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Internet Engineering Task Force (IETF) G. Almes Request for Comments: 7680 Texas A&M STD: 82 S. Kalidindi Obsoletes: 2680 Ixia Category: Standards Track M. Zekauskas ISSN: 2070-1721 Internet2

                                                        A. Morton, Ed.
                                                             AT&T Labs
                                                          January 2016
      A One-Way Loss Metric for IP Performance Metrics (IPPM)

Abstract

 This memo defines a metric for one-way loss of packets across
 Internet paths.  It builds on notions introduced and discussed in the
 IP Performance Metrics (IPPM) Framework document, RFC 2330; the
 reader is assumed to be familiar with that document.  This memo makes
 RFC 2680 obsolete.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 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/rfc7680.

Almes, et al. Standards Track [Page 1] RFC 7680 A One-Way Loss Metric for IPPM January 2016

Copyright Notice

 Copyright (c) 2016 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Almes, et al. Standards Track [Page 2] RFC 7680 A One-Way Loss Metric for IPPM January 2016

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   1.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   5
   1.2.  General Issues regarding Time . . . . . . . . . . . . . .   6
 2.  A Singleton Definition for One-Way Packet Loss  . . . . . . .   7
   2.1.  Metric Name . . . . . . . . . . . . . . . . . . . . . . .   7
   2.2.  Metric Parameters . . . . . . . . . . . . . . . . . . . .   7
   2.3.  Metric Units  . . . . . . . . . . . . . . . . . . . . . .   7
   2.4.  Definition  . . . . . . . . . . . . . . . . . . . . . . .   7
   2.5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . .   8
   2.6.  Methodologies . . . . . . . . . . . . . . . . . . . . . .   9
   2.7.  Errors and Uncertainties  . . . . . . . . . . . . . . . .  10
   2.8.  Reporting the Metric  . . . . . . . . . . . . . . . . . .  11
     2.8.1.  Type-P  . . . . . . . . . . . . . . . . . . . . . . .  11
     2.8.2.  Loss Threshold  . . . . . . . . . . . . . . . . . . .  11
     2.8.3.  Calibration Results . . . . . . . . . . . . . . . . .  11
     2.8.4.  Path  . . . . . . . . . . . . . . . . . . . . . . . .  12
 3.  A Definition for Samples of One-Way Packet Loss . . . . . . .  12
   3.1.  Metric Name . . . . . . . . . . . . . . . . . . . . . . .  12
   3.2.  Metric Parameters . . . . . . . . . . . . . . . . . . . .  13
   3.3.  Metric Units  . . . . . . . . . . . . . . . . . . . . . .  13
   3.4.  Definition  . . . . . . . . . . . . . . . . . . . . . . .  13
   3.5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . .  13
   3.6.  Methodologies . . . . . . . . . . . . . . . . . . . . . .  14
   3.7.  Errors and Uncertainties  . . . . . . . . . . . . . . . .  15
   3.8.  Reporting the Metric  . . . . . . . . . . . . . . . . . .  15
 4.  Some Statistics Definitions for One-Way Packet Loss . . . . .  15
   4.1.  Type-P-One-way-Packet-Loss-Ratio  . . . . . . . . . . . .  15
 5.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
 6.  Changes from RFC 2680 . . . . . . . . . . . . . . . . . . . .  17
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
   7.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
   7.2.  Informative References  . . . . . . . . . . . . . . . . .  20
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  21
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

Almes, et al. Standards Track [Page 3] RFC 7680 A One-Way Loss Metric for IPPM January 2016

1. Introduction

 This memo defines a metric for one-way packet loss across Internet
 paths.  It builds on notions introduced and discussed in the IPPM
 Framework document, [RFC2330]; the reader is assumed to be familiar
 with that document and its recent update [RFC7312].
 This memo is intended to be parallel in structure to a companion
 document for One-way Delay ("A One-Way Delay Metric for IP
 Performance Metrics (IPPM)") [RFC7679]; the reader is assumed to be
 familiar with that document.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].  Although
 [RFC2119] was written with protocols in mind, the key words are used
 in this document for similar reasons.  They are used to ensure the
 results of measurements from two different implementations are
 comparable and to note instances when an implementation could perturb
 the network.
 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.
 The structure of the memo is as follows:
 o  A 'singleton*' analytic metric, called Type-P-One-way-Packet-Loss,
    is introduced to measure a single observation of packet
    transmission or loss.
 o  Using this singleton metric, a 'sample*' called Type-P-One-way-
    Packet-Loss-Poisson-Stream is introduced to measure a sequence of
    singleton transmissions and/or losses measured at times taken from
    a Poisson process, as defined in Section 11.1.1 of [RFC2330].
 o  Using this sample, several 'statistics*' of the sample will be
    defined and discussed.
 This progression from singleton to sample to statistics, with clear
 separation among them, is important.

