draft-ietf-ippm-2679-bis-05.txt   rfc7679.txt 
Network Working Group G. Almes Internet Engineering Task Force (IETF) G. Almes
Internet-Draft Texas A&M Request for Comments: 7679 Texas A&M
Obsoletes: 2679 (if approved) S. Kalidindi STD: 81 S. Kalidindi
Intended status: Standards Track Ixia Obsoletes: 2679 Ixia
Expires: February 21, 2016 M. Zekauskas Category: Standards Track M. Zekauskas
Internet2 ISSN: 2070-1721 Internet2
A. Morton, Ed. A. Morton, Ed.
AT&T Labs AT&T Labs
August 20, 2015 January 2016
A One-Way Delay Metric for IPPM A One-Way Delay Metric for IP Performance Metrics (IPPM)
draft-ietf-ippm-2679-bis-05
Abstract Abstract
This memo (RFC 2679 bis) defines a metric for one-way delay of This memo defines a metric for one-way delay of packets across
packets across Internet paths. It builds on notions introduced and Internet paths. It builds on notions introduced and discussed in the
discussed in the IPPM Framework document, RFC 2330; the reader is IP Performance Metrics (IPPM) Framework document, RFC 2330; the
assumed to be familiar with that document. This memo makes RFC 2679 reader is assumed to be familiar with that document. This memo makes
obsolete. RFC 2679 obsolete.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on February 21, 2016. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7679.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Changes from RFC 2679 . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Motivation .................................................4
2.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 6 2. General Issues regarding Time ...................................6
2.2. General Issues Regarding Time . . . . . . . . . . . . . . 7 3. A Singleton Definition for One-Way Delay ........................7
3. A Singleton Definition for One-way Delay . . . . . . . . . . 8 3.1. Metric Name ................................................7
3.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Metric Parameters ..........................................7
3.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 8 3.3. Metric Units ...............................................7
3.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 8 3.4. Definition .................................................7
3.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 8 3.5. Discussion .................................................8
3.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 9 3.6. Methodologies ..............................................9
3.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 10 3.7. Errors and Uncertainties ..................................10
3.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 11 3.7.1. Errors or Uncertainties Related to Clocks ..........10
3.7.1. Errors or uncertainties related to Clocks . . . . . . 11 3.7.2. Errors or Uncertainties Related to Wire
3.7.2. Errors or uncertainties related to Wire-time vs Host- Time vs. Host Time .................................11
time . . . . . . . . . . . . . . . . . . . . . . . . 12 3.7.3. Calibration of Errors and Uncertainties ............12
3.7.3. Calibration . . . . . . . . . . . . . . . . . . . . . 13 3.8. Reporting the Metric ......................................14
3.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 15 3.8.1. Type-P .............................................14
3.8.1. Type-P . . . . . . . . . . . . . . . . . . . . . . . 15 3.8.2. Loss Threshold .....................................15
3.8.2. Loss Threshold . . . . . . . . . . . . . . . . . . . 16 3.8.3. Calibration Results ................................15
3.8.3. Calibration Results . . . . . . . . . . . . . . . . . 16 3.8.4. Path ...............................................15
3.8.4. Path . . . . . . . . . . . . . . . . . . . . . . . . 16 4. A Definition for Samples of One-Way Delay ......................15
4. A Definition for Samples of One-way Delay . . . . . . . . . . 16 4.1. Metric Name ...............................................16
4.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . 17 4.2. Metric Parameters .........................................16
4.2. Metric Parameters: . . . . . . . . . . . . . . . . . . . 17 4.3. Metric Units ..............................................16
4.3. Metric Units: . . . . . . . . . . . . . . . . . . . . . . 17 4.4. Definition ................................................17
4.4. Definition: . . . . . . . . . . . . . . . . . . . . . . . 18 4.5. Discussion ................................................17
4.5. Discussion: . . . . . . . . . . . . . . . . . . . . . . . 18 4.6. Methodologies .............................................18
4.6. Methodologies: . . . . . . . . . . . . . . . . . . . . . 19 4.7. Errors and Uncertainties ..................................18
4.7. Errors and Uncertainties: . . . . . . . . . . . . . . . . 19 4.8. Reporting the Metric ......................................18
4.8. Reporting the metric: . . . . . . . . . . . . . . . . . . 19 5. Some Statistics Definitions for One-Way Delay ..................18
5. Some Statistics Definitions for One-way Delay . . . . . . . . 19 5.1. Type-P-One-way-Delay-Percentile ...........................19
5.1. Type-P-One-way-Delay-Percentile . . . . . . . . . . . . . 20 5.2. Type-P-One-way-Delay-Median ...............................19
5.2. Type-P-One-way-Delay-Median . . . . . . . . . . . . . . . 20 5.3. Type-P-One-way-Delay-Minimum ..............................20
5.3. Type-P-One-way-Delay-Minimum . . . . . . . . . . . . . . 21 5.4. Type-P-One-way-Delay-Inverse-Percentile ...................20
5.4. Type-P-One-way-Delay-Inverse-Percentile . . . . . . . . . 21 6. Security Considerations ........................................21
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7. Changes from RFC 2679 ..........................................22
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 8. References .....................................................24
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23 8.1. Normative References ......................................24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 8.2. Informative References ....................................25
9.1. Normative References . . . . . . . . . . . . . . . . . . 23 Acknowledgements ..................................................26
9.2. Informative References . . . . . . . . . . . . . . . . . 24 Authors' Addresses ................................................27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Changes from RFC 2679
Note: This section's placement currently preserves minimal
differences between this memo and RFC 2679. The RFC Editor should
place this section in an appropriate place, and remove this note.
The following text constitutes RFC 2769 bis proposed for advancement
on the IETF Standards Track. This section tracks the changes from
[RFC2679].
[RFC6808] provides the test plan and results supporting [RFC2679]
advancement along the standards track, according to the process in
[RFC6576]. The conclusions of [RFC6808] list four minor
modifications:
1. Section 6.2.3 of [RFC6808] asserts that the assumption of post-
processing to enforce a constant waiting time threshold is
compliant, and that the text of the RFC should be revised
slightly to include this point. The applicability of post-
processing was added in the last list item of section 3.6, below.
2. Section 6.5 of [RFC6808] indicates that Type-P-One-way-Delay-
Inverse-Percentile statistic has been ignored in both
implementations, so it is a candidate for removal or deprecation
in RFC2679bis (this small discrepancy does not affect candidacy
for advancement). This statistic was deprecated in section 5.4,
below.
3. The IETF has reached consensus on guidance for reporting metrics
in [RFC6703], and this memo should be referenced in RFC2679bis to
incorporate recent experience where appropriate. This reference
was added in the last list item of section 3.6, section 3.8, and
in section 5 below.
4. There is currently one erratum with status "Held for document
update" for [RFC2679], and this minor revision and additional
text was incorporated in RFC2679bis in section 5.1, below.
A number of updates to the [RFC2679] text have been implemented in
the text below, to reference key IPPM RFCs that were approved after
[RFC2679], and to address comments on the IPPM mailing list
describing current conditions and experience.
1. Near the end of section 2.1, update of a network example using
ATM and clarification of TCP's affect on queue occupation and
importance of one-way delay measurement.
2. Explicit inclusion of the maximum waiting time input parameter
in section 3.2 and 4.2, reflecting recognition of this parameter
in more recent RFCs and ITU-T Recommendation Y.1540.
3. Addition of reference to RFC6703 in the discussion of packet
life time and application timeouts in section 3.5.
4. Addition of reference to the default requirement (that packets
be standard-formed) from RFC2330 as a new list item in section
3.5.
5. GPS-based NTP experience replaces "to be tested" in section 3.5.
6. Replaced "precedence" with updated terminology (DS Field) in 3.6
and 3.8.1 (with reference).
7. Added parenthetical guidance on minimizing interval between
timestamp placement to send time in section 3.6.
8. Section 3.7.2 notes that some current systems perform host time
stamping on the network interface hardware.
9. "instrument" replaced by the defined term "host" in sections
3.7.3 and 3.8.3.
10. Added reference to RFC 3432 Periodic sampling alongside Poisson
sampling in section 4, and also noting that a truncated Poisson
distribution may be needed with modern networks as described in
the IPPM Framework update, RFC7312.
11. Add reference to RFC 4737 Reordering metric in the related
discussion of section 4.6, Methodologies.
12. Formatting of Example in section 5.1 modified to match the
original (issue with conversion to XML in bis version).
13. Clarifying the conclusions on two related points on harm to
measurements (recognition of measurement traffic for unexpected
priority treatment and attacker traffic which emulates
measurement) in section 6, Security Considerations.
14. Expanded and updated the material on Privacy, and added cautions
on use of measurements for reconnaissance in section 6, Security
Considerations.
Section 5.4.4 of [RFC6390] suggests a common template for performance
metrics partially derived from previous IPPM and BMWG RFCs, but also
contains some new items. All of the [RFC6390] Normative points are
covered, but not quite in the same section names or orientation.
Several of the Informative points are covered. Maintaining the
familiar outline of IPPM literature has both value and minimizes
unnecessary differences between this revised RFC and current/future
IPPM RFCs.
The publication of RFC 6921 suggested an area where this memo might
need updating. Packet transfer on Faster-Than-Light (FTL) networks
could result in negative delays and packet reordering, however both
are covered as possibilities in the current text and no revisions are
deemed necessary (we also note that this is an April 1st RFC).
2. Introduction 1. Introduction
This memo defines a metric for one-way delay of packets across This memo defines a metric for one-way delay of packets across
Internet paths. It builds on notions introduced and discussed in the Internet paths. It builds on notions introduced and discussed in the
IPPM Framework document, [RFC2330]; the reader is assumed to be IPPM Framework document, [RFC2330]; the reader is assumed to be
familiar with that document, and its recent update [RFC7312]. familiar with that document and its recent update [RFC7312].
