Network Working Group A. Morton
Internet-Draft AT&T Labs
Expires: August 30, 2006 E. Stephan
France Telecom Division R&D
February 26, 2006
Spatial Composition of Metrics
draft-ietf-ippm-spatial-composition-00
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 30, 2006.
Copyright Notice
Copyright (C) The Internet Society (2006).
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
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.
Morton & Stephan Expires August 30, 2006 [Page 1]
Internet-Draft Spatial Composition February 2006
Requirements Language
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].
In this memo, the characters "<=" should be read as "less than or
equal to" and ">=" as "greater than or equal to".
Table of Contents
1. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Scope, Application, and Terminology . . . . . . . . . . . . . 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 and Metric Units . . . . . . . . . . . . . 8
4.1.3. Discussion and other details . . . . . . . . . . . . . 8
4.1.4. Mean Statistic . . . . . . . . . . . . . . . . . . . . 8
4.1.5. Composition Relationship: Sum of Means . . . . . . . . 9
4.1.6. Statement of Conjecture . . . . . . . . . . . . . . . 9
4.1.7. Justification of Composite Relationship . . . . . . . 9
4.1.8. Sources of Error . . . . . . . . . . . . . . . . . . . 10
4.1.9. Specific cases where the conjecture might fail . . . . 10
4.1.10. Application of Measurement Methodology . . . . . . . . 10
5. Loss Metrics and Statistics . . . . . . . . . . . . . . . . . 11
5.1. Name:
Type-P-One-way-Packet-Loss-Poisson/Periodic-Stream . . . . 11
5.1.1. Metric Parameters: . . . . . . . . . . . . . . . . . . 11
5.1.2. Definition and Metric Units . . . . . . . . . . . . . 11
5.1.3. Discussion and other details . . . . . . . . . . . . . 11
5.1.4. Statistic:
Type-P-One-way-Packet-Loss-Empirical-Probability . . . 11
5.1.5. Composition Relationship: Composition of Empirical
Probabilities . . . . . . . . . . . . . . . . . . . . 11
5.1.6. Statement of Conjecture . . . . . . . . . . . . . . . 12
5.1.7. Justification of Composite Relationship . . . . . . . 12
5.1.8. Sources of Error . . . . . . . . . . . . . . . . . . . 12
5.1.9. Specific cases where the conjecture might fail . . . . 12
5.1.10. Application of Measurement Methodology . . . . . . . . 13
6. Delay Variation Metrics and Statistics . . . . . . . . . . . . 13
Morton & Stephan Expires August 30, 2006 [Page 2]
Internet-Draft Spatial Composition February 2006
6.1. Name:
Type-P-One-way-ipdv-refmin-Poisson/Periodic-Stream . . . . 13
6.1.1. Metric Parameters: . . . . . . . . . . . . . . . . . . 13
6.1.2. Definition and Metric Units . . . . . . . . . . . . . 14
6.1.3. Discussion and other details . . . . . . . . . . . . . 14
6.1.4. Statistics: Mean, Variance, Skewness, Quanitle . . . . 14
6.1.5. Composition Relationships: . . . . . . . . . . . . . . 15
6.1.6. Statement of Conjecture . . . . . . . . . . . . . . . 16
6.1.7. Justification of Composite Relationship . . . . . . . 16
6.1.8. Sources of Error . . . . . . . . . . . . . . . . . . . 16
6.1.9. Specific cases where the conjecture might fail . . . . 16
6.1.10. Application of Measurement Methodology . . . . . . . . 16
7. Other Metrics and Statistics: One-way Combined Metric . . . . 16
7.1. Metric Name: . . . . . . . . . . . . . . . . . . . . . . . 16
7.1.1. Metric Parameters: . . . . . . . . . . . . . . . . . . 16
7.1.2. Definition and Metric Units . . . . . . . . . . . . . 16
7.1.3. Discussion and other details . . . . . . . . . . . . . 17
7.1.4. Type-P-One-way-Combo-subpathes-stream . . . . . . . . 17
7.1.5. Type-P-One-way-composition . . . . . . . . . . . . . . 17
7.1.6. Type-P-One-way-composition . . . . . . . . . . . . . . 17
7.1.7. Statement of Conjecture . . . . . . . . . . . . . . . 18
7.1.8. Justification of Composite Relationship . . . . . . . 18
7.1.9. Sources of Error . . . . . . . . . . . . . . . . . . . 18
7.1.10. Specific cases where the conjecture might fail . . . . 18
7.1.11. Application of Measurement Methodology . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8.1. Denial of Service Attacks . . . . . . . . . . . . . . . . 19
8.2. User Data Confidentiality . . . . . . . . . . . . . . . . 19
8.3. Interference with the metrics . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 20
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
13.1. Normative References . . . . . . . . . . . . . . . . . . . 21
13.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
Intellectual Property and Copyright Statements . . . . . . . . . . 23
Morton & Stephan Expires August 30, 2006 [Page 3]
Internet-Draft Spatial Composition February 2006
1. 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>
2. Introduction
The IPPM framework RFC 2330 [RFC2330] describes two forms of metric
composition, spatial and temporal. The new composition framework
[FRMWK] 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 sub-paths.
