Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions
"Black, David" <David.Black@dell.com> Thu, 07 November 2019 21:00 UTC
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From: "Black, David" <David.Black@dell.com>
To: Sebastian Moeller <moeller0@gmx.de>, Greg White <g.white@CableLabs.com>
CC: tsvwg IETF list <tsvwg@ietf.org>, "Black, David" <David.Black@dell.com>
Thread-Topic: [tsvwg] draft-ietf-tsvwg-nqb, more questions
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tsvwg/LcHWt8fTdQ2yS2IuYMoSNGm1GN0>
Subject: Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions
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> > BTW, just to avoid confusion, I'm reading your "strong +1" to be solely > about adding warnings/advice in case the "final SHOULD" is not implemented > (and similar, for other SHOULDs in the draft as well). That's correct. Thanks, --David > -----Original Message----- > From: Sebastian Moeller <moeller0@gmx.de> > Sent: Thursday, November 7, 2019 3:53 PM > To: Greg White > Cc: Black, David; tsvwg IETF list > Subject: Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions > > > [EXTERNAL EMAIL] > > > > > On Nov 7, 2019, at 21:36, Greg White <g.white@CableLabs.com> wrote: > > > > Noted, and I agree that it is important. I'll write some appropriate warning > text. > > > > BTW, just to avoid confusion, I'm reading your "strong +1" to be solely > about adding warnings/advice in case the "final SHOULD" is not implemented > (and similar, for other SHOULDs in the draft as well). You also quoted some > text from Sebastian which was factually incorrect (that an AP complying with > the SHOULD is NQB aware). > > [SM] Are you talking about: > > "In order to preserve the incentives principle, WiFi systems SHOULD > configure the EDCA parameters for the Video Access Category to match > those of the Best Effort Access Category." > > in the context of non NQB-aware APs? How feasible di you think it will be to > expect all deployed APs to have the AC_VI EDCA parameters changed to > comply with this recommendations, especially in the light that almost no APs > actually offer to configure these parameters at all? Does it really make sense > to propose a SHOULD that is known to be almost impossible to actually > implement in virtually all existing APs? > I guess I must be misunderstanding you here, because the remedy for > (arguably) misusing a prioritization system can not really be "disable the > priority system", color me confuzed. > > Best Regards > Sebastian > > > > I'm assuming you weren't "+1" on his conclusions from that, but correct me > if I'm wrong. > > > > -Greg > > > > > > On 11/7/19, 1:02 PM, "Black, David" <David.Black@dell.com> wrote: > > > > I wanted to strongly +1 this portion of the discussion: > > > >>> The final SHOULD is intended to address your concern about > prioritization > >> (since it results in segregation without prioritization). > >> > >> [SM] Ah, in that case the AP needs to be be NQB aware anyway, > >> would it then not be better to use an appropriate scheduler/AQM in front > of > >> the AC_BE queue and keep all traffic in the same priority class? The > >> disadvantage of setting AC_VI to the same EDCA values as AC_BE is then > that > >> applications that expect an airtime access boost from using AC_VI will not > get > >> it any more (not necessarily a deal-breaker but certainly unexpected > enough > >> to merit clear communication of that side-effect). > >> > >>> Absent this requirement (or the ability to comply with it operationally), > the > >> operator would need to consider (and perhaps limit) which applications > are > >> allowed to be marked as NQB. This aspect isn't discussed in the draft, but > I > >> will add it based on your input. > >> > >> [SM] Great! I would guess the safest would be to have the NQB- > >> aware scheduler in an AP apply some (proportional) rate-limiting if NQB > >> traffic is getting preferential air-time access. > > > > This is an example of a good thing to do with all uses of "SHOULD" - at > least warn about the risks and/or consequences of not following the > "SHOULD" (or "SHOULD NOT"), and (even better) provide some advice on > staying out of serious trouble in that case (as will be done here). > > > > Thanks!, --David > > > >> -----Original Message----- > >> From: tsvwg <tsvwg-bounces@ietf.org> On Behalf Of Sebastian Moeller > >> Sent: Tuesday, November 5, 2019 3:59 AM > >> To: Greg White > >> Cc: tsvwg IETF list > >> Subject: Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions > >> > >> > >> [EXTERNAL EMAIL] > >> > >> Hi Greg, > >> > >> > >>> On Nov 5, 2019, at 01:28, Greg White <g.white@CableLabs.com> wrote: > >>> > >>> Hi Sebastian, > >>> > >>> Interoperability with existing WiFi equipment is an important aspect, > since > >> WiFi latency can be considerable. By default, many existing APs only > support > >> 4 priority queues, and thus it is not possible to meet all of the > requirements > >> of the NQB PHB (at least in this