Almes, et al. Standards Track [Page 4] RFC 7680 A One-Way Loss Metric for IPPM January 2016

1.1. Motivation

 Understanding one-way packet loss of Type-P* packets from a source
 host* to a destination host is useful for several reasons:
 o  Some applications do not perform well (or at all) if end-to-end
    loss between hosts is large relative to some threshold value.
 o  Excessive packet loss may make it difficult to support certain
    real-time applications (where the precise threshold of "excessive"
    depends on the application).
 o  The larger the value of packet loss, the more difficult it is for
    transport-layer protocols to sustain high bandwidths.
 o  The sensitivity of real-time applications and of transport-layer
    protocols to loss become especially important when very large
    delay-bandwidth products must be supported.
 The measurement of one-way loss instead of round-trip loss is
 motivated by the following factors:
 o  In today's Internet, the path from a source to a destination may
    be different than the path from the destination back to the source
    ("asymmetric paths"), such that different sequences of routers are
    used for the forward and reverse paths.  Therefore, round-trip
    measurements actually measure the performance of two distinct
    paths together.  Measuring each path independently highlights the
    performance difference between the two paths that may traverse
    different Internet service providers and even radically different
    types of networks (for example, research versus commodity
    networks, or networks with asymmetric link capacities, or wireless
    versus wireline access).
 o  Even when the two paths are symmetric, they may have radically
    different performance characteristics due to asymmetric queuing.
 o  Performance of an application may depend mostly on the performance
    in one direction.  For example, a TCP-based communication will
    experience reduced throughput if congestion occurs in one
    direction of its communication.  Troubleshooting may be simplified
    if the congested direction of TCP transmission can be identified.
 o  In networks in which quality of service (QoS) is enabled,
    provisioning in one direction may be radically different than
    provisioning in the reverse direction and thus the QoS guarantees
    differ.  Measuring the paths independently allows the verification
    of both guarantees.

Almes, et al. Standards Track [Page 5] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 It is outside the scope of this document to say precisely how loss
 metrics would be applied to specific problems.

1.2. General Issues regarding Time

 {Comment: The terminology below differs from that defined by ITU-T
 documents (e.g., G.810, "Definitions and terminology for
 synchronization networks" and I.356, "B-ISDN ATM layer cell transfer
 performance") but is consistent with the IPPM Framework document.  In
 general, these differences derive from the different backgrounds; the
 ITU-T documents historically have a telephony origin, while the
 authors of this document (and the Framework document) have a computer
 systems background.  Although the terms defined below have no direct
 equivalent in the ITU-T definitions, after our definitions we will
 provide a rough mapping.  However, note one potential confusion: our
 definition of "clock" is the computer operating systems definition
 denoting a time-of-day clock, while the ITU-T definition of clock
 denotes a frequency reference.}
 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.
 As described more fully in the Framework document, there are four
 distinct, but related notions of clock uncertainty:
 synchronization*
 measures the extent to which two clocks agree on what time it is.
 For example, the clock on one host might be 5.4 msec ahead of the
 clock on a second host. {Comment: A rough ITU-T equivalent is "time
 error".}
 accuracy*
 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:
 A rough ITU-T equivalent is "time error from UTC".}
 resolution*
 is a specification of the smallest unit by which the clock's time is
 updated.  It gives a lower bound on the clock's uncertainty.  For
 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".}

Almes, et al. Standards Track [Page 6] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 skew*
 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
 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
 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
 another clock, which threatens synchronization. {Comment: A rough
 ITU-T equivalent is "time drift".}

2. A Singleton Definition for One-Way Packet Loss

2.1. Metric Name

 Type-P-One-way-Packet-Loss

2.2. Metric Parameters

 o  Src, the IP address of a host
 o  Dst, the IP address of a host
 o  T, a time
 o  Tmax, a loss threshold waiting time

2.3. Metric Units

 The value of a Type-P-One-way-Packet-Loss is either a zero
 (signifying successful transmission of the packet) or a one
 (signifying loss).

