Re: [tsvwg] L4S drafts: Next Steps

Bob Briscoe <ietf@bobbriscoe.net> Thu, 11 March 2021 21:18 UTC

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To: "Black, David" <David.Black@dell.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>
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From: Bob Briscoe <ietf@bobbriscoe.net>
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Date: Thu, 11 Mar 2021 21:18:03 +0000
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Subject: Re: [tsvwg] L4S drafts: Next Steps
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David,

Where does the concern about transport protocol independence come from? 
No-one expects that to be a problem for L4S implementers.

Similarly RFC3168 became a PS when ECN was solely supported (and solely 
defined) for TCP over IP. No-one believed that it would not be possible 
to implement over other transports. Of course there could be practical 
difficulties, e.g. the API for setting ECN codepoints, different 
deployment difficulties, due to middlebox treatments, etc. But I don't 
think you are talking about those sort of difficulties, because you are 
talking about the requirements in the draft (that the authors set up as 
our goals for the L4S service right from the start).

Actually, there are already implementations of scalable CC over TCP 
(two), RMCAT/RTP/UDP, a proprietary protocol over UDP, there was a port 
to QUIC/UDP produced during a hackathon a couple of years ago, I don't 
know of others, but that doesn't mean there aren't people out there 
working on them. This doesn't say anything about how 'full' they are, 
but it does say that no-one's reported any problems with the 
requirements that are due to choice of transport protocol.

This is what I mean by "No, bring me a different rock" - new arbitrary 
requirements popping up, that are not good tests of whether the 
experiment will succeed, but which would send everyone spinning hamster 
wheels if we allowed them to pass unchallenged.


