Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bundle-negotiation-32 (Part I)
Flemming Andreasen <fandreas@cisco.com> Thu, 22 September 2016 23:24 UTC
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To: Christer Holmberg <christer.holmberg@ericsson.com>, Eric Rescorla <ekr@rtfm.com>, mmusic WG <mmusic@ietf.org>
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From: Flemming Andreasen <fandreas@cisco.com>
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Date: Thu, 22 Sep 2016 19:23:58 -0400
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Subject: Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bundle-negotiation-32 (Part I)
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Hi Ekr It's been more than 3 weeks and I don't believe I have seen a reply. We need to get this document moving forward, so if you are still interested in having your comments addressed, can you please follow-up. Thanks -- Flemming (with chair hat on) On 8/29/16 3:54 PM, Christer Holmberg wrote: > > Hi Ekr, > > Thanks for the comments! Please see inline. > > OVERALL > > >The overall framing of this document as being about attaching multiple > > >m= sections to a single "shared address" is extremely problematic, > > >for two reasons: > > > > > >- With ICE there isn't actually any notion of a shared address except > > > in some vague sense. I suppose you could argue that because with > > > ICE you are required to specify a port on the m= line then you > > > still have a concept of an address, but that's not true in > > > trickle ICE, where the port is 9, so all m= lines share the same > > > address/port. So, actually when you use trickle a whole bunch of > > > the statements in this document are wrong. > > > > > >- A lot more is being overloaded here than addresses. In fact, a whole > > > pile of semantics are being overloaded, so the way to think about > > > this is actually as gluing a whole bunch of m= lines together at > > > the transport level. > > > > > > I think the right concept here is not "shared address" but "bundle group" > > > and the document should be written in that way, namely that there are > > > a bunch of m= lines in a bundle group and the one with the bundle tag > > > is the one that sets all the shared parameters. > > It is true that the actual port value in the m- line, and the IP > address in the c- line address, represent the address that is actually > being used. > > But, even with ICE there is a shared address, isn’t there? Yes, that > shared address may change, but at any given time there will be one > address that is shared among the media streams within the BUNDLE > group. Or? > > > The document is badly in need of some overall framing that explains > > > what we are trying to accomplish and the rationale for why any > > > particular m= section property needs to be the same for all members of > > > a bundle group and why other ones do not. I'm not saying it's > > > necessarily bad to be explicit in (for instance Sections 11 and 12) > > > but it would be better if it were clear where these rules come > > > from. One way to deal with this would be to simply defer this to the > > > mux-attributes draft. > > Ok, I’ll look into that. People are also welcome to provide text > suggestions. > > > I'll just note again that I find the overloading of "associated" > makes this > > > document very hard to read. At minimum it would be best to talk about > > > an m= line as "belonging" to a BUNDLE group. If others agree I would > > > be happy to provide a PR that cleans this up. > > The intention is to say “m= line within a BUNDLE group”. If there are > instances of “associated” I am happy to fix that. > > MAJOR TECHNICAL > > > Maybe I missed this, but I don't see any requirement that m= lines > > > appear in the a=group:BUNDLE line in the order they appear in the > > > SDP. That would make life a lot easier. > > There is no such requirement. > > AFAIR, it was discussed at some point, but it was agreed to not > mandate m- lines to be listed in the order of preference (as far as > selecting the BUNDLE address is concerned). > > Also, if you mid-session adds a new m- line, and wants that to > represent the new BUNDLE address you have to place the new m- line > after the existing m- lines, but you have to place it first in the > a=group:BUNDLE attribute list. > > DETAILED COMMENTS (MIXED EDITORIAL/TECHNICAL) > > >S 1. > > >This really needs some explanation of why you would want this feature. > > You represent the community that wants the feature, so feel free to > suggest some text explaining why you want it :) > > >S 2; Initial offer. > > >"The first offer, within" . This comma is superfluous. > > Will be fixed. > > >S 5. > > >The first three grafs of this section seem to duplicate the intro > > >and the abstract. > > > > > >Also, this claim about sharing a 5-tuple