Minutes interim-2020-tsvwg-01: Thu 09:00

Meeting Minutes Transport Area Working Group (tsvwg) WG
Title Minutes interim-2020-tsvwg-01: Thu 09:00
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Last updated 2020-03-04

Meeting Minutes

   TSVWG Virtual Interim (2/20/2020 - 9am-11am US/Eastern)

Posted agenda:
1. Agenda bashing (chairs - 1 min)
2. Plan for Vancouver (David Black's charts - ~10min)
3. Some Congestion Experienced (Morton/Heist/Grimes/etc.? - ~30 min)
4. Update on status and near-term plans for the set of L4S drafts (Bob? - 4 min)
5. Update on L4S & TCP Prague implementation, test, evaluation
(Greg/Bob/Koen? - 15 min)
6. L4S Issues List Discussion (goal is to see if we can agree on what more
needs to be done on each issue to suffice for Experimental/Informational RFCs):
    6.1 Discuss status on (Bob - ~30 min):
          #16 on classic ECN interaction
          #21 CE codepoint semantics (closely related to #16)
          #20 ECT(1) codepoint usage
    6.2  Discuss plans forward to address (Bob - ~15 min):
          #26 on admission control
          #27 on terminology
          #22 on deployment feasibility
          #24 on evaluation & testing results
          #28 on DualQ suitability
    6.3 (We will try to handle the issues below by mailing list prior to the
        If needed, discuss close-out of (~15 min):
          #25 on IPR
          #18 on loss detection in time-units
          #23 on implementation status
          #19 on the single codepoint
          #17 on FQ interaction

1. Agenda bashing - David Black indicated we'd like to make sure to have 30
minutes for SCE discussion.

2. Plan for Vancouver - David Black led discussion "ECT(1) and the Internet"

- TSVWG chairs propose to make decision in Vancouver on what ECT(1) is used for.
- Need to determine for the Internet whether ECT(1) is an input (as in L4s) or
output (as in SCE) - Koen and asked about the distinction between choosing
between input/output and L4S/SCE. - Steve Blake mentioned that L4S could be
made compatible with each. - Use of DSCP to scope this was discussed.  At least
with L4S, this is not the current approach (mentioned by Gorry and David). -
Jake Holland asked about the decision not to use DSCP.  David replied that due
to DSCP bleaching, there can be problems at AS boundaries. - Steve Blake noted
anyone running these experiments will tinker with boxes, so may handle the DSCP
bleaching concern. - Jonathan Morton said this looks good. - Jake Holland noted
the FQ statement "no coexistence problems" is too strong.  David will adjust
this. - Steve explained that routers will have to change for either approach. 
Gorry and David answered there may be some routers that haven't changed on the
path. - Question of "what is starvation" should be taken offline.

3. Some Congestion Experienced - presented by Jonathan Morton and Pete Heist

- This covered 4 drafts (sce, codel-approx-fair, lightweight-fair-queueing,
cheap-nasty-queuing). - Asking for SCE adoption by TSVWG, but not expecting
decision today. - SCE problem statement and goals summarized. - Results from
several test scenarios were shared, showing how SCE works. - LFQ was explained
and some results with LFQ were shared. - CNQ-CodelAF (Controlled Delay
Approximate Fairness) was introduced and test scenario results shown. -
Approach on RTT fairness will be to adapt CUBIC.

- Greg White asked about LFQ and uses of FIFOs.  Jonathan explained 3 FIFO
construction for recirculation. - Greg asked if AF eliminated the latency
benefit for SCE.  Jonathan explained this is due to a single queue. - The point
of CNQ-CodelAF is that SCE can use the spare capacity.

- Gorry asked about latency benefits.  Jonathan explained eliminating the
sawtooth. - David clarified question as what needs to be done in the network to
acheive lower latency for SCE flows. - Jonathan explained best option is FQ,
and will discuss more w/ Gorry offline. - Pete explained CodelAF in single
queue is an approach to incremental deployment. - Bob mentioned it should work
right away in order to get deployed, or there is no benefit to deploying. -
Pete pointed out improved link utilization. - Greg White asked if data is
anecdotal cases and time series, rather than wider range, CDFs.

4. L4S Draft Status - updates discussed by Bob Briscoe

- overviewed changes to drafts, some just recently uploaded.

5. L4S and TCP Prague status - discussed by Bob Briscoe

- L4S implementation status overview provided.
- Only reference implementation discussed here, others for IETF 107.
- Evaluation in progress for reducing RTT dependence.
- classic bottleneck detection algorithm discussed (for issue #16)
  - score-based gradual transition, not modal
  - should take question offline on hysteresis and oscillation; Bob's answer is
  around stickiness rather than hysteresis. - paper available is just the
  design, evaluation is starting, Linux TCP Prague work by Asad Ahmed
- RTT Independence in TCP Prague work by Olivier Tilmans & Koen De Schepper
  - described impact of queuing delays and shorter L4S queues
  - explained new Prague add-on to steer RTT dependence, controlling additive
  increase and EWMA update frequency
- demo video played
  - Sebastian Moeller asked about the issue with dual queue's only approximate
  sharing, and short L4S queue crowding out the classic queue - Koen responded
  about policing functionality in the network at appropriate places. - There
  should be continued discussion on the distinction between requirements for
  flows to get into the L4S queue versus means to enforce them.
- Accurate ECN feedback in TCP implemented by Ilpo Jaarvinen in Linux
- Paced chirping code is being worked on in TCP Prague (Joakim Misund)
- Bob says all code has been available for some time.

6. L4S Issues List Discussion
- Issue #16 - interaction w/ 3168-only ECN
  - should still remain open, but making progress on detection/fallback

Meeting officially concluded based on time; some participants continued on the
webex session to discuss additional issues list items as "hallway conversation".