Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S
Ingemar Johansson S <ingemar.s.johansson@ericsson.com> Tue, 17 March 2020 13:45 UTC
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From: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
To: Sebastian Moeller <moeller0@gmx.de>, Bob Briscoe <in@bobbriscoe.net>
CC: Ingemar Johansson S <ingemar.s.johansson=40ericsson.com@dmarc.ietf.org>, "iccrg@irtf.org" <iccrg@irtf.org>, "tsvwg@ietf.org" <tsvwg@ietf.org>, Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
Thread-Topic: [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S
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Subject: Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S
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Hi It is true that the "CoDel" implementation in the test code is a botched version. The CoDel algorithm implemented in our system simulator that was used to produce these examples is however _the_ CoDel /Ingemar > -----Original Message----- > From: Sebastian Moeller <moeller0@gmx.de> > Sent: den 17 mars 2020 14:16 > To: Bob Briscoe <in@bobbriscoe.net> > Cc: Ingemar Johansson S > <ingemar.s.johansson=40ericsson.com@dmarc.ietf.org>; Ingemar Johansson S > <ingemar.s.johansson@ericsson.com>; iccrg@irtf.org; tsvwg@ietf.org > Subject: Re: [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S > > Hi Bob, > > > > On Mar 17, 2020, at 02:32, Bob Briscoe <in@bobbriscoe.net> wrote: > > > > Sebastian, > > > > I suspect it is the 20ms interval that is the main cause the extra queuing delay > with CoDel. > > [SM] That and the fact that rfc3168 asserts ECE until it receives the CWR > from the sender and that on Ingemar's test path takes 20ms, so the temporal > fifelity of rfc3168 ECN is simply too low for SCReAM's feed-back fidelity > requirements. > > > > > > The 20:1 ratio between interval and target was really designed around loss. > > [SM] I do not think that this actually makes a big difference for rfc3168 > ECN, CE will be asserted just as a drop would be for NON-ECN packets, and it > will take a while for a drop being registered by the receiver and send back to the > sender as well. Note how the 5% rule has no bearing on that. > > > The need to filter out brief excursions in the queue is only necessary when > you're using impairments (losses) as signals. > > [SM] I disagree, (limited) burst tolerance is not only helpful if loss is > involved. > > > > If you're using explicit signals, you can signal unfiltered queue variations, > because there is no harm having higher ECN marking levels. > > [SM] Sure, but I strongly believe the bigger issue here is that L4S CE > feedback simply has higher temporal fidelity not being limited by the 1RTT ECE- > >CWR dance. > > > > For that matter, you might as well use Eric Dumazet's simple patch to CoDel > that adds immediate ECN marking at a shallow threshold, bypassing all the > CoDel machinery, which is really tailored for loss. > > [SM] Note how I asked Ingemar about whether he tested codel's > ce_threshold... But I am still wondering whether Ingemar's test where done with > SCReAM's own limited Codel implementation or with a full fledged Linux AQM > node in the path (looking at the SCReAM repository makes me believe its own > Codel being very vrudimentary and not implementing ce_threshold and as it > appears not even the square law drop interval calculation, @Ingemar, I am sure > I am reading something wrong here, so please help me see what I am missing*). > > > *) I am 99.999% sure I am missing something ;) > > > > > Of course, unless you have FQ (which you can't at the RLC layer) > > [SM] Then use feedback the queueing information from the RLC layer > back up to where at least IP packets are handled/seen, akin