TCP ACK Pull
draft-gomez-tcpm-ack-pull-00

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TCPM Working Group                                              C. Gomez
Internet-Draft                                                       UPC
Intended status: Experimental                               J. Crowcroft
Expires: January 2, 2020                         University of Cambridge
                                                            July 1, 2019

                              TCP ACK Pull
                      draft-gomez-tcpm-ack-pull-00

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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 2, 2020.

Copyright Notice

   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
   publication of this document.  Please review these documents

Gomez & Crowcroft        Expires January 2, 2020                [Page 1]
Internet-Draft                TCP ACK Pull                     July 2019

   carefully, as they describe your rights and restrictions with respect
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  ACK Pull Mechanism  . . . . . . . . . . . . . . . . . . . . .   4
   4.  The ACK Pull Flag . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Actions  . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

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 (typically, 200 ms), 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
   dramatically reduced, as the Delayed ACK timeout is several orders of
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