The link is that the L queue starves the other queue, and indeed the envisaged queue protection mechanism is supposed to react to that behavior by black-listing the misbehaving sender. This would be the third coupled component in L4S (the senders, the AQM and the policer). Which is currently non-mandatory.
The level of starvation is a parameter in dualQ as the service ratio between the two queues has to be set but the AQM owner. How to set this ratio is yet another knob that is unclear how to optimally set under a general traffic mix, that includes unresponsive traffic. I have already raised this issue in the past. On Tue, Apr 28, 2020 at 9:26 PM Gorry Fairhurst <go...@erg.abdn.ac.uk> wrote: > This seems all interesting, but isn't this true of any network technology. > If I use a UDP app with my own style of CC I can just take all the capacity > if I want. > > A solution could be to apply a circuit-breaker/policer in the network to > perform admission control, but I don't see the link to L4S. Have I missed > something ? > > Gorry > On 28/04/2020 20:04, Luca Muscariello wrote: > > Hi Jake, > > Thanks for the notes. Very useful. > The other issue with the meeting was that the virtual mic queue control > channel was the WebEx Meeting chat that does not exist in WebEx Teams. So, > I had to switch to Meetings and lost some pieces of the discussion. > > Yes there might be a terminology difference. Elastic traffic is usually > used in the sense of bandwidth sharing not just to define variable bit > rates. > > The point is that there are incentives to cheat in L4S. > > There is a priority queue that my application can enter by providing as > input ECT(1). > Applications such as on-line meetings will have a relatively low and > highly paced rate. > > This traffic is conformant to dualQ L queue but is unresponsive to > congestion notifications. > > This is especially true for FEC streams which could be used to ameliorate > the media quality in presence of losses(e.g. Wi-Fi) > or increased jitter. > > > That was one more point on why using ECT(1) as input assumes trust or a > black list after being caught. > > In both cases the ECT(1) as input is DoSable. > > > > On Tue, Apr 28, 2020 at 7:12 PM Holland, Jake <jholl...@akamai.com> wrote: > >> Hi Luca, >> >> >> >> To your point about the discussion being difficult to follow: I tried to >> capture the intent of everyone who commented while taking notes: >> >> https://etherpad.ietf.org:9009/p/notes-ietf-interim-2020-tsvwg-03 >> >> >> >> I think this was intended to take the place of a need for everyone to >> re-send the same points to the list, but of course some of the most crucial >> points could probably use fleshing out with on-list follow up. >> >> >> >> It got a bit rough in places because I was disconnected a few times and >> had to cut over to a local text file, and I may have failed to correctly >> understand or summarize some of the comments, so there’s chances I might >> have missed something, but I did my best to capture them all. >> >> >> >> I encourage people to review comments and check whether they came out >> more or less correct, and to offer formatting and cleanup suggestions if >> there’s a good way to make it easier to follow. >> >> >> >> I had timestamps at the beginning of each main point of discussion, with >> the intent that after the video is published it would be easier to go back >> and check precisely what was said. It looks like someone has been making >> cleanup edits that removed the first half of those so far, but my local >> text file still has most of those and I can go back and re-insert them if >> it seems useful. >> >> >> >> @Luca: during your comments in particular I think there might have been a >> disruption--I had a “first comment missed, please check video” placeholder >> and I may have misunderstood the part about video elasticity, but my >> interpretation at the time was that Stuart was claiming that video was >> elastic in that it would adjust downward to avoid overflowing a loaded >> link, and I thought you were claiming that it was not elastic in that it >> would not exceed a maximum rate, which I summarized as perhaps a semantic >> disagreement, but if you’d like to help clean that up, it might be useful. >> >> >> >> From this message, it sounds like the key point you were making was that >> it also will not go below a certain rate, and perhaps that quality can stay >> relatively good in spite of high network loss? >> >> >> >> Best regards, >> >> Jake >> >> >> >> *From: *Luca Muscariello <muscarie...