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rfc:rfc2680

Network Working Group G. Almes Request for Comments: 2680 S. Kalidindi Category: Standards Track M. Zekauskas

                                           Advanced Network & Services
                                                        September 1999
               A One-way Packet Loss Metric for IPPM

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

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, RFC 2330 [1]; the reader is assumed to be
 familiar with that document.
 This memo is intended to be parallel in structure to a companion
 document for One-way Delay ("A One-way Delay Metric for IPPM") [2];
 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 RFC 2119 [5].
 Although RFC 2119 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.
 The structure of the memo is as follows:
 +  A 'singleton' analytic metric, called Type-P-One-way-Loss, is
    introduced to measure a single observation of packet transmission
    or loss.

Almes, et al. Standards Track [Page 1] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

 +  Using this singleton metric, a 'sample', called Type-P-One-way-
    Loss-Poisson-Stream, is introduced to measure a sequence of
    singleton transmissions and/or losses measured at times taken from
    a Poisson process.
 +  Using this sample, several 'statistics' of the sample are defined
    and discussed.
 This progression from singleton to sample to statistics, with clear
 separation among them, is important.
 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.

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:
 +  Some applications do not perform well (or at all) if end-to-end
    loss between hosts is large relative to some threshold value.
 +  Excessive packet loss may make it difficult to support certain
    real-time applications (where the precise threshold of "excessive"
    depends on the application).
 +  The larger the value of packet loss, the more difficult it is for
    transport-layer protocols to sustain high bandwidths.
 +  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:
 +  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 which may traverse
    different Internet service providers, and even radically different
    types of networks (for example, research versus commodity
    networks, or ATM versus packet-over-SONET).

Almes, et al. Standards Track [Page 2] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

 +  Even when the two paths are symmetric, they may have radically
    different performance characteristics due to asymmetric queueing.
 +  Performance of an application may depend mostly on the performance
    in one direction.  For example, a file transfer using TCP may
    depend more on the performance in the direction that data flows,
    rather than the direction in which acknowledgements travel.
 +  In quality-of-service (QoS) enabled networks, 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.
 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) 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*
      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".}

Almes, et al. Standards Track [Page 3] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

 accuracy*
      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*
      Resolution measures the precision of a given clock.  For
      example, the clock on an old Unix host might advance 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.  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:

    +  Src, the IP address of a host
    +  Dst, the IP address of a host
    +  T, a 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).

Almes, et al. Standards Track [Page 4] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

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.

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:
 +  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 [3], simple upper bounds (such as the
    255 seconds theoretical upper bound on the lifetimes of IP
    packets [4]) 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.}
 +  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.  Counting
    these packets as lost but packet with corruption in other parts of
    the packet as not lost would be inconsistent.}
 +  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.
 +  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 5] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

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,
 precedence).
 Generally, for a given Type-P, one possible methodology would proceed
 as follows:
 +  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).
 +  At the Src host, select Src and Dst IP addresses, and form a test
    packet of Type-P with these addresses.
 +  At the Dst host, arrange to receive the packet.
 +  At the Src host, place a timestamp in the prepared Type-P packet,
    and send it towards Dst.
 +  If the packet arrives within a reasonable period of time, the one-
    way packet-loss is taken to be zero.
 +  If the packet fails to arrive within a reasonable period of time,
    the one-way packet-loss is taken to be one.  Note that the
    threshold of "reasonable" here is a parameter of the methodology.
    {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 along the measured path.  If there is a single
    value 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.  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.}
 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 elsewhere our own work in describing such more
 detailed implementation techniques and we encourage others to as
 well.}

Almes, et al. Standards Track [Page 6] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

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:
 +  Synchronization between clocks on Src and Dst.
 +  The packet-loss threshold (which is related to the synchronization
    between clocks).
 +  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 0 if the test packet does not arrive, or if it does
 arrive and the difference between Src timestamp and 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 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 [2]
 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.
 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 the 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.

Almes, et al. Standards Track [Page 7] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

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.

2.8.1. Type-P

 As noted in the Framework document [1], 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 precedence or RSVP) changes.  The exact Type-P
 used to make the measurements MUST be accurately reported.

2.8.2. Loss threshold

 The threshold (or methodology to distinguish) between a large 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, possibility that a test packet that arrives
 at the Dst network interface is reported as lost due to resource
 exhaustion on Dst SHOULD be reported.

