Requirements for Time-Based Loss Detection

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Document Type Active Internet-Draft (tcpm WG)
Last updated 2020-06-08 (latest revision 2020-05-13)
Replaces draft-allman-tcpm-rto-consider
Stream IETF
Intended RFC status Best Current Practice
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Stream WG state Submitted to IESG for Publication (wg milestone: May 2020 - Submit document on R... )
Document shepherd Yoshifumi Nishida
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IANA IANA review state Version Changed - Review Needed
Internet Engineering Task Force                                M. Allman
INTERNET-DRAFT                                                      ICSI
File: draft-ietf-tcpm-rto-consider-15.txt                   June 8, 2020
Intended Status: Best Current Practice
Expires: December 8, 2020

               Requirements for Time-Based Loss Detection

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
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    Many protocols must detect packet loss for various reasons (e.g., to
    ensure reliability using retransmissions or to understand the level
    of congestion along a network path).  While many mechanisms have
    been designed to detect loss, protocols ultimately can only count on
    the passage of time without delivery confirmation to declare a
    packet "lost".  Each implementation of a time-based loss detection
    mechanism represents a balance between correctness and timeliness
    and therefore no implementation suits all situations.  This document

Expires: December 8, 2020                                       [Page 1]
draft-ietf-tcpm-rto-consider-15.txt                            June 2020

    provides high-level requirements for time-based loss detectors
    appropriate for general use in the Internet.  Within the
    requirements, implementations have latitude to define particulars
    that best address each situation.


    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    document are to be interpreted as described in BCP 14, RFC 2119

1   Introduction

    As a network of networks, the Internet consists of a large variety
    of links and systems that combine to form "best effort" network
    paths.  The path that traffic takes through the network is generally
    unknown a priori.  Further, the path and the path properties that
    traffic experiences dynamically vary over time.  As two examples,
    consider delay and loss.  In the general case, delay across a
    network path depends not only on distance, but also a number of
    variable components such as the route and the level of buffering in
    intermediate devices.  Since our wide-area network paths are best
    effort, packet loss is a regular occurrence.  While there are
    numerous causes of packet loss, the conservative general approach
    that has historically served us well---and we use in this
    document---is to treat loss as an implicit indication of network

    Given that packet loss is routine in best effort networks, loss
    detection is a crucial activity for many protocols and applications
    and is generally undertaken for two major reasons:

      (1) Ensuring reliable data delivery.

            This requires a data sender to develop an understanding of
            which transmitted packets have not arrived at the receiver.
            This knowledge allows the sender to retransmit missing data.
      (2) Congestion control.

            As we mention above, packet loss is often taken as an
            implicit indication that the sender is transmitting too fast
            and is overwhelming some portion of the network path.  Data
            senders can therefore use loss to trigger transmission rate

    Various mechanisms are used to detect losses in a packet stream.
    Often we use continuous or periodic acknowledgments from the
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