Bob

On 11/03/2021 20:08, Black, David wrote:
>
> >>          1. Transport-protocol-independent requirements to use L4S 
> service
>
> >>                        – Goal: Interoperability – multiple 
> transport protocols able to meet requirements
>
> >> • Specifications and/or implementations – WG decides what is sufficient
>
> >>                        – Location: draft-ietf-tsvwg-ecn-l4s-id
>
> >>
>
> > [BB] I think the number 'two' comes from wanting to be sure that 
> developers other than the author-team can understand the spec. 
> sufficiently to implement.
> >
> > Pls confirm that could also be satisfied by /each/ requirement 
> having been implemented by /at least one other/ team than the authors 
> (or reasonably expected to implement).
>
> No, definitely not confirmed.
>
> Use of the ECT(1) codepoint entails meeting all the requirements.  If 
> only TCP Prague will be able to meet all the requirements, then that 
> set of requirements for ECT(1) codepoint usage is not 
> transport-protocol-independent.
>
> Thanks, --David
>
> *From:* Bob Briscoe <ietf@bobbriscoe.net>
> *Sent:* Thursday, March 11, 2021 1:42 PM
> *To:* Black, David; tsvwg@ietf.org
> *Subject:* Re: [tsvwg] L4S drafts: Next Steps
>
> [EXTERNAL EMAIL]
>
> David,
>
> On 10/03/2021 18:01, Black, David wrote:
>
>     Bob,
>
>     Reproducing text from the slide used in today's meeting:
>
>     ------------------------
>
>     _L4S Drafts: What Needs To Be Done_
>
>     1. Transport-protocol-independent requirements to use L4S service
>
>     – Goal: Interoperability – multiple transport protocols able to
>     meet requirements
>
>     • Specifications and/or implementations – WG decides what is
>     sufficient
>
>     – Location: draft-ietf-tsvwg-ecn-l4s-id
>
>     2. Safety of Internet-wide L4S experiment
>
>     – Goal: L4S experiment unlikely to cause significant damage to the
>     Internet, and
>
>     • Any damage that results is expected to be tolerable
>
>     – Location: draft-white-tsvwg-l4s-ops (candidate for WG adoption)
>
>     • WG Last Call on l4s-ops draft not required to meet safety goal
>
>     • Criteria: WG “rough consensus” that each goal has been reached
>
>     – WG chairs will run initial consensus calls before next IETF
>     meeting week
>
>     ------------------------
>
>     This discussion is about the first goal:
>     Transport-protocol-independent requirements to use L4S service
>
>     > I accept that we're messing with core protocols here, so the bar
>     should be higher.
>
>     > But, 2 independent full implementations for an EXP would be way
>     beyond any interpretation of IETF process.
>
>     Two independent full implementations of protocols that meet the
>     requirements ought to suffice, but may not be necessary.
>
>     As stated on the slide (and quoted above): " Specifications and/or
>     implementations – WG decides what is sufficient."
>
>
> [BB] I think the number 'two' comes from wanting to be sure that 
> developers other than the author-team can understand the spec. 
> sufficiently to implement.
>
> Pls confirm that could also be satisfied by /each/ requirement having 
> been implemented by /at least one other/ team than the authors (or 
> reasonably expected to implement).
>
> The reason this is important is that there is a heavy performance 
> evaluation burden attached to each requirement, because they are 
> nearly all about impact on the queuing delay of other hosts (or impact 
> on throughput of others in the case of the Classic ECN AQM one).
>
> For a second CC developer to invest the time and effort in the 
> performance testing necessary for every requirement, they would have 
> to be very confident that the IETF was going to follow through with 
> codepoint assignment. A great job has been done in undermining that 
> confidence in the last couple of years.
>
> To be clear, there are many implementations of the network part, and a 
> load of network operators ready to deploy the network part. There's no 
> problem there (other than all those projects have gone cold waiting 
> for the IETF). The focus here is CC development, I assume.
>
>
>     > This part of your original email (which was as a chair) asked us
>     to /restructure/ the drafts. I said they already have the
>     structure you want.
>
>     > No reply to that point. Now what you talk about above (albeit as
>     an individual now) are wording changes not restructuring.
>
>     > We've been doing wording changes with the survey of
>     implementers. Fine with that.
>     >
>     > But I'd like confirmation (as a chair) that restructuring is not
>     needed.
>
>
>     Confirmed.
>
>
> Good. Thank you.
>
>
> Bob
>
>     Thanks, --David (as a TSVWG chair)
>
>     *From:* Bob Briscoe <ietf@bobbriscoe.net>
>     <mailto:ietf@bobbriscoe.net>
>     *Sent:* Wednesday, March 10, 2021 7:53 AM
>     *To:* Black, David; tsvwg@ietf.org <mailto:tsvwg@ietf.org>
>     *Subject:* Re: [tsvwg] L4S drafts: Next Steps
>
>     [EXTERNAL EMAIL]
>
>     David,
>
>     As you've just pointed this old thread out, I'll continue on this
>     thread. See [BB] inline...
>
>     On 09/12/2020 22:28, Black, David wrote:
>
>         Bob,
>
>         Reminder of the goal for [1] (Rework the “Prague Requirements”
>         into the following two entities ...):
>
>              >> Success of this exercise will be judged by the WG
>         reaching “rough consensus” that multiple transport protocol
>         implementations
