Re: [tsvwg] Fwd: Qs on your 5G L4S slides
Ingemar Johansson S <ingemar.s.johansson@ericsson.com> Tue, 16 March 2021 14:00 UTC
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From: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
To: Sebastian Moeller <moeller0@gmx.de>, Bob Briscoe <ietf@bobbriscoe.net>
CC: "tsvwg@ietf.org" <tsvwg@ietf.org>, Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
Thread-Topic: [tsvwg] Fwd: Qs on your 5G L4S slides
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Date: Tue, 16 Mar 2021 14:00:25 +0000
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Subject: Re: [tsvwg] Fwd: Qs on your 5G L4S slides
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And.. for the record. I hope that it is obvious for everybody that, even though the title says "5G", the discussion here has left that particular topic a couple of round trips ago 😊 /Ingemar > -----Original Message----- > From: tsvwg <tsvwg-bounces@ietf.org> On Behalf Of Sebastian Moeller > Sent: den 16 mars 2021 12:01 > To: Bob Briscoe <ietf@bobbriscoe.net> > Cc: tsvwg@ietf.org > Subject: Re: [tsvwg] Fwd: Qs on your 5G L4S slides > > Bob, > > more below prefixed [SM]. > > > On Mar 16, 2021, at 11:48, Bob Briscoe <ietf@bobbriscoe.net> wrote: > > > > Ruediger, > > > > On 16/03/2021 08:12, Ruediger.Geib@telekom.de wrote: > >> Bob, Greg > >> > >> Thanks Bob, I’m having a clear perception. I appreciate that work is being > done to implement an L4S WiFi scheduler by one vendor. An L4S scheduler is > a requirement for all kinds of wireless access, I think. > >> > >> I’m also having a clear perception about the fairness resulting if a classic > transport flow scheduled default on a WiFi access competes with L4S being > scheduled priority. While I understand that L4S won’t perform as desired, if > scheduled default on WiFi under adverse operational conditions, it’s not a > good idea to solve that issue by scheduling L4S by priority on WiFi. > > > > [BB] My point was that the world is the other way up. Choosing a DSCP or > ECN codepoint is not where the scheduling decision is made. The 'blame' for > a scheduling decision is where a DSCP or ECN codepoint is mapped to a PHB. > WiFi access points are being produced that map blocks of DSCPs by default to > different access categories with different priority scheduling. That is where > you need to direct your concerns. It's only because of those default > mappings that everyone (including L4S and NQB) is then choosing the most > appropriate DSCP to make best use of the scheduling (from their point of > view). > > > > This might look like dodging blame, but it's not - it's a genuine dilemma due > to having to cope with the imperfect world we find. > > [SM] Sorry, that is no excuse for advertizing the use of AC_VI as it > exists today for capacity searching traffic. Really go test it. I have flent runs > that show that a macosx client using AC_VO and AC_VI will almost > completely starve reverse traffic from the AP that also uses AC_VO and > AC_VI. Once you start exercising these ACs > BE with more than sparse low- > rate traffic you will unearth such behaviour all over the place. The question > then is who is going to be holding the bag in the end... All my concerns about > safety and functionality of L4S from the wired world carry over into the WiFi > space, except there the fall-out range is even larger, all users with sufficient > band-overlap with an AP over-exercising higher ACs is going to suffer from air > time shortage... You really need to fully accept the shared-medium property > without central arbiter nature of deployed WiFi when proposing to use > something else that AC_BE for the bulk of the WiFi traffic. > > All this is going to lead to is a war of ACs.. if e.g. my DOCSIS neighbors will > start to hog all airtime by over-use of AC_VO/AC _VI, I will accept that > challenge and increase my AP's and clients default AC to the same AC_VI/VO > that the offenders use, this is an arms race nobody can win (but I am not > playing for win, I am just playing to stay in the game). Thinking this over, it > might be time to implement that feature "adaptive airtime access > arbitration" inside of OpenWrt soon. > > Best Regards > Sebastian > > > > > > > > Bob > > > >> I however note that NQB PHB can support also non-L4S traffic and L4S and > NQB don’t have to be linked. > >> > >> Having read also Greg’s response, I’d like to add that the Home-Gateway > market in Germany is deregulated and any WiFi scheduler configuration > which isn’t implemented by all vendors serving this market will best be > expected absent. That is to say, no IETF standard should specify an undesired > behaviour. Deutsche Telekom is able to control BNG policies and L4S might > be relevant