TCP ACK Pull
draft-gomez-tcpm-ack-pull-01

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TCPM Working Group                                              C. Gomez
Internet-Draft                                                       UPC
Intended status: Experimental                               J. Crowcroft
Expires: May 7, 2020                             University of Cambridge
                                                        November 4, 2019

                              TCP ACK Pull
                      draft-gomez-tcpm-ack-pull-01

Abstract

   Delayed Acknowledgments (ACKs) allow reducing protocol overhead in
   many scenarios.  However, in some cases, Delayed ACKs may
   significantly degrade network and device performance in terms of link
   utilization, latency, memory usage and/or energy consumption.  This
   document defines the TCP ACK Pull (AKP) mechanism, which allows a
   sender to request the ACK for a data segment to be sent without
   additional delay by the receiver.  AKP makes use of one of the
   reserved bits in the TCP header, which is defined in this
   specification as the AKP flag.

Status of This Memo

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   This Internet-Draft will expire on May 7, 2020.

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   Copyright (c) 2019 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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   (https://trustee.ietf.org/license-info) in effect on the date of
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Gomez & Crowcroft          Expires May 7, 2020                  [Page 1]
Internet-Draft                TCP ACK Pull                 November 2019

   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   4
   3.  ACK Pull Mechanism  . . . . . . . . . . . . . . . . . . . . .   4
   4.  The ACK Pull Flag . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Actions  . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Annex: Alternative approaches . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Delayed Acknowledgments (ACKs) were specified 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 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 it 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 traffic patterns and scenarios for which Delayed
   ACKs can actually be detrimental to performance.  When a segment
   carrying a message of a size up to one Maximum Segment Size (MSS) is
   transferred, if the message does not elicit an application-layer
   response, and a second data segment is not transferred earlier than
   the Delayed ACK timeout, the ACK is unnecessarily delayed, with a
   number of negative consequences.

   When the Nagle algorithm is used, in some cases the sender may be
   prevented from sending more data while awaiting the Delayed ACK.  In
   some high bit rate environment (e.g.  Gigabit Ethernet) use cases,
   such a delay may be very large, and link utilitzation may be
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