The purpose of this memo is to define relationships that yield the
complete path metrics using metrics of the sub-paths. 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:
o the specific conjecture applied to the metric,
o a justification of the practical utility of the composition in
terms of making accurate measurements of the metric on the path,
Morton & Stephan Expires August 30, 2006 [Page 4]
Internet-Draft Spatial Composition February 2006
o a justification of the usefulness of the composition in terms of
making analysis of the path using A-frame concepts more effective,
and
o 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 time slot assignment. 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 its own
policy, using its own measurement tools and methods, and within its
own measurement time slot. Under the appropriate conditions, one can
combine the sub-path One-way metric results to estimate the complete
path One-way measurement metric with some accuracy.
3. Scope, Application, and Terminology
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
Morton & Stephan Expires August 30, 2006 [Page 5]
Internet-Draft Spatial Composition February 2006
be composed from the same or similar sub-path metrics. This means
that the complete path metric may be composed from:
o the same metric for each sub-path;
o multiple metrics for each sub-path (possibly one that is the same
as the complete path metric);
o a single sub-path metrics that is different from the complete path
metric;
o different measurement techniques like active and passive
(recognizing that PSAMP WG will define capabilities to sample
packets to support measurement).
3.2. Application
The new composition framework [FRMWK] requires the specification of
the applicable circumstances for each metric. In particular, the
application of Spatial Composition metrics are addressed as to
whether the metric:
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 defines the terminology applicable to Spatial
Composition metrics.
Measurement Points:
Morton & Stephan Expires August 30, 2006 [Page 6]
Internet-Draft Spatial Composition February 2006
<there must be a suitable definition for this in IPPM's literature>
Complete path:
The complete path is the true path that a packet would follow as it
traverses from the packet's Source to its Destination.
Complete path metric:
The complete path metric is the Source to Destination metric that a
composed metric is estimating. A complete path metric represents the
ground-truth for a composed metric.
Composite Metric (or Composed Metric):
A composite metric is type of metric that is derived from other
metrics principally by applying a composition relationship.
Composition Relationship:
A composition relationship is a deterministic process applied to Sub-
path metrics to derive another metric (such as a Composite metric).
Sub-path:
A Sub-path is a portion of the complete path where at least the Sub-
path Source and Destination hosts are constituents of the complete
path. We say that this sub-path is "involved" in the complete path.
Sub-path metrics:
A sub-path path metric is an element of the process to derive a
Composite metric, quantifying some aspect of the performance a
particular sub-path from its Source to Destination.
4. One-way Delay Composition Metrics and Statistics
4.1. Name: Type-P-Finite-One-way-Delay-Poisson/Periodic-Stream
This metric is a necessary element of Delay Composition metrics, and
its definition does not formally exist elsewhere in IPPM literature.
4.1.1. Metric Parameters:
o Src, the IP address of a host + Dst, the IP address of a host
Morton & Stephan Expires August 30, 2006 [Page 7]
Internet-Draft Spatial Composition February 2006
o T, a time (start of test interval)
o Tf, a time (end of test interval)
o lambda, a rate in reciprocal seconds (for Poisson Streams)
o incT, the nominal duration of inter-packet interval, first bit to
first bit (for Periodic Streams)
o 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)
o TstampSrc, the wire time of the packet as measured at MP(Src)
o TstampDst, the wire time of the packet as measured at MP(Dst),
assigned to packets that arrive within a "reasonable" time.
o Tmax, a maximum waiting time for packets at the destination.