2.4. Definition

 >>The *Type-P-One-way-Packet-Loss* from Src to Dst at T is 0<< means
 that Src sent the first bit of a Type-P packet to Dst at wire time* T
 and that Dst received that packet.
 >>The *Type-P-One-way-Packet-Loss* from Src to Dst at T is 1<< 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 packet (within the loss threshold
 waiting time, Tmax).

Almes, et al. Standards Track [Page 7] RFC 7680 A One-Way Loss Metric for IPPM January 2016

2.5. Discussion

 Thus, Type-P-One-way-Packet-Loss is 0 exactly when Type-P-One-way-
 Delay is a finite value, and it is 1 exactly when Type-P-One-way-
 Delay is undefined.
 The following issues are likely to come up in practice:
 o  A given methodology will have to include a way to distinguish
    between a packet loss and a very large (but finite) delay.  As
    noted by Mahdavi and Paxson [RFC2678], simple upper bounds (such
    as the 255-second theoretical upper bound on the lifetimes of IP
    packets [RFC791]) could be used, but good engineering, including
    an understanding of packet lifetimes, will be needed in practice.
    {Comment: Note that, for many applications of these metrics, there
    may be no harm in treating a large delay as packet loss.  An audio
    playback packet, for example, that arrives only after the playback
    point may as well have been lost.  See Section 4.1.1 of [RFC6703]
    for examination of unusual packet delays and application
    performance estimation.}
 o  If the packet arrives but is corrupted, then it is counted as
    lost. {Comment: One is tempted to count the packet as received
    since corruption and packet loss are related but distinct
    phenomena.  If the IP header is corrupted, however, one cannot be
    sure about the source or destination IP addresses and is thus on
    shaky grounds about knowing that the corrupted received packet
    corresponds to a given sent test packet.  Similarly, if other
    parts of the packet needed by the methodology to know that the
    corrupted received packet corresponds to a given sent test packet,
    then such a packet would have to be counted as lost.  It would be
    inconsistent to count packets with corrupted methodology-specific
    fields as lost, and not to count packets with other corrupted
    aspects in the same category.} Section 15 of [RFC2330] defines the
    "standard-formed" packet that is applicable to all metrics.  Note
    that at this time the definition of standard-formed packets only
    applies to IPv4 (see also [IPPM-UPDATES]).
 o  If the packet is duplicated along the path (or paths) so that
    multiple non-corrupt copies arrive at the destination, then the
    packet is counted as received.
 o  If the packet is fragmented and if, for whatever reason,
    reassembly does not occur, then the packet will be deemed lost.

Almes, et al. Standards Track [Page 8] RFC 7680 A One-Way Loss Metric for IPPM January 2016

2.6. Methodologies

 As with other Type-P-* metrics, the detailed methodology will depend
 on the Type-P (e.g., protocol number, UDP/TCP port number, size,
 Differentiated Services (DS) Field [RFC2780]).
 Generally, for a given Type-P, one possible methodology would proceed
 as follows:
 o  Arrange that Src and Dst have clocks that are synchronized with
    each other.  The degree of synchronization is a parameter of the
    methodology and depends on the threshold used to determine loss
    (see below).
 o  At the Src host, select Src and Dst IP addresses and form a test
    packet of Type-P with these addresses.
 o  At the Dst host, arrange to receive the 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).
 o  If the packet arrives within a reasonable period of time, the one-
    way packet loss is taken to be zero (and take a timestamp as soon
    as possible upon the receipt of the packet).
 o  If the packet fails to arrive within a reasonable period of time,
    Tmax, the one-way packet loss is taken to be one.  Note that the
    threshold of "reasonable" here is a parameter of the metric.
 {Comment: The definition of reasonable is intentionally vague and is
 intended to indicate a value "Th" so large that any value in the
 closed interval [Th-delta, Th+delta] is an equivalent threshold for
 loss.  Here, delta encompasses all error in clock synchronization and
 timestamp acquisition and assignment along the measured path.  If
 there is a single value, Tmax, after which the packet must be counted
 as lost, then we reintroduce the need for a degree of clock
 synchronization similar to that needed for one-way delay, and
 virtually all practical measurement systems combine methods for delay
 and loss.  Therefore, if a measure of packet loss parameterized by a
 specific non-huge "reasonable" time-out value is needed, one can
 always measure one-way delay and see what percentage of packets from
 a given stream exceed a given time-out value.  This point is examined
 in detail in [RFC6703], including analysis preferences to assign
 undefined delay to packets that fail to arrive with the difficulties
 emerging from the informal "infinite delay" assignment, and an
 estimation of an upper bound on waiting time for packets in transit.
 Further, enforcing a specific constant waiting time on stored