This memo is intended to be parallel in structure to a companion This memo is intended to be parallel in structure to a companion
document for Packet Loss ("A One-way Packet Loss Metric for IPPM") document for Packet Loss ("A One-way Packet Loss Metric for IPPM")
[RFC2680]. [RFC7680].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in [RFC2119]. Although
Although [RFC2119] was written with protocols in mind, the key words [RFC2119] was written with protocols in mind, the key words are used
are used in this document for similar reasons. They are used to in this document for similar reasons. They are used to ensure the
ensure the results of measurements from two different implementations results of measurements from two different implementations are
are comparable, and to note instances when an implementation could comparable and to note instances when an implementation could perturb
perturb the network. the network.
The structure of the memo is as follows: Whenever a technical term from the IPPM Framework document is first
used in this memo, it will be tagged with a trailing asterisk. For
example, "term*" indicates that "term" is defined in the Framework
document.
+ A 'singleton' analytic metric, called Type-P-One-way-Delay, will be The structure of the memo is as follows:
introduced to measure a single observation of one-way delay.
+ Using this singleton metric, a 'sample', called Type-P-One-way- o A 'singleton*' analytic metric, called Type-P-One-way-Delay, will
Delay-Poisson-Stream, will be introduced to measure a sequence of be introduced to measure a single observation of one-way delay.
singleton delays sent at times taken from a Poisson process.
+ Using this sample, several 'statistics' of the sample will be o Using this singleton metric, a 'sample*' called Type-P-One-way-
defined and discussed. This progression from singleton to sample to Delay-Poisson-Stream is introduced to measure a sequence of
statistics, with clear separation among them, is important. singleton delays sent at times taken from a Poisson process,
defined in Section 11.1.1 of [RFC2330].
Whenever a technical term from the IPPM Framework document is first o Using this sample, several 'statistics*' of the sample will be
used in this memo, it will be tagged with a trailing asterisk. For defined and discussed. This progression from singleton to sample
example, "term*" indicates that "term" is defined in the Framework. to statistics, with clear separation among them, is important.
2.1. Motivation 1.1. Motivation
One-way delay of a Type-P* packet from a source host* to a Understanding one-way delay of a Type-P* packet from a source host*
destination host is useful for several reasons: to a destination host is useful for several reasons:
+ Some applications do not perform well (or at all) if end-to-end o Some applications do not perform well (or at all) if end-to-end
delay between hosts is large relative to some threshold value. delay between hosts is large relative to some threshold value.
+ Erratic variation in delay makes it difficult (or impossible) to o Erratic variation in delay makes it difficult (or impossible) to
support many real-time applications. support many real-time applications.
+ The larger the value of delay, the more difficult it is for o The larger the value of delay, the more difficult it is for
transport-layer protocols to sustain high bandwidths. transport-layer protocols to sustain high bandwidths.
+ The minimum value of this metric provides an indication of the o The minimum value of this metric provides an indication of the
delay due only to propagation and transmission delay. delay due only to propagation and transmission delay.
+ The minimum value of this metric provides an indication of the o The minimum value of this metric provides an indication of the
delay that will likely be experienced when the path* traversed is delay that will likely be experienced when the path* traversed is
lightly loaded. lightly loaded.
+ Values of this metric above the minimum provide an indication of o Values of this metric above the minimum provide an indication of
the congestion present in the path. the congestion present in the path.
The measurement of one-way delay instead of round-trip delay is The measurement of one-way delay instead of round-trip delay is
motivated by the following factors: motivated by the following factors:
+ In today's Internet, the path from a source to a destination may be o In today's Internet, the path from a source to a destination may
different than the path from the destination back to the source be different than the path from the destination back to the source
("asymmetric paths"), such that different sequences of routers are ("asymmetric paths"), such that different sequences of routers are
used for the forward and reverse paths. Therefore round-trip used for the forward and reverse paths. Therefore, round-trip
measurements actually measure the performance of two distinct paths measurements actually measure the performance of two distinct
together. Measuring each path independently highlights the paths together. Measuring each path independently highlights the
performance difference between the two paths which may traverse performance difference between the two paths that may traverse
different Internet service providers, and even radically different different Internet service providers and even radically different
types of networks (for example, research versus commodity networks, types of networks (for example, research versus commodity
or networks with asymmetric link capacities, or wireless vs. wireline networks, or networks with asymmetric link capacities, or wireless
access). versus wireline access).
+ Even when the two paths are symmetric, they may have radically o Even when the two paths are symmetric, they may have radically
different performance characteristics due to asymmetric queueing. different performance characteristics due to asymmetric queuing.
+ Performance of an application may depend mostly on the performance o Performance of an application may depend mostly on the performance
in one direction. For example, a TCP-based communication will in one direction. For example, a TCP-based communication will
experience reduced throughput if congestion occurs in one direction experience reduced throughput if congestion occurs in one
of its communication. Trouble shooting may be simplified if the direction of its communication. Troubleshooting may be simplified
congested direction of TCP transmission can be identified. if the congested direction of TCP transmission can be identified.
+ In quality-of-service (QoS) enabled networks, provisioning in one o In networks in which quality of service (QoS) is enabled,
direction may be radically different than provisioning in the reverse provisioning in one direction may be radically different than
direction, and thus the QoS guarantees differ. Measuring the paths provisioning in the reverse direction and thus the QoS guarantees
independently allows the verification of both guarantees. differ. Measuring the paths independently allows the verification
of both guarantees.
It is outside the scope of this document to say precisely how delay It is outside the scope of this document to say precisely how delay
metrics would be applied to specific problems. metrics would be applied to specific problems.
2.2. General Issues Regarding Time 2. General Issues regarding Time
{Comment: the terminology below differs from that defined by ITU-T {Comment: The terminology below differs from that defined by ITU-T
documents (e.g., G.810, "Definitions and terminology for documents (e.g., G.810, "Definitions and terminology for
synchronization networks" and I.356, "B-ISDN ATM layer cell transfer synchronization networks" and I.356, "B-ISDN ATM layer cell transfer
performance"), but is consistent with the IPPM Framework document. performance") but is consistent with the IPPM Framework document. In
In general, these differences derive from the different backgrounds; general, these differences derive from the different backgrounds; the
the ITU-T documents historically have a telephony origin, while the ITU-T documents historically have a telephony origin, while the
authors of this document (and the Framework) have a computer systems authors of this document (and the Framework document) have a computer
background. Although the terms defined below have no direct systems background. Although the terms defined below have no direct
equivalent in the ITU-T definitions, after our definitions we will equivalent in the ITU-T definitions, after our definitions we will
provide a rough mapping. However, note one potential confusion: our provide a rough mapping. However, note one potential confusion: our
definition of "clock" is the computer operating systems definition definition of "clock" is the computer operating systems definition
denoting a time-of-day clock, while the ITU-T definition of clock denoting a time-of-day clock, while the ITU-T definition of clock
denotes a frequency reference.} denotes a frequency reference.}
Whenever a time (i.e., a moment in history) is mentioned here, it is Whenever a time (i.e., a moment in history) is mentioned here, it is
understood to be measured in seconds (and fractions) relative to UTC. understood to be measured in seconds (and fractions) relative to UTC.
As described more fully in the Framework document, there are four As described more fully in the Framework document, there are four
skipping to change at page 8, line 4 skipping to change at page 6, line 41
clock on a second host. {Comment: A rough ITU-T equivalent is "time clock on a second host. {Comment: A rough ITU-T equivalent is "time
error".} error".}
accuracy* accuracy*
measures the extent to which a given clock agrees with UTC. For measures the extent to which a given clock agrees with UTC. For
example, the clock on a host might be 27.1 msec behind UTC. {Comment: example, the clock on a host might be 27.1 msec behind UTC. {Comment:
A rough ITU-T equivalent is "time error from UTC".} A rough ITU-T equivalent is "time error from UTC".}
resolution* resolution*
measures the precision of a given clock. For example, the clock on
an old Unix host might tick only once every 10 msec, and thus have a specification of the smallest unit by which the clock's time is
resolution of only 10 msec. {Comment: A very rough ITU-T equivalent updated. It gives a lower bound on the clock's uncertainty. For
is "sampling period".} example, the clock on an old Unix host might tick only once every 10
msec, and thus have a resolution of only 10 msec. {Comment: A very
rough ITU-T equivalent is "sampling period".}
skew* skew*
measures the change of accuracy, or of synchronization, with time. measures the change of accuracy, or of synchronization, with time.
For example, the clock on a given host might gain 1.3 msec per hour For example, the clock on a given host might gain 1.3 msec per hour
and thus be 27.1 msec behind UTC at one time and only 25.8 msec an and thus be 27.1 msec behind UTC at one time and only 25.8 msec an
hour later. In this case, we say that the clock of the given host hour later. In this case, we say that the clock of the given host
has a skew of 1.3 msec per hour relative to UTC, which threatens has a skew of 1.3 msec per hour relative to UTC, which threatens
accuracy. We might also speak of the skew of one clock relative to accuracy. We might also speak of the skew of one clock relative to
another clock, which threatens synchronization. {Comment: A rough another clock, which threatens synchronization. {Comment: A rough
ITU-T equivalent is "time drift".} ITU-T equivalent is "time drift".}
3. A Singleton Definition for One-way Delay 3. A Singleton Definition for One-Way Delay
3.1. Metric Name: 3.1. Metric Name
Type-P-One-way-Delay Type-P-One-way-Delay
3.2. Metric Parameters: 3.2. Metric Parameters
+ Src, the IP address of a host o Src, the IP address of a host
+ Dst, the IP address of a host o Dst, the IP address of a host
+ T, a time o T, a time
+ Tmax, a loss threshold waiting time o Tmax, a loss threshold waiting time
3.3. Metric Units: 3.3. Metric Units
The value of a Type-P-One-way-Delay is either a real number, or an The value of a Type-P-One-way-Delay is either a real number or an
undefined (informally, infinite) number of seconds. undefined (informally, infinite) number of seconds.
