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Network Working Group                                  A.Morton,Editor
Internet Draft                                                AT&T Labs
Document: <draft-morton-ippm-composition-01.txt>              E.Stephan
                                                          FranceTelecom
Category: Individual






                      Spatial Composition of Metrics


Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This memo utilizes IPPM metrics that are applicable to both complete
   paths and sub-paths, and defines relationships to compose a complete
   path metric from the sub-path metrics with some accuracy w.r.t. the
   actual metrics.  This is called Spatial Composition in RFC 2330. The
   current version of the memo gives some background and proposes
   wording for a Scope and Application section to define this new work.
   The description of several example metrics and statistics follow.

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Spatial Composition of Metrics                            October 2005




Contents

   Status of this Memo................................................1
   Copyright Notice...................................................1
   Abstract...........................................................1
   Authors/Contributors...............................................3
   1. Conventions used in this document...............................3
   2. Introduction....................................................3
   2.1  Motivation....................................................4
   3. Proposed Scope and Application..................................5
   3.1  Scope of Work.................................................5
   3.2  Application...................................................6
   3.3  Terminology...................................................6
   4. One-way Delay Composition Metrics and Statistics................7
   4.1 Name: Type-P-Finite-One-way-Delay-Poisson/Periodic-Stream......7
   4.1.1 Metric Parameters:...........................................7
   4.1.2 Definition:..................................................7
   4.1.3 Discussion and other details.................................7
   4.1.4 Mean Statistic...............................................7
   4.1.5 Composition Relationship: Sum of Mean Delays.................8
   4.1.6 Statement of Conjecture......................................8
   4.1.7 Justification for the composite relationship.................8
   4.1.8 Sources of Error.............................................8
   4.1.9 Specific cases where the conjecture might fail...............9
   4.1.10 Application of Measurement Methodology......................9
   5. Loss Metrics/Statistics.........................................9
   5.1 Name: Type-P-One-way-Packet-Loss-Poisson/Periodic-Stream.......9
   5.1.1 Metric Parameters:..........................................10
   5.1.2 Metric Units:...............................................10
   5.1.3 Discussion and other details................................10
   5.1.4 Statistic: Type-P-One-way-Packet-Loss-Empirical-Probability 10
   5.1.5 Composition Relationship: Combination of Empirical
   Probabilities.....................................................11
   5.1.6 Statement of Conjecture.....................................11
   5.1.7 Justification for the composite relationship................11
   5.1.8 Sources of Error............................................11
   5.1.9 Specific cases where the conjecture might fail..............12
   5.1.10 Application of Measurement Methodology.....................12
   6. Delay Variation Metrics/Statistics.............................12
   7. Other Metrics/Statistics: One-way combined Metric..............12
   7.1 Metric Name...................................................13
   7.1.1 Metric Parameters:..........................................13
   7.1.2 Definition:.................................................13
   7.1.3 Discussion and other details................................13
   7.1.4 Type-P-One-way-Combo-subpathes-stream.......................13
   7.1.5 Type-P-One-way-composition..................................14
   7.1.6 Type-P-One-way-composition-stream...........................14
   7.1.7 Statement of Conjecture.....................................15
   7.1.8 Justification for the composite relationship................15
   7.1.9 Sources of Error............................................15

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   7.1.10 Specific cases where the conjecture might fail.............15
   7.1.11 Application of Measurement Methodology.....................15
   8. Security Considerations........................................15
   8.1 Denial of Service Attacks.....................................15
   8.2 User data confidentiality.....................................16
   8.3 Interference with the metric..................................16
   9. IANA Considerations............................................16
   10. Normative References..........................................16
   11. Informative References........................................17
   12. Open issues...................................................18
   13. Acknowledgments...............................................18
   14. Author's Addresses............................................18
   Full Copyright Statement..........................................18
   Intellectual Property.............................................19
   Acknowledgement...................................................19

Authors/Contributors

   Thus far, the following people have contributed useful ideas,
   suggestions, or the text of sections that have been incorporated
   into this memo:

   - Phil Chimento <vze275m9@verizon.net>
   - Reza Fardid <RFardid@Covad.COM>
   - Roman Krzanowski <roman.krzanowski@verizon.com>
   - Maurizio Molina <maurizio.molina@dante.org.uk>
   - Al Morton <acmorton@att.com>
   - Emile Stephan <emile.stephan@francetelecom.com>
   - Lei Liang <L.Liang@surrey.ac.uk>


1. Conventions used in this 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 [RFC2119].
   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.