Almes, et al. Standards Track [Page 9] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 singletons of one-way delay is compliant with this specification and
 may allow the results to serve more than one reporting audience.}
 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
 synchronized are outside the scope of this document. {Comment: We
 plan to document the implementation techniques of our work in much
 more detail elsewhere; we encourage others to do so as well.}

2.7. Errors and Uncertainties

 The description of any specific measurement method should include an
 accounting and analysis of various sources of error or uncertainty.
 The Framework document provides general guidance on this point.
 For loss, there are three sources of error:
 o  synchronization between clocks on Src and Dst.
 o  the packet-loss threshold (which is related to the synchronization
    between clocks).
 o  resource limits in the network interface or software on the
    receiving instrument.
 The first two sources are interrelated and could result in a test
 packet with finite delay being reported as lost.  Type-P-One-way-
 Packet-Loss is 1 if the test packet does not arrive, or if it does
 arrive and the difference between the Src timestamp and the Dst
 timestamp is greater than the "reasonable period of time" or loss
 threshold.  If the clocks are not sufficiently synchronized, the loss
 threshold may not be "reasonable" - the packet may take much less
 time to arrive than its Src timestamp indicates.  Similarly, if the
 loss threshold is set too low, then many packets may be counted as
 lost.  The loss threshold must be high enough and the clocks
 synchronized well enough so that a packet that arrives is rarely
 counted as lost.  (See the discussions in the previous two sections.)
 Since the sensitivity of packet-loss measurement alone to lack of
 clock synchronization is less than for delay, we refer the reader to
 the treatment of synchronization errors in the "One-way Delay Metric
 for IPPM" [RFC2330] for more details.
 The last source of error, resource limits, cause the packet to be
 dropped by the measurement instrument and counted as lost when in
 fact the network delivered the packet in reasonable time.

Almes, et al. Standards Track [Page 10] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 The measurement instruments should be calibrated such that the loss
 threshold is reasonable for application of the metrics and the clocks
 are synchronized enough so the loss threshold remains reasonable.
 In addition, the instruments should be checked to ensure that the
 possibility a packet arrives at the network interface but is lost due
 to congestion on the interface or to other resource exhaustion (e.g.,
 buffers) on the instrument is low.

2.8. Reporting the Metric

 The calibration and context in which the metric is measured MUST be
 carefully considered and SHOULD always be reported along with metric
 results.  We now present four items to consider: Type-P of the test
 packets, the loss threshold, instrument calibration, and the path
 traversed by the test packets.  This list is not exhaustive; any
 additional information that could be useful in interpreting
 applications of the metrics should also be reported (see [RFC6703]
 for extensive discussion of reporting considerations for different
 audiences).

2.8.1. Type-P

 As noted in Section 13 of the Framework document [RFC2330], the value
 of the metric may depend on the type of IP packets used to make the
 measurement, or "Type-P".  The value of Type-P-One-way-Delay could
 change if the protocol (UDP or TCP), port number, size, or
 arrangement for special treatment (e.g., IP DS Field [RFC2780],
 Explicit Congestion Notification (ECN) [RFC3168], or RSVP) changes.
 Additional packet distinctions identified in future extensions of the
 Type-P definition will apply.  The exact Type-P used to make the
 measurements MUST be accurately reported.

2.8.2. Loss Threshold

 The threshold, Tmax, between a large finite delay and loss (or other
 methodology to distinguish between finite delay and loss) MUST be
 reported.

2.8.3. Calibration Results

 The degree of synchronization between the Src and Dst clocks MUST be
 reported.  If possible, a test packet that arrives at the Dst network
 interface and is reported as lost due to resource exhaustion on Dst
 SHOULD be reported.

