would like to get comments from
> the SIP community. The underlying issue is that we need to decide which
> policy we want to apply to these types of registrations in SIP.
> 
> 1) We decide that an RFC is always needed. Then, we can just use the SIP
> registry. We would probably need to clarify or to stress somewhere that
> the global tree is not appropriate for SIP tags.
> 
> 2) We decide that an expert review is good enough. Then we would
> probably need to amend RFC 2506 or RFC 3840 to reflect this.
> 
> Comments are welcome.
> 
> Thanks,
> 
> Gonzalo
> 
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