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This memo utilizes IPPM metrics that are applicable to both complete paths and subpaths, and defines relationships to compose a complete path metric from the subpath metrics with some accuracy w.r.t. the actual metrics. This is called Spatial Composition in RFC 2330. The memo refers to the Framework for Metric Composition, and provides background and motivation for combining metrics to derive others. The descriptions of several composed metrics and statistics follow.
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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].
In this memo, the characters "<=" should be read as "less than or equal to" and ">=" as "greater than or equal to".
1.
Contributors
2.
Introduction
2.1.
Motivation
3.
Scope and Application
3.1.
Scope of work
3.2.
Application
3.3.
Incomplete Information
4.
Common Specifications for Composed Metrics
4.1.
Name: TypeP
4.1.1.
Metric Parameters
4.1.2.
Definition and Metric Units
4.1.3.
Discussion and other details
4.1.4.
Statistic:
4.1.5.
Composition Function
4.1.6.
Statement of Conjecture and Assumptions
4.1.7.
Justification of the Composition Function
4.1.8.
Sources of Deviation from the Ground Truth
4.1.9.
Specific cases where the conjecture might fail
4.1.10.
Application of Measurement Methodology
5.
Oneway Delay Composed Metrics and Statistics
5.1.
Name: TypePFiniteOnewayDelayPoisson/PeriodicStream
5.1.1.
Metric Parameters
5.1.2.
Definition and Metric Units
5.1.3.
Discussion and other details
5.2.
Name: TypePFiniteCompositeOnewayDelayMean
5.2.1.
Metric Parameters
5.2.2.
Definition and Metric Units of the Mean Statistic
5.2.3.
Discussion and other details
5.2.4.
Composition Function: Sum of Means
5.2.5.
Statement of Conjecture and Assumptions
5.2.6.
Justification of the Composition Function
5.2.7.
Sources of Deviation from the Ground Truth
5.2.8.
Specific cases where the conjecture might fail
5.2.9.
Application of Measurement Methodology
5.3.
Name: TypePFiniteCompositeOnewayDelayMinimum
5.3.1.
Metric Parameters
5.3.2.
Definition and Metric Units of the Mean Statistic
5.3.3.
Discussion and other details
5.3.4.
Composition Function: Sum of Means
5.3.5.
Statement of Conjecture and Assumptions
5.3.6.
Justification of the Composition Function
5.3.7.
Sources of Deviation from the Ground Truth
5.3.8.
Specific cases where the conjecture might fail
5.3.9.
Application of Measurement Methodology
6.
Loss Metrics and Statistics
6.1.
TypePCompositeOnewayPacketLossEmpiricalProbability
6.1.1.
Metric Parameters:
6.1.2.
Definition and Metric Units
6.1.3.
Discussion and other details
6.1.4.
Statistic: TypePOnewayPacketLossEmpiricalProbability
6.1.5.
Composition Function: Composition of Empirical Probabilities
6.1.6.
Statement of Conjecture and Assumptions
6.1.7.
Justification of the Composition Function
6.1.8.
Sources of Deviation from the Ground Truth
6.1.9.
Specific cases where the conjecture might fail
6.1.10.
Application of Measurement Methodology
7.
Delay Variation Metrics and Statistics
7.1.
Name: TypePOnewaypdvrefminPoisson/PeriodicStream
7.1.1.
Metric Parameters:
7.1.2.
Definition and Metric Units
7.1.3.
Discussion and other details
7.1.4.
Statistics: Mean, Variance, Skewness, Quanitle
7.1.5.
Composition Functions:
7.1.6.
Statement of Conjecture and Assumptions
7.1.7.
Justification of the Composition Function
7.1.8.
Sources of Deviation from the Ground Truth
7.1.9.
Specific cases where the conjecture might fail
7.1.10.
Application of Measurement Methodology
8.
Security Considerations
8.1.
Denial of Service Attacks
8.2.
User Data Confidentiality
8.3.
Interference with the metrics
9.
IANA Considerations
10.
Acknowlegements
11.