   In this memo, the characters "<=" should be read as "less than or
   equal to" and ">=" as "greater than or equal to".


2. Introduction

   The IPPM framework RFC 2330 [RFC2330] describes two forms of metric
   composition, spatial and temporal. Spatial composition encompasses
   the definitions of performance metrics that are applicable to the
   complete path, and to various sub-paths. Also, the text suggests

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   that the concepts of the analytical framework (or A-frame) would
   help to define useful relationships between the complete path
   metrics and the sub-path metrics. The effectiveness of such metrics
   is dependent on their usefulness in analysis and applicability with
   practical measurement methods.

   The relationships may involve conjecture, and [RFC2330] lists four
   points that the metric definitions should include:

   +  the specific conjecture applied to the metric,
   +  a justification of the practical utility of the composition in
      terms of making accurate measurements of the metric on the path,
   +  a justification of the usefulness of the composition in terms of
      making analysis of the path using A-frame concepts more
      effective, and
   +  an analysis of how the conjecture could be incorrect.

   RFC 2330 also gives an example where a conjecture that the delay of
   a path is very nearly the sum of the delays of the exchanges and
   clouds of the corresponding path digest. This example is
   particularly relevant to those who wish to assess the performance of
   an Inter-domain path without direct measurement, and the performance
   estimate of the complete path is related to the measured results for
   various sub-paths instead.

   Approximate relationships between the sub-path and complete path
   metrics are useful, with knowledge of the circumstances where the
   relationships are/are not applicable. For example, we would not
   expect that delay singletons from each sub-path would sum to produce
   an accurate estimate of a delay singleton for the complete path
   (unless all the delays were essentially constant - very unlikely).
   However, other delay statistics (based on a reasonable sample size)
   may have a sufficiently large set of circumstances where they are
   applicable.

2.1  Motivation

   One-way metrics defined in other IPPM RFCs all assume that the
   measurement can be practically carried out between the source and
   the destination of the interest. Sometimes there are reasons that
   the measurement can not be executed from the source to the
   destination. For instance, the measurement path may cross several
   independent domains that have conflicting policies, measurement
   tools and methods, and measurement timeslot assignment. and the
   simple One-way measurement can not be carried out. The solution then
   may be the composition of several sub-path measurements. That means
   each domain performs the One-way measurement on a sub path between
   two nodes that are involved in the complete path following it own
   policy, using its own measurement tools and methods, and within its
   own measurement timeslot. One can combine all the sub-path One-way
   mmetric results to estimate the complete path One-way measurement
   metric with some accuracy.

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   >>>>>>>>>>>>Open issue:
   What is the relationship between the decomposition and composition
   metrics? Should we put both kinds in one draft to make up a
   framework? The motivation of decomposition is as follows:

   The One-way measurement can provide result to show what the network
   performance between two end hosts is and whether it meets operator
   expectations or not. It cannot provide further information to
   engineers where and how to improve the performance between the
   source and the destination. For instance, if the network performance
   is not acceptable in terms of the One-way measurement, in which part
   of the network the engineers should put their efforts. This question
   can to be answered by decompose the One-way measurement to sub-path
   measurement to investigate the performance of different part of the
   network.

   Editor’s Questions for clarification:
   What additional information would be provided to the decomposition
   process, beyond the measurement of the complete path?

   Is the decomposition described above intended to estimate a metric
   for some/all disjoint sub-paths involved in the complete path?

   >>>>>>>>>>>>>>>>>>>


3. Proposed Scope and Application

3.1  Scope of Work

   For the primary IPPM metrics (currently Loss, Delay, and Delay
   Variation), this memo gives a set of complete path metrics that can
   be composed from the same or similar sub-path metrics. This means
   that the complete path metric may be composed from:

   +  the same metric for each sub-path;

   +  multiple metrics for each sub-path (possibly one that is the same
      as the complete path metric);

   +  a single sub-path metrics that is different from the complete
      path metric;

   + different measurement techniques like active and passive
     (recognizing that PSAMP WG will define capabilities to sample
     packets to support measurement).