@ieee.org> >> *Date: *Tuesday, April 28, 2020 at 1:54 AM >> *To: *Dave Taht <dave.t...@gmail.com> >> *Cc: *tsvwg IETF list <ts...@ietf.org>, bloat < >> bloat@lists.bufferbloat.net> >> *Subject: *Re: [Bloat] my backlogged comments on the ECT(1) interim call >> >> >> >> Hi Dave and list members, >> >> >> >> It was difficult to follow the discussion at the meeting yesterday. >> >> Who said what in the first place. >> >> >> >> There have been a lot of non-technical comments such as: this solution >> >> is better than another in my opinion. "better" has often been used >> >> as when evaluating the taste of an ice cream: White chocolate vs black >> chocolate. >> >> This has taken a significant amount of time at the meeting. I haven't >> learned >> >> much from that kind of discussion and I do not think that helped to make >> >> much progress. >> >> >> >> If people can re-make their points in the list it would help the debate. >> >> >> >> Another point that a few raised is that we have to make a decision as >> fast as possible. >> >> I dismissed entirely that argument. Trading off latency with resilience >> of the Internet >> >> is entirely against the design principle of the Internet architecture >> itself. >> >> Risk analysis is something that we should keep in mind even when >> deploying any experiment >> >> and should be a substantial part of it. >> >> >> >> Someone claimed that on-line meeting traffic is elastic. This is not >> true, I tried to >> >> clarify this. These applications (WebEx/Zoom) are low rate, a typical >> maximum upstream >> >> rate is 2Mbps and is not elastic. These applications have often a >> stand-alone app >> >> that is not using the browser WebRTC stack (the standalone app typically >> works better). >> >> >> >> A client sends upstream one or two video qualities unless the video >> camera is switched off. >> >> In presence of losses, FEC is used but it is still non elastic. >> >> Someone claimed (at yesterday's meeting) that fairness is not an issue >> (who cares, I heard!) >> >> Well, fairness can constitute a differentiation advantage between two >> companies that are >> >> commercializing on-line meetings products. Unless at the IETF we accept >> >> "law-of-the-jungle" behaviours from Internet applications developers, we >> should be careful >> >> about making such claims. >> >> Any opportunity to cheat, that brings a business advantage WILL be used. >> >> >> >> /Luca >> >> >> >> TL;DR >> >> To Dave: you asked several times what Cisco does on latency reduction in >> >> network equipment. I tend to be very shy when replying on these questions >> >> as this is not vendor neutral. If chairs think this is not appropriate for >> >> the list, please say it and I'll reply privately only. >> >> >> >> What I write below can be found in Cisco products data sheets and is not >> >> trade secret. There are very good blog posts explaining details. >> >> Not surprisingly Cisco implements the state of the art on the topic >> >> and it is totally feasible to do-the-right-thing in software and hardware. >> >> >> >> Cisco implements AFD (one queue + a flow table) accompanied by a priority >> queue for >> >> flows that have a certain profile in rate and size. The concept is well >> known and well >> >> studied in the literature. AFD is safe and can well serve a complex >> traffic mix when >> >> accompanied by a priority queue. This prio-queue should not be confused >> with a strict >> >> priority queue (e.g. EF in diffserv). There are subtleties related to the >> DOCSIS >> >> shared medium which would be too long to describe here. >> >> >> >> This is available in Cisco CMTS for the DOCSIS