Identifying Modified Explicit Congestion Notification (ECN) Semantics for Ultra-Low Queuing Delay (L4S)
draft-ietf-tsvwg-ecn-l4s-id-05

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Transport Services (tsv)                                  K. De Schepper
Internet-Draft                                           Nokia Bell Labs
Intended status: Experimental                            B. Briscoe, Ed.
Expires: May 9, 2019                                           CableLabs
                                                        November 5, 2018

 Identifying Modified Explicit Congestion Notification (ECN) Semantics
                   for Ultra-Low Queuing Delay (L4S)
                     draft-ietf-tsvwg-ecn-l4s-id-05

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 'Classic'
   flow under the same conditions.  However, the much more frequent
   control signals and the finer responses to them result in ultra-low
   queuing delay without compromising link utilization, and low delay is
   maintained during high load.  Examples of new active queue management
   (AQM) marking algorithms and examples of new transports (whether TCP-
   like or real-time) are specified separately.  The new L4S identifier
   is the key piece that enables them to interwork and distinguishes
   them from 'Classic' traffic.  It gives an incremental migration path
   so that existing 'Classic' TCP traffic will be no worse off, but it
   can be prevented from degrading the ultra-low delay and loss of the
   new scalable transports.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any

De Schepper & Briscoe      Expires May 9, 2019                  [Page 1]
Internet-Draft     ECN Semantics for Low Queuing Delay     November 2018

   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 9, 2019.

Copyright Notice

   Copyright (c) 2018 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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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Problem . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Consensus Choice of L4S Packet Identifier: Requirements . . .   7
   3.  L4S Packet Identification at Run-Time . . . . . . . . . . . .   8
   4.  Prerequisite Transport Layer Behaviour  . . . . . . . . . . .   8
     4.1.  Prerequisite Codepoint Setting  . . . . . . . . . . . . .   8
     4.2.  Prerequisite Transport Feedback . . . . . . . . . . . . .   8
     4.3.  Prerequisite Congestion Response  . . . . . . . . . . . .   9
   5.  Prerequisite Network Node Behaviour . . . . . . . . . . . . .  10
     5.1.  Prerequisite Classification and Re-Marking Behaviour  . .  10
     5.2.  The Meaning of L4S CE Relative to Drop  . . . . . . . . .  11
     5.3.  Exception for L4S Packet Identification by Network Nodes
           with Transport-Layer Awareness  . . . . . . . . . . . . .  12
     5.4.  Interaction of the L4S Identifier with other Identifiers   12
       5.4.1.  Examples of Other Identifiers Complementing L4S
               Identifiers . . . . . . . . . . . . . . . . . . . . .  12
         5.4.1.1.  Inclusion of Additional Traffic with L4S  . . . .  12