   Each metric will clearly state:


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   -  the definition (and statistic, where appropriate);

   -  the composition relationship;

   -  the specific conjecture on which the relationship is based;

   -  a justification of practical utility or usefulness for analysis
      using the A-frame concepts;

   -  one or more examples of how the conjecture could be incorrect and
      lead to inaccuracy;

   -  the information to be reported;

3.2  Application

   For each metric, the applicable circumstances are defined, in terms
   of whether the composition:

   Requires the same test packets to traverse all sub-paths, or may use
   similar packets sent and collected separately in each sub-path.

   Requires homogeneity of measurement methodologies, or can allow a
   degree of flexibility (e.g., active or passive methods produce the
   "same" metric). Also, the applicable sending streams will be
   specified, such as Poisson, Periodic, or both.

   Needs information or access that will only be available within an
   operator's domain, or is applicable to Inter-domain composition.

   Requires synchronized measurement time intervals in all sub-paths,
   or largely overlapping, or no timing requirements.

   Requires assumption of sub-path independence w.r.t. the metric being
   defined/composed, or other assumptions.

   Has known sources of inaccuracy/error, and identifies the sources.

3.3  Terminology

   This section will define the terminology applicable to both complete
   path and sub-path metrics.

   Measurement Points:

   <there must be a suitable definition for this in IPPM’s literature>

   Equivalent measure:

   The equivalent measure is the end-to-end metric that a composite
   metric is estimating.


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   Equivalent path:

   The Equivalent path is the list of sub path that is equivalent to
   the path of the end-to-end measure the composition measure is
   estimating.


4. One-way Delay Composition Metrics and Statistics


4.1 Name: Type-P-Finite-One-way-Delay-Poisson/Periodic-Stream


4.1.1 Metric Parameters:

   +  Src, the IP address of a host

   +  Dst, the IP address of a host

   +  T, a time (start of test interval)

   +  Tf, a time (end of test interval)

   +  lambda, a rate in reciprocal seconds (for Poisson Streams)

   +  incT, the nominal duration of inter-packet interval, first bit to
      first bit (for Periodic Streams)

   +  T0, a time that MUST be selected at random from the interval
      [T, T+dT] to start generating packets and taking measurements
      (for Periodic Streams)

   +  TstampSrc, the wire time of the packet as measured at MP(Src)

   +  TstampDst, the wire time of the packet as measured at MP(Dst),
      assigned to packets that arrive within a "reasonable" time.

4.1.2 Definition:

   Using the parameters above, we obtain the value of Type-P-One-way-
   Delay singleton as per RFC 2679 [RFC2679]. For each packet [i] that
   has a finite One-way Delay (in other words, excluding packets which
   have undefined, or infinite one-way delay):

   Type-P-Finite-One-way-Delay-Poisson/Periodic-Stream[i] =
                  FiniteDelay[i] = TstampDst - TstampSrc

4.1.3 Discussion and other details...

4.1.4 Mean Statistic

   +  L,  the total number of packets received at Dst (sent between T0

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      and Tf)

   The

   Type-P-Finite-One-way-Delay-Mean =

              MeanDelay = (1/L)Sum(from i=1 to L, FiniteDelay[i])

   where all packets i= 1 through L have finite singleton delays.

4.1.5 Composition Relationship: Sum of Mean Delays

   The Type-P-Finite—Composite-One-way-Delay-Mean, or MeanDelay for the
   complete Source to Destination path can be calculated from sum of
   the Mean Delays of all its S constituent sub-paths.

   +  S,  the number of sub-paths involved in the complete Src-Dst path

   Then the

   Type-P-Finite-Composite-One-way-Delay-Mean =

              CompMeanDelay = (1/S)Sum(from i=1 to S, MeanDelay[i])



4.1.6 Statement of Conjecture

   The mean of a sufficiently large stream of packets measured on each
   sub-path during the interval [T, Tf] will be representative of the
   true mean of the delay distribution (and the distributions
   themselves are sufficiently independent), such that the means may be
   added to produce an estimate of the complete path mean delay.