3.4. Definition: 3.4. Definition
For a real number dT, >>the *Type-P-One-way-Delay* from Src to Dst at For a real number dT, >>the *Type-P-One-way-Delay* from Src to Dst at
T is dT<< means that Src sent the first bit of a Type-P packet to Dst T is dT<< means that Src sent the first bit of a Type-P packet to Dst
at wire-time* T and that Dst received the last bit of that packet at at wire time* T and that Dst received the last bit of that packet at
wire-time T+dT. wire time T+dT.
>>The *Type-P-One-way-Delay* from Src to Dst at T is undefined >>The *Type-P-One-way-Delay* from Src to Dst at T is undefined
(informally, infinite)<< means that Src sent the first bit of a (informally, infinite)<< means that Src sent the first bit of a
Type-P packet to Dst at wire-time T and that Dst did not receive that Type-P packet to Dst at wire time T and that Dst did not receive that
packet (within the loss threshold waiting time, Tmax). packet (within the loss threshold waiting time, Tmax).
Suggestions for what to report along with metric values appear in Suggestions for what to report and metric values appear in
Section 3.8 after a discussion of the metric, methodologies for Section 3.8 after a discussion of the metric, methodologies for
measuring the metric, and error analysis. measuring the metric, and error analysis.
3.5. Discussion: 3.5. Discussion
Type-P-One-way-Delay is a relatively simple analytic metric, and one Type-P-One-way-Delay is a relatively simple analytic metric, and one
that we believe will afford effective methods of measurement. that we believe will afford effective methods of measurement.
The following issues are likely to come up in practice: The following issues are likely to come up in practice:
+ Real delay values will be positive. Therefore, it does not make o Real delay values will be positive. Therefore, it does not make
sense to report a negative value as a real delay. However, an sense to report a negative value as a real delay. However, an
individual zero or negative delay value might be useful as part of a individual zero or negative delay value might be useful as part of
stream when trying to discover a distribution of a stream of delay a stream when trying to discover a distribution of a stream of
values. delay values.
+ Since delay values will often be as low as the 100 usec to 10 msec o Since delay values will often be as low as the 100 usec to 10 msec
range, it will be important for Src and Dst to synchronize very range, it will be important for Src and Dst to synchronize very
closely. GPS systems afford one way to achieve synchronization to closely. Global Positioning System (GPS) systems afford one way
within several 10s of usec. Ordinary application of NTP may allow to achieve synchronization to within several tens of usec.
synchronization to within several msec, but this depends on the Ordinary application of NTP may allow synchronization to within
stability and symmetry of delay properties among those NTP agents several msec, but this depends on the stability and symmetry of
used, and this delay is what we are trying to measure. A combination delay properties among those NTP agents used, and this delay is
of some GPS-based NTP servers and a conservatively designed and what we are trying to measure. A combination of some GPS-based
deployed set of other NTP servers should yield good results. This NTP servers and a conservatively designed and deployed set of
was tested in [RFC6808], where a GPS measurement system's results other NTP servers should yield good results. This was tested in
compared well with a GPS-based NTP synchronized system for the same [RFC6808], where a GPS measurement system's results compared well
intercontinental path. with a GPS-based NTP synchronized system for the same
intercontinental path.
+ A given methodology will have to include a way to determine whether o A given methodology will have to include a way to determine
a delay value is infinite or whether it is merely very large (and the whether a delay value is infinite or whether it is merely very
packet is yet to arrive at Dst). As noted by Mahdavi and Paxson large (and the packet is yet to arrive at Dst). As noted by
[RFC2678], simple upper bounds (such as the 255 seconds theoretical Mahdavi and Paxson [RFC2678], simple upper bounds (such as the 255
upper bound on the lifetimes of IP packets [RFC0791]) could be used; seconds theoretical upper bound on the lifetimes of IP packets
but good engineering, including an understanding of packet lifetimes, [RFC791]) could be used; but good engineering, including an
will be needed in practice. {Comment: Note that, for many understanding of packet lifetimes, will be needed in practice.
applications of these metrics, the harm in treating a large delay as {Comment: Note that, for many applications of these metrics, the
infinite might be zero or very small. A TCP data packet, for harm in treating a large delay as infinite might be zero or very
example, that arrives only after several multiples of the RTT may as small. A TCP data packet, for example, that arrives only after
well have been lost. See section 4.1.1 of [RFC6703] for examination several multiples of the RTT may as well have been lost. See
of unusual packet delays and application performance estimation.} Section 4.1.1 of [RFC6703] for examination of unusual packet
delays and application performance estimation.}
+ If the packet is duplicated along the path (or paths) so that o If the packet is duplicated along the path (or paths) so that
multiple non-corrupt copies arrive at the destination, then the multiple non-corrupt copies arrive at the destination, then the
packet is counted as received, and the first copy to arrive packet is counted as received, and the first copy to arrive
determines the packet's one-way delay. determines the packet's one-way delay.
+ If the packet is fragmented and if, for whatever reason, reassembly o If the packet is fragmented and if, for whatever reason,
does not occur, then the packet will be deemed lost. reassembly does not occur, then the packet will be deemed lost.
+ The packet is standard-formed, the default criteria for all metric o A given methodology will include a way to determine whether the
definitions defined in Section 15 of [RFC2330], otherwise the packet packet is standard-formed, the default criteria for all metric
will be deemed lost. Note: At this time, the definition of standard- definitions defined in Section 15 of [RFC2330], otherwise the
formed packets only applies to IPv4, but also see packet will be deemed lost. Note: At this time, the definition of
[I-D.morton-ippm-2330-stdform-typep]. standard-formed packets only applies to IPv4, but also see
[IPPM-UPDATES].
3.6. Methodologies: 3.6. Methodologies
As with other Type-P-* metrics, the detailed methodology will depend As with other Type-P-* metrics, the detailed methodology will depend
on the Type-P (e.g., protocol number, UDP/TCP port number, size, on the Type-P (e.g., protocol number, UDP/TCP port number, size,
Differentiated Services (DS) Field [RFC2780]). Differentiated Services (DS) Field [RFC2780]).
Generally, for a given Type-P, the methodology would proceed as Generally, for a given Type-P, the methodology would proceed as
follows: follows:
+ Arrange that Src and Dst are synchronized; that is, that they have o Arrange that Src and Dst are synchronized; that is, that they have
clocks that are very closely synchronized with each other and each clocks that are very closely synchronized with each other and each
fairly close to the actual time. fairly close to the actual time.
+ At the Src host, select Src and Dst IP addresses, and form a test o At the Src host, select Src and Dst IP addresses, and form a test
packet of Type-P with these addresses. Any 'padding' portion of the packet of Type-P with these addresses. Any 'padding' portion of
packet needed only to make the test packet a given size should be the packet needed only to make the test packet a given size should
filled with randomized bits to avoid a situation in which the be filled with randomized bits to avoid a situation in which the
measured delay is lower than it would otherwise be, due to measured delay is lower than it would otherwise be, due to
compression techniques along the path. Also see section 3.1.2 of compression techniques along the path. Also, see Section 3.1.2 of
[RFC7312]. [RFC7312].
+ At the Dst host, arrange to receive the packet. o At the Dst host, arrange to receive the packet.
+ At the Src host, place a timestamp in the prepared Type-P packet, o At the Src host, place a timestamp in the prepared Type-P packet,
and send it towards Dst (ideally minimizing time before sending). and send it towards Dst (ideally minimizing time before sending).
+ If the packet arrives within a reasonable period of time, take a o If the packet arrives within a reasonable period of time, take a
timestamp as soon as possible upon the receipt of the packet. By timestamp as soon as possible upon the receipt of the packet. By
subtracting the two timestamps, an estimate of one-way delay can be subtracting the two timestamps, an estimate of one-way delay can
computed. Error analysis of a given implementation of the method be computed. Error analysis of a given implementation of the
must take into account the closeness of synchronization between Src method must take into account the closeness of synchronization
and Dst. If the delay between Src's timestamp and the actual sending between Src and Dst. If the delay between Src's timestamp and the
of the packet is known, then the estimate could be adjusted by actual sending of the packet is known, then the estimate could be
subtracting this amount; uncertainty in this value must be taken into adjusted by subtracting this amount; uncertainty in this value
account in error analysis. Similarly, if the delay between the must be taken into account in error analysis. Similarly, if the
actual receipt of the packet and Dst's timestamp is known, then the delay between the actual receipt of the packet and Dst's timestamp
estimate could be adjusted by subtracting this amount; uncertainty in is known, then the estimate could be adjusted by subtracting this
this value must be taken into account in error analysis. See the amount; uncertainty in this value must be taken into account in
next section, "Errors and Uncertainties", for a more detailed error analysis. See "Errors and Uncertainties" (Section 3.7) for
discussion. a more detailed discussion.
+ If the packet fails to arrive within a reasonable period of time, o If the packet fails to arrive within a reasonable period of time,
Tmax, the one-way delay is taken to be undefined (informally, Tmax, the one-way delay is taken to be undefined (informally,
infinite). Note that the threshold of 'reasonable' is a parameter of infinite). Note that the threshold of "reasonable" is a parameter
the metric. These points are examined in detail in [RFC6703], of the metric. These points are examined in detail in [RFC6703],
including analysis preferences to assign undefined delay to packets including analysis preferences to assign undefined delay to
that fail to arrive with the difficulties emerging from the informal packets that fail to arrive with the difficulties emerging from
"infinite delay" assignment, and an estimation of an upper bound on the informal "infinite delay" assignment, and an estimation of an
waiting time for packets in transit. Further, enforcing a specific upper bound on waiting time for packets in transit. Further,
constant waiting time on stored singletons of one-way delay is enforcing a specific constant waiting time on stored singletons of
compliant with this specification and may allow the results to serve one-way delay is compliant with this specification and may allow
more than one reporting audience. the results to serve more than one reporting audience.
