TCP ETS: Extensible Timestamp Options

Document Type Active Internet-Draft (individual)
Authors Kevin Yang  , Neal Cardwell  , Yuchung Cheng  , Eric Dumazet 
Last updated 2020-11-02
Stream (None)
Intended RFC status (None)
Formats plain text xml pdf htmlized (tools) htmlized bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
TCP Maintenance Working Group                                   K. Yang
Internet-Draft                                               N. Cardwell
Intended status: Standards Track                                Y. Cheng
Expires: May 6, 2021                                          E. Dumazet
                                                             Google, Inc
                                                        November 2, 2020

                 TCP ETS: Extensible Timestamp Options


   This document presents ETS: an Extensible TimeStamps option for TCP.
   It allows hosts to use microseconds as the unit for timestamps to
   improve the precision of timestamps, and advertise the maximum ACK
   delay for its own delayed ACK mechanism.  Furthermore, it extends the
   information provided in the [RFC7323] TCP Timestamps Option by
   including the receiver delay in the TSecr echoing, so that the
   receiver of the ACK is able to more accurately estimate the portion
   of the RTT that resulted from time traveling through the network.
   The ETS option format is extensible, so that future extensions can
   add further information without the overhead of extra TCP option kind
   and length fields.

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

   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 May 6, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Yang, et al.               Expires May 6, 2021                  [Page 1]
Internet-Draft                     ETS                     November 2020

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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.

1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.  In this document, these words will appear
   with that interpretation only when in UPPER CASE.  Lower case uses of
   these words are not to be interpreted as carrying [RFC2119]

2.  Introduction

   Accurate round-trip time (RTT) estimation is necessary for TCP to
   adapt to diverse and dynamic traffic conditions.

   The TCP timestamp option specified in [RFC7323] is designed largely
   for RTT samples intended for computing TCP's retransmission (RTO)
   timer [RFC6298].

   Some congestion control algorithms may wish to use a form of RTT
   measurement as one of several congestion signals, since elevated RTT
   measurements can reflect increases in network queueing delays.  For
   example, the Swift congestion control algorithm [KDJWWM20],
   successfully deployed in data-center environments, requires precise
   and accurate measurements of both network and host delays.  However,
   the existing TCP RTT sampling mechanisms that measure the delay
   between data transmission and ACK receipt [RFC6298] do not separate
   network and host delays, and cannot measure the RTT of retransmitted
   data.  Even the TCP timestamp option specified in [RFC7323] is not
   well-suited to use as a congestion signal, for a number of reasons.

   With the TCP Timestamps Option [RFC7323], data senders can measure an
   RTT sample by computing the difference between the data sender's
   current timestamp clock value and the received TSecr value.  However,
   there are some drawbacks in this [RFC7323] measurement method:

Yang, et al.               Expires May 6, 2021                  [Page 2]
Internet-Draft                     ETS                     November 2020

   1.  The TCP endpoint can compute an [RFC7323] RTT measurement only if
       the ACK advances the left edge of the send window, i.e. SND.UNA
Show full document text