segment. Bottleneck traffic >> >> does not negatively impact non-bottlenecked-traffic such as an on-line >> meeting like >> >> the WebEx call we had yesterday. It is safe from a network neutrality >> point-of-view >> >> and no applications get hurt. >> >> >> >> Cisco implements AFD+prio also for some DC switches such as the Nexus 9k. >> There >> >> is a blog post written by Tom Edsal online that explains pretty well how >> that works. >> >> This includes mechanisms such as p-fabric to approximate SRPT (shortest >> remaining processing time) >> >> and minimize flow completion time for many DC workloads. The mix of the >> two >> >> brings FCT minimization AND latency minimization. This is silicon and >> scales at any speed. >> >> For those who are not familiar with these concepts, please search the >> research work of Balaji >> >> Prabhakar and Ron Pang at Stanford. >> >> >> >> Wi-Fi: Cisco does airtime fairness in Aironet but I think in the Meraki >> series too. >> >> The concept is similar to what described above but there are several >> queues, one per STA. >> >> Packets are enqueued in the access (category) queue at dequeue time from >> the air-time >> >> packet scheduler. >> >> >> >> On Mon, Apr 27, 2020 at 9:24 PM Dave Taht <dave.t...@gmail.com> wrote: >> >> It looks like the majority of what I say below is not related to the >> fate of the "bit". The push to take the bit was >> strong with this one, and me... can't we deploy more of what we >> already got in places where it matters? >> >> .... >> >> so: A) PLEA: From 10 years now, of me working on bufferbloat, working >> on real end-user and wifi traffic and real networks.... >> >> I would like folk here to stop benchmarking two flows that run for a long >> time >> and in one direction only... and thus exclusively in tcp congestion >> avoidance mode. >> >> Please. just. stop. Real traffic looks nothing like that. The internet >> looks nothing like that. >> The netops folk I know just roll their eyes up at benchmarks like this >> that prove nothing and tell me to go to ripe meetings instead. >> When y'all talk about "not looking foolish for not mandating ecn now", >> you've already lost that audience with benchmarks like these. >> >> Sure, setup a background flow(s) like that, but then hit the result >> with a mix of >> far more normal traffic? Please? networks are never used unidirectionally >> and both directions congesting is frequent. To illustrate that problem... >> >> I have a really robust benchmark that we have used throughout the >> bufferbloat >> project that I would like everyone to run in their environments, the flent >> "rrul" test. Everybody on both sides has big enough testbeds setup that a >> few >> hours spent on doing that - and please add in asymmetric networks >> especially - >> and perusing the results ought to be enlightening to everyone as to the >> kind >> of problems real people have, on real networks. >> >> Can the L4S and SCE folk run the rrul test some day soon? Please? >> >> I rather liked this benchmark that tested another traffic mix, >> >> ( >> https://www.cablelabs.com/wp-content/uploads/2014/06/DOCSIS-AQM_May2014.pdf >> <https://urldefense.proofpoint.com/v2/url?u=https-3A__www.cablelabs.com_wp-2Dcontent_uploads_2014_06_DOCSIS-2DAQM-5FMay2014.pdf&d=DwMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bqnFROivDo_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=j5nEJ3W8fRmqjnBSWapTVKj6dNbpegl4kSeynebCQT4&s=DrB4ENWjWbVu9SqtIh7lXKJj96fwm6TqESC6E8_IdnY&e=> >> ) >> >> although it had many flaws (like not doing dns lookups), I wish it >> could be dusted off and used to compare this >> new fangled ecn enabled stuff with the kind of results you can merely get >> with packet loss and rtt awareness. It would be so great to be able >> to directly compare all these new algorithms against this benchmark. >> >> Adding in a non ecn'd udp based routing protocol on heavily >> oversubscribed 100mbit link is also enlightening. >> >> I'd rather like to see that benchmark improved for a more modernized >> home traffic mix >> where it is projected there may be 30 