is not quite right with ICE > > >because ICE can switch 5-tuples during aggressive nomination. > > Yes. But, at any given time there will only be one 5-tuple, won’t it? > > >S 6. > > > The usage of the 'bundle-only' attribute is only defined for a > > > bundled "m=" line with a zero port value, within an offer. Other > > > usage is unspecified. > > > > > > It would probably be better to actually forbid this, because it seems > > > like an interop problem if you somehow were to introduce it later. > > Ok, I’ll look into that. > > >S 8. > > >Nit: > > >List the forward references in section order. > > Will be fixed. > > >S 8.1. > > >This seems like a key concept: there are a number of different categories > > >of attributes and some are shared with all members of a bundle group > > >and some are not. To what extent is this draft just duplicative of those > > >listed in the mux-attributes draft? > > Not sure I understand the question. > > >S 8.2 and following > > >Really would be useful to have some examples here to make it less > > >abstract. > > You don’t think the examples in section 17 are enough? You want > examples in the normative sections describing how to create offers, > answers etc? > > >S 8.3.3. > > >It seems like the implication here is that an answerer cannot debundle > > >something that was bundled in a previous o/a transaction. Can you > > >make that point clearly? > > Ok, I’ll look into that. > > >S 8.5. > > >How does this interact with ICE Restart? > > From a pure ICE Restart perspective, I don’t see any conflict. ICE > Restart is triggered by changing the user name and password, and the > text does not forbid that. > > If you also want to change the BUNDLE address, you follow the rules in > section 8.5.1. > > >S 8.5.2 > > >When you say "extend" do you mean "add to the end"? > > Yes. I can fix that. > > >S 10.1 > > >In this first bullet is "if" "iff"? > > “iff”? > > >S 10.3.1.1. > > > When an offerer generates an initial offer, the offerer MUST > > > associate either an SDP 'rtcp-mux' attribute [RFC5761] or an SDP > > > 'rtcp-mux-only' attribute [I-D.ietf-mmusic-mux-exclusive] with each > > > bundled RTP-based "m=" line in the offer. The offerer MUST associate > > > an SDP 'rtcp-mux-only' attribute with each bundle-only "m=" line. If > > > the offerer associates a 'rtcp-mux-only' attribute with an "m=" line, > > > the offerer may also associate a 'rtcp-mux' attribute with the same > > > "m=" line, as described in [I-D.ietf-mmusic-mux-exclusive]. > > > > > > This is a particularly egregious case of associate disease that could > > > be easily solved by using "add" when referring to the attributes > > > you put in the m= section. > > People have previously said that you don’t “add” attributes to m- > lines: you add port values etc, but not attributes. > > This is an example of where I’ve had to re-write big parts of the > documents a number of times already, because every time someone else > reads the document he/she is not happy with the terminology. I just > don’t want to do it again. > > >S 11.1 > > > When an offerer associates a unique address with a bundled "m=" line > > > (excluding any bundle-only "m=" line), the offerer MUST associate SDP > > > 'candidate' attributes (and other applicable ICE-related media-level > > > SDP attributes), containing unique ICE properties (candidates etc), > > > with the "m=" line, according to the procedures in > > > [I-D.ietf-mmusic-ice-sip-sdp]. > > > > > > Here is an example of where the "address" framing doesn't work, if you > > > are using trickle. > > See top of e-mail. > > Regards, > > Christer > > > > _______________________________________________ > mmusic mailing list > mmusic@ietf.org > https://www.ietf.org/mailman/listinfo/mmusic
- [MMUSIC] Review of draft-ietf-mmusic-sdp-bundle-n… Eric Rescorla
- Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bund… Christer Holmberg
- Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bund… Flemming Andreasen
- Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bund… Eric Rescorla
- Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bund… Christer Holmberg
- Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bund… Eric Rescorla
- Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bund… Christer Holmberg
- Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bund… Eric Rescorla
- Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bund… Christer Holmberg
- [MMUSIC] Bundle and "m=" line terminology [Re: Re… Flemming Andreasen
- Re: [MMUSIC] Bundle and "m=" line terminology [Re… Eric Rescorla
- Re: [MMUSIC] Bundle and "m=" line terminology [Re… Christer Holmberg
- Re: [MMUSIC] Bundle and "m=" line terminology [Re… Eric Rescorla
- Re: [MMUSIC] Bundle and "m=" line terminology [Re… Flemming Andreasen
- Re: [MMUSIC] Bundle and "m=" line terminology [Re… Christer Holmberg