Issues such as the packet format, the means by which Dst knows when Issues such as the packet format, the means by which Dst knows when
to expect the test packet, and the means by which Src and Dst are to expect the test packet, and the means by which Src and Dst are
synchronized are outside the scope of this document. {Comment: We synchronized are outside the scope of this document. {Comment: We
plan to document elsewhere our own work in describing such more plan to document the implementation techniques of our work in much
detailed implementation techniques and we encourage others to as more detail elsewhere; we encourage others to do so as well.}
well.}
3.7. Errors and Uncertainties: 3.7. Errors and Uncertainties
The description of any specific measurement method should include an The description of any specific measurement method should include an
accounting and analysis of various sources of error or uncertainty. accounting and analysis of various sources of error or uncertainty.
The Framework document provides general guidance on this point, but The Framework document provides general guidance on this point, but
we note here the following specifics related to delay metrics: we note here the following specifics related to delay metrics:
+ Errors or uncertainties due to uncertainties in the clocks of the o Errors or uncertainties due to uncertainties in the clocks of the
Src and Dst hosts. Src and Dst hosts.
+ Errors or uncertainties due to the difference between 'wire time' o Errors or uncertainties due to the difference between 'wire time'
and 'host time'. and 'host time'.
In addition, the loss threshold may affect the results. Each of In addition, the loss threshold may affect the results. Each of
these are discussed in more detail below, along with a section these are discussed in more detail below, along with a section
("Calibration") on accounting for these errors and uncertainties. (Section 3.7.3) on accounting for these errors and uncertainties.
3.7.1. Errors or uncertainties related to Clocks 3.7.1. Errors or Uncertainties Related to Clocks
The uncertainty in a measurement of one-way delay is related, in The uncertainty in a measurement of one-way delay is related, in
part, to uncertainties in the clocks of the Src and Dst hosts. In part, to uncertainties in the clocks of the Src and Dst hosts. In
the following, we refer to the clock used to measure when the packet the following, we refer to the clock used to measure when the packet
was sent from Src as the source clock, we refer to the clock used to was sent from Src as the source clock, we refer to the clock used to
measure when the packet was received by Dst as the destination clock, measure when the packet was received by Dst as the destination clock,
we refer to the observed time when the packet was sent by the source we refer to the observed time when the packet was sent by the source
clock as Tsource, and the observed time when the packet was received clock as Tsource, and we refer to the observed time when the packet
by the destination clock as Tdest. Alluding to the notions of was received by the destination clock as Tdest. Alluding to the
synchronization, accuracy, resolution, and skew mentioned in the notions of synchronization, accuracy, resolution, and skew mentioned
Introduction, we note the following: in the Introduction, we note the following:
+ Any error in the synchronization between the source clock and the o Any error in the synchronization between the source clock and the
destination clock will contribute to error in the delay measurement. destination clock will contribute to error in the delay
We say that the source clock and the destination clock have a measurement. We say that the source clock and the destination
synchronization error of Tsynch if the source clock is Tsynch ahead clock have a synchronization error of Tsynch if the source clock
of the destination clock. Thus, if we know the value of Tsynch is Tsynch ahead of the destination clock. Thus, if we know the
exactly, we could correct for clock synchronization by adding Tsynch value of Tsynch exactly, we could correct for clock
to the uncorrected value of Tdest-Tsource. synchronization by adding Tsynch to the uncorrected value of
Tdest-Tsource.
+ The accuracy of a clock is important only in identifying the time o The accuracy of a clock is important only in identifying the time
at which a given delay was measured. Accuracy, per se, has no at which a given delay was measured. Accuracy, per se, has no
importance to the accuracy of the measurement of delay. When importance to the accuracy of the measurement of delay. When
computing delays, we are interested only in the differences between computing delays, we are interested only in the differences
clock values, not the values themselves. between clock values, not the values themselves.
+ The resolution of a clock adds to uncertainty about any time o The resolution of a clock adds to uncertainty about any time
measured with it. Thus, if the source clock has a resolution of 10 measured with it. Thus, if the source clock has a resolution of
msec, then this adds 10 msec of uncertainty to any time value 10 msec, then this adds 10 msec of uncertainty to any time value
measured with it. We will denote the resolution of the source clock measured with it. We will denote the resolution of the source
and the destination clock as Rsource and Rdest, respectively. clock and the destination clock as Rsource and Rdest,
respectively.
+ The skew of a clock is not so much an additional issue as it is a o The skew of a clock is not so much an additional issue as it is a
realization of the fact that Tsynch is itself a function of time. realization of the fact that Tsynch is itself a function of time.
Thus, if we attempt to measure or to bound Tsynch, this needs to be Thus, if we attempt to measure or to bound Tsynch, this needs to
done periodically. Over some periods of time, this function can be be done periodically. Over some periods of time, this function
approximated as a linear function plus some higher order terms; in can be approximated as a linear function plus some higher order
these cases, one option is to use knowledge of the linear component terms; in these cases, one option is to use knowledge of the
to correct the clock. Using this correction, the residual Tsynch is linear component to correct the clock. Using this correction, the
made smaller, but remains a source of uncertainty that must be residual Tsynch is made smaller but remains a source of
accounted for. We use the function Esynch(t) to denote an upper uncertainty that must be accounted for. We use the function
bound on the uncertainty in synchronization. Thus, |Tsynch(t)| <= Esynch(t) to denote an upper bound on the uncertainty in
Esynch(t). synchronization. Thus, |Tsynch(t)| <= Esynch(t).
Taking these items together, we note that naive computation Tdest- Taking these items together, we note that naive computation Tdest-
Tsource will be off by Tsynch(t) +/- (Rsource + Rdest). Using the Tsource will be off by Tsynch(t) +/- (Rsource + Rdest). Using the
notion of Esynch(t), we note that these clock-related problems notion of Esynch(t), we note that these clock-related problems
introduce a total uncertainty of Esynch(t)+ Rsource + Rdest. This introduce a total uncertainty of Esynch(t)+ Rsource + Rdest. This
estimate of total clock-related uncertainty should be included in the estimate of total clock-related uncertainty should be included in the
error/uncertainty analysis of any measurement implementation. error/uncertainty analysis of any measurement implementation.
3.7.2. Errors or uncertainties related to Wire-time vs Host-time 3.7.2. Errors or Uncertainties Related to Wire Time vs. Host Time
As we have defined one-way delay, we would like to measure the time As we have defined one-way delay, we would like to measure the time
between when the test packet leaves the network interface of Src and between when the test packet leaves the network interface of Src and
when it (completely) arrives at the network interface of Dst, and we when it (completely) arrives at the network interface of Dst: we
refer to these as "wire times." If the timings are themselves refer to these as "wire times." If the timings are themselves
performed by software on Src and Dst, however, then this software can performed by software on Src and Dst, however, then this software can
only directly measure the time between when Src grabs a timestamp only directly measure the time between when Src grabs a timestamp
just prior to sending the test packet and when Dst grabs a timestamp just prior to sending the test packet and when Dst grabs a timestamp
just after having received the test packet, and we refer to these two just after having received the test packet: we refer to these two
points as "host times". points as "host times".
We note that some systems perform host time stamping on the network We note that some systems perform host time stamping on the network-
interface hardware, in an attempt to minimize the difference from interface hardware, in an attempt to minimize the difference from
wire times. wire times.
To the extent that the difference between wire time and host time is To the extent that the difference between wire time and host time is
accurately known, this knowledge can be used to correct for host time accurately known, this knowledge can be used to correct for host time
measurements, and the corrected value more accurately estimates the measurements, and the corrected value more accurately estimates the
desired (wire time) metric. desired (wire-time) metric.
To the extent, however, that the difference between wire time and To the extent, however, that the difference between wire time and
host time is uncertain, this uncertainty must be accounted for in an host time is uncertain, this uncertainty must be accounted for in an
analysis of a given measurement method. We denote by Hsource an analysis of a given measurement method. We denote by Hsource an
upper bound on the uncertainty in the difference between wire time upper bound on the uncertainty in the difference between wire time
and host time on the Src host, and similarly define Hdest for the Dst and host time on the Src host, and similarly define Hdest for the Dst
host. We then note that these problems introduce a total uncertainty host. We then note that these problems introduce a total uncertainty
of Hsource+Hdest. This estimate of total wire-vs-host uncertainty of Hsource+Hdest. This estimate of total wire-vs-host uncertainty
should be included in the error/uncertainty analysis of any should be included in the error/uncertainty analysis of any
measurement implementation. measurement implementation.
3.7.3. Calibration 3.7.3. Calibration of Errors and Uncertainties
Generally, the measured values can be decomposed as follows: Generally, the measured values can be decomposed as follows:
measured value = true value + systematic error + random error measured value = true value + systematic error + random error
If the systematic error (the constant bias in measured values) can be If the systematic error (the constant bias in measured values) can be
determined, it can be compensated for in the reported results. determined, it can be compensated for in the reported results.
reported value = measured value - systematic error reported value = measured value - systematic error
therefore therefore:
reported value = true value + random error reported value = true value + random error
The goal of calibration is to determine the systematic and random The goal of calibration is to determine the systematic and random
error generated by the hosts themselves in as much detail as error generated by the hosts themselves in as much detail as
possible. At a minimum, a bound ("e") should be found such that the possible. At a minimum, a bound ("e") should be found such that the
reported value is in the range (true value - e) to (true value + e) reported value is in the range (true value - e) to (true value + e)
at least 95 percent of the time. We call "e" the calibration error at least 95% of the time. We call "e" the calibration error for the
for the measurements. It represents the degree to which the values measurements. It represents the degree to which the values produced
produced by the measurement host are repeatable; that is, how closely by the measurement host are repeatable; that is, how closely an
an actual delay of 30 ms is reported as 30 ms. {Comment: 95 percent actual delay of 30 ms is reported as 30 ms. {Comment: 95% was chosen
was chosen because (1) some confidence level is desirable to be able because (1) some confidence level is desirable to be able to remove
to remove outliers, which will be found in measuring any physical outliers, which will be found in measuring any physical property; (2)
property; (2) a particular confidence level should be specified so a particular confidence level should be specified so that the results
that the results of independent implementations can be compared; and of independent implementations can be compared; and (3) even with a
(3) even with a prototype user-level implementation, 95% was loose prototype user-level implementation, 95% was loose enough to exclude
enough to exclude outliers.} outliers.}
From the discussion in the previous two sections, the error in From the discussion in the previous two sections, the error in
measurements could be bounded by determining all the individual measurements could be bounded by determining all the individual
uncertainties, and adding them together to form uncertainties, and adding them together to form:
Esynch(t) + Rsource + Rdest + Hsource + Hdest. Esynch(t) + Rsource + Rdest + Hsource + Hdest.
