Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (June 6th)
Christer Holmberg <christer.holmberg@ericsson.com> Sun, 09 June 2013 18:13 UTC
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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
Thread-Topic: [MMUSIC] BUNDLE TEXT: Offerer procedures (June 6th)
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Date: Sun, 09 Jun 2013 18:13:37 +0000
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Cc: "mmusic@ietf.org" <mmusic@ietf.org>
Subject: Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (June 6th)
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Hi, >>>> After reading Paul's and Martin's comments, I am suggesting a change to the separation between BSO and BRO. >>>> >>>> Again, the names will be changed, but I'll leave that for now - but I DO like the Bundle Negotiation Offer (BNO) suggestion made by Martin :) >>>> >>>> In the current text, I separate between BSO and BRO pretty much based on the type address information in the "m=" lines of the SDP Offer. I have realized that it doesn't work very well. >>>> >>>> So, a new suggestion is that the separation is done based on the PURPOSE of the SDP Offer, NOT the type of address information in the "m=" lines (of course, in many cases they go hand-in-hand). >>> >>> Note that offers and answers may contain more than just one set of >>> bundled m-lines. They may contain unbundled m-lines, and multiple >>> bundles. So the purpose of a particular offer may be complex, trying to >>> satisfy different needs for various parts of the SDP. That complicates >>> making such a distinction. >> >> I guess it should be more clear that the definition is per bundle group within an SDP Offer, not necessairly the whole SDP body. > > I think the BSO must be determined over the entire O/A, not on a > per-bundle basis. Otherwise the new offer is being sent with the intent > to change *something* in it. Sure, but you could change things which are non-BUNDLE related. For example, if you use ICE, you could combine the BUNDLE BSO with the ICE Offer which informs the other endpoint of the selected candidates (sorry, I don't remember all ICE terminology at the moment :) >>>> A BSO would be used ONLY for synchronization purpose, or making the SDP "stable". >>> >>> So this is just intended to describe the case where both ends have >>> reached agreement on what they want to do, and don't want to change >>> that, but the agreed pair of SDPs doesn't describe that agreement in the >>> standard way? This additional O/A is used *solely* to put things into >>> the standardized representation? >> >> Correct. >> >>> And if things end up in the standardized form without a BSO then one is >>> not sent? >> >> Correct. >> >>> If so, then the receiver of the offer can tell that it is a BSO by >>> analyzing it in the context of what the prior O/A had been. But there is >>> no particular reason to do so, because it doesn't affect the behavior of >>> the answerer. >>> >>> The value of the term must be simply to facilitate the description of >>> offerer behavior. Following an O/A exchange that has left things in a >>> non-canonical form, the offerer in that exchange is required to send a BSO. >>> >>> And I think the need for a BSO can indeed only be determined after >>> receiving the answer. It is largly driven by the structure of the offer, >> but even so, certain answers may eliminate the need for the BSO. >> >> The reason for sending the BSO is not the Answerer - it is because of intermediaries that don't understand BUNDLE. > > I realize that the BSO is not being sent for the benefit of the > answerer. My point was that the need to send the BSO is determined by > the offerer, but cannot be determined until the answer has been received. Correct. >>>>> A BRO would be used to negotiate the usage of BUNDLE, to add/remove/modify "m=" lines and/or the bundle address. So, even an with >>>>> the same address information in each "m=" line could be an BRO, if the purpose is to modify the SDP in one way or another. >>>> >>> So an offer that *changes* *anything* is a BRO, while one that changes >>> nothing but puts things in the correct form is called a BSO. >> >> Correct. >> >>> That definition might work from the point of view of the offer. >>> But note that even with a BSO the answer might change something. >>> >>> E.g. the answerer could change its bundle address, or it could reject >>> some m-lines. (But I don't think it is possible for the answer to do >>> anything valid that will prevent the intent of the BSO from being achieved.) >> >> I think that's ok. >> >> Because, even without BUNDLE, if an Offerer sends a SIP re-INVITE/UPDATE with an unmodified SDP Offer (e.g. because of session-timer usage), the SDP Answer may still change. >> >> One question, though, is whether the SDP o= line version number should be incremented when sending a BSO (assuming everything, including the non-BUNDLE >> stuff, in the SDP body is unmodified). From a pure SDP perspective, the address information for certain "m=" lines may have changed, eventhough from a BUNDLE perspective it is just about synchronization. > > I've always had a problem with o-lines. > AFAICT the only value they bring (at least in the context of O/A) is as > an optimization: if the new one says via the o-line that it is identical > to the prior one then perhaps you can simply not process it. > > But I think an implementation would be insane to trust this. There is > too much of a chance that there will be a changed SDP with an unchanged > o-line. So I think a reasonable implementation will at least do a > comparison of the whole body before optimizing for an unchanged one. (Or > else it will do any optimization on an element by element basis.) Actually, I have seen entities that do NOT perform any check if the o-line value is unchanged :) > BUT, on the off chance that anybody does use the o-line that way, then I > think it must be marked as changed. It isn't identical, and the reason > its not, and is being sent, is because of the changes it contains. Those > changes may have different significance to intermediaries than to the > UAS, but its important that the difference be recognized. I agree. > If *nothing* is changed, then there is no reason to send the BSO. Correct. > Of course the *answer* to the BSO most likely will be unchanged from the > prior answer, so the o-line for that ought to reflect that. Correct. Regards, Christer
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Martin Thomson
- [MMUSIC] BUNDLE TEXT: Offerer procedures (June 6t… Christer Holmberg
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Martin Thomson
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Paul Kyzivat
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Paul Kyzivat
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Christer Holmberg
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Christer Holmberg
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Martin Thomson
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Paul Kyzivat
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Christer Holmberg
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Martin Thomson
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Christer Holmberg
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Paul Kyzivat
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Christer Holmberg
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Christer Holmberg
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Paul Kyzivat
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Martin Thomson
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Christer Holmberg
- Re: [MMUSIC] BUNDLE TEXT: Offerer procedures (Jun… Martin Thomson