default configuration). > >> > >> [SM] I agree the question is how to deal with that "impedance > >> mismatch". > >> > >>> Nonetheless, it is possible to utilize two of the four queues in order to > >> meet some of the requirements, and thus provide some of the benefits > of > >> the NQB PHB. > >> > >> [SM] Unless you opt for selecting AC_BK for the NQB traffic, for most > >> users the value of NQB will be mostly in the priority boost on wifi and the > >> resulting air-time access advantage (which results in both lower latency > and > >> potentially higher bandwidth). > >> > >>> With proper configuration and/or policies, this can be done safely. > >> > >> [SM] Sure, I am concerned about the status quo wich does not entail > >> "proper configuration and/or policies", and hence I believe the NQB > special > >> treatment on WIFI should be opt-in and not "opt-out" (in quotes as most > >> endusers will not be able to opt-out). For thid reaon I believe that the > >> proposal to use a code point that by default is mapped to AC_BK is the > only > >> correct solution (as a bonus it seems that such a code point also has a > better > >> chance to survive transit over the internet). NQB-aware APs then simply > >> treat that NQB-codepoint however they want. If for example a priority > boost > >> is desired such an AP can easily implement the required rate-limiting so > that > >> AC_BE traffic does not get starved out. In short, I fully agree that special > >> treatment requires "proper configuration and/or policies" and the > desirable > >> strategy if that can not guaranteed should be "do no harm". > >> > >>> The final SHOULD is intended to address your concern about > prioritization > >> (since it results in segregation without prioritization). > >> > >> [SM] Ah, in that case the AP needs to be be NQB aware anyway, > >> would it then not be better to use an appropriate scheduler/AQM in front > of > >> the AC_BE queue and keep all traffic in the same priority class? The > >> disadvantage of setting AC_VI to the same EDCA values as AC_BE is then > that > >> applicatons that expect an airtime access boost from using AC_VI will not > get > >> it any more (not necessarily a deal-breaker but certainly unexpected > enough > >> to merit clear communication of that side-effect). > >> > >>> Absent this requirement (or the ability to comply with it operationally), > the > >> operator would need to consider (and perhaps limit) which applications > are > >> allowed to be marked as NQB. This aspect isn't discussed in the draft, but > I > >> will add it based on your input. > >> > >> [SM] Great! I would guess the safest would be to have the NQB- > >> aware scheduler in an AP apply some (proportional) rate-limiting if NQB > >> traffic is getting preferential air-time access. > >> > >>> > >>> Network operators understand the value of segregating NQB traffic on > WiFi > >> links, and will almost certainly select a DSCP in practice that achieves that > >> goal. > >> > >> [SM] That is exactly part of my concern with the default mapping to > >> AC_VI approach, I expect that very quickly a lot of traffic will utilize the > AC_VI > >> queue potentially starving normal AC_BE traffic in the process. > >> > >>> Assigning a different DSCP in this draft would do nothing to prevent > them > >> from doing so. > >> > >> [SM] Sure, but is that really a good justification for proposing a DSCP > >> with known side-effects? As far as I am concerned an RFC should propose > >> sane defaults and hope for the best. > >> > >>> Instead, what we need to do is clearly articulate how to make best use > of > >> the existing WiFi tools, and how to avoid conflicts. > >> > >> [SM] I believe the last two are mutually exclusive... > >> > >>> > >>> In existing RFCs, the IETF already recommends that video conferencing > >> applications mark their traffic as either AF4x or CS4, all of which get > mapped > >> to AC_VI. The remaining language in the NQB draft describes sparser > flows > >> than these. > >> > >> [SM] as an implementer I read "relatively low data rates", without > >> further guidance I have very little intuition what to use as reference. > Could > >> this be made more explicit? This is orthogonal to the question whether > such > >> a limit should be enforced in any way, here the question really is about > >> getting a feel what is considered acceptable for NQB treatment. > >> > >>> > >>> Based on your comments, I attempted to remove all text that could be > >> interpreted as recommending that high-data-rate traffic be marked NQB. > >> > >> [SM] Thanks, as long as the aggregate NQB traffic is relative sparse > >> compared to the available WiFi bandwidth (or the number of tx_ops) > most of > >> my WiFi concerns get less and less relevant. To be explicit, I do not object > on > >> principle to using AC_VI or even AC_VO as long as this does not eat > >> significantly into the tx_ops for AC_BE, the current draft improves in that > >> direction. Would it be possible to make