Issues (Open and Closed)
12.
Acknowledgements
13.
References
13.1.
Normative References
13.2.
Informative References
§
Authors' Addresses
TOC 
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@orangeftgroup.com>
 Lei Liang <L.Liang@surrey.ac.uk>
 Dave Hoeflin <dhoeflin@att.com>
TOC 
The IPPM framework [RFC2330] (Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” May 1998.) describes two forms of metric composition, spatial and temporal. The new composition framework [I‑D.ietf‑ippm‑framework‑compagg] (Morton, A., “Framework for Metric Composition,” December 2009.) expands and further qualifies these original forms into three categories. This memo describes Spatial Composition, one of the categories of metrics under the umbrella of the composition framework.
Spatial composition encompasses the definition of performance metrics that are applicable to a complete path, based on metrics collected on various subpaths.
The main purpose of this memo is to define the deterministic functions that yield the complete path metrics using metrics of the subpaths. 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] (Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” May 1998.) lists four points that the metric definitions should include:
Also, [RFC2330] (Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” May 1998.) gives an example using the 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 Interdomain path without direct measurement, and the performance estimate of the complete path is related to the measured results for various subpaths instead.
Approximate functions between the subpath 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 subpath 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.
TOC 
Oneway 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 time assignment. The solution then may be the composition of several subpath measurements. This means each domain performs the Oneway measurement on a sub path between two nodes that are involved in the complete path following its own policy, using its own measurement tools and methods, and using its own measurement timing. Under the appropriate conditions, one can combine the subpath Oneway metric results to estimate the complete path Oneway measurement metric with some degree of accuracy.
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For the primary IPPM metrics of Loss, Delay, and Delay Variation, this memo gives a set of metrics that can be composed from the same or similar subpath metrics. This means that the composition function may utilize:
TOC 
The new composition framework [I‑D.ietf‑ippm‑framework‑compagg] (Morton, A., “Framework for Metric Composition,” December 2009.) requires the specification of the applicable circumstances for each metric. In particular, each section addresses whether the metric:
Requires the same test packets to traverse all subpaths, or may use similar packets sent and collected separately in each subpath.
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 Interdomain composition.
Requires synchronized measurement time intervals in all subpaths, or largely overlapping, or no timing requirements.
Requires assumption of subpath independence w.r.t. the metric being defined/composed, or other assumptions.
Has known sources of inaccuracy/error, and identifies the sources.
TOC 
In practice, when measurements cannot be initiated on a subpath (and perhaps the measurement system gives up during the test interval), then there will not be a value for the subpath reported, and the entire test result SHOULD be recorded as "undefined". This case should be distinguished from the case where the measurement system continued to send packets throughout the test interval, but all were declared lost.
When a composed metric requires measurements from sub paths A, B, and C, and one or more of the subpath results are undefined, then the composed metric SHOULD also be recorded as undefined.
TOC 
To reduce the redundant information presented in the detailed metrics sections that follow, this section presents the specifications that are common to two or more metrics. The section is organized using the same subsections as the individual metrics, to simplify comparisons.
TOC 
All metrics use the TypeP convention as described in [RFC2330] (Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” May 1998.). The rest of the name is unique to each metric.
TOC 
TOC 
This section is unique for every metric.
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This section is unique for every metric.
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This section is unique for every metric.
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This section is unique for every metric.
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This section is unique for each metric.
TOC 
It is sometimes impractical to conduct active measurements between every SrcDst pair. Since the full mesh of N measurement points grows as N x N, the scope of measurement may be limited by testing resources.
There may be varying limitations on active testing in different parts of the network. 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 lowspeed access link may be understood wellenough to permit use of a small sample size/rate, while a larger sample size/rate may be used on other subpaths.
Also, since measurement operations have a real monetary cost, there is value in reusing measurements where they are applicable, rather than launching new measurements for every possible sourcedestination pair.