>              >> currently meet and/or are reasonably expected to be
>         able to meet the normative requirements (a).
>
>         If the L4S folks believe that this has already been done, then
>         it’s time to start bringing forward the multiple transport
>         protocols that demonstrate success of that exercise.
>
>
>     [BB] This is understood and fine. This is where our focus is.
>
>     I assume readers are aware that the IETF's requirement for 2
>     independent implementations is for progressions from Proposed
>     Standard to full Internet Standard, and few RFCs have ever taken
>     that step (only 118 RFCs are STDs or parts of STDs) (e.g. RFC3168
>     is not).
>     https://www.rfc-editor.org/search/rfc_search_detail.php?sortkey=Number&sorting=DESC&page=All&pubstatus%5B%5D=Standards%20Track&std_trk=Internet%20Standard
>     <https://www.rfc-editor.org/search/rfc_search_detail.php?sortkey=Number&sorting=DESC&page=All&pubstatus%5B%5D=Standards%20Track&std_trk=Internet%20Standard>
>
>     I accept that we're messing with core protocols here, so the bar
>     should be higher. But, 2 independent full implementations for an
>     EXP would be way beyond any interpretation of IETF process.
>
>
>
>
>         >Nonetheless, if there are specific items in S.4 that someone
>         believes should or shouldn't be there, or should be worded
>         differently, let's have those discussions now on the list -
>         I'm all ears
>
>         Speaking only for myself as an individual beyond this point,
>         these two normative requirements struck me as ones that might
>         be better stated as design and implementation guidelines:
>
>           
>
>             o  A scalable congestion control MUST eliminate RTT bias as much as
>
>                possible in the range between the minimum likely RTT and typical
>
>                RTTs expected in the intended deployment scenario (see
>
>                Appendix A.1.5  <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-ecn-l4s-id-12#appendix-A.1.5>  for rationale).
>
>           
>
>             o  A scalable congestion control SHOULD remain responsive to
>
>                congestion when typical RTTs over the public Internet are
>
>                significantly smaller because they are no longer inflated by
>
>                queuing delay (seeAppendix A.1.6  <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-ecn-l4s-id-12#appendix-A.1.6>  for rationale).
>
>         The use of “as much as possible” in the first bullet makes it
>         hard to figure out whether a specific congestion control meets
>         that mandatory requirement for participation in the L4S
>         experiment.  The second bullet appears to involve a prediction
>         of the future as currently written.
>
>
>     [BB] I'll refrain from getting into text-specifics in this thread,
>     'cos I'm trying to be absolutely sure I understand what the chairs
>     want. We've felt subjected to a "No, bring me a different rock"
>     process so far, so we want to be absolutely clear what sort of
>     rock you want.
>
>     This part of your original email (which was as a chair) asked us
>     to /restructure/ the drafts. I said they already have the
>     structure you want. No reply to that point. Now what you talk
>     about above (albeit as an individual now) are wording changes not
>     restructuring. We've been doing wording changes with the survey of
>     implementers. Fine with that.
>
>     But I'd like confirmation (as a chair) that restructuring is not
>     needed.
>
>     ==============================================================================================
>     FYI, here's the structure of the transport requirements (I already
>     explained this in the previous email in this thread):
>
>     ecn-l4s-id
>     * Sec.4. (Normative) Transport Layer Behaviour
>         All the factors that involve potential harm to others
>     (containing MUSTs and now some SHOULDs)
>         With a pointer from each one to further guidance in Appx A.1
>     * Sec 5 (Normative) Network Node Behaviour
>     ...
>     * Appx A.1 (Informative) Requirements for Scalable Transport Protocols
>         Guidance on features that involve potential harm to others
>     * Appx A.2 (Informative) Scalable Transport Protocol Optimizations
>        Guidance on features that would benefit the flow itself
>
>     draft-briscoe-iccrg-prague-congestion-control (just posted)
>     * Detailed guidance, specification, implementation notes, etc.
>
>
>
>     Bob
>
>
>
>         Thanks, --David
>
>         *From:* Bob Briscoe <ietf@bobbriscoe.net>
>         <mailto:ietf@bobbriscoe.net>
>         *Sent:* Tuesday, December 8, 2020 6:01 PM
>         *To:* Black, David; tsvwg@ietf.org <mailto:tsvwg@ietf.org>
>         *Subject:* Re: [tsvwg] L4S drafts: Next Steps
>
>         [EXTERNAL EMAIL]
>
>         David and chairs,
>
>         On 04/12/2020 15:54, Black, David wrote:
>
>             The WG chairs have consulted among ourselves and with our
>             AD (Martin Duke).
>
>             Our guidance to the WG and the L4S draft authors is that
>             at least the following two things need to be done before
>             WGLC will become possible on the L4S drafts:
>
>             [1] Rework the “Prague Requirements” into the following
>             two entities, which will overlap:
>
>             1.Transport-protocol-agnostic normative requirements for
