A One-Way Loss Metric for IPPM
draft-ietf-ippm-2680-bis-04

Internet-Draft       A One-Way Loss Metric for IPPM          August 2015

2.8.1.  Type-P

   As noted in the Framework document, section 13 of [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], ECN
   [RFC3168], or RSVP) changes.  Additional packet distinctions included
   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, (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: Backbone path selection services come and
   go.  A historical example was Merit's NetNow setup, where a Src on
   one NAP can reach a Dst on another NAP by either of several different
   backbone networks.}

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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.

   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

3.2.  Metric Parameters:

   + Src, the IP address of a host

   + Dst, the IP address of a host

   + T0, a time

   + Tf, a time

   + Tmax, a loss threshold waiting 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

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   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 [RFC2330], 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 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 un-biased packet streams with randomized inter-
   packet time intervals will be converted to some new distribution
   after encountering a time-slotted links, possibly with strong
   periodic characteristics instead.

   {Comment: there is, of course, no claim that real Internet traffic
   arrives according to a Poisson arrival process.

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   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:

   + 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].  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 pseudo-random 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.}

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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.)

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.

   Example: suppose we take a sample and the results are:

   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.

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   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 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 which 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
   "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 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

   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.

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   For RFC 2680 bis, 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.

7.  Changes from RFC 2680

   Note: This section's placement currently preserves minimal
   differences between this memo and RFC 2680.  The RFC Editor should
   place this section in an appropriate place.

   The text above constitutes RFC 2680 bis proposed for advancement on
   the IETF Standards Track.

   [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.

   2.  Section 6.5 of [RFC7290] indicates that Type-P-One-way-Packet-
       Loss-Average statistic is more commonly called Packet Loss Ratio,
       so it is re-named in RFC2680bis (this small discrepancy does not
       affect candidacy for advancement) The re-naming was implemented
       in section 4.1, above.

   3.  The IETF has reached consensus on guidance for reporting metrics
       in [RFC6703], and this memo should be referenced in RFC2680bis 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" and "Held
       for document update" for [RFC2680], and these minor revisions
       were incorporated in section 1 and section 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.

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   1.  Near the end of section 1.1, update of a network example using
       ATM and clarification of TCP's affect on queue occupation and
       importance of one-way delay measurement.

   2.  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 reference to RFC 6703 in the discussion of packet
       life time and application timeouts in section 2.5.

   5.  Replaced "precedence" with updated terminology (DS Field) in 2.6
       and 2.8.1 (with reference).

   6.  Added parenthetical guidance on minimizing 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 require the max waiting time parameter).

   7.  Added reference to RFC 3432 Periodic sampling alongside Poisson
       sampling in section 3, and also noting that a truncated Poisson
       distribution may be needed with modern networks as described in
       the IPPM Framework update, [RFC7312].

   8.  Recognition that Time-slotted links described in [RFC7312] can
       greatly modify the sample characteristics, in section 3.5.

   9.  Add reference to RFC 4737 Reordering metric in the related
       discussion of section 3.6, Methodologies.

   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 value and minimizes
   unnecessary differences between this revised RFC and current/future
   IPPM RFCs.

8.  IANA Considerations

   This memo makes no requests of IANA.

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9.  References

9.1.  Normative References

   [RFC0791]  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>.

   [RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Delay Metric for IPPM", RFC 2679, DOI 10.17487/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
              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>.

   [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>.

   [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>.

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   [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>.

9.2.  Informative References

   [I-D.morton-ippm-2330-stdform-typep]
              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", draft-
              morton-ippm-2330-stdform-typep-00 (work in progress),
              August 2015.

   [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>.

   [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>.

Authors' Addresses

   Guy Almes
   Texas A&M

   Email: almes@acm.org

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   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
   USA

   Phone: +1 732 420 1571
   Fax:   +1 732 368 1192
   Email: acmorton@att.com
   URI:   http://home.comcast.net/~acmacm/

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