4.1.2. Definition and Metric Units
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
The "Type-P-Finite-One-way-Delay" metric allows calculation of the
mean statistic. This avoids the need to include lost packets in the
sample (whose delay is undefined), and the issue with the prescribed
assignment of infinite delay to lost packets when practical systems
can only assign some very large value.
4.1.4. Mean Statistic
We add the following parameter:
o N, the total number of packets received at Dst (sent between T0
and Tf)
and define
Morton & Stephan Expires August 30, 2006 [Page 8]
Internet-Draft Spatial Composition February 2006
Type-P-Finite-One-way-Delay-Mean =
N
---
1 \
- * > (FiniteDelay [i])
N /
---
i = 1
where all packets i= 1 through N have finite singleton delays.
4.1.5. Composition Relationship: Sum of Means
The Type-P-Finite--Composite-One-way-Delay-Mean, or CompMeanDelay for
the complete Source to Destination path can be calculated from sum of
the Mean Delays of all its S constituent sub-paths.
o 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 of 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.
Morton & Stephan Expires August 30, 2006 [Page 9]
Internet-Draft Spatial Composition February 2006
4.1.8. 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...
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.
Morton & Stephan Expires August 30, 2006 [Page 10]
Internet-Draft Spatial Composition February 2006
5. Loss Metrics and Statistics
5.1. Name: Type-P-One-way-Packet-Loss-Poisson/Periodic-Stream
5.1.1. Metric Parameters:
Same as section 4.1.1.
5.1.2. Definition and 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:
o TstampSrc, as above
o 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
o 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 =
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: Composition of Empirical Probabilities
The 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)}
Morton & Stephan Expires August 30, 2006 [Page 11]
Internet-Draft Spatial Composition February 2006
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 of 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...
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
Morton & Stephan Expires August 30, 2006 [Page 12]
Internet-Draft Spatial Composition February 2006
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 and Statistics
6.1. Name: Type-P-One-way-ipdv-refmin-Poisson/Periodic-Stream
This metric is a necessary element of Composed Delay Variation
metrics, and its definition does not formally exist elsewhere in IPPM
literature.
6.1.1. Metric Parameters:
In addition to the parameters of section 4.1.1:
o TstampSrc[i], the wire time of packet[i] as measured at MP(Src)
o TstampDst[i], the wire time of packet[i] as measured at MP(Dst),
assigned to packets that arrive within a "reasonable" time.
Morton & Stephan Expires August 30, 2006 [Page 13]
Internet-Draft Spatial Composition February 2006
o B, a packet length in bits
o F, a selection function unambiguously defining the packets from
the stream that are selected for the packet-pair computation of
this metric. F(first packet), the first packet of the pair, MUST
have a valid Type-P-Finite-One-way-Delay less than Tmax (in other
words, excluding packets which have undefined, or infinite one-way
delay) and MUST have been transmitted during the interval T, Tf.
The second packet in the pair MUST be the packet with the minimum
valid value of Type-P-Finite-One-way-Delay for the stream, in
addition to the criteria for F(first packet). If multiple packets
have equal minimum Type-P-Finite-One-way-Delay values, then the
value for the earliest arriving packet SHOULD be used.
o MinDelay, the Type-P-Finite-One-way-Delay value for F(second
packet) given above.
o N, the number of packets received at the Destination meeting the
F(first packet) criteria.
6.1.2. Definition and Metric Units
Using the definition above in section 4.1.2, we obtain the value of
Type-P-Finite-One-way-Delay-Poisson/Periodic-Stream[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: Type-P-One-way-ipdv-refmin-Poisson/Periodic-Stream[i] =
IPDVRefMin[i] = FiniteDelay[i] - MinDelay
where IPDVRefMin[i] is in units of time (seconds, milliseconds).
6.1.3. Discussion and other details
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].
