Changing the Default QUIC ACK Policy
draft-fairhurst-quic-ack-scaling-03

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Internet Engineering Task Force                             G. Fairhurst
Internet-Draft                                                A. Custura
Intended status: Informational                                  T. Jones
Expires: March 18, 2021                           University of Aberdeen
                                                      September 14, 2020

                  Changing the Default QUIC ACK Policy
                  draft-fairhurst-quic-ack-scaling-03

Abstract

   Acknowledgement packets (ACKs) are used by transport protocols to
   confirm the delivery of packets, and their reception is used in a
   variety of other ways (to measure path round trip time, to gauge path
   congestion, etc).  However, the transmission of ACKs also consumes
   resources at the receiver, forwarding resource in the network and
   processing resources at the sender.

   On network paths with significant path asymmetry, transmission of
   ACKs can limit the available throughput or can reduce the efficient
   use of network capacity.  This occurs when the return capacity is
   significantly more constrained than the forward capacity, and/or the
   cost of transmission per packet is a significant component of the
   total transmission cost.  In these cases, reducing the ratio of ACK
   packets to data packets can improve link utilisation and reduce link
   transmission costs.  It can also reduce processing overhead at the
   sender and receiver.

   This document proposes a change to the default acknowledgement policy
   of the QUIC transport protocol to improve performance over paths with
   appreciable asymmetry.

Status of This Memo

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Fairhurst, et al.        Expires March 18, 2021                 [Page 1]
Internet-Draft    Changing the Default QUIC ACK Policy    September 2020

   This Internet-Draft will expire on March 18, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  ACK Ratio Impact on Asymmetric Paths  . . . . . . . . . .   3
     2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Adapting the ACK Ratio in Current Transport
           Specifications  . . . . . . . . . . . . . . . . . . . . .   4
     2.4.  Adapting the TCP ACK Ratio in the Network . . . . . . . .   4
     2.5.  QUIC ACKs . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Updating the Default ACK Ratio for QUIC . . . . . . . . . . .   6
     3.1.  Considerations Updating the Default QUIC ACK Policy . . .   6
     3.2.  Mitigating the Impact of ACKs during Slow Start . . . . .   7
     3.3.  ACKs after Slow Start . . . . . . . . . . . . . . . . . .   8
     3.4.  ACKs after re-ordering is Detected  . . . . . . . . . . .   8
     3.5.  Further Tuning of the ACK Policy  . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Summary of Recommended ACK Policy for TCP  . . . . .  11
   Appendix B.  Understanding ACKs in Slow Start . . . . . . . . . .  12
   Appendix C.  Experiments Exploring an ACK Ratio of 1:10 . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Acknowledgement packets (ACKs) are used by transport protocols to
   confirm the delivery of packets, and their reception is used in a
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