Almes, et al. Standards Track [Page 11] RFC 7680 A One-Way Loss Metric for IPPM January 2016

2.8.4. Path

 Finally, the path traversed by the packet SHOULD be reported, if
 possible.  In general, it is impractical to know the precise path a
 given packet takes through the network.  The precise path may be
 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
 header, and the path is short enough, and all routers* on the path
 support record (or loose-source) route, then the path will be
 precisely recorded.  This is impractical because the route must be
 short enough, many routers do not support (or are not configured for)
 record route, and use of this feature would often artificially worsen
 the performance observed by removing the packet from common-case
 processing.  However, partial information is still valuable context.
 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
 valuable context. {Comment: Backbone path selection services come and
 go.  A historical example was Merit's NetNow setup, where a Src on
 one Network Access Point (NAP) can reach a Dst on another NAP by
 either of several different backbone networks.}

3. A Definition for Samples of One-Way Packet Loss

 Given the singleton metric Type-P-One-way-Packet-Loss, we now define
 one particular sample of such singletons.  The idea of the sample is
 to select a particular binding of the parameters Src, Dst, and Type-
 P, 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
 time Tf, and an average rate lambda, then define a pseudorandom
 Poisson process of rate lambda, whose values fall between T0 and Tf.
 The time interval between successive values of T will then average 1/
 lambda.
 Note that Poisson sampling is only one way of defining a sample.
 Poisson has the advantage of limiting bias, but other methods of
 sampling will be appropriate for different situations.  For example,
 a truncated Poisson distribution may be needed to avoid reactive
 network state changes during intervals of inactivity, see Section 4.6
 of [RFC7312].  Sometimes the goal is sampling with a known bias, and
 [RFC3432] describes a method for periodic sampling with random start
 times.

3.1. Metric Name

 Type-P-One-way-Packet-Loss-Poisson-Stream

Almes, et al. Standards Track [Page 12] RFC 7680 A One-Way Loss Metric for IPPM January 2016

3.2. Metric Parameters

 o  Src, the IP address of a host
 o  Dst, the IP address of a host
 o  T0, a time
 o  Tf, a time
 o  Tmax, a loss threshold waiting time
 o  lambda, a rate in reciprocal seconds

3.3. Metric Units

 A sequence of pairs; the elements of each pair are:
 o  T, a time, and
 o  L, either a zero or a one.
 The values of T in the sequence are monotonic increasing.  Note that
 T would be a valid parameter to Type-P-One-way-Packet-Loss and that L
 would be a valid value of Type-P-One-way-Packet-Loss.

3.4. Definition

 Given T0, Tf, and lambda, we compute a pseudorandom Poisson process
 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
 and less than or equal to Tf are then selected.  At each of the
 selected times in this process, we obtain one value of Type-P-One-
 way-Delay.  The value of the sample is the sequence made up of the
 resulting <time, loss> pairs.  If there are no such pairs, the
 sequence is of length zero and the sample is said to be empty.

3.5. Discussion

 The reader should be familiar with the in-depth discussion of Poisson
 sampling in the Framework document [RFC2330], which includes methods
 to compute and verify the pseudorandom Poisson process.
 We specifically do not constrain the value of lambda except to note
 the extremes.  If the rate is too large, then the measurement traffic
 will perturb the network and itself cause congestion.  If the rate is
 too small, then you might not capture interesting network behavior.
 {Comment: We expect to document our experiences with, and suggestions

Almes, et al. Standards Track [Page 13] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 for, lambda elsewhere, culminating in a "Best Current Practice"
 document.}
 Since a pseudorandom number sequence is employed, the sequence of
 times, and hence the value of the sample, is not fully specified.
 Pseudorandom number generators of good quality will be needed to
 achieve the desired qualities.
 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
 statistically as unbiased as possible.  The Poisson process is used
 to schedule the loss measurements.  The test packets will generally
 not arrive at Dst according to a Poisson distribution, since they are
 influenced by the network.  Time-slotted links described in
 Section 3.4 [RFC7312] can greatly modify the sample characteristics.
 The main concern is that unbiased packet streams with randomized
 inter-packet time intervals will be converted to some new
 distribution after encountering a time-slotted link, possibly with
 strong periodic characteristics instead.
 {Comment: there is, of course, no claim that real Internet traffic
 arrives according to a Poisson arrival process.
 It is important to note that, in contrast to this metric, loss ratios
 observed by transport connections do not reflect unbiased samples.
 For example, TCP transmissions both (1) occur in bursts, which can
 induce loss due to the burst volume that would not otherwise have
 been observed, and (2) adapt their transmission rate in an attempt to
 minimize the loss ratio observed by the connection.}
 All the singleton Type-P-One-way-Packet-Loss metrics in the sequence
 will have the same values of Src, Dst, and Type-P.
 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
 subsequence of the given sample whose time values fall between T0'
 and Tf' are also a valid Type-P-One-way-Packet-Loss-Poisson-Stream
 sample.

