Re: [siprec] Review of draft-yan-siprec-msrp-recording-02
Paul Kyzivat <pkyzivat@alum.mit.edu> Mon, 16 February 2015 20:32 UTC
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Date: Mon, 16 Feb 2015 15:32:16 -0500
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [siprec] Review of draft-yan-siprec-msrp-recording-02
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Brian, and others, Below is the last message on this draft. It came in the midst of IETF91, so the discussion never came to completion. I don't think my co-author is interested in further work on it, and I no longer have any sponsorship to work on it, but I'd still like to finish it if there is interest. But I won't do so unless there is active interest. A start at that would be to finish off the discussion started in this thread. Thanks, Paul On 11/11/14 5:23 AM, Paul Kyzivat wrote: > On 11/10/14 9:06 PM, Brian Rosen wrote: >> I have reviewed -02 and have the following comments > > Thanks. Obviously this draft *needed* a review! > >> 1. I don’t see value in multiplexing separate CSs in one RS. We don’t >> do that for other media, we need completely separate metadata, and >> generally I don’t think session state is very meaningful. The >> applications I have in mind would not see any significant advantage and >> the complexity I think outweighs it. I could imagine a large investment >> company needing a huge number of sessions and maybe they would think it >> was worth it. > > I brought it up because I was uncertain. I'll take your comment as one > data point. > > The advantage is that you need less MSRP sessions on the RS. > > There is an analogy to audio/video: we do allow a single RS media > session to be multiplexed *serially* for multiple CS media sessions. > This mechanism for MSRP could be used that way. > >> 2. In section 3.1 it says “If the MSRP client/SRC is aware the MSRP >> session needs to be >> >> recorded, it can initiate the establishment of a SIP RS by sending an >> INVITE to SRS, or vice-versa.”“or vice-versa” is confusing as is. >> The SRS would have to either have knowledge of the CS or set up the RS >> in advance of a CS. >> >> Please expand this sentence (or maybe refer to another doc that >> explains how an SRS can initiate the RS. > > This is unchanged from -01, but I agree it is messed up and needs to be > reworked. > >> 3. Just beyond that, the text says“is responsible” (2 places). Should >> that be a normative MUST? > > Same comment as above. > >> 4. In Section 4, it says “If the SRC mixes >> >> MSRP media from multiple senders, then each message that isn't >> already in CPIM format SHOULD be embedded in a CPIM message, and the >> From and To headers of that CPIM wrapper SHOULD identify the sending >> and receiving participants for that message. >> >> >> Is SHOULD correct? What circumstance would it not CPIM wrap? > > I screwed up here. The text is unchanged from -01, but it should have > been changed. This comment is wrong - the new wrapper type replaces this. > >> 5. The last paragraph in Section 6 is replicated from Section 5. Do >> we need that? > > Yet another thing that was wrong in -01. :-( > >> 6. In Section 8, I think it’s MUST. Can’t come up with a reason why >> it shouldn’t do that. > > I was thinking there might be an SRC that has a policy of not disclosing > this. But I'm not sure why. But in general I think an SRC should be > allowed to censor as much as it wants. > >> 7. Re the note about prefixes in the extension. Even if it doesn’t >> require them, it seems to me that it’s helpful here, so I think you >> can just do it and not question it. > > I was mostly not sure if I fully understood how the extension mechanism > was intended to be used. It just needs a bit more research to be sure it > is being done right. > >> 8. In Section 10.1 it says “The 'drop' token indicates that the >> content of a SEND message in the >> >> CS is not being sent to the RS for recording. >> >> >> This confused me. There wouldn’t be a body in this case, right? This >> is the case where the SRS doesn’t support, say file transfer, and >> we’re recording that fact Seems like we need more text here, perhaps >> just a reference to Section 11.2. > > This message gets used in multiple circumstances. If a CS message is > being dropped because the SRS doesn't want that type, then yes, there > will be no body from the CS message. The MSRP message on the RS will > still have the "wrapper" body, but it won't be wrapping anything. All > the info will be in the wrapper headers. > >> 9. Since the SRC can reassemble a fragmented message, it can also >> fragment it. Therefore, it may be able to not drop a large message on >> the CS by fragmenting on the RS. The text in 11.2 doesn’t cover that, >> and probably should be explicitly noted elsewhere. > > The negotiated size is not the limit on *fragments* - it is a limit on > the unfragmented message. > > One challenge is that when the SRC receives the first fragment it may > not be able to tell how big the complete message will be. (That info is > optional.) So it may send one or a few fragments before it discovers > that the message in total will be too big. At *that* time it sends a > drop message. > >> 10. I don’t think this text: >> >> When a 'drop' message is sent: >> >> o it MUST be terminated with a continuation-flag of "#"; >> >> >> is correct. I think that is only true if the SRC sent a prior >> fragment. You are telling me that if you were fragmenting, and you >> dropped, that that is the end of the message, >> >> so we ended continuatiuon. Fine, but that’s only if you were >> fragmenting. > > Yeah, this needs a bit more work. If some fragments have been sent, and > then the SRC discovers the message is too big, it can't send the drop as > part of the fragmented message. It needs to send a last (empty?) > fragment with a "#", and *then* it can send a drop message with the same > rs.Message-ID. And then the drop message can end with "$". > >> 11. I don’t know why SHOULD is not MUST in 11.3 > > In some sense they are redundant, since the nickname is sent to the SRS > in the wrapper with each message. It might be interesting for the SRS to > see the requests for nicknames, and especially denials of those. But it > the general spirit of giving the SRC discretion, I thought it can be > allowed to drop based on policy. > >> 12. Generally, I think the recording should record failures at the >> SRC, so I think we need a way to record them, and I don’t think they >> are optional (assuming its a CS error). > > I would expect that would be the normal case. I just can't think of a > strong reason to *insist* that the SRC do so. > > Thanks, > Paul > > _______________________________________________ > siprec mailing list > siprec@ietf.org > https://www.ietf.org/mailman/listinfo/siprec >
- [siprec] Review of draft-yan-siprec-msrp-recordin… Brian Rosen
- Re: [siprec] Review of draft-yan-siprec-msrp-reco… Paul Kyzivat
- Re: [siprec] Review of draft-yan-siprec-msrp-reco… Paul Kyzivat