4.1.7 Justification for the composite relationship

   It is sometimes impractical to conduct active measurements between
   every Src-Dst pair. For example, it may not be possible to collect
   the desired sample size in each test interval when access link speed
   is limited, because of the potential for measurement traffic to
   degrade the user traffic performance. The conditions on a low-speed
   access link may be understood well-enough to permit use of a small
   sample size/rate, while a larger sample size/rate may be used on
   other sub-paths.

   Also, since measurement operations have a real monetary cost, there
   is value in re-using measurements where they are applicable, rather
   than launching new measurements for every possible source-
   destination pair.

4.1.8 Sources of Error


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   The measurement packets, each having source and destination
   addresses intended for collection at edges of the sub-path, may take
   a different specific path through the network equipment and parallel
   exchanges than packets with the source and destination addresses of
   the complete path. Therefore, the sub-path measurements may differ
   from the performance experienced by packets on the complete path.
   Multiple measurements employing sufficient sub-path address pairs
   might produce bounds on the extent of this error.

   others...

4.1.9 Specific cases where the conjecture might fail

   If any of the sub-path distributions are bimodal, then the measured
   means may not be stable, and in this case the mean will not be a
   particularly useful statistic when describing the delay distribution
   of the complete path.

   The mean may not be sufficiently robust statistic to produce a
   reliable estimate, or to be useful even if it can be measured.

   others...

4.1.10 Application of Measurement Methodology

   The methodology:

   SHOULD use similar packets sent and collected separately in each
   sub-path.

   Allows a degree of flexibility (e.g., active or passive methods can
   produce the "same" metric, but timing and correlation of passive
   measurements is much more challenging).

   Poisson and/or Periodic streams are RECOMMENDED.

   Applicable to both Inter-domain and Intra-domain composition.

   SHOULD have synchronized measurement time intervals in all sub-
   paths, but largely overlapping intervals MAY suffice.

   REQUIRES assumption of sub-path independence w.r.t. the metric being
   defined/composed.

5. Loss Metrics/Statistics

   >>>>>>>>>>>>>>>>>
   Editor’s note: there is considerable redundancy between the material
   in sections 5.1 and 4.1, need to determine how best to reduce it.

5.1 Name: Type-P-One-way-Packet-Loss-Poisson/Periodic-Stream


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5.1.1 Metric Parameters:

   +  Src, the IP address of a host

   +  Dst, the IP address of a host

   +  T, a time (start of test interval)

   +  Tf, a time (end of test interval)

   +  lambda, a rate in reciprocal seconds (for Poisson Streams)

   +  incT, the nominal duration of inter-packet interval, first bit to
      first bit (for Periodic Streams)

   +  T0, a time that MUST be selected at random from the interval
      [T, T+dT] to start generating packets and taking measurements
      (for Periodic Streams)

   +  TstampSrc, the wire time of the packet as measured at MP(Src)

   +  TstampDst, the wire time of the packet as measured at MP(Dst),
      assigned to packets that arrive within a "reasonable" time.

   +  Tmax, a maximum waiting time for packets at the destination


5.1.2 Metric Units:

   Using the parameters above, we obtain the value of Type-P-One-way-
   Packet-Loss singleton and stream as per RFC 2680 [RFC2680]. We
   obtain a sequence of pairs with elements as follows:

   +  TstampSrc, as above

   +  L, either zero or one, where L=1 indicates loss and L=0 indicates
     arrival at the destination within TstampSrc + Tmax.


5.1.3 Discussion and other details...

5.1.4  Statistic: Type-P-One-way-Packet-Loss-Empirical-Probability

   Given the following stream parameter

   +  N,  the total number of packets sent between T0 and Tf

   We can define the Empirical Probability of Loss Statistic (Ep),
   consistent with Average Loss in [RFC2680], as follows:

   Type-P-One-way-Packet-Loss-Empirical-Probability =

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                                   Ep = (1/N)Sum(from i=1 to N, L[i])

   where all packets i= 1 through N have a value for L.

