QUIC Loss Detection and Congestion Control
draft-ietf-quic-recovery-34

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QUIC                                                     J. Iyengar, Ed.
Internet-Draft                                                    Fastly
Intended status: Standards Track                           I. Swett, Ed.
Expires: 19 July 2021                                             Google
                                                         15 January 2021

               QUIC Loss Detection and Congestion Control
                      draft-ietf-quic-recovery-34

Abstract

   This document describes loss detection and congestion control
   mechanisms for QUIC.

Note to Readers

   Discussion of this draft takes place on the QUIC working group
   mailing list (quic@ietf.org (mailto:quic@ietf.org)), which is
   archived at https://mailarchive.ietf.org/arch/
   search/?email_list=quic.

   Working Group information can be found at https://github.com/quicwg;
   source code and issues list for this draft can be found at
   https://github.com/quicwg/base-drafts/labels/-recovery.

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
   working documents as Internet-Drafts.  The list of current Internet-
   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
   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 19 July 2021.

Copyright Notice

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

Iyengar & Swett           Expires 19 July 2021                  [Page 1]
Internet-Draft             QUIC Loss Detection              January 2021

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  Design of the QUIC Transmission Machinery . . . . . . . . . .   5
   4.  Relevant Differences Between QUIC and TCP . . . . . . . . . .   6
     4.1.  Separate Packet Number Spaces . . . . . . . . . . . . . .   6
     4.2.  Monotonically Increasing Packet Numbers . . . . . . . . .   6
     4.3.  Clearer Loss Epoch  . . . . . . . . . . . . . . . . . . .   7
     4.4.  No Reneging . . . . . . . . . . . . . . . . . . . . . . .   7
     4.5.  More ACK Ranges . . . . . . . . . . . . . . . . . . . . .   7
     4.6.  Explicit Correction For Delayed Acknowledgments . . . . .   7
     4.7.  Probe Timeout Replaces RTO and TLP  . . . . . . . . . . .   7
     4.8.  The Minimum Congestion Window is Two Packets  . . . . . .   8
   5.  Estimating the Round-Trip Time  . . . . . . . . . . . . . . .   8
     5.1.  Generating RTT samples  . . . . . . . . . . . . . . . . .   8
     5.2.  Estimating min_rtt  . . . . . . . . . . . . . . . . . . .   9
     5.3.  Estimating smoothed_rtt and rttvar  . . . . . . . . . . .  10
   6.  Loss Detection  . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  Acknowledgment-Based Detection  . . . . . . . . . . . . .  12
       6.1.1.  Packet Threshold  . . . . . . . . . . . . . . . . . .  13
       6.1.2.  Time Threshold  . . . . . . . . . . . . . . . . . . .  13
     6.2.  Probe Timeout . . . . . . . . . . . . . . . . . . . . . .  14
       6.2.1.  Computing PTO . . . . . . . . . . . . . . . . . . . .  14
       6.2.2.  Handshakes and New Paths  . . . . . . . . . . . . . .  16
       6.2.3.  Speeding Up Handshake Completion  . . . . . . . . . .  17
       6.2.4.  Sending Probe Packets . . . . . . . . . . . . . . . .  18
     6.3.  Handling Retry Packets  . . . . . . . . . . . . . . . . .  19
     6.4.  Discarding Keys and Packet State  . . . . . . . . . . . .  19
   7.  Congestion Control  . . . . . . . . . . . . . . . . . . . . .  20
     7.1.  Explicit Congestion Notification  . . . . . . . . . . . .  20
     7.2.  Initial and Minimum Congestion Window . . . . . . . . . .  21
     7.3.  Congestion Control States . . . . . . . . . . . . . . . .  21
       7.3.1.  Slow Start  . . . . . . . . . . . . . . . . . . . . .  22
       7.3.2.  Recovery  . . . . . . . . . . . . . . . . . . . . . .  22
       7.3.3.  Congestion Avoidance  . . . . . . . . . . . . . . . .  23