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The measurement packets, each having source and destination addresses intended for collection at edges of the subpath, may take a different specific path through the network equipment and parallel links when compared to packets with the source and destination addresses of the complete path. Therefore, the performance estimated from the composition of subpath measurements may differ from the performance experienced by packets on the complete path. Multiple measurements employing sufficient subpath address pairs might produce bounds on the extent of this error.
TOC 
Related to the case of an alternate path described above is the case where elements in the measured path are unique to measurement system connectivity. For example, a measurement system may use a dedicated link to a LAN switch, and packets on the complete path do not traverse that link. The performance of such a dedicated link would be measured continuously, and its contribution to the subpath metrics SHOULD be minimized as a source of error.
TOC 
Measurements of subpath performance may not cover all the network elements on the complete path. For example, the network exchange points might be excluded unless a cooperative measurement is conducted. In this example, test packets on the previous subpath are received just before the exchange point and test packets on the next subpath are injected just after the same exchange point. Clearly, the set of subpath measurements SHOULD cover all critical network elements in the complete path.
TOC 
********************
Note: this section may be expressing the point of 4.1.8.1 in different words  its status is TBD.
********************
Subpath destination addresses and complete path addresses do not belong to the same network. Therefore routes selected to reach each subpath destinations differ from the route that would be selected to reach the destination address of the complete path. Consequently spatial composition may produce finite estimation of a ground true metric between a source Src and a destination Dst when the route between Src and Dst is undefined.
TOC 
This section is unique for each metric (see the metricspecific sections).
TOC 
The methodology:
SHOULD use similar packets sent and collected separately in each subpath.
Allows a degree of flexibility regarding test stream generation (e.g., active or passive methods can produce an equivalent result, but the lack of control over the source, timing and correlation of passive measurements is much more challenging).
Poisson and/or Periodic streams are RECOMMENDED.
Applies to both Interdomain and Intradomain composition.
SHOULD have synchronized measurement time intervals in all subpaths, but largely overlapping intervals MAY suffice.
REQUIRES assumption of subpath independence w.r.t. the metric being defined/composed.
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This metric is a necessary element of Delay Composition metrics, and its definition does not formally exist elsewhere in IPPM literature.
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See the common parameters section above.
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Using the parameters above, we obtain the value of TypePOnewayDelay singleton as per [RFC2679] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” September 1999.).
For each packet [i] that has a finite Oneway Delay (in other words, excluding packets which have undefined oneway delay):
TypePFiniteOnewayDelayPoisson/PeriodicStream[i] =
FiniteDelay[i] = TstampDst  TstampSrc
The units of measure for this metric are time in seconds, expressed in sufficiently low resolution to convey meaningful quantitative information. For example, resolution of microseconds is usually sufficient.
TOC 
The “TypePFiniteOnewayDelay” metric permits calculation of the sample mean statistic. This resolves the problem of including lost packets in the sample (whose delay is undefined), and the issue with the informal assignment of infinite delay to lost packets (practical systems can only assign some very large value).
The FiniteOnewayDelay approach handles the problem of lost packets by reducing the event space. We consider conditional statistics, and estimate the mean oneway delay conditioned on the event that all packets in the sample arrive at the destination (within the specified waiting time, Tmax). This offers a way to make some valid statements about oneway delay, and at the same time avoiding events with undefined outcomes. This approach is derived from the treatment of lost packets in [RFC3393] (Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” November 2002.), and is similar to [Y.1540] (ITUT Recommendation Y.1540, “Internet protocol data communication service  IP packet transfer and availability performance parameters,” December 2002.) .
TOC 
This section describes a statistic based on the TypePFiniteOnewayDelayPoisson/PeriodicStream metric.
TOC 
See the common parameters section above.
TOC 
We define
TypePFiniteOnewayDelayMean =
N  1 \ MeanDelay =  * > (FiniteDelay [i]) N /  i = 1
where all packets i= 1 through N have finite singleton delays.
The units of measure for this metric are time in seconds, expressed in sufficiently low resolution to convey meaningful quantitative information. For example, resolution of microseconds is usually sufficient.
TOC 
The TypePFiniteOnewayDelayMean metric requires the conditional delay distribution described in section 5.1.