6.1.4. Statistics: Mean, Variance, Skewness, Quanitle
We define the mean IPDVRefMin as follows (where all packets i= 1
through N have a value for IPDVRefMin):
Morton & Stephan Expires August 30, 2006 [Page 14]
Internet-Draft Spatial Composition February 2006
Type-P-One-way-ipdv-refmin-Mean = MeanIPDVRefMin =
N
---
1 \
- * > (IPDVRefMin [i])
N /
---
i = 1
We define the variance of IPDVRefMin as follows:
Type-P-One-way-ipdv-refmin-Variance = VarIPDVRefMin =
N
---
1 \ 2
------- > (IPDVRefMin [i] - MeanIPDVRefMin)
(N - 1) /
---
i = 1
We define the skewness of IPDVRefMin as follows:
Type-P-One-way-ipdv-refmin-Skewness = SkewIPDVRefMin =
N
--- 3
\ / \
> | IPDVRefMin[i]- MeanIPDVRefMin |
/ \ /
---
i = 1
-------------------------------------------
/ \
| ( 3/2 ) |
\ (N - 1) * VarIPDVRefMin /
We define the Quantile of the IPDVRefMin sample as the value where
the specified fraction of points is less than the given value.
6.1.5. Composition Relationships:
The Type-P-One-way-Composite-ipdv-refmin-<something> for the complete
Source to Destination path can be calculated by combining statistics
of all the constituent sub-paths in the following process:
< to be provided >
Morton & Stephan Expires August 30, 2006 [Page 15]
Internet-Draft Spatial Composition February 2006
6.1.6. Statement of Conjecture
6.1.7. Justification of Composite Relationship
6.1.8. Sources of Error
6.1.9. Specific cases where the conjecture might fail
6.1.10. Application of Measurement Methodology
7. Other Metrics and Statistics: One-way Combined Metric
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 RFC 3432 [RFC3432];
- Type-P-One-way-Composition-Stream as defined below;
- Type-P-subpath-One-way-Delay-Stream as per
I-D.stephan-ippm-multimetrics [I-D.stephan-ippm-multimetrics].
7.1.2. Definition and Metric Units
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).
Morton & Stephan Expires August 30, 2006 [Page 16]
Internet-Draft Spatial Composition February 2006
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.
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 complete path.
+ {<D0,L0>, <D1,L1>, <D2,L2>, ... <Dn,Ln>}, the composition stream of
the sub-paths 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
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.
Morton & Stephan Expires August 30, 2006 [Page 17]
Internet-Draft Spatial Composition February 2006
Parameters:
+ T1,..., Tn, a list of times;
+ <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>
7.1.7. Statement of Conjecture
7.1.8. Justification of 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 sub-path 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;
Morton & Stephan Expires August 30, 2006 [Page 18]
Internet-Draft Spatial Composition February 2006
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
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 metrics
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 RFC
4148 [RFC4148].
Morton & Stephan Expires August 30, 2006 [Page 19]
Internet-Draft Spatial Composition February 2006
10. Security Considerations
11. Open Issues
>>>>>>>>>>>>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?
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>OPEN Issue
Section 7 defines a new type of metric, a "combination" of metrics
for one-way 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.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> OPEN Issue
How 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)?
Morton & Stephan Expires August 30, 2006 [Page 20]
Internet-Draft Spatial Composition February 2006
12. Acknowledgements
13. References
13.1. Normative References
[FRMWK] Morton, A. and S.Van Den Berghe, "Framework for Metric
Composition", February 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
May 1998.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680, September 1999.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "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.
13.2. Informative References
[I-D.stephan-ippm-multimetrics]
Stephan, E., "IP Performance Metrics (IPPM) for spatial
and multicast", draft-stephan-ippm-multimetrics-02 (work
in progress), October 2005.
[Y.1540] ITU-T Recommendation Y.1540, "Internet protocol data
communication service - IP packet transfer and
availability performance parameters", December 2002.
Morton & Stephan Expires August 30, 2006 [Page 21]
Internet-Draft Spatial Composition February 2006
Authors' Addresses
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, F-22307
France
Phone:
Fax: +33 2 96 05 18 52
Email: emile.stephan@francetelecom.com
URI:
Morton & Stephan Expires August 30, 2006 [Page 22]
Internet-Draft Spatial Composition February 2006
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM 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.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Morton & Stephan Expires August 30, 2006 [Page 23]