However, reasonable bounds on both the clock-related uncertainty However, reasonable bounds on both the clock-related uncertainty
captured by the first three terms and the host-related uncertainty captured by the first three terms and the host-related uncertainty
captured by the last two terms should be possible by careful design captured by the last two terms should be possible by careful design
techniques and calibrating the hosts using a known, isolated, network techniques and calibrating the hosts using a known, isolated network
in a lab. in a lab.
For example, the clock-related uncertainties are greatly reduced For example, the clock-related uncertainties are greatly reduced
through the use of a GPS time source. The sum of Esynch(t) + Rsource through the use of a GPS time source. The sum of Esynch(t) + Rsource
+ Rdest is small, and is also bounded for the duration of the + Rdest is small and is also bounded for the duration of the
measurement because of the global time source. measurement because of the global time source.
The host-related uncertainties, Hsource + Hdest, could be bounded by The host-related uncertainties, Hsource + Hdest, could be bounded by
connecting two hosts back-to-back with a high-speed serial link or connecting two hosts back-to-back with a high-speed serial link or
isolated LAN segment. In this case, repeated measurements are isolated LAN segment. In this case, repeated measurements are
measuring the same one-way delay. measuring the same one-way delay.
If the test packets are small, such a network connection has a If the test packets are small, such a network connection has a
minimal delay that may be approximated by zero. The measured delay minimal delay that may be approximated by zero. The measured delay
therefore contains only systematic and random error in the therefore contains only systematic and random error in the
measurement hosts. The "average value" of repeated measurements is measurement hosts. The "average value" of repeated measurements is
the systematic error, and the variation is the random error. the systematic error, and the variation is the random error.
One way to compute the systematic error, and the random error to a One way to compute the systematic error, and the random error to a
95% confidence is to repeat the experiment many times - at least 95% confidence is to repeat the experiment many times -- at least
hundreds of tests. The systematic error would then be the median. hundreds of tests. The systematic error would then be the median.
The random error could then be found by removing the systematic error The random error could then be found by removing the systematic error
from the measured values. The 95% confidence interval would be the from the measured values. The 95% confidence interval would be the
range from the 2.5th percentile to the 97.5th percentile of these range from the 2.5th percentile to the 97.5th percentile of these
deviations from the true value. The calibration error "e" could then deviations from the true value. The calibration error "e" could then
be taken to be the largest absolute value of these two numbers, plus be taken to be the largest absolute value of these two numbers, plus
the clock-related uncertainty. {Comment: as described, this bound is the clock-related uncertainty. {Comment: as described, this bound is
relatively loose since the uncertainties are added, and the absolute relatively loose since the uncertainties are added, and the absolute
value of the largest deviation is used. As long as the resulting value of the largest deviation is used. As long as the resulting
value is not a significant fraction of the measured values, it is a value is not a significant fraction of the measured values, it is a
skipping to change at page 15, line 32 skipping to change at page 14, line 32
checks should be made to ensure that packets reported as losses were checks should be made to ensure that packets reported as losses were
really lost. First, the threshold for loss should be verified. In really lost. First, the threshold for loss should be verified. In
particular, ensure the "reasonable" threshold is reasonable: that it particular, ensure the "reasonable" threshold is reasonable: that it
is very unlikely a packet will arrive after the threshold value, and is very unlikely a packet will arrive after the threshold value, and
therefore the number of packets lost over an interval is not therefore the number of packets lost over an interval is not
sensitive to the error bound on measurements. Second, consider the sensitive to the error bound on measurements. Second, consider the
possibility that a packet arrives at the network interface, but is possibility that a packet arrives at the network interface, but is
lost due to congestion on that interface or to other resource lost due to congestion on that interface or to other resource
exhaustion (e.g. buffers) in the host. exhaustion (e.g. buffers) in the host.
3.8. Reporting the metric: 3.8. Reporting the Metric
The calibration and context in which the metric is measured MUST be The calibration and context in which the metric is measured MUST be
carefully considered, and SHOULD always be reported along with metric carefully considered and SHOULD always be reported along with metric
results. We now present four items to consider: the Type-P of test results. We now present four items to consider: the Type-P of test
packets, the threshold of infinite delay (if any), error calibration, packets, the threshold of infinite delay (if any), error calibration,
and the path traversed by the test packets. This list is not and the path traversed by the test packets. This list is not
exhaustive; any additional information that could be useful in exhaustive; any additional information that could be useful in
interpreting applications of the metrics should also be reported (see interpreting applications of the metrics should also be reported (see
[RFC6703] for extensive discussion of reporting considerations for [RFC6703] for extensive discussion of reporting considerations for
different audiences). different audiences).
3.8.1. Type-P 3.8.1. Type-P
As noted in the Framework document, section 13 of [RFC2330], the As noted in Section 13 of the Framework document [RFC2330], the value
value of the metric may depend on the type of IP packets used to make of the metric may depend on the type of IP packets used to make the
the measurement, or "Type-P". The value of Type-P-One-way-Delay measurement, or "Type-P". The value of Type-P-One-way-Delay could
could change if the protocol (UDP or TCP), port number, size, or change if the protocol (UDP or TCP), port number, size, or
arrangement for special treatment (e.g., IP DS Field [RFC2780], ECN arrangement for special treatment (e.g., IP DS Field [RFC2780],
[RFC3168], or RSVP) changes. Additional packet distinctions Explicit Congestion Notification (ECN) [RFC3168], or RSVP) changes.
identified in future extensions of the Type-P definition will apply.
The exact Type-P used to make the measurements MUST be accurately Additional packet distinctions identified in future extensions of the
reported. Type-P definition will apply. The exact Type-P used to make the
measurements MUST be accurately reported.
3.8.2. Loss Threshold 3.8.2. Loss Threshold
In addition, the threshold (or methodology to distinguish) between a In addition, the threshold (or methodology to distinguish) between a
large finite delay and loss MUST be reported. large finite delay and loss MUST be reported.
3.8.3. Calibration Results 3.8.3. Calibration Results
+ If the systematic error can be determined, it SHOULD be removed o If the systematic error can be determined, it SHOULD be removed
from the measured values. from the measured values.
+ You SHOULD also report the calibration error, e, such that the true o You SHOULD also report the calibration error, e, such that the
value is the reported value plus or minus e, with 95% confidence (see true value is the reported value plus or minus e, with 95%
the last section.) confidence (see the last section.)
+ If possible, the conditions under which a test packet with finite o If possible, the conditions under which a test packet with finite
delay is reported as lost due to resource exhaustion on the delay is reported as lost due to resource exhaustion on the
measurement host SHOULD be reported. measurement host SHOULD be reported.
3.8.4. Path 3.8.4. Path
Finally, the path traversed by the packet SHOULD be reported, if Finally, the path traversed by the packet SHOULD be reported, if
possible. In general it is impractical to know the precise path a possible. In general, it is impractical to know the precise path a
given packet takes through the network. The precise path may be given packet takes through the network. The precise path may be
known for certain Type-P on short or stable paths. If Type-P known for certain Type-P on short or stable paths. If Type-P
includes the record route (or loose-source route) option in the IP includes the record route (or loose-source route) option in the IP
header, and the path is short enough, and all routers* on the path header, and the path is short enough, and all routers* on the path
support record (or loose-source) route, then the path will be support record (or loose-source) route, then the path will be
precisely recorded. This is impractical because the route must be precisely recorded. This is impractical because the route must be
short enough, many routers do not support (or are not configured for) short enough, many routers do not support (or are not configured for)
record route, and use of this feature would often artificially worsen record route, and use of this feature would often artificially worsen
the performance observed by removing the packet from common-case the performance observed by removing the packet from common-case
processing. However, partial information is still valuable context. processing. However, partial information is still valuable context.
For example, if a host can choose between two links* (and hence two For example, if a host can choose between two links* (and hence, two
separate routes from Src to Dst), then the initial link used is separate routes from Src to Dst), then the initial link used is
valuable context. {Comment: For example, with Merit's NetNow setup, a valuable context. {Comment: For example, with Merit's NetNow setup, a
Src on one NAP can reach a Dst on another NAP by either of several Src on one Network Access Point (NAP) can reach a Dst on another NAP
different backbone networks.} by either of several different backbone networks.}
4. A Definition for Samples of One-way Delay 4. A Definition for Samples of One-Way Delay
Given the singleton metric Type-P-One-way-Delay, we now define one Given the singleton metric Type-P-One-way-Delay, we now define one
particular sample of such singletons. The idea of the sample is to particular sample of such singletons. The idea of the sample is to
select a particular binding of the parameters Src, Dst, and Type-P, select a particular binding of the parameters Src, Dst, and Type-P,
then define a sample of values of parameter T. The means for then define a sample of values of parameter T. The means for
defining the values of T is to select a beginning time T0, a final defining the values of T is to select a beginning time T0, a final
time Tf, and an average rate lambda, then define a pseudo-random time Tf, and an average rate lambda, then define a pseudorandom
Poisson process of rate lambda, whose values fall between T0 and Tf. Poisson process of rate lambda, whose values fall between T0 and Tf.
The time interval between successive values of T will then average 1/ The time interval between successive values of T will then average 1/
lambda. lambda.
Note that Poisson sampling is only one way of defining a sample. Note that Poisson sampling is only one way of defining a sample.