TOC 
The TypePFinite—CompositeOnewayDelayMean, or CompMeanDelay, for the complete Source to Destination path can be calculated from sum of the Mean Delays of all its S constituent subpaths.
Then the
TypePFiniteCompositeOnewayDelayMean =
S  \ CompMeanDelay = > (MeanDelay [i]) /  i = 1
TOC 
The mean of a sufficiently large stream of packets measured on each subpath during the interval [T, Tf] will be representative of the ground truth 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.
It is assumed that the oneway delay distributions of the subpaths and the complete path are continuous.
TOC 
See the common section.
TOC 
See the common section.
TOC 
If any of the subpath 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...
TOC 
The requirements of the common section apply here as well.
TOC 
This section describes is a statistic based on the TypePFiniteOnewayDelayPoisson/PeriodicStream metric, and the composed metric based on that statistic.
TOC 
See the common parameters section above.
TOC 
We define
TypePFiniteOnewayDelayMinimum =
= MinDelay = (FiniteDelay [j]) such that for some index, j, where 1<= j <= N FiniteDelay[j] <= FiniteDelay[i] for all i
where all packets i= 1 through N have finite singleton delays.
The units of measure for this metric are time in seconds, expressed in sufficiently low resolution to convey meaningful quantitative information. For example, resolution of microseconds is usually sufficient.
TOC 
The TypePFiniteOnewayDelayMinimum metric requires the conditional delay distribution described in section 5.1.3.
TOC 
The TypePFinite—CompositeOnewayDelayMinimum, or CompMinDelay, for the complete Source to Destination path can be calculated from sum of the Minimum Delays of all its S constituent subpaths.
Then the
TypePFiniteCompositeOnewayDelayMinimum =
S  \ CompMinDelay = > (MinDelay [i]) /  i = 1
TOC 
The minimum of a sufficiently large stream of packets measured on each subpath during the interval [T, Tf] will be representative of the ground truth minimum of the delay distribution (and the distributions themselves are sufficiently independent), such that the minima may be added to produce an estimate of the complete path minimum delay.
It is assumed that the oneway delay distributions of the subpaths and the complete path are continuous.
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See the common section.
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See the common section.
TOC 
If the routing on any of the subpaths is not stable, then the measured minimum may not be stable. In this case the composite minimum would tend to produce an estimate for the complete path that may be too low for the current path.
others???
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The requirements of the common section apply here as well.
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Same as section 4.1.1.
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Using the parameters above, we obtain the value of TypePOnewayPacketLoss singleton and stream as per [RFC2680] (Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” September 1999.).
We obtain a sequence of pairs with elements as follows:
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Given the stream parameter M, the number of packets sent, we can define the Empirical Probability of Loss Statistic (Ep), consistent with Average Loss in [RFC2680], as follows:
TypePOnewayPacketLossEmpiricalProbability =
M  1 \ Ep =  * > (L[i]) M /  i = 1
where all packets i= 1 through M have a value for L.
TOC 
The TypePOnewayCompositePacketLossEmpiricalProbability, or CompEp for the complete Source to Destination path can be calculated by combining Ep of all its constituent subpaths (Ep1, Ep2, Ep3, ... Epn) as
TypePCompositeOnewayPacketLossEmpiricalProbability =
CompEp = 1  {(1  Ep1) x (1  Ep2) x (1  Ep3) x ... x (1  Epn)}
If any Epn is undefined in a particular measurement interval, possibly because a measurement system failed to report a value, then any CompEp that uses subpath n for that measurement interval is undefined.
TOC 
The empirical probability of loss calculated on a sufficiently large stream of packets measured on each subpath during the interval [T, Tf] will be representative of the ground truth empirical loss probability (and the probabilities themselves are sufficiently independent), such that the subpath probabilities may be combined to produce an estimate of the complete path empirical loss probability.
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See the common section.
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See the common section.
TOC 
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 catastrophic event like a fire in a tunnel 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 emailborn worm, loss due to queue overflow in one network may help another network to carry its traffic without loss.
others...
