Identifying Modified Explicit Congestion Notification (ECN) Semantics for Ultra-Low Queuing Delay (L4S)
draft-ietf-tsvwg-ecn-l4s-id-09

Document Type Active Internet-Draft (tsvwg WG)
Last updated 2020-02-20
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 23, 2020                                     Independent
                                                       February 20, 2020

 Identifying Modified Explicit Congestion Notification (ECN) Semantics
                   for Ultra-Low Queuing Delay (L4S)
                     draft-ietf-tsvwg-ecn-l4s-id-09

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 ultra-low
   queuing delay (sub-millisecond) for L4S traffic without compromising
   link utilization, and this low delay can be maintained during high
   traffic load.

   The L4S identifier defined in this document is the key piece that
   distinguishes L4S from TCP-Reno-Friendly (or 'Classic') traffic.  It
   gives an incremental migration path so that suitably modified network
   bottlenecks can distinguish and isolate existing Classic traffic from
   L4S traffic to prevent it from degrading the ultra-low queuing delay
   and loss of the new scalable transports, without harming Classic
   performance.  Examples of new active queue management (AQM) marking
   algorithms and examples of new transports (whether TCP-like or real-
   time) are specified separately.

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
   Task Force (IETF).  Note that other groups may also distribute

De Schepper & Briscoe    Expires August 23, 2020                [Page 1]
Internet-Draft     ECN Semantics for Low Queuing Delay     February 2020

   working documents as Internet-Drafts.  The list of current Internet-
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   This Internet-Draft will expire on August 23, 2020.

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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Latency, Loss and Scaling Problems  . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   7
     1.3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   2.  Consensus Choice of L4S Packet Identifier: Requirements . . .   9
   3.  L4S Packet Identification at Run-Time . . . . . . . . . . . .  10
   4.  Prerequisite Transport Layer Behaviour  . . . . . . . . . . .  10
     4.1.  Prerequisite Codepoint Setting  . . . . . . . . . . . . .  10
     4.2.  Prerequisite Transport Feedback . . . . . . . . . . . . .  10
     4.3.  Prerequisite Congestion Response  . . . . . . . . . . . .  11
   5.  Prerequisite Network Node Behaviour . . . . . . . . . . . . .  13
     5.1.  Prerequisite Classification and Re-Marking Behaviour  . .  13
     5.2.  The Meaning of L4S CE Relative to Drop  . . . . . . . . .  14
     5.3.  Exception for L4S Packet Identification by Network Nodes
           with Transport-Layer Awareness  . . . . . . . . . . . . .  15
     5.4.  Interaction of the L4S Identifier with other Identifiers   15
       5.4.1.  DualQ Examples of Other Identifiers Complementing L4S
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