there, but as WiFi is customer premises, an IETF standardized > NQB DSCP shouldn’t result in a fair chance to busy the hotline. Looking at this > market environment, Bob’s statement applies in general, L4S requires > appropriately adapted scheduling from BNG to Terminating Equipment, and > prior art won’t do. That’s a long way to go. > >> > >> Regards, > >> > >> Ruediger > >> > >> Von: Bob Briscoe <ietf@bobbriscoe.net> > >> Gesendet: Montag, 15. März 2021 19:06 > >> An: Geib, Rüdiger <Ruediger.Geib@telekom.de>; > >> ingemar.s.johansson@ericsson.com > >> Cc: Kevin.Smith@vodafone.com; tsvwg@ietf.org > >> Betreff: Re: AW: [tsvwg] Fwd: Qs on your 5G L4S slides > >> > >> Ruediger, > >> > >> ==DOCSIS== > >> Whoa! NQB is not L4S traffic. NQB is a Diffserv codepoint. L4S is identified > by the ECN field. In DOCSIS the NQB Diffserv codepoint classifies into the > /same queue/ as L4S traffic (renamed the Low Latency queue due to its dual > role). Allowing in unresponsive traffic was only considered in DOCSIS because > there was already a sufficient policing function in front of the queue (per- > flow queue protection). > >> > >> ==Mobile== > >> If a mobile operator (or in this case a masters student), uses the ECT(1) > codepoint to classify traffic into a priority bearer, then it's not L4S. It's an ECN > codepoint intended for L4S but used (abused?) in a Diffserv priority > scheduler. > >> > >> The problem that the DualQ Coupled AQM solved was how to isolate low > latency flows without having to know how much bandwidth to set aside for > them. So if there are M L4S flows and N Classic flows, M and N can take any > value, including zero. That's because the coupling makes the two queues > appear as one - from a bandwidth and congestion control perspective > (approximately). > >> > >> So, if you have a Diffserv scheduler and no L4S mechanism, you would > need to go back to using traditional Diffserv techniques like guessing what M > and N might be most of the time, to decide how much bandwidth to > configure for a separate priority queue, then policing it. > >> > >> To summarize, the answers to your question: > >> > >> The underlying question is, to which extend does the end-to-end > performance of L4S depend on suitable radio schedulers coupling two > congestion control algos or queuing behaviours, like L4S standardises for > fixed line schedulers. And how to operate a network, if these are absent. > >> > >> An operator that wants to support any technology without deploying the > technology isn't going to get very far! L4S depends on using an L4S > mechanism (obviously), specifically the DualQ Coupled AQM (or FQ). How to > operate a network if L4S is absent - well, you go back to what you had > before. But then you can't support applications that need consistently low > latency /and/ the full available bandwidth, which is the point of L4S. > >> > >> > >> ==WiFi== > >> You say that the NQB draft "specifies mapping L4S to a priority bearer > based PHB". This is because NQB is having to cope with the WiFi situation as it > finds it. It's not ideal, but you'll see below how it could evolve to something > better. > >> I understand that the video access category (AC_VI) was the only choice > that offered decent enough latency without excessive bandwidth priority. > NQB just needs to be isolated from bursty traffic - it didn't choose AC_VI > because of any need for /bandwidth/ priority, per se. NQB should work with > quite weakly weighted priority as long as it's isolated. But that wasn't > available in current WiFI. > >> > >> > >> L4S is also walking into the WiFi environment as it finds it. With today's > non-L4S products, I would also recommend that the L4S-ECN codepoints are > mapped to the video access category, if possible. > >> Nokia's latest WiFi products (in the 'Beacon' range) already include an L4S > DualQ Coupled AQM. And as other L4S WiFi products come out, the coupling > will introduce the recommended congestion signals that can be used as back- > pressure against the priority scheduler. Users don't want to abuse scheduling > priority at the expense of the balance between their own applications. But > they have no choice until there's a mechanism that allows their applications > to balance against other apps. > >> > >> Finally, once there's an L4S queue in WiFi kit, NQB traffic could be > classified into it, as was done in DOCSIS. > >> > >> FQ offers an alternative path for WiFi - neither precludes the other. > >> > >> Does this help explain? > >> > >> > >> Bob > >> > >> On 15/03/2021 11:19, Ruediger.Geib@telekom.de wrote: > >> Hi Ingemar, > >> > >> I’m not having trouble with wireless default scheduling. I’d favour the > development of a DiffServ scheduler on packet layer combined