[sipcore] Feature-Caps - Terminology [was: Draft new version: draft-holmberg-sipcore-proxy-feature-03 (featuring the Feature-Caps header field)]
Christer Holmberg <christer.holmberg@ericsson.com> Wed, 02 November 2011 20:00 UTC
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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
Date: Wed, 02 Nov 2011 21:00:36 +0100
Thread-Topic: Feature-Caps - Terminology [was: Draft new version: draft-holmberg-sipcore-proxy-feature-03 (featuring the Feature-Caps header field)]
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Subject: [sipcore] Feature-Caps - Terminology [was: Draft new version: draft-holmberg-sipcore-proxy-feature-03 (featuring the Feature-Caps header field)]
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Hi, >>> Here are comments on the new version. >>> >>> From the introduction: >>> >>> This document defines a new SIP header field, Feature-Caps, that can >>> be used by entities to indicate support of features and capabilities, >>> in case they cannot use the Contact header field for that purpose. >>> >>> This is really loose!!! >>> Its not limited to proxies. It could be any UA that "cannot use the >>> Contact header field for that purpose". What constitutes a such a reason? >>> >>> The Definitions section has a very non-standard definition of Proxy: >>> >>> Proxy: Within this specification, a "proxy" refers to an entity that >>> does not indicate supported features using the Contact header field. >>> Normally, however, entities that indicate support of features do not >>> act as pure proxies, as defined by RFC 3261, but rather contain >>> different levels of B2BUAs functionality. >>> >>> IMO Proxy should be defined only as it is in 3261. >> >> As I said when I submitted the draft, and which Hadriel also indicated, we DO need to sort out the terminology :) > > Consider these comments to be input to the terminology restructuring. > Its something that we need to get right, because it goes to the heart of > what this is about. I agree. The intention was not to keep the currently proposed terminology, but in order to be able to submit the draft start with something "familiar", and then work from there. ---------- >>> Section 4.1 says: >>> >>> A UA MUST NOT, except when it acts as a SIP registrar, insert a >>> Feature-Caps header field in a SIP request or response. >>> >>> By this do you intend that a B2BUA/SBC cannot use this? >>> >>> Or are you drawing a fine line, where an element nominally acting as a >>> proxy inserts this, even if it describes a feature that will require it >>> starting to act as a B2BUA in the same dialog? >> >> The issue is not whether the entity is a proxy or a B2BUA, or a registrar. >> >> It's about an entity which is not "represented" by the Contact header field, or an entity which is not allowed (by SIP rules) to use the Contact header field. > > I like your characterization of the difference here better than what I have seen before. And, in addition to the definition of the entity, we of course also need to decided what to call it :) ---------- >>> In section 6.2: >>> >>> If a feature tag is inserted in a Feature-Caps header field of an >>> initial SIP request or response for a dialog, the feature associated >>> with the feature tag MUST be supported for the dialog, until the >>> dialog is terminated. >>> >>> Do you mean that it cannot be changed by subsequent signaling within the >>> dialog? If Feature-Caps can be used by a 3pcc (b2bua) controller (can >>> it?) then this limitation could break 3pcc transfers, where the >>> transfer-target has different features. >> >> The limitation seems to be a left-over from when the draft used Record-Route. >> >> If needed, for Feature-Caps, we can always specify that entities must include it e.g. also in target refresh requests within a session. > > I think that is needed. I'll note that down. ---------- >>> Section 8: >>> >>> Since this is using feature tags, it has to live with the IANA >>> registration mechanism defined in 2506. I think that means, at best, you >>> can require that certain material be included in the "Related standards >>> or documents" that can optionally be included in a feature tag >>> registration. That means it won't be possible to discern from a feature >>> tag registration whether it applicable for use in Feature-Caps. >> >> I don't know remember whether the references are optional or not, but at least 3GPP has provided them for all feature tags. > > I checked - they are optional. > >> But, in general, I still think we can provide guidance and recommendations in the spec on what kind of information needs to be provided in the definition/registration. > > I guess you can say that a feature-tag can only be used in this way if > the registration of the tag references a document that has some specific > content. That would rule out all the existing ones, until their > registration is updated. I'll move this to the other thread, as it's not related to the entity terminology. Regards, Christer Thanks, Paul > Regards, > > Christer > > > > > > > On 10/28/11 6:09 AM, Christer Holmberg wrote: >> >> Hi, >> >> I've submitted a new version (-03) of draft-holmberg-sipcore-proxy-feature, which suggests a solution based on the proxy feature requirements. >> >> The MAJOR CHANGE, based on the list discussions, is that the mechanism now uses a new header field, Feature-Caps, rather than existing header fields (Record-Route, Path etc). >> >> I did not include the "SIP-URI alternative" at this point. >> >> We will also have to think about the "proxy" terminology, as it has been indicated that entities using the mechanism might not be pure proxies. But, I don't think that should prevent us from moving forward the the mechanism as such. >> >> Thanks to everyone who has provided feedback and input! >> >> Regards, >> >> Christer >> > >
- [sipcore] Feature-Caps - Terminology [was: Draft … Christer Holmberg
- [sipcore] Feature-Caps - Terminology Christer Holmberg