Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions
Greg White <g.white@CableLabs.com> Thu, 07 November 2019 21:40 UTC
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From: Greg White <g.white@CableLabs.com>
To: Sebastian Moeller <moeller0@gmx.de>, "Black, David" <David.Black@dell.com>
CC: tsvwg IETF list <tsvwg@ietf.org>
Thread-Topic: [tsvwg] draft-ietf-tsvwg-nqb, more questions
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Subject: Re: [tsvwg] draft-ietf-tsvwg-nqb, more questions
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Sebastian, As far as I am aware, EDCA parameters are adjustable via user configuration on many Access Points. It is available via the factory firmware in some cases, and it is available via openWRT. -Greg On 11/7/19, 2:04 PM, "Sebastian Moeller" <moeller0@gmx.de> wrote: Hi David, > On Nov 7, 2019, at 22:00, Black, David <David.Black@dell.com> wrote: > >>> 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. Regarding my point, what is the purpose of adding SHOULDs that for all means and purposes are impossible to see quantitatively implemented, even if the consequences are well discussed? Sebastian > > 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