Poisson has the advantage of limiting bias, but other methods of Poisson has the advantage of limiting bias, but other methods of
sampling will be appropriate for different situations. For example, sampling will be appropriate for different situations. For example,
a truncated Poisson distribution may be needed to avoid reactive a truncated Poisson distribution may be needed to avoid reactive
network state changes during intervals of inactivity, see section 4.6 network state changes during intervals of inactivity, see Section 4.6
of [RFC7312]. Sometimes, the goal is sampling with a known bias, and of [RFC7312]. Sometimes the goal is sampling with a known bias, and
[RFC3432] describes a method for periodic sampling with random start [RFC3432] describes a method for periodic sampling with random start
times. times.
4.1. Metric Name: 4.1. Metric Name
Type-P-One-way-Delay-Poisson-Stream Type-P-One-way-Delay-Poisson-Stream
4.2. Metric Parameters: 4.2. Metric Parameters
+ Src, the IP address of a host o Src, the IP address of a host
+ Dst, the IP address of a host o Dst, the IP address of a host
+ T0, a time o T0, a time
+ Tf, a time o Tf, a time
+ Tmax, a loss threshold waiting time o Tmax, a loss threshold waiting time
+ lambda, a rate in reciprocal seconds (or parameters for another o lambda, a rate in reciprocal seconds (or parameters for another
distribution) distribution)
4.3. Metric Units: 4.3. Metric Units
A sequence of pairs; the elements of each pair are: A sequence of pairs; the elements of each pair are:
+ T, a time, and o T, a time, and
+ dT, either a real number or an undefined number of seconds. o dT, either a real number or an undefined number of seconds.
The values of T in the sequence are monotonic increasing. Note that The values of T in the sequence are monotonic increasing. Note that
T would be a valid parameter to Type-P-One-way-Delay, and that dT T would be a valid parameter to Type-P-One-way-Delay and that dT
would be a valid value of Type-P-One-way-Delay. would be a valid value of Type-P-One-way-Delay.
4.4. Definition: 4.4. Definition
Given T0, Tf, and lambda, we compute a pseudo-random Poisson process Given T0, Tf, and lambda, we compute a pseudorandom Poisson process
beginning at or before T0, with average arrival rate lambda, and beginning at or before T0, with average arrival rate lambda, and
ending at or after Tf. Those time values greater than or equal to T0 ending at or after Tf. Those time values greater than or equal to T0
and less than or equal to Tf are then selected. At each of the times and less than or equal to Tf are then selected. At each of the
in this process, we obtain the value of Type-P-One-way-Delay at this selected times in this process, we obtain one value of Type-P-One-
time. The value of the sample is the sequence made up of the way-Delay. The value of the sample is the sequence made up of the
resulting <time, delay> pairs. If there are no such pairs, the resulting <time, delay> pairs. If there are no such pairs, the
sequence is of length zero and the sample is said to be empty. sequence is of length zero and the sample is said to be empty.
4.5. Discussion: 4.5. Discussion
The reader should be familiar with the in-depth discussion of Poisson The reader should be familiar with the in-depth discussion of Poisson
sampling in the Framework document [RFC2330], which includes methods sampling in the Framework document [RFC2330], which includes methods
to compute and verify the pseudo-random Poisson process. to compute and verify the pseudorandom Poisson process.
We specifically do not constrain the value of lambda, except to note We specifically do not constrain the value of lambda except to note
the extremes. If the rate is too large, then the measurement traffic the extremes. If the rate is too large, then the measurement traffic
will perturb the network, and itself cause congestion. If the rate will perturb the network and itself cause congestion. If the rate is
is too small, then you might not capture interesting network too small, then you might not capture interesting network behavior.
behavior. {Comment: We expect to document our experiences with, and {Comment: We expect to document our experiences with, and suggestions
suggestions for, lambda elsewhere, culminating in a "best current for, lambda elsewhere, culminating in a "Best Current Practice"
practices" document.} document.}
Since a pseudo-random number sequence is employed, the sequence of Since a pseudorandom number sequence is employed, the sequence of
times, and hence the value of the sample, is not fully specified. times, and hence the value of the sample, is not fully specified.
Pseudo-random number generators of good quality will be needed to Pseudorandom number generators of good quality will be needed to
achieve the desired qualities. achieve the desired qualities.
The sample is defined in terms of a Poisson process both to avoid the The sample is defined in terms of a Poisson process both to avoid the
effects of self-synchronization and also capture a sample that is effects of self-synchronization and also capture a sample that is
statistically as unbiased as possible. {Comment: there is, of course, statistically as unbiased as possible. {Comment: there is, of course,
no claim that real Internet traffic arrives according to a Poisson no claim that real Internet traffic arrives according to a Poisson
arrival process.} The Poisson process is used to schedule the delay arrival process.} The Poisson process is used to schedule the delay
measurements. The test packets will generally not arrive at Dst measurements. The test packets will generally not arrive at Dst
according to a Poisson distribution, since they are influenced by the according to a Poisson distribution, since they are influenced by the
network. network.
All the singleton Type-P-One-way-Delay metrics in the sequence will All the singleton Type-P-One-way-Delay metrics in the sequence will
have the same values of Src, Dst, and Type-P. have the same values of Src, Dst, and Type-P.
Note also that, given one sample that runs from T0 to Tf, and given Note also that, given one sample that runs from T0 to Tf, and given
new time values T0' and Tf' such that T0 <= T0' <= Tf' <= Tf, the new time values T0' and Tf' such that T0 <= T0' <= Tf' <= Tf, the
subsequence of the given sample whose time values fall between T0' subsequence of the given sample whose time values fall between T0'
and Tf' are also a valid Type-P-One-way-Delay-Poisson-Stream sample. and Tf' are also a valid Type-P-One-way-Delay-Poisson-Stream sample.
4.6. Methodologies: 4.6. Methodologies
The methodologies follow directly from: The methodologies follow directly from:
+ the selection of specific times, using the specified Poisson o The selection of specific times using the specified Poisson
arrival process, and arrival process, and
+ the methodologies discussion already given for the singleton Type- o The methodologies discussion already given for the singleton Type-
P-One-way-Delay metric. P-One-way-Delay metric.
Care must, of course, be given to correctly handle out-of-order Care must be given to correctly handle out-of-order arrival of test
arrival of test packets; it is possible that the Src could send one packets; it is possible that the Src could send one test packet at
test packet at TS[i], then send a second one (later) at TS[i+1], TS[i], then send a second one (later) at TS[i+1] while the Dst could
while the Dst could receive the second test packet at TR[i+1], and receive the second test packet at TR[i+1], and then receive the first
then receive the first one (later) at TR[i]. Metrics for reordering one (later) at TR[i]. Metrics for reordering may be found in
may be found in [RFC4737]. [RFC4737].
4.7. Errors and Uncertainties: 4.7. Errors and Uncertainties
In addition to sources of errors and uncertainties associated with In addition to sources of errors and uncertainties associated with
methods employed to measure the singleton values that make up the methods employed to measure the singleton values that make up the
sample, care must be given to analyze the accuracy of the Poisson sample, care must be given to analyze the accuracy of the Poisson
process with respect to the wire-times of the sending of the test process with respect to the wire times of the sending of the test
packets. Problems with this process could be caused by several packets. Problems with this process could be caused by several
things, including problems with the pseudo-random number techniques things, including problems with the pseudorandom number techniques
used to generate the Poisson arrival process, or with jitter in the used to generate the Poisson arrival process, or with jitter in the
value of Hsource (mentioned above as uncertainty in the singleton value of Hsource (mentioned above as uncertainty in the singleton
delay metric). The Framework document shows how to use the Anderson- delay metric). The Framework document shows how to use the Anderson-
Darling test to verify the accuracy of a Poisson process over small Darling test to verify the accuracy of a Poisson process over small
time frames. {Comment: The goal is to ensure that test packets are time frames. {Comment: The goal is to ensure that test packets are
sent "close enough" to a Poisson schedule, and avoid periodic sent "close enough" to a Poisson schedule and avoid periodic
behavior.} behavior.}
4.8. Reporting the metric: 4.8. Reporting the Metric
You MUST report the calibration and context for the underlying The calibration and context for the underlying singletons MUST be
singletons along with the stream. (See "Reporting the metric" for reported along with the stream. (See "Reporting the Metric" for
Type-P-One-way-Delay.) Type-P-One-way-Delay in Section 3.8.)
5. Some Statistics Definitions for One-way Delay 5. Some Statistics Definitions for One-Way Delay
Given the sample metric Type-P-One-way-Delay-Poisson-Stream, we now Given the sample metric Type-P-One-way-Delay-Poisson-Stream, we now
offer several statistics of that sample. These statistics are offer several statistics of that sample. These statistics are
offered mostly to illustrate what could be done. See [RFC6703] for offered mostly to illustrate what could be done. See [RFC6703] for
additional discussion of statistics that are relevant to different additional discussion of statistics that are relevant to different
audiences. audiences.
5.1. Type-P-One-way-Delay-Percentile 5.1. Type-P-One-way-Delay-Percentile
Given a Type-P-One-way-Delay-Poisson-Stream and a percent X between Given a Type-P-One-way-Delay-Poisson-Stream and a percent X between
0% and 100%, the Xth percentile of all the dT values in the Stream. 0% and 100%, the Xth percentile of all the dT values in the stream.
In computing this percentile, undefined values are treated as In computing this percentile, undefined values are treated as
infinitely large. Note that this means that the percentile could infinitely large. Note that this means that the percentile could
thus be undefined (informally, infinite). In addition, the Type-P- thus be undefined (informally, infinite). In addition, the Type-P-
One-way-Delay-Percentile is undefined if the sample is empty. One-way-Delay-Percentile is undefined if the sample is empty.