TOC 
See the common section.
TOC 
TOC 
This packet delay variation (PDV) metric is a necessary element of Composed Delay Variation metrics, and its definition does not formally exist elsewhere in IPPM literature.
TOC 
In addition to the parameters of section 4.1.1:
TOC 
Using the definition above in section 5.1.2, we obtain the value of TypePFiniteOnewayDelayPoisson/PeriodicStream[i], the singleton for each packet[i] in the stream (a.k.a. FiniteDelay[i]).
For each packet[i] that meets the F(first packet) criteria given above: TypePOnewaypdvrefminPoisson/PeriodicStream[i] =
PDV[i] = FiniteDelay[i] – MinDelay
where PDV[i] is in units of time in seconds, expressed in sufficiently low resolution to convey meaningful quantitative information. For example, resolution of microseconds is usually sufficient.
TOC 
This metric produces a sample of delay variation normalized to the minimum delay of the sample. The resulting delay variation distribution is independent of the sending sequence (although specific FiniteDelay values within the distribution may be correlated, depending on various stream parameters such as packet spacing). This metric is equivalent to the IP Packet Delay Variation parameter defined in [Y.1540] (ITUT Recommendation Y.1540, “Internet protocol data communication service  IP packet transfer and availability performance parameters,” December 2002.).
TOC 
We define the mean PDV as follows (where all packets i= 1 through N have a value for PDV[i]):
TypePOnewaypdvrefminMean = MeanPDV =
N  1 \  * > (PDV[i]) N /  i = 1
We define the variance of PDV as follows:
TypePOnewaypdvrefminVariance = VarPDV =
N  1 \ 2  > (PDV[i]  MeanPDV) (N  1) /  i = 1
We define the skewness of PDV as follows:
TypePOnewaypdvrefminSkewness = SkewPDV =
N  3 \ / \ >  PDV[i] MeanPDV  / \ /  i = 1  / \  ( 3/2 )  \ (N  1) * VarPDV /
We define the Quantile of the IPDVRefMin sample as the value where the specified fraction of singletons is less than the given value.
TOC 
This section gives two alternative composition functions. The objective is to estimate a quantile of the complete path delay variation distribution. The composed quantile will be estimated using information from the subpath delay variation distributions.
TOC 
The TypePFiniteOnewayDelayPoisson/PeriodicStream samples from each subpath are summarized as a histogram with 1 ms bins representing the oneway delay distribution.
From [TBP], the distribution of the sum of independent random variables can be derived using the relation:
TypePCompositeOnewaypdvrefminquantilea =
/ / P(X + Y + Z <= a) =   P(X <= ayz) * P(Y = y) * P(Z = z) dy dz / / z y
where X, Y, and Z are random variables representing the delay variation distributions of the subpaths of the complete path (in this case, there are three subpaths), and a is the quantile of interest. Note dy and dz indicate partial integration here.
This relation can be used to compose a quantile of interest for the complete path from the subpath delay distributions. The histograms with 1 ms bins are discrete approximations of the delay distributions.TOC 
TypePOnewayCompositepdvrefminNPA for the complete Source to Destination path can be calculated by combining statistics of all the constituent subpaths in the following process:
< see [Y.1541] (ITUT Recommendation Y.1541, “Network Performance Objectives for IPbased Services,” February 2006.) clause 8 and Appendix X >
TOC 
The delay distribution of a sufficiently large stream of packets measured on each subpath during the interval [T, Tf] will be sufficiently stationary and the subpath distributions themselves are sufficiently independent, so that summary information describing the subpath distributions can be combined to estimate the delay distribution of complete path.
It is assumed that the oneway delay distributions of the subpaths and the complete path are continuous.
TOC 
See the common section.
TOC 
In addition to the common deviations, a few additional sources exist here. For one, very tight distributions with range on the order of a few milliseconds are not accurately represented by a histogram with 1 ms bins. This size was chosen assuming an implicit requirement on accuracy: errors of a few milliseconds are acceptable when assessing a composed distribution quantile.