this point even stronger? > >> > >>> It appears that I missed one instance (in the Introduction it gives > >> "interactive voice and video" as an example). Aside from this (which I can > >> correct), I think the draft currently recommends that NQB only be used > for > >> sparse traffic. That said, the section where this guidance is intended to be > >> given is still lacking in specificity, and poses some open questions that may > >> need to be addressed in a subsequent revision. > >> > >> [SM] Sounds great. Now this then cycles back to one of the other > >> open topics, "enforcement". Ideally NQB-aware APs should monitor both > >> queues and re-assign flows between them based on flow-behavior in > >> relation to time-variant bandwidth experienced by that flow. > >> > >> Best Regards > >> Sebastian > >> > >>> > >>> Best Regards, > >>> Greg > >>> > >>> > >>> On 11/4/19, 3:25 PM, "tsvwg on behalf of Sebastian Moeller" <tsvwg- > >> bounces@ietf.org on behalf of moeller0@gmx.de> wrote: > >>> > >>> Regarding https://datatracker.ietf.org/doc/draft-ietf-tsvwg- > >> nqb/?include_text=1 > >>> > >>> 7.3. WiFi Networks > >>> > >>> WiFi networking equipment compliant with 802.11e generally > supports > >>> either four or eight transmit queues and four sets of associated EDCA > >>> parameters (corresponding to the four WiFi Multimedia Access > >>> Categories) that are used to enable differentiated media access > >>> characteristics. Implementations typically utilize the IP DSCP field > >>> to select a transmit queue, but should be considered as Non- > >>> Differentiated Services-Compliant Nodes as described in Section 4 of > >>> [RFC2475]. As a result this document discusses interoperability with > >>> WiFi networks, as opposed to PHB compliance. > >>> > >>> As discussed in [RFC8325], most existing implementations use a > >>> default DSCP to User Priority mapping that utilizes the most > >>> significant three bits of the DiffServ Field to select "User > >>> Priority" which is then mapped to the four WMM Access Categories. > In > >>> order to increase the likelihood that NQB traffic is provided a > >>> separate queue from QB traffic in existing WiFi equipment, the 0x2A > >>> codepoint is preferred for NQB. This would map NQB to UP_5 which is > >>> in the "Video" Access Category. > >>> > >>> Systems that utilize [RFC8325], SHOULD map the NQB codepoint to > >> UP_5 > >>> in the "Video" Access Category. > >>> > >>> In order to preserve the incentives principle, WiFi systems SHOULD > >>> configure the EDCA parameters for the Video Access Category to > match > >>> those of the Best Effort Access Category. > >>> > >>> > >>> [SM] This last section is puzzling: if the wifi system configures AC_VI > with > >> EDCA parameters that match the AC_BE parameters, AC_VI ceases to be > >> different from AC_BE, in that case picking a codepoint that automatically > >> maps to CS0 and hence to AC_BE seems much safer, simpler and straight > >> forward to me. > >>> Especially since essentially none of the millions deployed WiFi APs out > >> there will a) have this configured like proposed already and b) none of the > >> consumer APs I know actually allow to easily adjust EDCA parameters at > all. I > >> guess I must be missing something and would be delighted to be shown > why > >> the proposed text is the right thing. > >>> My take on this still is, if NQB traffic is sufficiently sparse using AC_VI > can > >> be justified, but without any rate limits this has the potential of being > quite > >> unfair to concurrent APs on the same channel (as well as the neighboring > >> channels that overlap with the selected). > >>> I do not want to sound alarmist, but given the number of cable-ISP > WiFi- > >> APs (as indicated by a SSID containing the ISPs name) in my city, I believe > >> making sure that those APs will not basically start hogging most airtime > >> seems the prudent thing to do. If there are sufficient backstops in place > (like > >> rate limiting or automatic down-marking if the traffic is not sparse > enough) to > >> avoid the described situation, I am all for it. > >>> > >>> The text probably should also openly discuss that in WiFi/WMM the > four > >> available queues by design have different priorities, and by moving NQB > out > >> of the default AC_BE while leaving QB flows in there, this effectively runs > >> against the following text in the draft: "The NQB queue SHOULD be given > >> equal priority compared to queue-building traffic of equivalent > importance." > >> (leaving alone the question how an AP or a station is supposed to > measure > >> importance) > >>> > >>> > >>> Sebastian > >>> > >>> > > > > > >
- [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Dave Taht
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Black, David
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Greg White
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Sebastian Moeller
- Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions Ruediger.Geib