devices on the network on average, >> in a few years. >> >> If there is any one thing y'all can do to reduce my blood pressure and >> keep me engaged here whilst you >> debate the end of the internet as I understand it, it would be to run >> the rrul test as part of all your benchmarks. >> >> thank you. >> >> B) Stuart Cheshire regaled us with several anecdotes - one concerning >> his problems >> with comcast's 1Gbit/35mbit service being unusable, under load, for >> videoconferencing. This is true. The overbuffering at the CMTSes >> still, has to be seen to be believed, at all rates. At lower rates >> it's possible to shape this, with another device (which is what >> the entire SQM deployment does in self defense and why cake has a >> specific docsis ingress mode), but it is cpu intensive >> and requires x86 hardware to do well at rates above 500Mbits, presently. >> >> So I wish CMTS makers (Arris and Cisco) were in this room. are they? >> >> (Stuart, if you'd like a box that can make your comcast link pleasurable >> under all workloads, whenever you get back to los gatos, I've got a few >> lying around. Was so happy to get a few ietfers this past week to apply >> what's off the shelf for end users today. :) >> >> C) I am glad bob said the L4S is finally looking at asymmetric >> networks, and starting to tackle ack-filtering and accecn issues >> there. >> >> But... I would have *started there*. Asymmetric access is the predominate >> form >> of all edge technologies. >> >> I would love to see flent rrul test results for 1gig/35mbit, 100/10, >> 200/10 >> services, in particular. (from SCE also!). "lifeline" service (11/2) >> would be good >> to have results on. It would be especially good to have baseline >> comparison data from the measured, current deployment >> of the CMTSes at these rates, to start with, with no queue management in >> play, then pie on the uplink, then fq_codel on the uplink, and then >> this ecn stuff, and so on. >> >> D) The two CPE makers in the room have dismissed both fq and sce as >> being too difficult to implement. They did say that dualpi was >> actually implemented in software, not hardware. >> >> I would certainly like them to benchmark what they plan to offer in L4S >> vs what is already available in the edgerouter X, as one low end >> example among thousands. >> >> I also have to note, at higher speeds, all the buffering moves into >> the wifi and the results are currently ugly. I imagine >> they are exploring how to fix their wifi stacks also? I wish more folk >> were using RVR + latency benchmarks like this one: >> >> >> http://flent-newark.bufferbloat.net/~d/Airtime%20based%20queue%20limit%20for%20FQ_CoDel%20in%20wireless%20interface.pdf >> <https://urldefense.proofpoint.com/v2/url?u=http-3A__flent-2Dnewark.bufferbloat.net_-7Ed_Airtime-2520based-2520queue-2520limit-2520for-2520FQ-5FCoDel-2520in-2520wireless-2520interface.pdf&d=DwMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bqnFROivDo_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=j5nEJ3W8fRmqjnBSWapTVKj6dNbpegl4kSeynebCQT4&s=UEzrGb3xL5zElDhYxB7wHpux1_SLFHGUcEkgTNMOe2Q&e=> >> >> Same goes for the LTE folk. >> >> E) Andrew mcgregor mentioned how great it would be for a closeted >> musician to >> be able to play in real time with someone across town. that has been my >> goal >> for nearly 30 years now!! And although I rather enjoyed his participation >> in >> my last talk on the subject ( >> >> https://blog.apnic.net/2020/01/22/bufferbloat-may-be-solved-but-its-not-over-yet/ >> <https://urldefense.proofpoint.com/v2/url?u=https-3A__blog.apnic.net_2020_01_22_bufferbloat-2Dmay-2Dbe-2Dsolved-2Dbut-2Dits-2Dnot-2Dover-2Dyet_&d=DwMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bqnFROivDo_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=j5nEJ3W8fRmqjnBSWapTVKj6dNbpegl4kSeynebCQT4&s=BSDbzxnB7k7krFmkHv9id0BeDC6Vh39LgPNxyHUIg34&e=> >> ) conflating >> a need for ecn and l4s signalling for low latency audio applications >> with what I actually said in that talk, kind of hurt. I achieved >> "my 2ms fiber based guitarist to fiber based drummer