Also, summary statistics cannot describe the subtleties of an empirical distribution exactly, especially when the distribution is very different from a classical form. Any procedure that uses these statistics alone may incur error.
TOC 
If the delay distributions of the subpaths are somehow correlated, then neither of these composition functions will be reliable estimators of the complete path distribution.
In practice, subpath delay distributions with extreme outliers have increased the error of the composed metric estimate.
TOC 
See the common section.
TOC 
TOC 
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 destination and/or the intervening network(s).
Administrators of source, destination, and the intervening network(s) should establish bilateral or multilateral 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.
TOC 
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.
TOC 
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.
TOC 
Metrics defined in this memo will be registered in the IANA IPPM METRICS REGISTRY as described in initial version of the registry [RFC4148] (Stephan, E., “IP Performance Metrics (IPPM) Metrics Registry,” August 2005.).
TOC 
A long time ago, in a galaxy far, far away (Minneapolis), Will Leland suggested the simple and elegant TypePFiniteOnewayDelay concept. Thanks Will.
TOC 
>>>>>>>>>>>>Issue:
Is Section 4.1.8.4 really describing a new error case, about Alternate Routing? Or does Section 4.1.8.1 on subpath differences cover it all?
>>>>>>>>>>>>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 Oneway 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 Oneway measurement, in which part of the network the engineers should put their efforts. This question can to be answered by decompose the Oneway measurement to subpath 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 subpaths involved in the complete path?
>>>>>>>>>>>>>>>>>>RESOLUTION: treat this topic in a separate memo
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>Issue
Section 7 defines a new type of metric, a “combination” of metrics for oneway delay and packet loss. The purpose of this metric is to link these two primary metrics in a convenient way.
Readers are asked to comment on the efficiency of the combination metric.
>>>>>>>>>>>>>>>>>RESOLUTION: If a delay singleton is recorded as having "undefined" delay when the packet does not arrive within the waiting time Tmax, then this information is sufficient to determine the fraction of lost packets in the sample, and the additional loss indication of this combo is not needed.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Issue
Can we introduce multicast metrics here, without causing too much confusion? Should the multicast version of this draft wait until the Unicast concepts are stable (or maybe appear in a separate draft)?
>>>>>>>>>>>>>>>>RESOLUTION: No and Yes.
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[ID.ietfippmframeworkcompagg]  Morton, A., “Framework for Metric Composition,” draftietfippmframeworkcompagg09 (work in progress), December 2009 (TXT). 
[RFC2119]  Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). 
[RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, “Framework for IP Performance Metrics,” RFC 2330, May 1998 (TXT, HTML, XML). 
[RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Delay Metric for IPPM,” RFC 2679, September 1999 (TXT). 
[RFC2680]  Almes, G., Kalidindi, S., and M. Zekauskas, “A Oneway Packet Loss Metric for IPPM,” RFC 2680, September 1999 (TXT). 
[RFC3393]  Demichelis, C. and P. Chimento, “IP Packet Delay Variation Metric for IP Performance Metrics (IPPM),” RFC 3393, November 2002 (TXT). 
[RFC4148]  Stephan, E., “IP Performance Metrics (IPPM) Metrics Registry,” BCP 108, RFC 4148, August 2005 (TXT). 
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[ID.ietfippmmultimetrics]  Stephan, E., Liang, L., and A. Morton, “IP Performance Metrics (IPPM) for spatial and multicast,” draftietfippmmultimetrics12 (work in progress), September 2009 (TXT). 
[Y.1540]  ITUT Recommendation Y.1540, “Internet protocol data communication service  IP packet transfer and availability performance parameters,” December 2002. 
[Y.1541]  ITUT Recommendation Y.1541, “Network Performance Objectives for IPbased Services,” February 2006. 
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Al Morton  
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/ 
Emile Stephan  
France Telecom Division R&D  
2 avenue Pierre Marzin  
Lannion, F22307  
France  
Phone:  
Fax:  +33 2 96 05 18 52 
Email:  emile.stephan@orangeftgroup.com 
URI: 