3.6. Methodologies

 The methodologies follow directly from:
 o  the selection of specific times using the specified Poisson
    arrival process, and
 o  the methodologies discussion already given for the singleton Type-
    P-One-way-Packet-Loss metric.

Almes, et al. Standards Track [Page 14] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 Care must be given to correctly handle out-of-order arrival of test
 packets; it is possible that the Src could send one test packet at
 TS[i], then send a second one (later) at TS[i+1] while the Dst could
 receive the second test packet at TR[i+1], and then receive the first
 one (later) at TR[i].  Metrics for reordering may be found in
 [RFC4737].

3.7. Errors and Uncertainties

 In addition to sources of errors and uncertainties associated with
 methods employed to measure the singleton values that make up the
 sample, care must be given to analyze the accuracy of the Poisson
 arrival process of the wire times of the sending of the test packets.
 Problems with this process could be caused by several things,
 including problems with the pseudorandom number techniques used to
 generate the Poisson arrival process.  The Framework document shows
 how to use the Anderson-Darling test to verify the accuracy of the
 Poisson process over small time frames. {Comment: The goal is to
 ensure that the test packets are sent "close enough" to a Poisson
 schedule and avoid periodic behavior.}

3.8. Reporting the Metric

 The calibration and context for the underlying singletons MUST be
 reported along with the stream (see "Reporting the Metric"
 (Section 2.8) for Type-P-One-way-Packet-Loss).

4. Some Statistics Definitions for One-Way Packet Loss

 Given the sample metric Type-P-One-way-Packet-Loss-Poisson-Stream, we
 now offer several statistics of that sample.  These statistics are
 offered mostly to be illustrative of what could be done.  See
 [RFC6703] for additional discussion of statistics that are relevant
 to different audiences.

4.1. Type-P-One-way-Packet-Loss-Ratio

 Given a Type-P-One-way-Packet-Loss-Poisson-Stream, the average of all
 the L values in the stream is the ratio of losses to total packets in
 the stream.  In addition, the Type-P-One-way-Packet-Loss-Ratio is
 undefined if the sample is empty.

Almes, et al. Standards Track [Page 15] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 For example, suppose we take a sample and the results are as follows:
 Stream1 = <
 <T1, 0>
 <T2, 0>
 <T3, 1>
 <T4, 0>
 <T5, 0>
 >
 Then, the average of loss results would be 0.2, the loss ratio.
 Note that, since healthy Internet paths should be operating at loss
 ratios below 1% (particularly if high delay-bandwidth products are to
 be sustained), the sample sizes needed might be larger than one would
 like.  Thus, for example, if one wants to discriminate between
 various fractions of 1% over one-minute periods, then several hundred
 samples per minute might be needed.  This would result in larger
 values of lambda than one would ordinarily want.
 Note that although the loss threshold should be set such that any
 errors in loss are not significant, if the possibility that a packet
 that arrived is counted as lost due to resource exhaustion is
 significant compared to the loss ratio of interest, Type-P-One-way-
 Packet-Loss-Ratio will be meaningless.

5. Security Considerations

 Conducting Internet measurements raises both security and privacy
 concerns.  This memo does not specify an implementation of the
 metrics, so it does not directly affect the security of the Internet
 nor of applications that run on the Internet.  However,
 implementations of these metrics must be mindful of security and
 privacy concerns.
 There are two types of security concerns: potential harm caused by
 the measurements and potential harm to the measurements.  The
 measurements could cause harm because they are active and inject
 packets into the network.  The measurement parameters MUST be
 carefully selected so that the measurements inject trivial amounts of
 additional traffic into the networks they measure.  If they inject

