Identifying Modified Explicit Congestion Notification (ECN) Semantics for Ultra-Low Queuing Delay (L4S)
draft-ietf-tsvwg-ecn-l4s-id-13

Document Type Active Internet-Draft (tsvwg WG)
Authors Koen De Schepper  , Bob Briscoe 
Last updated 2021-02-22
Replaces draft-briscoe-tsvwg-ecn-l4s-id
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Document shepherd Wesley Eddy
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Send notices to Wesley Eddy <wes@mti-systems.com>
Transport Services (tsv)                                  K. De Schepper
Internet-Draft                                           Nokia Bell Labs
Intended status: Experimental                            B. Briscoe, Ed.
Expires: August 26, 2021                                     Independent
                                                       February 22, 2021

 Identifying Modified Explicit Congestion Notification (ECN) Semantics
                   for Ultra-Low Queuing Delay (L4S)
                     draft-ietf-tsvwg-ecn-l4s-id-13

Abstract

   This specification defines the identifier to be used on IP packets
   for a new network service called low latency, low loss and scalable
   throughput (L4S).  L4S uses an Explicit Congestion Notification (ECN)
   scheme that is similar to the original (or 'Classic') ECN approach.
   'Classic' ECN marking was required to be equivalent to a drop, both
   when applied in the network and when responded to by a transport.
   Unlike 'Classic' ECN marking, for packets carrying the L4S
   identifier, the network applies marking more immediately and more
   aggressively than drop, and the transport response to each mark is
   reduced and smoothed relative to that for drop.  The two changes
   counterbalance each other so that the throughput of an L4S flow will
   be roughly the same as a non-L4S flow under the same conditions.
   Nonetheless, the much more frequent control signals and the finer
   responses to them result in much more fine-grained adjustments, so
   that ultra-low and consistently low queuing delay (typically sub-
   millisecond on average) becomes possible for L4S traffic without
   compromising link utilization.  Thus even capacity-seeking (TCP-like)
   traffic can have high bandwidth and very low delay at the same time,
   even during periods of high traffic load.

   The L4S identifier defined in this document distinguishes L4S from
   'Classic' (e.g. TCP-Reno-friendly) traffic.  It gives an incremental
   migration path so that suitably modified network bottlenecks can
   distinguish and isolate existing traffic that still follows the
   Classic behaviour, to prevent it degrading the low queuing delay and
   low loss of L4S traffic.  This specification defines the rules that
   L4S transports and network elements need to follow to ensure they
   neither harm each other's performance nor that of Classic traffic.
   Examples of new active queue management (AQM) marking algorithms and
   examples of new transports (whether TCP-like or real-time) are
   specified separately.

De Schepper & Briscoe    Expires August 26, 2021                [Page 1]
Internet-Draft     ECN Semantics for Low Queuing Delay     February 2021

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 26, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Latency, Loss and Scaling Problems  . . . . . . . . . . .   5
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   7
     1.3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   2.  Consensus Choice of L4S Packet Identifier: Requirements . . .   9
   3.  L4S Packet Identification at Run-Time . . . . . . . . . . . .  10
   4.  Prerequisite Transport Layer Behaviour (the 'Prague
       Requirements')  . . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  Prerequisite Codepoint Setting  . . . . . . . . . . . . .  11
     4.2.  Prerequisite Transport Feedback . . . . . . . . . . . . .  11
     4.3.  Prerequisite Congestion Response  . . . . . . . . . . . .  12
     4.4.  Filtering or Smoothing of ECN Feedback  . . . . . . . . .  14
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