with a > default scheduler below. It seems to me that 3 GPP choose different > approaches for 4G and 5G. > >> > >> I wonder which scheduling was recommended for 3GPP access types, if > there’s an RFC recommending a priority bearer for L4S at WiFi interfaces. > >> > >> Regards, > >> > >> Ruediger > >> > >> Von: Ingemar Johansson S <ingemar.s.johansson@ericsson.com> > >> Gesendet: Montag, 15. März 2021 12:08 > >> An: Geib, Rüdiger <Ruediger.Geib@telekom.de> > >> Cc: Kevin.Smith@vodafone.com; ietf@bobbriscoe.net; tsvwg@ietf.org; > >> Ingemar Johansson S <ingemar.s.johansson@ericsson.com> > >> Betreff: RE: [tsvwg] Fwd: Qs on your 5G L4S slides > >> > >> Hi Ruediger > >> > >> I can’t really comment on how this is handled for WiFi. But I also notice > that DOCSIS has a mechanism that demotes misbehaving L4S flows into a > classic queue. > >> > >> For 3GPP access already L4S with default bearers gives quite some > improvement. > >> The use of L4S with priority scheduling can enhance performance even > more but poses some additional concerns, where the use of a DBS scheduler > is one extreme in this context. There are other alternatives such as increased > scheduling weight that has a more limited impact on other traffic that runs on > default bearers. > >> But this problem is not unique to L4S. You would face the same issue with > e.g., GBR bearers for the cases where an endpoint gets in bad coverage. > Additional methods can be needed here to avoid that one bearer gets > unduly large share of the radio resources. > >> > >> /Ingemar > >> > >> From: Ruediger.Geib@telekom.de <Ruediger.Geib@telekom.de> > >> Sent: den 15 mars 2021 11:48 > >> To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com> > >> Cc: Kevin.Smith@vodafone.com; ietf@bobbriscoe.net; tsvwg@ietf.org > >> Subject: AW: [tsvwg] Fwd: Qs on your 5G L4S slides > >> > >> Hi Ingemar, > >> > >> That depends. For WiFi, draft-ietf-tsvwg-nqb-05 specifies mapping L4S to > a priority bearer based PHB. Then this stops to be an L4S problem. I’d like to > be clear about that issue and the question is, whether there will be a > recommendation to assign L4S traffic to a 4G or 5G priority bearer. If your > answer is no, why is there a draft specifying a priority bearer for WiFi L4S > traffic? > >> > >> The underlying question is, to which extend does the end-to-end > performance of L4S depend on suitable radio schedulers coupling two > congestion control algos or queuing behaviours, like L4S standardises for > fixed line schedulers. And how to operate a network, if these are absent. > >> > >> Regards, > >> > >> Ruediger > >> > >> Von: tsvwg <tsvwg-bounces@ietf.org> Im Auftrag von Ingemar > Johansson > >> S > >> Gesendet: Montag, 15. März 2021 10:55 > >> An: Smith, Kevin, Vodafone Group > >> <Kevin.Smith=40vodafone.com@dmarc.ietf.org>; Bob Briscoe > >> <ietf@bobbriscoe.net>; tsvwg IETF list <tsvwg@ietf.org> > >> Betreff: Re: [tsvwg] Fwd: Qs on your 5G L4S slides > >> > >> Hi Kevin, Bob + others > >> CC Davide (thesis author) > >> > >> Yes, there was a test with the use of the dedicated bearer (DBS) and no- > L4S. This is exemplified in section 5.3.6 in the thesis report. In short the > outcome is that the background traffic will be severely affected. The reason > is that the DBS scheduler (originally devised for e.g. VoLTE) prioritizes a > bearer when the queue delay exceeds a given low threshold (e.g 10ms). And > because SCReAM without L4S targets larger queue delay, the outcome is that > it will hog an unreasonable share of the available resourses. > >> What this means is that it is necessary to use some extra guard > mechanism when prioritized bearers are used, but this is of course not only > an L4S problem. > >> > >> /Ingemar > >> > >> * > >> http://www.diva- > portal.org/smash/record.jsf?pid=diva2%3A1484466&dswid > >> =-2512 > >> > >> > >> From: tsvwg <tsvwg-bounces@ietf.org> On Behalf Of Smith, Kevin, > >> Vodafone Group > >> Sent: den 12 mars 2021 14:56 > >> To: Bob Briscoe <ietf@bobbriscoe.net>; tsvwg IETF list > >> <tsvwg@ietf.org> > >> Subject: Re: [tsvwg] Fwd: Qs on your 5G L4S slides > >> > >> Hi Ingemar, > >> > >> Just to ask, was there also a variant of the test with no L4S but with the > dedicated bearer? I’d be interested to see that comparison. > >> > >> @Bob, regarding UPF placement: the ability to virtualise network > functions in 5G Core allows easier scaling of UPFs as required. > >> > >> All best, > >> Kevin > >> > >> > >> > >> > >> C2 General > >> From: tsvwg <tsvwg-bounces@ietf.org> On Behalf Of Bob Briscoe > >> Sent: 10 March 2021 17:41 > >> To: tsvwg IETF list <tsvwg@ietf.org> > >> Subject: [tsvwg] Fwd: Qs on your 5G L4S slides > >> > >> CYBER SECURITY WARNING: This email is from an external source - be > careful of