Subject: [tsvwg] Low Latency Low Loss and Scalable Throughput (L4S) updates

From: Bob Briscoe <[email-masked]>
Date: Wed, 11 Jul 2018 23:09:31 +0100

Folks,

In this IETF cycle we've updated 2 of the 3 tsvwg L4S drafts. And we 
updated the informational one about interaction with Diffserv (which is 
still an individual draft). Each has 1 or 2 main changes described 
below, as well as numerous small updates. Pls use the diff facility for 
details.

      Identifying Modified ECN Semantics for Ultra-Low Queuing Delay
      (L4S); draft-ietf-tsvwg-ecn-l4s-id-03
      <https://tools.ietf.org/html/draft-ietf-tsvwg-ecn-l4s-id-03>

  * Additional requirement for scalable (L4S) congestion controls: MUST
    NOT detect loss in units of packets (e.g. 3DupACK), instead MUST
    count in units of time (c.f. RACK).
      o Rationale is given in a new appendix section A.1.7. Measuring
        Reordering Tolerance in Time Units
        <https://tools.ietf.org/html/draft-ietf-tsvwg-ecn-l4s-id-03#appendix-A.1.7>.
        Essentially, it gives certainty to an L4S queue in the network,
        so it can relax ordering, which removes head-of-line blocking.
      o I expect to spend a good deal of the allotted presentation slot
        in Montreal explaining this, 'cos it's powerful but subtle. Or
        you can read the appendix.
  * The other main change is a better explanation of the "A.2.3. Faster
    Convergence at Flow Start" problem. We will be presenting a solution
    to this called Paced Chirping in ICCRG, which has led to deeper
    understanding of the problem too.

      DualQ Coupled AQMs for L4S; draft-ietf-tsvwg-aqm-dualq-coupled-05
      <https://tools.ietf.org/html/draft-ietf-tsvwg-aqm-dualq-coupled-05>

  * Closed off open issue on defining flexibility for operators to add
    classifiers.
      o Essentially, the classifier MUST NOT alter ECN or Diffserv
        codepoints to reflect its reclassification. Also the draft now
        contains rules on how an AQM does ECN-marking of reclassified
        packets given their ECN codepoint will often be unexpected in a
        particular queue.

      Interactions between L4S and Diffserv;
      draft-briscoe-tsvwg-l4s-diffserv-01
      <https://tools.ietf.org/html/draft-briscoe-tsvwg-l4s-diffserv-01>

  * Removed CS5 (application signalling) from list of Diffserv
    codepoints compatible with the L4S service, 'cos it's used for
    broadcast video by at least one major vendor.

Cheers

Bob

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