Re: [tsvwg] Status of ECN encapsulation drafts (i.e., stuck)
"Holland, Jake" <jholland@akamai.com> Tue, 17 March 2020 07:57 UTC
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From: "Holland, Jake" <jholland@akamai.com>
To: Bob Briscoe <ietf@bobbriscoe.net>, Jonathan Morton <chromatix99@gmail.com>
CC: "tsvwg@ietf.org" <tsvwg@ietf.org>
Thread-Topic: [tsvwg] Status of ECN encapsulation drafts (i.e., stuck)
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Date: Tue, 17 Mar 2020 07:56:23 +0000
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Subject: Re: [tsvwg] Status of ECN encapsulation drafts (i.e., stuck)
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Hi Bob, > To be unambiguous, I've provided a schematic here: > http://bobbriscoe.net/projects/netsvc_i-f/consig/encap/ecn-reassembly.pdf Thanks for clarifying, I think your message confirms the speculation Jonathan and I landed on as the source of the misunderstanding. As I said there, it turns out this was just about semantics, not a disagreement about what's happening on the wire, and so I don't think the point needs more discussion, but I just wanted to confirm I believe I now understand what you meant, and your message reinforced that belief. And thanks for the schema diagram, I was able to see it and it was helpful. As I tried to say, I think the reason I got confused about your meaning was that I thought separating the number and proportion of CE-marked packets into 2 values would only make sense for 2 values that were able to vary differently from each other, and so thought you were saying by "number" (as a meaningfully different value from "proportion") that the reassembly process was increasing the report to the receiver of the number of CE marks actually emitted by the network. I agree that when fragmented and getting a fixed proportion of marked packets with an even random distribution of markings, it obviously increases the number of marked packets relative to an equal unfragmented stream. Although I wouldn't have thought to phrase it as "both number and proportion" since it's so nearly the same thing as just "proportion", I acknowledge that your phrasing is not an invalid construction, and that for some reasonable AQMs, you're accurately describing a sense in which the number of marks can be increased due to fragmentation. I hope you likewise agree that the logical-OR reassembly doesn't ever increase the count of CE marks seen by the receiver to a value above the count of CE marks actually emitted by the network (and for threshold-based systems often reduces that number, since fragments will often be marked together), and that the concern you were addressing comes because fragmentation provides more opportunities to the network to emit CE marks, not because logical-OR reassembly can increase the raw count of CE marks actually delivered. And also that you can see this as a reasonable interpretation of "number of CE-marked packets" that can reasonably result in confusion. Best, Jake PS: I also think I understand the proposal outlined in section 5 of update-shim-10, but I think allowing generalized behaviors like that text tried to do, in pursuit of preserving the proportion of marking instead of the fact of marks on a packet, requires a much more precise and careful treatment than the one outlined there, and would be better done as a separate proposal if it's to be done at all (I agree with Jonathan that it's not clear it's worthwhile). The sample algorithm permitted by that text clearly would require a 3168 update, but also makes some very specific assumptions about the AQM's behavior that may not be justified without specific knowledge of the network. It's not hard to imagine a situation where the later fragment(s) of a packet are more likely to receive a mark (for instance if the later fragments are back to back more often than the head, so that later fragments arrive with a systematically fuller queue). If that's the case, examining only the head of the fragment would systematically suppress delivery of CE marks in fragmented packets, because of the violated assumption about an even probability distribution for marks. This further seems like it could give perverse throughput incentives to degenerate behaviors like fragmenting packets at the sender, to get the benefits of reduced loss from ECN but receive fewer marks, even though the network might emit more, and thus pushing out unfragmented competing flows. So the specific example algorithm given seems like an unsafe or at least counterproductive thing to encourage reassemblers to do. But that's a discussion for another thread, really.
- [tsvwg] Status of ECN encapsulation drafts (i.e.,… Black, David
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Black, David
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- [tsvwg] SCE / L4S and fragmentation (was: Status … Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Holland, Jake
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Holland, Jake
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Holland, Jake
- Re: [tsvwg] SCE / L4S and fragmentation (was: Sta… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Sebastian Moeller
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Rodney W. Grimes
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Sebastian Moeller
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] SCE / L4S and fragmentation Bob Briscoe
- Re: [tsvwg] SCE / L4S and fragmentation Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Rodney W. Grimes
- Re: [tsvwg] SCE / L4S and fragmentation Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joseph Touch
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joseph Touch
- Re: [tsvwg] SCE / L4S and fragmentation Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Bob Briscoe
- Re: [tsvwg] SCE / L4S and fragmentation Bob Briscoe
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Sebastian Moeller
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Sebastian Moeller
- Re: [tsvwg] SCE / L4S and fragmentation Sebastian Moeller
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] SCE / L4S and fragmentation Wesley Eddy
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joseph Touch
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joseph Touch
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joseph Touch
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Rodney W. Grimes
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joseph Touch
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Jonathan Morton
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joseph Touch
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Rodney W. Grimes
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joseph Touch
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Rodney W. Grimes
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Joe Touch
- Re: [tsvwg] Status of ECN encapsulation drafts (i… John Leslie
- Re: [tsvwg] Status of ECN encapsulation drafts (i… Holland, Jake
- Re: [tsvwg] SCE / L4S and fragmentation Black, David