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: For example, with Merit's NetNow setup,

Almes, et al. Standards Track [Page 8] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

 a Src on one 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 pseudo-random
 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.
 {Comment: Note that Poisson sampling is only one way of defining a
 sample.  Poisson has the advantage of limiting bias, but other
 methods of sampling might be appropriate for different situations.
 We encourage others who find such appropriate cases to use this
 general framework and submit their sampling method for
 standardization.}

3.1. Metric Name:

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

3.2. Metric Parameters:

 +  Src, the IP address of a host
 +  Dst, the IP address of a host
 +  T0, a time
 +  Tf, a time
 +  lambda, a rate in reciprocal seconds

3.3. Metric Units:

 A sequence of pairs; the elements of each pair are:
 +  T, a time, and
 +  L, either a zero or a one

Almes, et al. Standards Track [Page 9] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

 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 pseudo-random 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 times
 in this process, we obtain the value of Type-P-One-way-Packet-Loss at
 this time.  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 [1], which includes methods to
 compute and verify the pseudo-random 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 for, lambda elsewhere, culminating in a "best current
 practices" document.}
 Since a pseudo-random number sequence is employed, the sequence of
 times, and hence the value of the sample, is not fully specified.
 Pseudo-random 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 delay measurements.  The test packets will generally
 not arrive at Dst according to a Poisson distribution, since they are
 influenced by the network.
 {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 rates
 observed by transport connections do not reflect unbiased samples.
 For example, TCP transmissions both (1) occur in bursts, which can

Almes, et al. Standards Track [Page 10] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

 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 rate 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:
 +  the selection of specific times, using the specified Poisson
    arrival process, and
 +  the methodologies discussion already given for the singleton Type-
    P-One-way-Packet-Loss metric.
 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].

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 pseudo-random number techniques used to
 generate the Poisson arrival process.  The Framework document shows
 how to use the Anderson-Darling test 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" for
 Type-P-One-way-Packet-Loss.)

Almes, et al. Standards Track [Page 11] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

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.

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

 Given a Type-P-One-way-Packet-Loss-Poisson-Stream, the average of all
 the L values in the Stream.  In addition, the Type-P-One-way-Packet-
 Loss-Average is undefined if the sample is empty.
 Example: suppose we take a sample and the results are:
    Stream1 = <
    <T1, 0>
    <T2, 0>
    <T3, 1>
    <T4, 0>
    <T5, 0>
    >
 Then the average would be 0.2.
 Note that, since healthy Internet paths should be operating at loss
 rates 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
 which arrived is counted as lost due to resource exhaustion is
 significant compared to the loss rate of interest, Type-P-One-way-
 Packet-Loss-Average 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 which run on the Internet.  However,
 implementations of these metrics must be mindful of security and
 privacy concerns.

Almes, et al. Standards Track [Page 12] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

 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
 "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
 rate will be artificially lowered.  Therefore, the measurement
 methodologies SHOULD include appropriate techniques to reduce the
 probability 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.
 The privacy concerns of network measurement are limited by the active
 measurements described in this memo.  Unlike passive measurements,
 there can be no release of existing user data.

6. Acknowledgements

 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.

7. References

 [1]  Paxson, V.,  Almes,G., Mahdavi, J. and M. Mathis, "Framework for
      IP Performance Metrics", RFC 2330, May 1998.
 [2]  Almes, G.,  Kalidindi, S.  and M. Zekauskas, "A One-way Delay
      Metric for IPPM", RFC 2679, September 1999.
 [3]  Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
      Connectivity", RFC 2678, September 1999.

Almes, et al. Standards Track [Page 13] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

 [4]  Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
 [5]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [6]  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.

8. Authors' Addresses

 Guy Almes
 Advanced Network & Services, Inc.
 200 Business Park Drive
 Armonk, NY  10504
 USA
 Phone: +1 914 765 1120
 EMail: almes@advanced.org
 Sunil Kalidindi
 Advanced Network & Services, Inc.
 200 Business Park Drive
 Armonk, NY  10504
 USA
 Phone: +1 914 765 1128
 EMail: kalidindi@advanced.org
 Matthew J. Zekauskas
 Advanced Network & Services, Inc.
 200 Business Park Drive
 Armonk, NY 10504
 USA
 Phone: +1 914 765 1112
 EMail: matt@advanced.org

Almes, et al. Standards Track [Page 14] RFC 2680 One Way Packet Loss Metric for IPPM September 1999

9. Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Almes, et al. Standards Track [Page 15]

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