TCP ACK Rate Request Option
draft-gomez-tcpm-ack-rate-request-00

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TCPM Working Group                                              C. Gomez
Internet-Draft                                                       UPC
Intended status: Experimental                               J. Crowcroft
Expires: January 14, 2021                        University of Cambridge
                                                           July 13, 2020

                      TCP ACK Rate Request Option
                  draft-gomez-tcpm-ack-rate-request-00

Abstract

   TCP Delayed Acknowledgments (ACKs) is a widely deployed mechanism
   that allows reducing protocol overhead in many scenarios.  However,
   Delayed ACKs may also contribute to suboptimal performance.  When a
   relatively large congestion window (cwnd) can be used, less frequent
   ACKs may be desirable.  On the other hand, in relatively small cwnd
   scenarios, eliciting an immediate ACK may avoid unnecessary delays
   that may be incurred by the Delayed ACKs mechanism.  This document
   specifies the TCP ACK Rate Request (TARR) option.  This option allows
   a sender to indicate the ACK rate to be used by a receiver, and it
   also allows to request an immediate ACK from a receiver.

Status of This Memo

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   This document is subject to BCP 78 and the IETF Trust's Legal
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Gomez & Crowcroft       Expires January 14, 2021                [Page 1]
Internet-Draft         TCP ACK Rate Request Option             July 2020

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  TCP ACK Rate Request Functionality  . . . . . . . . . . . . .   3
     3.1.  Sender behavior . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Receiver behavior . . . . . . . . . . . . . . . . . . . .   4
   4.  Option Format . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Delayed Acknowledgments (ACKs) were specified for TCP with the aim to
   reduce protocol overhead [RFC1122].  With Delayed ACKs, a TCP delays
   sending an ACK by up to 500 ms (often 200 ms, with lower values in
   recent implementations such as ~50 ms also reported), and typically
   sends an ACK for at least every second segment received in a stream
   of full-sized segments.  This allows combining several segments into
   a single one (e.g. the application layer response to an application
   layer data message, and the corresponding ACK), and also saves up to
   one of every two ACKs, under many traffic patterns (e.g. bulk
   transfers).  The "SHOULD" requirement level for implementing Delayed
   ACKs in RFC 1122, along with its expected benefits, has led to a
   widespread deployment of this mechanism.

   However, there exist scenarios where Delayed ACKs contribute to
   suboptimal performance.  We next roughly classify such scenarios into
   two main categories, in terms of the congestion window (cwnd) size
   and the Maximum Segment Size (MSS) that would be used therein: i)
   "large" cwnd scenarios (i.e. cwnd >> MSS), and ii) "small" cwnd
   scenarios (e.g. cwnd up to ~MSS).

   In "large" cwnd scenarios, increasing the number of data segments
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