>             all congestion-controlled traffic that uses the L4S low
>             latency queue.
>
>             1.The DualQ AQM design relies upon traffic adhering to
>             these requirements.
>
>             2.Design and implementation guidelines for new congestion
>             controls that meet the normative requirements (a).
>
>             1.Ultimately, the choice of whether a particular aspect is
>             a guideline (b) or requirement (a) is a WG “rough
>             consensus” decision.
>
>
>         [BB] I believe draft-ietf-tsvwg-ecn-l4s-id is already
>         structured for this division between normative requirements
>         and design and implementation guidelines.
>         * [1]a) is Section 4 "Prerequisite Transport Layer Behaviour".
>         Nearly every paragraph also refers off to subsections of
>         Appendix A.1 for extra non-normative info, headed
>         "Requirements for Scalable Transport Protocols". [Actually, it
>         might be useful to swap these two headings]
>         * [1]b) is Appendix A.2: "Scalable Transport Protocol
>         Optimizations"
>
>         The rule that determined which aspect went in which was:
>         [1]a) if it's about an aspect of one transport's behaviour
>         that has potential to impact/harm others
>         [1]b) if it's solely about how a transport can improve it's
>         own performance.
>         They have been divided like that from the very first ad hoc
>         meeting in Prague that formulated them (in 2015)
>
>         Code to address all the requirements and most of the
>         optimizations has been implemented. Over the last year, 3 or 4
>         of the later requirements in a) have become SHOULDs not MUSTs.
>         Personally I would have left most as MUSTs, but I've tried to
>         reflect what the WG wanted. Those demoted to SHOULD have
>         generally been considered a lower risk of harm (either low
>         likelihood of occuring or minor harm if they do) - taking into
>         account the complexity of implementing them.
>
>         We could certainly flag the point where the transition from
>         MUSTs to SHOULDs occurs within section 4. But I think we
>         should still group all the items with potential for harm
>         together in the same section. Because assessment of risk will
>         change as the Internet landscape changes (possibly over the
>         duration of the experiment).
>
>         Now I've explained, I hope the chairs will all agree that
>         "rework the Prague Requirements into two entities" (normative
>         requirements and design and implementation guidelines) is
>         already done and dusted.
>
>         Nonetheless, if there are specific items in S.4 that someone
>         believes should or shouldn't be there, or should be worded
>         differently, let's have those discussions now on the list -
>         I'm all ears.
>
>
>
>         Bob
>
>
>
>
>                  Success of this exercise will be judged by the WG
>             reaching “rough consensus” that multiple transport
>             protocol implementations
>                  currently meet and/or are reasonably expected to be
>             able to meet the normative requirements (a).
>
>             [2] Build the safety case for L4S experimental
>             Internet-wide deployment in the L4S Ops draft.
>
>             1.This safety case does not rely on endpoints running TCP
>             Prague, though it can assume endpoints are meeting the
>             reworked Prague requirements
>
>             2.Ops draft will provide guidance on how to detect L4S
>             problems on their RFC 3168 network, and how to mitigate them.
>
>             3.Ops draft must consider these scenarios:
>
>             1. An unsophisticated user purchases an L4S endpoint and
>             runs it on a service provider's single-queue RFC 3168 network.
>
>             2. L4S traffic from another domain enters an RFC 3168
>             single-queue network (e.g. a peer-to-peer application)
>
>                  Success of this exercise will be judged by the WG
>             reaching “rough consensus” that deployment of the L4S
>             experiment
>                  is unlikely to cause significant damage to the
>             Internet, and that any damage that results is expected to
>             be tolerable.
>
>             Thanks, --David [as TSVWG WG co-chair]
>
>             ----------------------------------------------------------------
>
>             David L. Black, Senior Distinguished Engineer
>
>             Dell Technologies, Infrastructure Systems Group
>
>             176 South St., Hopkinton, MA  01748
>
>             +1 (774) 350-9323 <tel:+17743509323> Mobile: +1 (978)
>             394-7754 <tel:+19783947754>
>
>             David.Black@dell.com <mailto:David.Black@dell.com>
>
>             ----------------------------------------------------------------
>
>
>
>
>
>         -- 
>
>         ________________________________________________________________
>
>         Bob Briscoehttp://bobbriscoe.net/  <http://bobbriscoe.net/>
>
>
>
>
>     -- 
>
>     ________________________________________________________________
>
>     Bob Briscoehttp://bobbriscoe.net/  <http://bobbriscoe.net/>
>
>
>
> -- 
> ________________________________________________________________
> Bob Briscoehttp://bobbriscoe.net/  <http://bobbriscoe.net/>

-- 
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/