Identifying Modified Explicit Congestion Notification (ECN) Semantics for Ultra-Low Queuing Delay (L4S)
draft-ietf-tsvwg-ecn-l4s-id-10

Document Type Active Internet-Draft (tsvwg WG)
Last updated 2020-03-09
Replaces draft-briscoe-tsvwg-ecn-l4s-id
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Transport Services (tsv)                                  K. De Schepper
Internet-Draft                                           Nokia Bell Labs
Intended status: Experimental                            B. Briscoe, Ed.
Expires: September 10, 2020                                  Independent
                                                           March 9, 2020

 Identifying Modified Explicit Congestion Notification (ECN) Semantics
                   for Ultra-Low Queuing Delay (L4S)
                     draft-ietf-tsvwg-ecn-l4s-id-10

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).  It is similar to the original (or 'Classic')
   Explicit Congestion Notification (ECN).  '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
   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 September 10, 2020               [Page 1]
Internet-Draft     ECN Semantics for Low Queuing Delay        March 2020

Status of This Memo

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Copyright Notice

   Copyright (c) 2020 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  . . . . . . . . . . .  11
     4.1.  Prerequisite Codepoint Setting  . . . . . . . . . . . . .  11
     4.2.  Prerequisite Transport Feedback . . . . . . . . . . . . .  11
     4.3.  Prerequisite Congestion Response  . . . . . . . . . . . .  12
   5.  Prerequisite Network Node Behaviour . . . . . . . . . . . . .  14
     5.1.  Prerequisite Classification and Re-Marking Behaviour  . .  14
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