Re: [tsvwg] L4S drafts: Next Steps

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

>>          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 <[e-mail]>
Sent: Thursday, March 11, 2021 1:42 PM
To: Black, David; [e-mail]
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 <[e-mail]><mailto:[e-mail]>
Sent: Wednesday, March 10, 2021 7:53 AM
To: Black, David; [e-mail]<mailto:[e-mail]>
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

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 (see Appendix 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 <[e-mail]><mailto:[e-mail]>
Sent: Tuesday, December 8, 2020 6:01 PM
To: Black, David; [e-mail]<mailto:[e-mail]>
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]
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David L. Black, Senior Distinguished Engineer
Dell Technologies, Infrastructure Systems Group
176 South St., Hopkinton, MA  01748
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[e-mail]<mailto:[e-mail]>
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________________________________________________________________

Bob Briscoe                               http://bobbriscoe.net/




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________________________________________________________________

Bob Briscoe                               http://bobbriscoe.net/



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________________________________________________________________

Bob Briscoe                               http://bobbriscoe.net/