5.1.5 Composition Relationship: Combination of Empirical Probabilities

   The Type Type-P-One-way-Composite-Packet-Loss-Empirical-Probability,
   or CompEp for the complete Source to Destination path can be
   calculated by combining Ep of all its constituent sub-paths (Ep1,
   Ep2, Ep3, ... Epn) as

   Type-P-One-way-Composite-Packet-Loss-Empirical-Probability =
   CompEp = 1 – {(1 - Ep1) x (1 – Ep2) x (1 – Ep3) x ... x (1 – Epn)}


5.1.6 Statement of Conjecture

   The empirical probability of loss calculated on a sufficiently large
   stream of packets measured on each sub-path during the interval [T,
   Tf] will be representative of the true loss probability (and the
   probabilities themselves are sufficiently independent), such that
   the sub-path probabilities may be combined to produce an estimate of
   the complete path loss probability.

5.1.7 Justification for the composite relationship

   It is sometimes impractical to conduct active measurements between
   every Src-Dst pair. For example, it may not be possible to collect
   the desired sample size in each test interval when access link speed
   is limited, because of the potential for measurement traffic to
   degrade the user traffic performance. The conditions on a low-speed
   access link may be understood well-enough to permit use of a small
   sample size/rate, while a larger sample size/rate may be used on
   other sub-paths.

   Also, since measurement operations have a real monetary cost, there
   is value in re-using measurements where they are applicable, rather
   than launching new measurements for every possible source-
   destination pair.

5.1.8 Sources of Error

   The measurement packets, each having source and destination
   addresses intended for collection at edges of the sub-path, may take
   a different specific path through the network equipment and parallel
   exchanges than packets with the source and destination addresses of
   the complete path. Therefore, the sub-path measurements may differ
   from the performance experienced by packets on the complete path.
   Multiple measurements employing sufficient sub-path address pairs
   might produce bounds on the extent of this error.

   others...

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5.1.9 Specific cases where the conjecture might fail

   A concern for loss measurements combined in this way is that root
   causes may be correlated to some degree.

   For example, if the links of different networks follow the same
   physical route, then a single event like a tunnel fire could cause
   an outage or congestion on remaining paths in multiple networks.
   Here it is important to ensure that measurements before the event
   and after the event are not combined to estimate the composite
   performance.

   Or, when traffic volumes rise due to the rapid spread of an email-
   born worm, loss due to queue overflow in one network may help
   another network to carry its traffic without loss.

   others...

5.1.10 Application of Measurement Methodology

   The methodology:

   SHOULD use similar packets sent and collected separately in each
   sub-path.

   Allows a degree of flexibility (e.g., active or passive methods can
   produce the "same" metric, but timing and correlation of passive
   measurements is much more challenging).

   Poisson and/or Periodic streams are RECOMMENDED.

   Applicable to both Inter-domain and Intra-domain composition.

   SHOULD have synchronized measurement time intervals in all sub-
   paths, but largely overlapping intervals MAY suffice.

   REQUIRES assumption of sub-path independence w.r.t. the metric being
   defined/composed.

6. Delay Variation Metrics/Statistics

   >>>>>>>>>>>>>
   Editor’s note:  We have studied various approaches and have at least
   one proposal for this section. We plan to add the text in the next
   version.
   >>>>>>>>>>>>>

7. Other Metrics/Statistics: One-way combined Metric




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   This definition may be the common part for the definition of "Loss
   Metrics/Statistics" and for the definition of "One-way Delay
   Composition Metrics and Statistics".


7.1 Metric Name

   Type-P-One-way-Combo-mean

7.1.1 Metric Parameters:

   Editorial notes (ES): parameters list to be completed

   <P1,T1,dt1>...<Pn,Tn,dtn>:

        It is a stream of One-way delay corresponding either to an end
        to end measure of a sub-path, or to the spatial measure of the
        sub-path:

        - Type-P-One-way-Delay-Poisson-Stream as per [RFC2679];
        - Type-P-One-way-Delay-Periodic-Stream a per [RFC3432];
        - Type-P-One-way-Composition-Stream as defined below;
        - Type-P-subpath-One-way-Delay-Stream as per [I-D.stephan-ippm-
          multimetrics].


