Requirements for Time-Based Loss Detection
draft-ietf-tcpm-rto-consider-16

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Document Type Active Internet-Draft (tcpm WG)
Last updated 2020-07-09 (latest revision 2020-06-19)
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... )
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Internet Engineering Task Force                                M. Allman
INTERNET-DRAFT                                                      ICSI
File: draft-ietf-tcpm-rto-consider-16.txt                  June 19, 2020
Intended Status: Best Current Practice
Expires: December 19, 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
    documents of the Internet Engineering Task Force (IETF), its areas,
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    This Internet-Draft will expire on December 19, 2020.

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Abstract

    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 19, 2020                                      [Page 1]
draft-ietf-tcpm-rto-consider-16.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.

Terminology

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
    "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.

1   Introduction

    As a network of networks, the Internet consists of a large variety
    of links and systems that support a wide variety of tasks and
    workloads.  The service provided by the network varies from best
    effort delivery among loosely connected components to highly
    predictable delivery within constrained environments (e.g., between
    physically connected nodes, within a tightly controlled data
    center).  Each path through the network has a set of path
    properties---e.g., available capacity, delay, packet loss.  Given
    the range of networks that make up the Internet, these properties
    range from largely static to highly dynamic.

    This document provides guidelines for developing an understanding of
    one path property: loss.  In particular, we offer guidelines for
    developing and implementing time-based loss detectors that have been
    gradually learned over the last several decades.  We focus on the
    general case where the loss properties of a path are (a) unknown a
    priori and (b) dynamically vary over time.  Further, while there are
    numerous root causes of packet loss, we leverage the conservative
    notion that loss is an implicit indication of congestion.  While
    this stance is not always correct, as a general assumption it has
    historically served us well.  As we discuss further in section 2,
    the guidelines in this document should be viewed as a general
    default for best effort networks and not as optimal---or even
    applicable---for all situations.

    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.
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