attachments and links. Please follow the Cyber Code and report > suspicious emails. > >> tsvwg, > >> > >> Fwd'ing to list, with permission... > >> In case anyone else had the same questions > >> > >> > >> -------- Forwarded Message -------- > >> Subject: > >> RE: Qs on your 5G L4S slides > >> Date: > >> Wed, 10 Mar 2021 14:33:42 +0000 > >> From: > >> Ingemar Johansson S <ingemar.s.johansson@ericsson.com> > >> To: > >> Bob Briscoe <research@bobbriscoe.net> > >> CC: > >> Ingemar Johansson S <ingemar.s.johansson@ericsson.com> > >> > >> > >> Hi > >> Please see inline [IJ] > >> > >> /Ingemar > >> > >> -----Original Message----- > >> From: Bob Briscoe <research@bobbriscoe.net> > >> Sent: den 10 mars 2021 14:46 > >> To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com> > >> Subject: Qs on your 5G L4S slides > >> > >> Ingemar, > >> > >> #5 "Dedicated bearer / QoS flow for L4S traffic" > >> Is this a per-app microflow or a per-user flow? > >> [IJ] It is per-user flows, i.e each bearer can handle many flows > >> > >> > >> And I think you'll need to explain where the UPF is typically > >> located. I believe it's close to the edge, isn't i? > >> Further into the network (beyond the UPF) these flows just become an > >> aggregate of all the users. > >> [IJ] The UPF is close to the edge somehow, it is hard to say for certain > where they are located, they can be real close to the base stations or >100km > away. > >> > >> > >> #6 Question: > >> Do you have any feel for qDelay & throughput if a "Classic ECN AQM" > >> like PIE or CoDel was used? > >> [IJ] No, it was not studied in the master thesis work. > >> > >> > >> #6 - #11: > >> Is the DBS scheduler between users, or between flows? > >> [IJ] Per user (bearer) > >> > >> > >> #12: L4S is meant to greatly reduce the throughput-delay tradeoff, > >> and in our results it did. > >> Any idea why not here? I guess, with video, it's the 'getting up to > >> speed' fast problem (that I'm working on with Joakim). > >> [IJ] One reason is the large variation in frame sizes that video coders > generate. > >> Another is that SCReAM paces out the video frames as 50% higher rate > than the nominal video target bitrate. This pacing overhead can be > configured lower but then the video frames (RTP packets) are more likely to > become queued up in the sender instead. I really believe that it can be done > better, was hoping to have time to improve SCReAM in this respect but the > work hours fly in other directions . > >> With that said. Also a DCTCP flow (with L4S) marking will get a reduced > throughput compared to e.g a Cubic flow (without L4S) over cellular. The > reason is that the large buffers with Cubic absorb the fast fading dips in LTE > and NR. With DCTCP + L4S some extra headroom is needed to avoid queue > build up. > >> > >> > >> > >> Bob > >> > >> -- > >> > __________________________________________________________ > >> ______ > >> Bob Briscoe https://protect2.fireeye.com/v1/url?k=828d3ddc- > >> dd1604f1-828d7d47-8692dc8284cb-1ab58b5eb7943901&q=1&e=b0160f51- > >> 6418-41ea-9221-efaca6b7cec8&u=http%3A%2F%2Fbobbriscoe.net%2F > >> > >> > >> > >> -- > >> > __________________________________________________________ > ______ > >> Bob Briscoe > https://protect2.fireeye.com/v1/url?k=0cc72809-535c124c-0cc76892- > 867b36d1634c-7a8fce5d5cf6c799&q=1&e=fc65dd24-5896-4c96-b5bb- > 53165a19839c&u=http%3A%2F%2Fbobbriscoe.net%2F > > > > -- > > > __________________________________________________________ > ______ > > Bob Briscoe > > https://protect2.fireeye.com/v1/url?k=87b7b840-d82c8205-87b7f8db- > 867b3 > > 6d1634c-2d566c73105d61db&q=1&e=fc65dd24-5896-4c96-b5bb- > 53165a19839c&u=http%3A%2F%2Fbobbriscoe.net%2F
- [tsvwg] Fwd: Qs on your 5G L4S slides Bob Briscoe
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Smith, Kevin, Vodafone Group
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Ingemar Johansson S
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Ruediger.Geib
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Ingemar Johansson S
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Ruediger.Geib
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Ingemar Johansson S
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Bob Briscoe
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Greg White
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Bob Briscoe
- Re: [tsvwg] Qs on your 5G L4S slides Sebastian Moeller
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Sebastian Moeller
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Ruediger.Geib
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Bob Briscoe
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Sebastian Moeller
- Re: [tsvwg] Fwd: Qs on your 5G L4S slides Ingemar Johansson S