7.1.2 Definition:

   Using the value <P1,T1,dt1>...<Pn,Tn,dtn> of one of the One-way
   delay Stream listed above, we define Type-P-One-way-Combo as the
   couple (D,L) where D is the mean of the delay of the packets that
   have a finite One-way, and where L is the average of lost of packets
   (which have undefined, or infinite one-way delay).

   D corresponds to the Type-P-Finite-One-way-Delay-Mean defined above.

   L corresponds to the Type-P-One-way-Packet-Loss-Empirical-
   Probability defined above.


7.1.3 Discussion and other details...

7.1.4 Type-P-One-way-Combo-subpathes-stream

   Parameters:


   + dT1,..., dTn a list of delay.


   + <Src, H1, H2,..., Hn, Dst>, the equivalent path.


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   Definition:

   Using Type-P-One-way-Combo-mean of each sub-path in the equivalent
   path we define a Type-P-One-way-subpathes-stream as the list of
   couples (D,L) of the sub-path list;

   Results: {<D0,L0>,  <D1,L1>,  <D2,L2>, … <Dn,Ln>}


7.1.5 Type-P-One-way-composition

   The composition over a path gives D and L which give an estimation
   of the end-to-end delay and end-to-end packet lost over this path.

   Parameters:



   + <Src, H1, H2,..., Hn, Dst>, the equivalent path.

   + {<D0,L0>,  <D1,L1>,  <D2,L2>, … <Dn,Ln>}, the composition stream
   of the sub-pathes of a path.

   Definition:

   Using Type-P-One-way-subpathes-stream we define Type-P-One-way-
   composition as the couple <D,L> where D is the mean of the delays Di
   and where L is the average of lost of Li.


   Results: <D,L>,  where D is a delay and L is the lost

7.1.6 Type-P-One-way-composition-stream

   The sample of Type-P-One-way-composition is defined to permit the
   usage of the results of Type-P-One-way-composition measure in
   computation of Type-P-One-way-Combo-mean composition.

   Parameters:

   +  T1,..., Tn,  a list of time;

   +  <D,L>, the delay and the lost computed by composition.

   Definition:

   Using Type-P-One-way-composition we define Type-P-One-way-
   composition-stream as the stream of couples <D,L> over time.

   Results: <T1,D1,L1>...<Tn,Dn,Ln>

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7.1.7 Statement of Conjecture



7.1.8 Justification for the composite relationship

   Combo metric is very easy to measure and to compose.

   It gives the delay and the lost, so most of the need.

   Combo metric may be performed on com metric too.


7.1.9 Sources of Error

   Packets may cross different sub path than the equivalent end-to-end
   measure because Type-P differ.

   Packets may experiment different behavior than the equivalent end-
   to-end measure because of access classification based on packet
   addresses.

7.1.10 Specific cases where the conjecture might fail

   When

   +  Sum of subpath differ from the equivalent path.

   +  Type-P differ.

   +  Size differ.


7.1.11 Application of Measurement Methodology

   The methodology:

   Is applicable to Intra and interdomain;

   SHOULD report the context of the measure;


8. Security Considerations

8.1 Denial of Service Attacks

   This metric requires a stream of packets sent from one host (source)
   to another host (destination) through intervening networks.  This
   method could be abused for denial of service attacks directed at


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   destination and/or the intervening network(s).

   Administrators of source, destination, and the intervening
   network(s) should establish bilateral or multi-lateral agreements
   regarding the timing, size, and frequency of collection of sample
   metrics.  Use of this method in excess of the terms agreed between
   the participants may be cause for immediate rejection or discard of
   packets or other escalation procedures defined between the affected
   parties.

8.2 User data confidentiality

   Active use of this method generates packets for a sample, rather
   than taking samples based on user data, and does not threaten user
   data confidentiality. Passive measurement must restrict attention to
   the headers of interest. Since user payloads may be temporarily
   stored for length analysis, suitable precautions MUST be taken to
   keep this information safe and confidential. In most cases, a
   hashing function will produce a value suitable for payload
   comparisons.

