Why do we need passive measurement of round trip time?
draft-trammell-why-measure-rtt-00

Document Type Active Internet-Draft (individual)
Last updated 2018-08-20
Stream (None)
Intended RFC status (None)
Formats plain text xml pdf html 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)
QUIC                                                         B. Trammell
Internet-Draft                                                ETH Zurich
Intended status: Informational                           August 20, 2018
Expires: February 21, 2019

         Why do we need passive measurement of round trip time?
                   draft-trammell-why-measure-rtt-00

Abstract

   This document describes the utility of passive two-way latency
   measurement, both for the generation of latency metrics, as well as
   for other measurement tasks, when passive latency measurement is the
   only facility available for measurement.  It additionally discusses
   other metrics derivable from the transport-independent latency spin
   signal defined in [TSVWG-SPIN].

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 https://datatracker.ietf.org/drafts/current/.

   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 February 21, 2019.

Copyright Notice

   Copyright (c) 2018 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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) 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

Trammell                Expires February 21, 2019               [Page 1]
Internet-Draft              Why measure RTT?                 August 2018

   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  About This Document . . . . . . . . . . . . . . . . . . .   3
   2.  Direct Utility of Passive RTT Measurement . . . . . . . . . .   3
     2.1.  Inter-domain Troubleshooting  . . . . . . . . . . . . . .   3
     2.2.  Bufferbloat Mitigation in Cellular Networks . . . . . . .   4
     2.3.  Locating WiFi Problems in Home Networks . . . . . . . . .   4
     2.4.  Internet Measurement Research . . . . . . . . . . . . . .   5
   3.  Indirect Utility of RTT Measurements  . . . . . . . . . . . .   5
   4.  Additional Metrics Derivable from the Spin Bit  . . . . . . .   6
     4.1.  Derived Loss and Reordering . . . . . . . . . . . . . . .   6
     4.2.  Two-Point Intradomain Measurement . . . . . . . . . . . .   7
   5.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Latency is a key metric to understanding network operation and
   performance.  Passive measurement allows inspection of latency on
   productive traffic, avoiding problems with different treatment of
   productive and measurement traffic, and enables opportunistic
   measurement of latency without active measurement overhead.

   Passive measurement of RTT, in particular, has both direct utility
   (see Section 2), generating RTT samples for the measurement of RTT
   for various use cases, as well as indirect utility (see Section 3),
   since RTT is correlated with other useful metrics.  In addition, the
   passive latency signal proposed in [TSVWG-SPIN] provides other
   opportunities for metric generation which are a consequence of its
   design (see Section 4).

   This document describes these use cases in order to motivate why
   passive measurability of RTT on a per-flow basis is an interesting
   and useful feature for a transport protocol to have.  In the absence
   of other directly observable metrics such as loss and retransmission,
   as is the case with protocols with mostly-encrypted wire images
   [WIRE-IMAGE] such as QUIC [QUIC].

Trammell                Expires February 21, 2019               [Page 2]
Internet-Draft              Why measure RTT?                 August 2018

1.1.  About This Document

   This document is maintained in the GitHub repository
Show full document text