Almes, et al. Standards Track [Page 16] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 "too much" traffic, they can skew the results of the measurement and
 in extreme cases cause congestion and denial of service.
 The measurements themselves could be harmed by routers giving
 measurement traffic a different priority than "normal" traffic or by
 an attacker injecting artificial measurement traffic.  If routers can
 recognize measurement traffic and treat it separately, the
 measurements will not reflect actual user traffic.  If an attacker
 injects artificial traffic that is accepted as legitimate, the loss
 ratio will be artificially lowered.  Therefore, the measurement
 methodologies SHOULD include appropriate techniques to reduce the
 probability that measurement traffic can be distinguished from
 "normal" traffic.  Authentication techniques, such as digital
 signatures, may be used where appropriate to guard against injected
 traffic attacks.
 When considering privacy of those involved in measurement or those
 whose traffic is measured, the sensitive information available to
 potential observers is greatly reduced when using active techniques
 that are within this scope of work.  Passive observations of user
 traffic for measurement purposes raise many privacy issues.  We refer
 the reader to the privacy considerations described in the Large Scale
 Measurement of Broadband Performance (LMAP) Framework [RFC7594],
 which covers active and passive techniques.
 Collecting measurements or using measurement results for
 reconnaissance to assist in subsequent system attacks is quite
 common.  Access to measurement results or control of the measurement
 systems to perform reconnaissance should be guarded against.  See
 Section 7 of [RFC7594] (the Security Considerations section of the
 LMAP Framework) for system requirements that help to avoid
 measurement system compromise.

6. Changes from RFC 2680

 The text above constitutes a revision to RFC 2680, which is now an
 Internet Standard.
 [RFC7290] provides the test plan and results supporting [RFC2680]
 advancement along the Standards Track, according to the process in
 [RFC6576].  The conclusions of [RFC7290] list four minor
 modifications for inclusion:
 1.  Section 6.2.3 of [RFC7290] 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 2.6, above.

Almes, et al. Standards Track [Page 17] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 2.  Section 6.5 of [RFC7290] indicates that the Type-P-One-way-
     Packet-Loss-Average statistic is more commonly called a Packet
     Loss Ratio, so it is renamed in this document (this small
     discrepancy does not affect candidacy for advancement).  The
     renaming was implemented in Section 4.1, above.
 3.  The IETF has reached consensus on guidance for reporting metrics
     in [RFC6703], and the memo is referenced this document to
     incorporate recent experience where appropriate.  This reference
     was added in the last list item of Section 2.6, in Section 2.8,
     and in Section 4 above.
 4.  There are currently two errata with status "Verified" (EID 1528)
     and "Held for Document Update" (EID 3186) for [RFC2680], and
     these minor revisions were incorporated in Sections 1 and 2.7.
 A number of updates to the [RFC2680] text have been implemented in
 the text to reference key IPPM RFCs that were approved after
 [RFC2680] (see Sections 3 and 3.6, above) 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.   Clarification of the definition of "resolution" in Section 1.2.
 3.   Explicit inclusion of the maximum waiting time input parameter
      in Sections 2.2, 2.4, and 3.2, reflecting recognition of this
      parameter in more recent RFCs and ITU-T Recommendation Y.1540.
 4.   Addition of a reference to RFC 6703 in the discussion of packet
      lifetime and application timeouts in Section 2.5.
 5.   Replaced "precedence" with updated terminology (DS Field) in
      Sections 2.6 and 2.8.1 (with reference).
 6.   Added parenthetical guidance on minimizing the interval between
      timestamp placement to send time or reception time in
      Section 2.6.  Also, the text now recognizes the timestamp
      acquisition process and that practical systems measure both
      delay and loss (thus requiring the max waiting time parameter).
 7.   Added a reference to RFC 3432 regarding periodic sampling
      alongside Poisson sampling in Section 3 and also noted that a
      truncated Poisson distribution may be needed with modern
      networks as described in the IPPM Framework update [RFC7312].

Almes, et al. Standards Track [Page 18] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 8.   Recognition that time-slotted links described in [RFC7312] can
      greatly modify the sample characteristics, in Section 3.5.
 9.   Added a reference to RFC 4737 regarding reordering metrics in
      the related discussion of Section 3.6, "Methodologies".
 10.  Expanded and updated the material on privacy and added cautions
      on use of measurements for reconnaissance in Section 5,
      "Security Considerations".
 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 value and minimizes unnecessary differences
 between this revised RFC and current/future IPPM RFCs.