8.3 Interference with the metric

   It may be possible to identify that a certain packet or stream of
   packets is part of a sample. With that knowledge at the destination
   and/or the intervening networks, it is possible to change the
   processing of the packets (e.g. increasing or decreasing delay) that
   may distort the measured performance.  It may also be possible to
   generate additional packets that appear to be part of the sample
   metric. These additional packets are likely to perturb the results
   of the sample measurement.

   To discourage the kind of interference mentioned above, packet
   interference checks, such as cryptographic hash, may be used.

9. IANA Considerations

   Metrics defined in this memo will be registered in the IANA IPPM
   METRICS REGISTRY as described in initial version of the registry
   [RFC4148].

10. Normative References

   [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.
              Obtain via: http://www.rfc-editor.org/rfc/rfc791.txt

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.
              Obtain via: http://www.rfc-editor.org/rfc/rfc2119.txt



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   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and Mathis, M.,
              "Framework for IP Performance Metrics", RFC 2330, May
              1998.
              Obtain via: http://www.rfc-editor.org/rfc/rfc2330.txt

   [RFC2679]  Almes, G., Kalidindi, S. and M. Zekauskas, "A one-way
              delay metric for IPPM", RFC 2679, September 1999.
              Obtain via: http://www.rfc-editor.org/rfc/rfc2679.txt

   [RFC2680]  Almes, G., Kalidindi, S. and M. Zekauskas, "A one-way
              packet loss metric for IPPM", RFC 2680, September 1999.
              Obtain via: http://www.rfc-editor.org/rfc/rfc2680.txt

   [RFC3148]  Mathis, M. and Allman, M., "A Framework for Defining
              Empirical Bulk Transfer Capacity Metrics", RFC 3148, July
              2001.
              Obtain via: http://www.rfc-editor.org/rfc/rfc3148.txt

   [RFC3432]  Raisanen, V., Grotefeld, G., and Morton, A., "Network
              performance measurement with periodic streams", RFC 3432,
              November 2002.

   [RFC4148]  Stephan, E., "IP Performance Metrics (IPPM) Metrics
              Registry", BCP 108, RFC 4148, August 2005.


11. Informative References


   [I.356]    ITU-T Recommendation I.356, "B-ISDN ATM layer cell
              transfer performance", March 2000.


   [Pax98]    V.Paxson, "Measurements and Analysis of End-to-End
              Internet Dynamics," Ph.D. dissertation, U.C. Berkeley,
              1997, ftp://ftp.ee.lbl.gov/papers/vp-thesis/dis.ps.gz.


   [RFC3393]  Demichelis, C., and Chimento, P., "IP Packet Delay
              Variation Metric for IP Performance Metrics (IPPM)", RFC
              3393, November 2002.

   [Y.1540]   ITU-T Recommendation Y.1540, "Internet protocol data
              communication service - IP packet transfer and
              availability performance parameters", December 2002.




   [I-D.stephan-ippm-multimetrics]
              Stephan, E., "IP Performance Metrics (IPPM) for spatial
              and multicast", draft-stephan-ippm-multimetrics-01 (work

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Spatial Composition of Metrics                            October 2005


              in progress), July 2005.


12. Open issues

   Point1:





13. Acknowledgments

   The authors would like to acknowledge many helpful discussions with
   . . . (lots of people, eventually).

14. Author's Addresses

   Al Morton
   AT&T Labs
   Room D3 - 3C06
   200 Laurel Ave. South
   Middletown, NJ 07748 USA
   Phone  +1 732 420 1571
   EMail: <acmorton@att.com>

   Need addresses for:
   - Phil Chimento <vze275m9@verizon.net>
   - Reza Fardid <RFardid@Covad.COM>
   - Roman Krzanowski <roman.krzanowski@verizon.com>
   - Maurizio Molina <maurizio.molina@dante.org.uk>

   - Emile Stephan <emile.stephan@francetelecom.com>
      Stephan Emile
      France Telecom Division R&D
      2 avenue Pierre Marzin
      Lannion,   F-22307

      Fax:   +33 2 96 05 18 52
      Email: emile.stephan@francetelecom.com

   - Lei Liang <L.Liang@surrey.ac.uk>



Full Copyright Statement

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   retain all their rights.

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