Re: [tsvwg] Status of ECN encapsulation drafts (i.e., stuck)
"Holland, Jake" <jholland@akamai.com> Fri, 13 March 2020 19:29 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: Fri, 13 Mar 2020 19:28:29 +0000
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Subject: Re: [tsvwg] Status of ECN encapsulation drafts (i.e., stuck)
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Hi Bob, On 3/13/20, 10:56 AM, "Bob Briscoe" <ietf@bobbriscoe.net> wrote: > Same answer as for Jonathan - I'm talking e2e, not just reassembly, > taking account of frag and re-assembly relative to another > non-fragmented flow. All carefully defined in the email (so pls don't > question this sentence, 'cos I didn't want to re-write all the carefully > defined stuff again). You have to read the build-up to the scenario too. > > Of course, if I'm wrong, I'll admit it. However, not if someone just > asserts that the summary is wrong without pointing to the flaw in the > body of the argument. I guess I'll try again with the example from further down the body of the email, which seems to contain a more explicit form of the claim in question: (From https://mailarchive.ietf.org/arch/msg/tsvwg/B2Gnb-jYPiZFYuA3YXNRhktKaT4/ ) The tunnel ingress doubles the packet rate of the flows it fragments. Therefore, during any congestion event, the AQM marks twice as many packets from the fragmented flows as the others {Note 1}. Reassembly restores the packet rate to that at the origin sender. And it removes some of the extra congestion markings that fragmentation added. For example, if 100 packets of the unfragmented flow received 2 marks, 100 packets of the fragmented flow would turn into 200 fragments, 4 would be marked, then reassembly would turn them back into 100 packets and a little more than 2 would be marked (because of the extra size of the inner headers). If reassembly used "logical OR" instead, of the 100 forwarded packets, 4 would be marked (3.96% to be precise). This seems mistaken to me. If 2 of the 100 packets are marked pre-fragmentation, then fragmentation makes it 4 of 200, then logical-OR reassembly will result in marking only for 2 packets of the 100 post-reassembly. There's no opportunity to increase the count of marked packets without receiving new CE marks while fragmented because the reassembly doesn't cross the un-fragmented packet boundaries. It seems to me you're asserting that this would happen, but using a count-based model (or maybe stream-based model?) that mistakenly fails to account for the way reassembly avoids crossing IP packet boundaries of the pre-fragmented packets. Also, since it seems to be an issue: I don't think this line of inquiry is just disagreeing with a summary or nitpicking at a minor point--the assertion that the count of CE-marked packets can increase e2e because of fragmentation and reassembly seems fundamental to the claim that logical-OR reassembly is broken. I still leave open the possibility that I've misunderstood, so I'm asking for an example of a packet sequence e2e that demonstrates how the count of CE-marked packets can increase due to fragmentation and reassembly, because until I can understand that it's possible, I tentatively conclude that the bulk of the argument presented was built on a fundamental error. I have read the email in its entirety and found no explanation of a fragmentation+ reassembly chain of events that allows a sequence of packets containing 2 pre-fragmented marked packets to turn into a sequence with 4 post-reassembly marked packets, unless at least 2 extra marks were added while fragmented (the quoted part above merely asserts it can happen, without an explanation of how anywhere I could find). If this is possible in a conformant network, I'm asking anyone who can explain it to please do so, of course I don't limit my request to Bob. Best regards, Jake
- [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