Re: [tsvwg] L4S drafts: Next Steps

["Black, David" <[e-mail]>]

> What I believe David Black is referring to - and I'm sure he'll correct me if necessary - is the (hopefully uncontroversial) notion that a specification
> is useless if it cannot be implemented, and indeed not very useful if distinct implementations are not automatically interoperable with each other.

That's the core idea.  In more detail, the transport requirements for use of the L4S service (section 4 of draft-ietf-tsvwg-ecn-l4s-id-14, particularly section 4.3 on congestion response) define a functional interface between the network and transport protocols, an interface that needs to interoperate with a variety of transport protocols in order to realize the L4S goal of being a widely usable service.  Looking back over the past few years, in 20/20 hindsight, some of these requirements were initially written too strictly to the point of being infeasible.

Turning to the current situation, the claim (in email below) that "No-one expects that [meeting these requirements] to be a problem for L4S implementers" does not align with the two "Needs experimental data" slides in Koen's meeting presentation on these requirements (see slides 6 and 7 of: https://datatracker.ietf.org/meeting/110/materials/slides-110-tsvwg-sessb-73-prague-requirements-00).  I have no problem with evaluation of some of these requirements being goals of the L4S experiment - if that is done, then mandating that the requirements involved be met in order to participate in the L4S experiment appears to set the bar for experimental use of ECT(1) too high.  To make this concrete, one of the "Needs experimental data" items (first item on slide 7) is:

		o MUST implement monitoring to detect non_L4S ECN AQM...
		   - Is detection itself required?
		   - Robust detection scheme needs real deployment experience.
		   - Combination with delay based control could minimize potential issues
		   - Develop during experiment as needed.

To purse such a course of action, "MUST implement monitoring to detect non_L4S ECN AQM..." cannot survive as a normative requirement (MUST) for use of the ECT(1) codepoint in the L4S experiment, although it would be fine to encourage that monitoring to be implemented.  If this sort of approach of converting problematic requirements to implementation guidance and/or goals to be evaluated by the experiment is followed for all of the "Needs experimental data" items, then the resulting WG consensus call on feasibility of the remaining requirements (effectively the rest of the contents of Koen's slides, including removal of the objectionable documentation requirements) should be quick and easy.

The l4s-ops draft would need to align with any resulting changes.

Thanks, --David

-----Original Message-----
From: Jonathan Morton <[e-mail]> 
Sent: Thursday, March 11, 2021 5:56 PM
To: Bob Briscoe
Cc: Black, David; [e-mail]
Subject: Re: [tsvwg] L4S drafts: Next Steps


[EXTERNAL EMAIL] 

> On 12 Mar, 2021, at 12:07 am, Bob Briscoe <[e-mail]> wrote:
> 
> The concern is requiring unnecessary work to prove things that are "bring me a different rock" exercises.

That does appear to be *your* concern at the moment.  I am merely trying to interpret the concerns of other people for your benefit.  Neither you nor I are the sole arbiters of what valid concerns may or may not exist.  I would however encourage you to consider what I have recently said about "externalised risk"; I can find a link to the YouTube recording of my talk the other day, if that would be helpful.

What I believe David Black is referring to - and I'm sure he'll correct me if necessary - is the (hopefully uncontroversial) notion that a specification is useless if it cannot be implemented, and indeed not very useful if distinct implementations are not automatically interoperable with each other.  This is part of the IETF credo of "rough consensus and running code".

As he explained, it is not necessary for two independent implementations to actually exist for an Experimental or Proposed Standard RFC, so long as there's a reasonable expectation that a second complete implementation is achievable by an ordinarily skilled practitioner of the art (to borrow some patent law jargon).  The existence of *one* complete implementation would, however, appear to be a prerequisite for such a determination.  If such an implementation is open-source and well documented, it's reasonable to expect a second implementer to refer to it in minor cases of doubt - but the major facets of requirement must also be well described in the specification.

I have entirely separate concerns about the specification itself, which I will keep to other threads.

 - Jonathan Morton