dream" 4+ years >> back with fq_codel and diffserv, no ecn required, >> no changes to the specs, no mandating packets be undroppable" and >> would like to rip the opus codec out of that mix one day. >> >> F) I agree with jana that changing the definition of RFC3168 to suit >> the RED algorithm (which is not pi or anything fancy) often present in >> network switches, >> today to suit dctcp, works. But you should say "configuring red to >> have l4s marking style" and document that. >> >> Sometimes I try to point out many switches have a form of DRR in them, >> and it's helpful to use that in conjunction with whatever diffserv >> markings you trust in your network. >> >> To this day I wish someone would publish how much they use DCTCP style >> signalling on a dc network relative to their other traffic. >> >> To this day I keep hoping that someone will publish a suitable >> set of RED parameters for a wide variety of switches and routers - >> for the most common switches and ethernet chips, for correct DCTCP usage. >> >> Mellonox's example: >> ( >> https://community.mellanox.com/s/article/howto-configure-ecn-on-mellanox-ethernet-switches--spectrum-x >> <https://urldefense.proofpoint.com/v2/url?u=https-3A__community.mellanox.com_s_article_howto-2Dconfigure-2Decn-2Don-2Dmellanox-2Dethernet-2Dswitches-2D-2Dspectrum-2Dx&d=DwMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bqnFROivDo_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=j5nEJ3W8fRmqjnBSWapTVKj6dNbpegl4kSeynebCQT4&s=nEIW1DhRXOHu3F5tMwpyO5rQUBMfCZx3Hs4wVvkVFIQ&e=> >> ) is not dctcp specific. >> >> many switches have a form of DRR in them, and it's helpful to use that >> in conjunction with whatever diffserv markings you trust in your >> network, >> and, as per the above example, segregate two red queues that way. From >> what I see >> above there is no way to differentiate ECT(0) from ECT(1) in that switch. >> (?) >> >> I do keep trying to point out the size of the end user ecn enabled >> deployment, starting with the data I have from free.fr >> <https://urldefense.proofpoint.com/v2/url?u=http-3A__free.fr&d=DwMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bqnFROivDo_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=j5nEJ3W8fRmqjnBSWapTVKj6dNbpegl4kSeynebCQT4&s=7gswGhl21lejSnIiu3yyUTPZEArHqQG6hD64BoW2Zco&e=>. >> Are we >> building a network for AIs or people? >> >> G) Jana also made a point about 2 queues "being enough" (I might be >> mis-remembering the exact point). Mellonoxes ethernet chips at 10Gig >> expose >> 64 hardware queues, some new intel hardware exposes 2000+. How do these >> queues work relative to these algorithms? >> >> We have generally found hw mq to be far less of a benefit than the >> manufacturers think, especially as regard to >> lower latency or reduced cpu usage (as cache crossing is a bear). >> There is a lot of software work in this area left to be done, however >> they are needed to match queues to cpus (and tenants) >> >> Until sch_pie gained timestamping support recently, the rate estimator >> did not work correctly in a hw mq environment. Haven't looked over >> dualpi in this respect. >> >> >> >> >> >> -- >> Make Music, Not War >> >> Dave Täht >> CTO, TekLibre, LLC >> http://www.teklibre.com >> <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.teklibre.com&d=DwMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bqnFROivDo_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=j5nEJ3W8fRmqjnBSWapTVKj6dNbpegl4kSeynebCQT4&s=DqPVjNVWDmF4_cwubNhhJS4Y1jCj71szPiBn9pmDZ70&e=> >> Tel: 1-831-435-0729 >> _______________________________________________ >> Bloat mailing list >> Bloat@lists.bufferbloat.net >> https://lists.bufferbloat.net/listinfo/bloat >> <https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.bufferbloat.net_listinfo_bloat&d=DwMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bqnFROivDo_4iF8Z3R4DyNWKbbMeXr0LOgLnElT1Ook&m=j5nEJ3W8fRmqjnBSWapTVKj6dNbpegl4kSeynebCQT4&s=DBDxIR6eSYcBOh7rqZx0PWzsHOfvvJeqioI3r2IQOA4&e=> >> >> -- > G. Fairhurst, School of Engineering > >
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