Example: suppose we take a sample and the results are: For example: suppose we take a sample and the results are as follows:
Stream1 = < Stream1 = <
<T1, 100 msec> <T1, 100 msec>
<T2, 110 msec> <T2, 110 msec>
<T3, undefined> <T3, undefined>
<T4, 90 msec> <T4, 90 msec>
<T5, 500 msec> <T5, 500 msec>
> >
Then the 50th percentile would be 110 msec, since 90 msec and 100 Then, the 50th percentile would be 110 msec, since 90 msec and 100
msec are smaller and 500 msec and 'undefined' are larger. See msec are smaller and 500 msec and 'undefined' are larger. See
Section 11.3 of [RFC2330] for computing percentiles. Section 11.3 of [RFC2330] for computing percentiles.
Note that if the possibility that a packet with finite delay is Note that if the possibility that a packet with finite delay is
reported as lost is significant, then a high percentile (90th or reported as lost is significant, then a high percentile (90th or
95th) might be reported as infinite instead of finite. 95th) might be reported as infinite instead of finite.
5.2. Type-P-One-way-Delay-Median 5.2. Type-P-One-way-Delay-Median
Given a Type-P-One-way-Delay-Poisson-Stream, the median of all the dT Given a Type-P-One-way-Delay-Poisson-Stream, the median of all the dT
values in the Stream. In computing the median, undefined values are values in the stream. In computing the median, undefined values are
treated as infinitely large. As with Type-P-One-way-Delay- treated as infinitely large. As with Type-P-One-way-Delay-
Percentile, Type-P-One-way-Delay-Median is undefined if the sample is Percentile, Type-P-One-way-Delay-Median is undefined if the sample is
empty. empty.
As noted in the Framework document, the median differs from the 50th As noted in the Framework document, the median differs from the 50th
percentile only when the sample contains an even number of values, in percentile only when the sample contains an even number of values, in
which case the mean of the two central values is used. which case the mean of the two central values is used.
Example: suppose we take a sample and the results are: For example, suppose we take a sample and the results are as follows:
Stream2 = < Stream2 = <
<T1, 100 msec> <T1, 100 msec>
<T2, 110 msec> <T2, 110 msec>
<T3, undefined> <T3, undefined>
<T4, 90 msec> <T4, 90 msec>
> >
skipping to change at page 21, line 14 skipping to change at page 20, line 19
<T1, 100 msec> <T1, 100 msec>
<T2, 110 msec> <T2, 110 msec>
<T3, undefined> <T3, undefined>
<T4, 90 msec> <T4, 90 msec>
> >
Then the median would be 105 msec, the mean of 100 msec and 110 msec, Then, the median would be 105 msec, the mean of 100 msec and 110
the two central values. msec, the two central values.
5.3. Type-P-One-way-Delay-Minimum 5.3. Type-P-One-way-Delay-Minimum
Given a Type-P-One-way-Delay-Poisson-Stream, the minimum of all the Given a Type-P-One-way-Delay-Poisson-Stream, the minimum of all the
dT values in the Stream. In computing this, undefined values are dT values in the stream. In computing this, undefined values are
treated as infinitely large. Note that this means that the minimum treated as infinitely large. Note that this means that the minimum
could thus be undefined (informally, infinite) if all the dT values could thus be undefined (informally, infinite) if all the dT values
are undefined. In addition, the Type-P-One-way-Delay-Minimum is are undefined. In addition, the Type-P-One-way-Delay-Minimum is
undefined if the sample is empty. undefined if the sample is empty.
In the above example, the minimum would be 90 msec. In the above example, the minimum would be 90 msec.
5.4. Type-P-One-way-Delay-Inverse-Percentile 5.4. Type-P-One-way-Delay-Inverse-Percentile
Note: This statistic is deprecated in this version of the memo Note: This statistic is deprecated in this document because of lack
because of lack of use. of use.
Given a Type-P-One-way-Delay-Poisson-Stream and a time duration Given a Type-P-One-way-Delay-Poisson-Stream and a time duration
threshold, the fraction of all the dT values in the Stream less than threshold, the fraction of all the dT values in the stream less than
or equal to the threshold. The result could be as low as 0% (if all or equal to the threshold. The result could be as low as 0% (if all
the dT values exceed threshold) or as high as 100%. Type-P-One-way- the dT values exceed threshold) or as high as 100%. Type-P-One-way-
Delay-Inverse-Percentile is undefined if the sample is empty. Delay-Inverse-Percentile is undefined if the sample is empty.
In the above example, the Inverse-Percentile of 103 msec would be In the above example, the Inverse-Percentile of 103 msec would be
50%. 50%.
6. Security Considerations 6. Security Considerations
Conducting Internet measurements raises both security and privacy Conducting Internet measurements raises both security and privacy
concerns. This memo does not specify an implementation of the concerns. This memo does not specify an implementation of the
metrics, so it does not directly affect the security of the Internet metrics, so it does not directly affect the security of the Internet
nor of applications which run on the Internet. However, nor of applications that run on the Internet. However,
implementations of these metrics must be mindful of security and implementations of these metrics must be mindful of security and
privacy concerns. privacy concerns.
There are two types of security concerns: potential harm caused by There are two types of security concerns: potential harm caused by
the measurements, and potential harm to the measurements. The the measurements and potential harm to the measurements. The
measurements could cause harm because they are active, and inject measurements could cause harm because they are active and inject
packets into the network. The measurement parameters MUST be packets into the network. The measurement parameters MUST be
carefully selected so that the measurements inject trivial amounts of carefully selected so that the measurements inject trivial amounts of
additional traffic into the networks they measure. If they inject additional traffic into the networks they measure. If they inject
"too much" traffic, they can skew the results of the measurement, and "too much" traffic, they can skew the results of the measurement and
in extreme cases cause congestion and denial of service. in extreme cases cause congestion and denial of service.
The measurements themselves could be harmed by routers giving The measurements themselves could be harmed by routers giving
measurement traffic a different priority than "normal" traffic, or by measurement traffic a different priority than "normal" traffic or by
an attacker injecting artificial measurement traffic. If routers can an attacker injecting artificial measurement traffic. If routers can
recognize measurement traffic and treat it separately, the recognize measurement traffic and treat it separately, the
measurements will not reflect actual user traffic. Therefore, the measurements will not reflect actual user traffic. Therefore, the
measurement methodologies SHOULD include appropriate techniques to measurement methodologies SHOULD include appropriate techniques to
reduce the probability measurement traffic can be distinguished from reduce the probability that measurement traffic can be distinguished
"normal" traffic. from "normal" traffic.
If an attacker injects packets emulating traffic that are accepted as If an attacker injects packets emulating traffic that are accepted as
legitimate, the loss ratio or other measured values could be legitimate, the loss ratio or other measured values could be
corrupted. Authentication techniques, such as digital signatures, corrupted. Authentication techniques, such as digital signatures,
may be used where appropriate to guard against injected traffic may be used where appropriate to guard against injected traffic
attacks. attacks.
When considering privacy of those involved in measurement or those When considering privacy of those involved in measurement or those
whose traffic is measured, the sensitive information available to whose traffic is measured, the sensitive information available to
potential observers is greatly reduced when using active techniques potential observers is greatly reduced when using active techniques
which are within this scope of work. Passive observations of user that are within this scope of work. Passive observations of user
traffic for measurement purposes raise many privacy issues. We refer traffic for measurement purposes raise many privacy issues. We refer
the reader to the privacy considerations described in the Large Scale the reader to the privacy considerations described in the Large Scale
Measurement of Broadband Performance (LMAP) Framework Measurement of Broadband Performance (LMAP) Framework [RFC7594],
[I-D.ietf-lmap-framework], which covers active and passive which covers active and passive techniques.
techniques.
Collecting measurements or using measurement results for Collecting measurements or using measurement results for
reconnaissance to assist in subsequent system attacks is quite reconnaissance to assist in subsequent system attacks is quite
common. Access to measurement results, or control of the measurement common. Access to measurement results, or control of the measurement
systems to perform reconnaissance should be guarded against. See systems to perform reconnaissance should be guarded against. See
Section 7 of [I-D.ietf-lmap-framework] (security considerations of Section 7 of [RFC7594] (Security Considerations of the LMAP
the LMAP Framework) for system requirements that help to avoid Framework) for system requirements that help to avoid measurement
measurement system compromise. system compromise.
7. IANA Considerations 7. Changes from RFC 2679
This memo makes no requests of IANA. The text above constitutes a revision to RFC 2769, which is now an
Internet Standard. This section tracks the changes from [RFC2679].
8. Acknowledgements [RFC6808] provides the test plan and results supporting [RFC2679]
advancement along the Standards Track, according to the process in
[RFC6576]. The conclusions of [RFC6808] list four minor
modifications:
For [RFC2679], special thanks are due to Vern Paxson of Lawrence 1. Section 6.2.3 of [RFC6808] asserts that the assumption of post-
Berkeley Labs for his helpful comments on issues of clock uncertainty processing to enforce a constant waiting time threshold is
and statistics. Thanks also to Garry Couch, Will Leland, Andy compliant and that the text of the RFC should be revised slightly
Scherrer, Sean Shapira, and Roland Wittig for several useful to include this point. The applicability of post-processing was
suggestions. added in the last list item of Section 3.6.
For RFC 2679 bis, thanks to Joachim Fabini, Ruediger Geib, Nalini 2. Section 6.5 of [RFC6808] indicates that the Type-P-One-way-Delay-
Elkins, and Barry Constantine for sharing their measurement Inverse-Percentile statistic has been ignored in both
experience as part of their careful reviews. Brian Carpenter and implementations, so it was a candidate for removal or deprecation
Scott Bradner provided useful feedback at IETF Last Call. in this document (this small discrepancy does not affect
candidacy for advancement). This statistic was deprecated in
Section 5.4.
9. References 3. The IETF has reached consensus on guidance for reporting metrics
in [RFC6703], and the memo is referenced in this document to
incorporate recent experience where appropriate. This reference
was added in the last list item of Section 3.6, Section 3.8, and
in Section 5.