7. References

7.1. Normative References

 [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791,
            DOI 10.17487/RFC0791, September 1981,
            <http://www.rfc-editor.org/info/rfc791>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
            "Framework for IP Performance Metrics", RFC 2330,
            DOI 10.17487/RFC2330, May 1998,
            <http://www.rfc-editor.org/info/rfc2330>.
 [RFC2678]  Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
            Connectivity", RFC 2678, DOI 10.17487/RFC2678, September
            1999, <http://www.rfc-editor.org/info/rfc2678>.
 [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>.

Almes, et al. Standards Track [Page 19] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 [RFC2780]  Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
            Values In the Internet Protocol and Related Headers",
            BCP 37, RFC 2780, DOI 10.17487/RFC2780, March 2000,
            <http://www.rfc-editor.org/info/rfc2780>.
 [RFC3432]  Raisanen, V., Grotefeld, G., and A. Morton, "Network
            performance measurement with periodic streams", RFC 3432,
            DOI 10.17487/RFC3432, November 2002,
            <http://www.rfc-editor.org/info/rfc3432>.
 [RFC6576]  Geib, R., Ed., Morton, A., Fardid, R., and A. Steinmitz,
            "IP Performance Metrics (IPPM) Standard Advancement
            Testing", BCP 176, RFC 6576, DOI 10.17487/RFC6576, March
            2012, <http://www.rfc-editor.org/info/rfc6576>.
 [RFC7312]  Fabini, J. and A. Morton, "Advanced Stream and Sampling
            Framework for IP Performance Metrics (IPPM)", RFC 7312,
            DOI 10.17487/RFC7312, August 2014,
            <http://www.rfc-editor.org/info/rfc7312>.
 [RFC7679]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
            Ed., "A One-Way Delay Metric for IP Performance Metrics
            (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
            2016, <http://www.rfc-editor.org/info/rfc7679>.

7.2. Informative References

 [IPPM-UPDATES]
            Morton, A., Fabini, J., Elkins, N., Ackermann, M., and V.
            Hegde, "Updates for IPPM's Active Metric Framework:
            Packets of Type-P and Standard-Formed Packets", Work in
            Progress, draft-morton-ippm-2330-stdform-typep-02,
            December 2015.
 [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
            of Explicit Congestion Notification (ECN) to IP",
            RFC 3168, DOI 10.17487/RFC3168, September 2001,
            <http://www.rfc-editor.org/info/rfc3168>.
 [RFC4737]  Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
            S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
            DOI 10.17487/RFC4737, November 2006,
            <http://www.rfc-editor.org/info/rfc4737>.
 [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
            Performance Metric Development", BCP 170, RFC 6390,
            DOI 10.17487/RFC6390, October 2011,
            <http://www.rfc-editor.org/info/rfc6390>.

Almes, et al. Standards Track [Page 20] RFC 7680 A One-Way Loss Metric for IPPM January 2016

 [RFC6703]  Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
            IP Network Performance Metrics: Different Points of View",
            RFC 6703, DOI 10.17487/RFC6703, August 2012,
            <http://www.rfc-editor.org/info/rfc6703>.
 [RFC7290]  Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test
            Plan and Results for Advancing RFC 2680 on the Standards
            Track", RFC 7290, DOI 10.17487/RFC7290, July 2014,
            <http://www.rfc-editor.org/info/rfc7290>.
 [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 [RFC2680], thanks are due to Matt Mathis for encouraging this
 work and for calling attention on so many occasions to the
 significance of packet loss.  Thanks are due also to Vern Paxson for
 his valuable comments on early drafts and to Garry Couch and Will
 Leland 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.

Almes, et al. Standards Track [Page 21] RFC 7680 A One-Way Loss Metric for IPPM January 2016

Authors' Addresses

 Guy Almes
 Texas A&M
 Email: almes@acm.org
 Sunil Kalidindi
 Ixia
 Email: skalidindi@ixiacom.com
 Matt Zekauskas
 Internet2
 Email: matt@internet2.edu
 Al Morton (editor)
 AT&T Labs
 200 Laurel Avenue South
 Middletown, NJ  07748
 United States
 Phone: +1 732 420 1571
 Fax:   +1 732 368 1192
 Email: acmorton@att.com
 URI:   http://home.comcast.net/~acmacm/

Almes, et al. Standards Track [Page 22]

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