Re: [Stox] Mapping for media signaling: still about the scope
Peter Saint-Andre <stpeter@stpeter.im> Sun, 28 July 2013 10:20 UTC
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Date: Sun, 28 Jul 2013 12:20:00 +0200
From: Peter Saint-Andre <stpeter@stpeter.im>
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Cc: stox@ietf.org, emcho@jitsi.org, saul@ag-projects.com
Subject: Re: [Stox] Mapping for media signaling: still about the scope
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On 6/20/13 1:12 PM, Markus.Isomaki@nokia.com wrote: > Hi Emil, Hi Markus, at the XMPP hackfest yesterday I chatted about related issues with Philipp Hancke, which triggered a few thoughts... > See inline. > > Emil Ivov [mailto:emcho@jitsi.org] wrote: > >> On 19.06.13, 13:56, Markus.Isomaki@nokia.com wrote: >>> Hi Emil, Saul, Peter, and others, >>> >>> Recently I raised some questions about the scope of the >>> 'sip-xmpp-media' and the related deliverable on the 'mapping for >>> media signaling': >>> http://www.ietf.org/mail-archive/web/stox/current/msg00025.html >>> >>> Now that STOX is officially up and running I'd like us to make >>> an actual plan on what the scope of this document should be, i.e. >>> what features are explicitly going to be part of this mapping >>> spec. Although people have successfully implemented SIP-to-XMPP >>> media signaling gateways, I at least see this topic to have some >>> complexity due to: >>> >>> -SDP offer/answer is a moving target as new features are being >>> added as we speak, >> >> Well ... it is and it isn't. 3264 isn't really changing and all >> extensions are supposed to keep backward compatibility with it. >> > > Right. That's good. > >>> including "bundle" and "trickle-ICE". We can't know about what >>> features will be added later on. >> >> No, but we could include some that we know of ... like "bundle" and >> "trickle- ICE" :). >> >> Trickle ICE would be easier because we already have it in Jingle >> and the SIP version shouldn't take long. >> > > That's one of the "administrative" decisions we should make about the > "first release" of the media signaling mapping *RFC*. Do we only take > in features/extensions that are completed RFCs or XSF XEPs, so that > we for quite big certainty can get a mature document to IESG in > October. And then extend it with new features once they complete, > perhaps one or two years later, perhaps in multiple small steps. Or, > do we already take features like "bundle" and "trickle-ICE" in, and > aim to get the document to IESG at some later point, for instance > March 2014. Trickle-ICE for SIP may not take long, but I bet it will > at least take longer than this WG is supposed to live ;-) > > I don't have an opinion about this as a co-chair. This is a question > to people implementing and deploying the gateways or relying on them. > What is the most useful initial scope for you? How important it is to > have an RFC out this year vs. covering as many features as possible? > I mean technically a draft might be as useful to an implementer as an > RFC on those parts that are stable while others are developed, but > would there be some > interoperability/technical/political/marketing/getting-actually-something-completed > reason to get an RFC out ASAP? > > The only guidance we have at this point is that our charter expects > us to complete in October, and in this case, unlike the normal IETF > WG process, I at least as a co-chair intend to take that seriously > :-) > >>> -There are features currently supported in XMPP that are not >>> currently supported in SIP (and perhaps vice versa?), such as the >>> trickle-ICE support in Jingle. >> >> As mentioned. I don't think trickle-ICE would be a problem. I >> believe separating transport and encoding information would be a >> bigger hurdle but if we accept that urn:ietf:rfc:3264 means one >> shouldn't do this. >> >>> -Regardless of what is supported in each protocol in general, >>> the actual SIP and XMPP clients will support different sets of >>> features. >> >> Right. >> >>> Ideally, some things might be mapped transparently in the gateway >>> in an "algorithmic" manner. >> >> I don't believe this would be possible. >> > > Good, then my understanding seems to be correct. > >>> And ideally, the clients supporting different feature sets can >>> negotiate end-to-end without needing for the gateway to mediate. >>> However, I'm not sure how easy this will be in practice. >>> >>> Actually one reason why I see these complications may be that I >>> don't have a very good overall understanding about how SDP O/A >>> (as in RFC 3264 syntax and semantics) is mapped to XMPP/Jingle >>> (as in its XML based syntax) are in general kept "in synch". For >>> instance, if IETF extends SDP O/A in some way, will that always >>> require an explicit corresponding extension XEP by the XSF, or is >>> there some more straightforward "algorithmic" way to convey >>> something new on the SIP/SDP side to the XMPP/Jingle side. >> >> Well, the good thing about O/A extensions is that they generally >> preserve backward compatibility. This is valid for things like ICE, >> trickle ICE, rtcp-mux, bundle. So as long as we support 3264 we >> should be OK. I think :) >> > > Yes, let's stick to that theory ;-) > > ... > >> >>> -What will happen to features supported on one or either side of >>> the gateway that the gateway is not aware of- can some things be >>> "transparently" mapped or will the gateway become the "blocking >>> factor" in the middle. (I.e., will the session setup be limited >>> to the features the gateway explicitly needs to "understand".) >> >> I don't think the gateway could just forward anything because this >> would imply a straightforward mapping from any SDP attribute to a >> Jingle element. >> >> Maybe gateways could behave as regular SIP B2BUAs: they forward >> the things that they understand and they remove those that they >> don't understand or support. >> > > OK, that simplifies things as well. (Again was just checking I'm not > missing any end-to-end magic that might exist. But apparently not > ;-) > >> Thoughts? >> >>> -How will we extend the mapping spec in the future and how should >>> the initial spec take this into account. >> >> As in administratively? >> > > In some sense yes. I would expect perhaps some brief section that > gives guidelines to the authors who in the future want to extend this > mapping spec with some new feature. > > And would be rather do a full-fledged '-bis' spec at some point or a > bunch or incremental extension drafts on top of the baseline. As an > example "An extension to SIP-XMPP media signaling mapping to support > trickle-ICE". I like that approach. The Jingle XEPs already define SDP mappings for the base use cases, and that content could be moved to the stox-media I-D. If additional features are defined in SIP, SDP, or Jingle (trickle-ICE, BUNDLE, multistream, etc.) then we can specify those in incremental extensions. Peter -- Peter Saint-Andre https://stpeter.im/
- [Stox] Mapping for media signaling: still about t… Markus.Isomaki
- Re: [Stox] Mapping for media signaling: still abo… Emil Ivov
- Re: [Stox] Mapping for media signaling: still abo… Philipp Hancke
- Re: [Stox] Mapping for media signaling: still abo… Markus.Isomaki
- Re: [Stox] Mapping for media signaling: still abo… Peter Saint-Andre
- Re: [Stox] Mapping for media signaling: still abo… Philipp Hancke
- Re: [Stox] Mapping for media signaling: still abo… Markus.Isomaki
- Re: [Stox] Mapping for media signaling: still abo… Peter Saint-Andre
- Re: [Stox] Mapping for media signaling: still abo… Saúl Ibarra Corretgé