draft-ietf-ippm-spatial-composition-14.txt   draft-ietf-ippm-spatial-composition-15.txt 
Network Working Group A. Morton Network Working Group A. Morton
Internet-Draft AT&T Labs Internet-Draft AT&T Labs
Intended status: Standards Track E. Stephan Intended status: Standards Track E. Stephan
Expires: January 2, 2011 France Telecom Division R&D Expires: January 3, 2011 France Telecom Division R&D
July 1, 2010 July 2, 2010
Spatial Composition of Metrics Spatial Composition of Metrics
draft-ietf-ippm-spatial-composition-14 draft-ietf-ippm-spatial-composition-15
Abstract Abstract
This memo utilizes IP Performance Metrics that are applicable to both This memo utilizes IP Performance Metrics that are applicable to both
complete paths and sub-paths, and defines relationships to compose a complete paths and sub-paths, and defines relationships to compose a
complete path metric from the sub-path metrics with some accuracy complete path metric from the sub-path metrics with some accuracy
w.r.t. the actual metrics. This is called Spatial Composition in RFC w.r.t. the actual metrics. This is called Spatial Composition in RFC
2330. The memo refers to the Framework for Metric Composition, and 2330. The memo refers to the Framework for Metric Composition, and
provides background and motivation for combining metrics to derive provides background and motivation for combining metrics to derive
others. The descriptions of several composed metrics and statistics others. The descriptions of several composed metrics and statistics
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 2, 2011. This Internet-Draft will expire on January 3, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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relationships are/are not applicable. For example, we would not relationships are/are not applicable. For example, we would not
expect that delay singletons from each sub-path would sum to produce expect that delay singletons from each sub-path would sum to produce
an accurate estimate of a delay singleton for the complete path an accurate estimate of a delay singleton for the complete path
(unless all the delays were essentially constant - very unlikely). (unless all the delays were essentially constant - very unlikely).
However, other delay statistics (based on a reasonable sample size) However, other delay statistics (based on a reasonable sample size)
may have a sufficiently large set of circumstances where they are may have a sufficiently large set of circumstances where they are
applicable. applicable.
1.1. Motivation 1.1. Motivation
One-way metrics defined in other RFCs (such as [RFC2680] and One-way metrics defined in other RFCs (such as [RFC2679] and
[RFC2680]) all assume that the measurement can be practically carried [RFC2680]) all assume that the measurement can be practically carried
out between the source and the destination of interest. Sometimes out between the source and the destination of interest. Sometimes
there are reasons that the measurement cannot be executed from the there are reasons that the measurement cannot be executed from the
source to the destination. For instance, the measurement path may source to the destination. For instance, the measurement path may
cross several independent domains that have conflicting policies, cross several independent domains that have conflicting policies,
measurement tools and methods, and measurement time assignment. The measurement tools and methods, and measurement time assignment. The
solution then may be the composition of several sub-path solution then may be the composition of several sub-path
measurements. This means each domain performs the One-way measurements. This means each domain performs the One-way
measurement on a sub path between two nodes that are involved in the measurement on a sub path between two nodes that are involved in the
complete path following its own policy, using its own measurement complete path following its own policy, using its own measurement
tools and methods, and using its own measurement timing. Under the tools and methods, and using its own measurement timing. Under the
appropriate conditions, one can combine the sub-path One-way metric appropriate conditions, one can combine the sub-path One-way metric
results to estimate the complete path One-way measurement metric with results to estimate the complete path One-way measurement metric with
some degree of accuracy. some degree of accuracy.
2. Scope and Application 2. Scope and Application
2.1. Scope of work 2.1. Scope of work
For the primary IPPM metrics of Loss [RFC2680], Delay [RFC2680], and For the primary IPPM metrics of Loss [RFC2680], Delay [RFC2679], and
Delay Variation [RFC3393], this memo gives a set of metrics that can Delay Variation [RFC3393], this memo gives a set of metrics that can
be composed from the same or similar sub-path metrics. This means be composed from the same or similar sub-path metrics. This means
that the composition function may utilize: that the composition function may utilize:
o the same metric for each sub-path; o the same metric for each sub-path;
o multiple metrics for each sub-path (possibly one that is the same o multiple metrics for each sub-path (possibly one that is the same
as the complete path metric); as the complete path metric);
o a single sub-path metric that is different from the complete path o a single sub-path metric that is different from the complete path
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and passive [RFC5474]. and passive [RFC5474].
We note a possibility: Using a complete path metric and all but one We note a possibility: Using a complete path metric and all but one
sub-path metric to infer the performance of the missing sub-path, sub-path metric to infer the performance of the missing sub-path,
especially when the "last" sub-path metric is missing. However, such especially when the "last" sub-path metric is missing. However, such
de-composition calculations, and the corresponding set of issues they de-composition calculations, and the corresponding set of issues they
raise, are beyond the scope of this memo. raise, are beyond the scope of this memo.
2.2. Application 2.2. Application
The new composition framework [RFC5835] requires the specification of The composition framework [RFC5835] requires the specification of the
the applicable circumstances for each metric. In particular, each applicable circumstances for each metric. In particular, each
section addresses whether the metric: section addresses whether the metric:
Requires the same test packets to traverse all sub-paths, or may use Requires the same test packets to traverse all sub-paths, or may use
similar packets sent and collected separately in each sub-path. similar packets sent and collected separately in each sub-path.
Requires homogeneity of measurement methodologies, or can allow a Requires homogeneity of measurement methodologies, or can allow a
degree of flexibility (e.g., active or passive methods produce the degree of flexibility (e.g., active or passive methods produce the
"same" metric). Also, the applicable sending streams will be "same" metric). Also, the applicable sending streams will be
specified, such as Poisson, Periodic, or both. specified, such as Poisson, Periodic, or both.
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