to say the wifi > airtime fairness approach? > > > , you would have to work out some other way to ensure coexistence with > existing congestion controls. That is left as an exercise for the reader - I > wouldn't want to be seen to be pushing any particular solution. But hopefully, > through scenarios like this, you might start to understand the set of > requirements that led to one solution rather than another. > > [SM] Well, I believe that neither 1/p type signaling, nor higer temporal > feed-back fidelity are really under discussion, we all want those, the question is > more what is the best and safest/backward compatiblest way of using those, but > I digress (this is not the thread for that discussion ;) ) > > Best Regards > Sebastian > > > > > > > > Bob > > > > On 10/03/2020 21:04, Ingemar Johansson S wrote: > >> Hi > >> Attached is a simulation of the same simple bottleneck case with target=1ms > and interval=20ms. > >> Two ECN beta values : 0.8 and 0.6. A larger backoff (0.6) does actually not > improve things as the CWND reduction leads to that packets from the video > coder are queued up in the RTP queue. > >> As you can see there is still a way to go to reach the L4S delays. > >> > >> Perhaps the SCReAM's response to CoDel - ECN marks can be optimized > further, don't know, but I already spent a considerable time to try and get where > the code is now, and I spent a lot more time on this than I spent on the response > to the L4S signal. > >> My impression is that it is the fractional congestion signal with L4S > >> that makes it easier to get a good algorithm behavior (and I > >> definitely believe that there is room for improvement) > >> > >> And as said earlier, the SCReAM code is freely available to experiment with > and occasionally it is quite fun > (https://www.youtube.com/watch?v=eU1crtEvMv4 ). > >> > >> > >> /Ingemar > >> > >>> -----Original Message----- > >>> From: Sebastian Moeller <moeller0@gmx.de> > >>> Sent: den 10 mars 2020 16:29 > >>> To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com> > >>> Cc: Ingemar Johansson S > >>> <ingemar.s.johansson=40ericsson.com@dmarc.ietf.org>; tsvwg@ietf.org; > >>> iccrg@irtf.org > >>> Subject: Re: [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S > >>> > >>> Hi Ingemar, > >>> > >>> > >>> > >>>> On Mar 10, 2020, at 13:37, Ingemar Johansson S > >>> <ingemar.s.johansson@ericsson.com> wrote: > >>>> Hi > >>>> > >>>> The SCReAM code is freely available on > >>> https://protect2.fireeye.com/v1/url?k=3fa4aff0-6370a99d-3fa4ef6b- > >>> 867011091b6c-c4d35656f5c9b268&q=1&e=16e2b451-36c7-4814-af9d- > >>> > 4acb21ac792b&u=https%3A%2F%2Fgithub.com%2FEricssonResearch%2Fscream > >>> for anybody interested to run their own experiment with whatever > >>> AQM/ECN configuration. > >>> > >>> [SM] Well, if you are not interested in figuring out what is > >>> happening with with rfc3168 ECN ans SCReAM that is your prerogative... > >>> > >>> > >>>> Please note that SCReAM is configured in an L4S mode when the > >>>> network AQM does L4S marking (mimicking ECT(1)). For CoDel-ECN > >>>> however, SCReAM runs in normal ECN mode with a beta of 0.8 (=20% > >>>> reduction on CWND for each congestion event) > >>> [SM] Okay, that is a far cry from Reno's 50% though, have you > >>> tested different reduction percentages or how did you arrive at 20%? > >>> But is it really 0.8? ScreamTx.h has the following: > >>> > >>> // CWND scale factor upon ECN-CE event static const float kEcnCeBeta > >>> = 0.9f; > >>> > >>> I am probably missing something somewhere... > >>> > >>>> I tried also with other different ramp markers (1ms/10ms), > >>> (2ms/10ms),(5ms/15ms). > >>> > >>> [SM] That means for L4S, or do you mean you tried different values > >>> for Codel's target ans