Network Working Group S. Shalunov
Internet-Draft Internet2
Expires: October 6, 2006 April 4, 2006
Reporting IP Performance Metrics to Users
draft-shalunov-ippm-reporting-00.txt
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Copyright (C) The Internet Society (2006).
Abstract
Network measurement has many purposes. Often, the ultimate purpose
is to report a concise set of metrics describing a network's state to
an end user. The aim of this document is to define a small set of
metrics that are robust, easy to understand, orthogonal, relevant,
and easy to compute.
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Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
2. Goals and Motivation . . . . . . . . . . . . . . . . . . . . . 4
3. Reportable Metrics Set . . . . . . . . . . . . . . . . . . . . 5
3.1. Delay . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Jitter . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. Duplication . . . . . . . . . . . . . . . . . . . . . . . 6
3.5. Reordering . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. Internationalization Considerations . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 10
Appendix B. Revision History . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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1. Requirements Notation
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 [RFC2119].
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2. Goals and Motivation
The IPPM working group has defined many richly parameterized
performance metrics with a number of variants (one-way delay, one-way
loss, delay variation, reordering, etc.) and a protocol for obtaining
the measurement data needed to compute these metrics (OWAMP). It
would be beneficial to define a standard way to report a set of
performance metrics to end users. Parameterization might be
acceptable in such a set, but there must still be defaults for
everything. It is especially important to get these defaults right.
Such a set would enable different tools to produce results that can
be compared against each other.
The set is meant for human consumption. It must therefore be small.
Anything greater than half-dozen numbers is certainly too confusing.
Each of the metrics must be statistically robust. Intuitively, this
means that having a small number of bad data points and a small
amount of noise must not dramatically change the metric.
Each metric in the set must have, qualitatively, an immediate
intuitive meaning that has to be obvious for an advanced end user
without consulting documentation (that is, it has to be clear what
rough meaning, intuitively, the larger values of a given metric
have).
To be small, the set has to be orthogonal: each of the metrics has to
express a property not covered by other metrics (otherwise, there's
redundancy).
The metrics in the set must be relevant. Partly, being easy to
understand will help achieve this, but additional constraint may be
placed by relevancy.
Finally, while this set will most frequently be computed for small
data sets, where efficiency is not a serious consideration, it must
be easy to compute for large data sets, too. In particular, it must
be possible to compute the metrics in a single pass over the data
using a limited amount of memory (i.e., it must be possible to take a
source of measurement data with a high data rate and compute the
metrics on the fly, discarding each data point after it is
processed).
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3. Reportable Metrics Set
The following metrics comprise the set:
1. delay;
2. loss;
3. jitter;
4. duplication;
5. reordering.
Each of the above is represented by a single numeric quantity,
computed as described below.
3.1. Delay
The reported delay is the median of all delays in the sample. When a
packet is lost, its delay is to be considered +infinity for the
purposes of this computation; therefore, if more than half of all
packets are lost, the delay is +infinity.
FIXME: References.
Loss is the fraction, expressed in per cent, of packets that did not
arrive intact within a timeout interval. Since this set of metrics
often has to be reported to a waiting human user, the default timeout
value has to be small. By default, 2 seconds MUST be the timeout
value.
FIXME: References.
3.3. Jitter
Jitter is the interquartile spread of delay. In other words, jitter
is equal to the difference of the 75th and 25th percentiles of delay.
When both percentiles are +infinity, the value of jitter is
undefined. Therefore, if less than 25% of packets are lost, jitter
is defined and finite; if between 75% and 25% of packets are lost,
jitter is +infinity; finally, if more than 75% of packets are lost,
jitter is undefined.
FIXME: References.
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3.4. Duplication
Duplication is the fraction of packets for which more than a single
copy of the packet was received within the timeout period, expressed
in percentage points.
Note: while most received packets can be ones previously seen,
duplication can never exceed 100%.
FIXME: References (tough one---IPPM hasn't defined duplication).
3.5. Reordering
Reordering is the fraction of sent packets for which the sequence
number of the packet received immediately before the first copy of
the given packet is not the decrement of the sequence number of the
given packet. For the purposes of this definition, assuming sequence
numbers starting with 1, an extra packet at the start of the stream
of received packets, with a sequence number of 0, is considered to be
present.
FIXME: References.
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4. Security Considerations
The reporting per se, not being a protocol, does not raise security
considerations.
An aspect of reporting relevant to security is how the reported
metrics are used and how they are collected. If it is important that
the metrics satisfy certain conditions (e.g., that the ISP whose
network is being measured be unable to make the metrics appear better
than they are), the collection mechanism MUST ensure that this is,
indeed, so. The exact mechanisms to do so our outside of scope of
this document and belong with discussion of particular measurement
data collection protocols.
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5. Internationalization Considerations
The reported metrics, while they might occasionally be parsed by
machine, are primarily meant for human consumption. As such, they
MAY be reported in the language preferred by the user, using an
encoding suitable for the purpose, such as UTF-8.
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6. IANA Considerations
This document requires no action from the IANA.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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The author gratefully acknowledges discussion with, encouragement
from, and contributions of Lawrence D. Dunn, Matt Mathis,
Henk Uijterwaal, and Matthew J. Zekauskas.
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FIXME: This section needs to be removed before publication.
$Log: draft-shalunov-ippm-reporting.xml,v $
Revision 1.2 2006/04/04 21:39:20 shalunov
Convert to xml2rfc 1.30 and RFC 3978 IPR statement.
Revision 1.1.1.1 2006/04/02 17:07:36 shalunov
Initial import into CVS.
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Author's Address
Stanislav Shalunov
Internet2
1000 Oakbrook Drive, Suite 300
Ann Arbor, MI 48104
US
Phone: +1-734-913-4260
Email: shalunov@internet2.edu
URI: http://www.internet2.edu/~shalunov/
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Acknowledgment
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Internet Society.
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