9.1. Normative References 4. There is currently one erratum with status "Held for Document
Update" (EID 398) for [RFC2679], and this minor revision and
additional text was incorporated in this document in Section 5.1.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, A number of updates to the [RFC2679] text have been implemented in
the text above to reference key IPPM RFCs that were approved after
[RFC2679] and to address comments on the IPPM mailing list describing
current conditions and experience.
1. Near the end of Section 1.1, there is an update of a network
example using ATM, a clarification of TCP's affect on queue
occupation, and discussion of the importance of one-way delay
measurement.
2. Explicit inclusion of the maximum waiting time input parameter
in Sections 3.2 and 4.2, reflecting recognition of this
parameter in more recent RFCs and ITU-T Recommendation Y.1540.
3. Addition of a reference to RFC 6703 in the discussion of packet
lifetime and application timeouts in Section 3.5.
4. Addition of a reference to the default requirement (that packets
be standard-formed) from RFC 2330 as a new list item in
Section 3.5.
5. GPS-based NTP experience replaces "to be tested" in Section 3.5.
6. Replaced "precedence" with updated terminology (DS Field) in
Sections 3.6 and 3.8.1(with reference).
7. Added parenthetical guidance on minimizing the interval between
timestamp placement to send time in Section 3.6.
8. Section 3.7.2 notes that some current systems perform host time
stamping on the network-interface hardware.
9. "instrument" replaced by the defined term "host" in
Section 3.7.3 and Section 3.8.3.
10. Added reference to RFC 3432 regarding periodic sampling
alongside Poisson sampling in Section 4 and also noted that a
truncated Poisson distribution may be needed with modern
networks as described in the IPPM Framework update [RFC7312].
11. Added a reference to RFC 4737 regarding reordering metrics in
the related discussion of "Methodologies (Section 4.6).
12. Modified the formatting of the example in Section 5.1 to match
the original (issue with conversion to XML in this version).
13. Clarified the conclusions on two related points on harm to
measurements (recognition of measurement traffic for unexpected
priority treatment and attacker traffic which emulates
measurement) in "Security Considerations (Section 6).
14. Expanded and updated the material on Privacy and added cautions
on the use of measurements for reconnaissance in "Security
Considerations" (Section 6).
Section 5.4.4 of [RFC6390] suggests a common template for performance
metrics partially derived from previous IPPM and Benchmarking
Methodology Working Group (BMWG) RFCs, but it also contains some new
items. All of the normative parts of [RFC6390] are covered, but not
quite in the same section names or orientation. Several of the
informative parts are covered. Maintaining the familiar outline of
IPPM literature has both value and minimizes unnecessary differences
between this revised RFC and current/future IPPM RFCs.
The publication of [RFC6921] suggested an area where this memo might
need updating. Packet transfer on Faster-Than-Light (FTL) networks
could result in negative delays and packet reordering; however, both
are covered as possibilities in the current text and no revisions are
deemed necessary (we also note that [RFC6921] is an April 1st RFC).
8. References
8.1. Normative References
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981, DOI 10.17487/RFC0791, September 1981,
<http://www.rfc-editor.org/info/rfc791>. <http://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, "Framework for IP Performance Metrics", RFC 2330,
skipping to change at page 23, line 44 skipping to change at page 24, line 42
<http://www.rfc-editor.org/info/rfc2330>. <http://www.rfc-editor.org/info/rfc2330>.
[RFC2678] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring [RFC2678] Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
Connectivity", RFC 2678, DOI 10.17487/RFC2678, September Connectivity", RFC 2678, DOI 10.17487/RFC2678, September
1999, <http://www.rfc-editor.org/info/rfc2678>. 1999, <http://www.rfc-editor.org/info/rfc2678>.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way [RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, DOI 10.17487/RFC2679, Delay Metric for IPPM", RFC 2679, DOI 10.17487/RFC2679,
September 1999, <http://www.rfc-editor.org/info/rfc2679>. September 1999, <http://www.rfc-editor.org/info/rfc2679>.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680,
DOI 10.17487/RFC2680, September 1999,
<http://www.rfc-editor.org/info/rfc2680>.
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For [RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", Values In the Internet Protocol and Related Headers",
BCP 37, RFC 2780, DOI 10.17487/RFC2780, March 2000, BCP 37, RFC 2780, DOI 10.17487/RFC2780, March 2000,
<http://www.rfc-editor.org/info/rfc2780>. <http://www.rfc-editor.org/info/rfc2780>.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network [RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432, performance measurement with periodic streams", RFC 3432,
DOI 10.17487/RFC3432, November 2002, DOI 10.17487/RFC3432, November 2002,
<http://www.rfc-editor.org/info/rfc3432>. <http://www.rfc-editor.org/info/rfc3432>.
[RFC6576] Geib, R., Ed., Morton, A., Fardid, R., and A. Steinmitz, [RFC6576] Geib, R., Ed., Morton, A., Fardid, R., and A. Steinmitz,
"IP Performance Metrics (IPPM) Standard Advancement "IP Performance Metrics (IPPM) Standard Advancement
Testing", BCP 176, RFC 6576, DOI 10.17487/RFC6576, March Testing", BCP 176, RFC 6576, DOI 10.17487/RFC6576, March
2012, <http://www.rfc-editor.org/info/rfc6576>. 2012, <http://www.rfc-editor.org/info/rfc6576>.
[RFC7312] Fabini, J. and A. Morton, "Advanced Stream and Sampling [RFC7312] Fabini, J. and A. Morton, "Advanced Stream and Sampling
Framework for IP Performance Metrics (IPPM)", RFC 7312, Framework for IP Performance Metrics (IPPM)", RFC 7312,
DOI 10.17487/RFC7312, August 2014, DOI 10.17487/RFC7312, August 2014,
<http://www.rfc-editor.org/info/rfc7312>. <http://www.rfc-editor.org/info/rfc7312>.
9.2. Informative References [RFC7680] Almes, G., Kalidini, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Loss Metric for IP Performance Metrics
(IPPM)", RFC 7680, DOI 10.17487/RFC7680, January 2016,
<http://www.rfc-editor.org/info/rfc7680>.
[I-D.ietf-lmap-framework] 8.2. Informative References
Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A framework for Large-Scale
Measurement of Broadband Performance (LMAP)", draft-ietf-
lmap-framework-14 (work in progress), April 2015.
[I-D.morton-ippm-2330-stdform-typep] [IPPM-UPDATES]
Morton, A., Fabini, J., Elkins, N., Ackermann, M., and V. Morton, A., Fabini, J., Elkins, N., Ackermann, M., and V.
Hegde, "Updates for IPPM's Active Metric Framework: Hegde, "Updates for IPPM's Active Metric Framework:
Packets of Type-P and Standard-Formed Packets", draft- Packets of Type-P and Standard-Formed Packets", Work in
morton-ippm-2330-stdform-typep-00 (work in progress), Progress, draft-morton-ippm-2330-stdform-typep-02,
August 2015. December 2015.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001, RFC 3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>. <http://www.rfc-editor.org/info/rfc3168>.
[RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, [RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
S., and J. Perser, "Packet Reordering Metrics", RFC 4737, S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
DOI 10.17487/RFC4737, November 2006, DOI 10.17487/RFC4737, November 2006,
<http://www.rfc-editor.org/info/rfc4737>. <http://www.rfc-editor.org/info/rfc4737>.
skipping to change at page 25, line 15 skipping to change at page 26, line 5
[RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting [RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
IP Network Performance Metrics: Different Points of View", IP Network Performance Metrics: Different Points of View",
RFC 6703, DOI 10.17487/RFC6703, August 2012, RFC 6703, DOI 10.17487/RFC6703, August 2012,
<http://www.rfc-editor.org/info/rfc6703>. <http://www.rfc-editor.org/info/rfc6703>.
[RFC6808] Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test [RFC6808] Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test
Plan and Results Supporting Advancement of RFC 2679 on the Plan and Results Supporting Advancement of RFC 2679 on the
Standards Track", RFC 6808, DOI 10.17487/RFC6808, December Standards Track", RFC 6808, DOI 10.17487/RFC6808, December
2012, <http://www.rfc-editor.org/info/rfc6808>. 2012, <http://www.rfc-editor.org/info/rfc6808>.
[RFC6921] Hinden, R., "Design Considerations for Faster-Than-Light
(FTL) Communication", RFC 6921, DOI 10.17487/RFC6921,
April 2013, <http://www.rfc-editor.org/info/rfc6921>.
[RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A Framework for Large-Scale
Measurement of Broadband Performance (LMAP)", RFC 7594,
DOI 10.17487/RFC7594, September 2015,
<http://www.rfc-editor.org/info/rfc7594>.
Acknowledgements
For [RFC2679], special thanks are due to Vern Paxson of Lawrence
Berkeley Labs for his helpful comments on issues of clock uncertainty
and statistics. Thanks also to Garry Couch, Will Leland, Andy
Scherrer, Sean Shapira, and Roland Wittig for several useful
suggestions.
For this document, thanks to Joachim Fabini, Ruediger Geib, Nalini
Elkins, and Barry Constantine for sharing their measurement
experience as part of their careful reviews. Brian Carpenter and
Scott Bradner provided useful feedback at IETF Last Call.
Authors' Addresses Authors' Addresses
Guy Almes Guy Almes
Texas A&M Texas A&M
Email: almes@acm.org Email: almes@acm.org
Sunil Kalidindi Sunil Kalidindi
Ixia Ixia
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Matt Zekauskas Matt Zekauskas
Internet2 Internet2
Email: matt@internet2.edu Email: matt@internet2.edu
Al Morton (editor) Al Morton (editor)
AT&T Labs AT&T Labs
200 Laurel Avenue South 200 Laurel Avenue South
Middletown, NJ 07748 Middletown, NJ 07748
USA United States
Phone: +1 732 420 1571 Phone: +1 732 420 1571
Fax: +1 732 368 1192 Fax: +1 732 368 1192
Email: acmorton@att.com Email: acmorton@att.com
URI: http://home.comcast.net/~acmacm/ URI: http://home.comcast.net/~acmacm/
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