ce_threshold parameters? > >>> > >>> > >>>> There are slight variations in throughput and latency but not dramatic. > >>> [SM] Well, these are also pretty slight variations in numerical > >>> values, at least if compared to codel's default interval of 100ms... > >>> > >>>> And truth to be told, the ECN behavior is better tuned in the code > >>>> than the L4S > >>> behavior. > >>> > >>> [SM] For a defintion of better that ignores that you seem to be > >>> much happier with the results L4S gives you. > >>> > >>>> There is room for improvement as regards to the L4S behavior (for > >>>> instance > >>> faster ramp-up) and it may well be the case that SCReAM is > >>> completely scrapped in favor of new designs. > >>>> But the bottomline, the L4S thresholds and L4S code is not > >>>> carefully picked to > >>> show a good performance. > >>> > >>> [SM] So, you tried different L4S parameters (and found the to have > >>> similar performance) but for rfc3168 ECN and Codel you only tried > >>> the default parameters? > >>> > >>> Best Regards > >>> Sebastian > >>> > >>>> /Ingemar > >>>> > >>>>> -----Original Message----- > >>>>> From: Sebastian Moeller <moeller0@gmx.de> > >>>>> Sent: den 10 mars 2020 11:28 > >>>>> To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com> > >>>>> Cc: Ingemar Johansson S > >>>>> <ingemar.s.johansson=40ericsson.com@dmarc.ietf.org>; > >>>>> tsvwg@ietf.org; iccrg@irtf.org > >>>>> Subject: Re: [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S > >>>>> > >>>>> Hi Ingemar, > >>>>> > >>>>> > >>>>>> On Mar 10, 2020, at 11:07, Ingemar Johansson S > >>>>> <ingemar.s.johansson@ericsson.com> wrote: > >>>>>> Hi > >>>>>> > >>>>>> For the future studies we will only focus on L4S as the scope is > >>>>>> to study the > >>>>> performance gain that L4S give for instance for AR/VR, gaming and > >>>>> remote control applications. > >>>>> > >>>>> [SM] How are you going to "study the performance gain that L4S > >>>>> give[s]" if you do not compare it with the best of class > >>>>> alternatives? I am truly puzzled. > >>>>> > >>>>>> Flow aware AQMs with RTT estimates as metadata in the packets is > >>>>>> outside > >>>>> the scope as it would require packet inspection, which is not > >>>>> feasible if queues build up on the RLC layer in the 3GPP stack. > >>>>> > >>>>> [SM] Fair enough. What is this comparison intended to show us then? > >>>>> > >>>>> As far as I can see you paired an application designed for > >>>>> 1/p-type congestion feed-back with an 1/sqrt(p)-type AQM that was > >>>>> also set for sub-optimal RTT and latency target for the test path. > >>>>> And lo and behold, the application does "better*" for the 1/p-type > >>>>> AQM (with lower latency target; I assume that L4S ramp-marker > >>>>> (Th_low=2ms, > >>>>> Th_high=10ms) was carefully selected to match what SCReAM expects). > >>>>> IMHO that simply demonstrates, that in communication it pays if > >>>>> sender and receiver of a symbol (CE here) assign the same meaning to it. > >>>>> > >>>>> But that can not be it, sohat am I missing here? > >>>>> > >>>>> Best Regards > >>>>> Sebastian > >>>>> > >>>>> > >>>>> *) Assuming one buys into your definition of better, in which > >>>>> (instantaneous) queueing delay is valued over video quality. From > >>>>> a network operators perspective that seems a valid position > >>>>> > >>>>> > >>>>> > >>>>> > >>>>>> /Ingemar > >>>>>> > >>>>>>> -----Original Message----- > >>>>>>> From: Sebastian Moeller <moeller0@gmx.de> > >>>>>>> Sent: den 10 mars 2020 10:45 > >>>>>>> To: Ingemar Johansson S > >>>>>>> <ingemar.s.johansson=40ericsson.com@dmarc.ietf.org> > >>>>>>> Cc: tsvwg@ietf.org; Ingemar Johansson S > >>>>>>> <ingemar.s.johansson@ericsson.com>; iccrg@irtf.org > >>>>>>> Subject: Re: [tsvwg] SCReAM (RFC8298) with CoDel-ECN and L4S > >>>>>>> > >>>>>>> Hi Ingemar, > >>>>>>> > >>>>>>> thanks for posting this interesting piece of data! > >>>>>>> > >>>>>>>> On Mar 10, 2020, at 09:02, Ingemar Johansson S > >>>>>>> <ingemar.s.johansson=40ericsson.com@dmarc.ietf.org> wrote: > >>>>>>>> Hi > >>>>>>>> > >>>>>>>> I recently updated the readme on the SCReAM github with a > >>>>>>>> comparison with > >>>>>>> SCReAM in three different settings > >>>>>>>> • No ECN > >>>>>>>> • CoDel ECN > >>>>>>>> • L4S > >>>>>>>> https://protect2.fireeye.com/v1/url?k=63019d27-3f884737-6301ddb > >>>>>>>> c-0 > >>>>>>>> cc > >>>>>>>> 47 > >>>>>>>> ad93e2a-489fa99c3277fb8a&q=1&e=5aab95a7-4aab-4a64-99a5- > >>>>>>> 5b55606e303b&u= > >>>>>>>> > https%3A%2F%2Fgithub.com%2FEricssonResearch%2Fscream%23ecn- > >>>>> explicit- > >>>>>>> co > >>>>>>>> ngestion-notification > >>>>>>>> > >>>>>>>> Even though it is more than a magnitude difference in queue > >>>>>>>> delay between CoDel-ECN and L4S, > >>>>>>> > >>>>>>> [SM] So, in this simulations of a 20ms path, SCReAM over L4S > >>>>>>> gives > >>>>>>> ~10 times less queueing delay, but also only ~2 less bandwidth > >>>>>>> compared to SCReAM over codel. You describe this as "L4S reduces > >>>>>>> the delay considerably more" and "L4S gives a somewhat lower > >>>>>>> media > >>> rate". > >>>>>>> I wonder how many end-users would tradeoff these 25ms in > >>>>>>> queueing delay against the decrease in video quality from halving the > bitrate? > >>>>>>> Could you repeat the Codel test with interval set to 20 and > >>>>>>> target to 1ms, please? > >>>>>>> > >>>>>>> If that improves things considerably it would argue for > >>>>>>> embedding the current best RTT estimate into SCReAM packets, so > >>>>>>> an AQM could tailor its signaling better to individual flow > >>>>>>> properties (and yes, that will require a flow-aware AQM). > >>>>>>> > >>>>>>> > >>>>>>> > >>>>>>>> it is fair to say that these simple simulations should of > >>>>>>>> course be seen as just a > >>>>>>> snapshot. > >>>>>>> > >>>>>>> [SM] Fair enough. > >>>>>>> > >>>>>>>> We hope to present some more simulations with 5G access, and > >>>>>>>> not just > >>>>>>> simple bottlenecks with one flow, after the summer. > >>>>>>> > >>>>>>> [Looking] forward to that. > >>>>>>> > >>>>>>>> Meanwhile, the SCReAM code on github is freely available for > >>>>>>>> anyone who > >>>>>>> wish to make more experiments. > >>>>>>>> /Ingemar > >>>>>>>> ================================ Ingemar Johansson M.Sc. > >>>>>>>> Master Researcher > >>>>>>>> > >>>>>>>> Ericsson Research > >>>>>>>> RESEARCHER > >>>>>>>> GFTL ER NAP NCM Netw Proto & E2E Perf Labratoriegränd 11 > >>>>>>>> 971 28, Luleå, Sweden > >>>>>>>> Phone +46-1071 43042 > >>>>>>>> SMS/MMS +46-73 078 3289 > >>>>>>>> ingemar.s.johansson@ericsson.com www.ericsson.com > >>>>>>>> > >>>>>>>> Reality, is the only thing… That’s real! > >>>>>>>> James Halliday, Ready Player One > >>>>>>>> ================================= > > > > -- > > > ________________________________________________________________ > > Bob Briscoe http://bobbriscoe.net/
- [iccrg] SCReAM (RFC8298) with CoDel-ECN and L4S Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Jonathan Morton
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Bob Briscoe
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Bob Briscoe
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Bob Briscoe
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Jonathan Morton
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Jonathan Morton
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Ingemar Johansson S
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Bob Briscoe
- Re: [iccrg] [tsvwg] SCReAM (RFC8298) with CoDel-E… Sebastian Moeller