Requirements for Time-Based Loss Detection

Document Type Active Internet-Draft (tcpm WG)
Author Mark Allman 
Last updated 2020-08-21 (latest revision 2020-07-27)
Replaces draft-allman-tcpm-rto-consider
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Intended RFC status Best Current Practice
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Internet Engineering Task Force                                M. Allman
INTERNET-DRAFT                                                      ICSI
File: draft-ietf-tcpm-rto-consider-17.txt                  July 27, 2020
Intended Status: Best Current Practice
Expires: January 27, 2021

               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, ultimately, protocols 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: January 27, 2021                                       [Page 1]
draft-ietf-tcpm-rto-consider-17.txt                            July 2020

    provides high-level requirements for time-based loss detectors
    appropriate for general use in unicast communication across 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",
    "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 controlled 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: packet 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 [RFC5681].  While this stance is not always correct, as a
    general assumption it has historically served us well [Jac88].  As
    we discuss further in section 2, the guidelines in this document
    should be viewed as a general default for unicast communication
    across 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
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