Network Working Group S. Shalunov
Internet-Draft Internet2
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Reporting IP Performance Metrics to Users
draft-ietf-ippm-reporting-00.txt
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Copyright (C) The Internet Society (2006).
Abstract
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. The IPPM WG has defined a large number of richly
parameterized metrics because 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. It is for this purpose
that the present set of metrics is defined.
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Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
2. Goals and Motivation . . . . . . . . . . . . . . . . . . . . . 4
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Reportable Metrics Set . . . . . . . . . . . . . . . . . . . . 7
4.1. Delay . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Jitter . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Duplication . . . . . . . . . . . . . . . . . . . . . . . 8
4.5. Reordering . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Sample Source . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. One-Way Active Measurement . . . . . . . . . . . . . . . . 9
5.2. Round-Trip Active Measurement . . . . . . . . . . . . . . 10
5.3. Passive Measurement . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Internationalization Considerations . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Normative References . . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 14
Appendix B. TODO . . . . . . . . . . . . . . . . . . . . . . . . 15
Appendix C. Revision History . . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 18
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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.
Existing tools already report statistic about the network. This is
done for varying reasons: network testing tools, such as the ping
program available in UNIX-derived operating systems as well as in
Microsoft Windows, report statistics with no knowledge of why the
user is running the program; networked games might report statistics
of the network connection to the server so users can better
understand why they get the results they get (e.g., if something is
slow, is this because of the network or the CPU?), so they can
compare their statistics to those of others (``you're not lagged any
more than I am'') or perhaps so that users can decide whether they
need to upgrade the connection to their home; IP telephony hardware
and software might report the statistics for similar reasons. While
existing tools report statistics all right, the particular set of
metrics they choose is ad hoc; some metrics are not statistically
robust, some are not relevant, and some are not easy to understand;
more important than specific shortcomings, however, is the
incompatibility: even if the sets of metrics were perfect, they would
still be all different, and, therefore, metrics reported by different
tools would not be comparable.
The set of metrics of this document 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
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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 possible 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. Scope
The metrics in this document are applicable to short-term network
measurements (seconds or at most minutes) and are aimed at real-time
display of such measurements.
One consideration that would have to be addressed to make these
metrics suitable for longer-term measurements (hours and days) is
that of network availability: during such long periods of time the
network may be completely down for some time and it does not seem to
make sense to average out the reports in such a way that the network
being down for 1% of the time becomes 1% packet loss.
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4. 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.
4.1. 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.
4.2. Loss
Loss is the fraction, expressed as a percentage, of packets that did
not arrive intact within a given number of seconds (timeout value)
after being sent. 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.
4.3. 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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4.4. Duplication
Duplication is the fraction of packets for which more than a single
copy of the packet was received within the timeout period (same
timeout as in the definition of loss), 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).
4.5. 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 determining the sequence number of
the preceding packet in 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 (this extra packet, of course, is not counted for the
purposes of computing the fraction).
FIXME: References.
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5. Sample Source
Section 4 describes the metrics to compute on a sample of
measurements. The source of the sample in not discussed there, and,
indeed, the metrics discussed (delay, loss, etc.) are simply
estimators that could be applied to any sample whatsoever. For the
names of the estimators to be applicable, of course, the measurements
need to come from a packet delivery network.
The data in the samples for the set of metrics discussed in this
document can come from the following sources: one-way active
measurement, round-trip measurement, and passive measurement. There
infrequently is a choice between active and passive measurement, as,
typically, only one is available; consequently, no preference is
given to one over the other. In cases where clocks can be expected
to be synchronized, in general, one-way measurements are preferred
over round-trip measurements (as one-way measurements are more
informative). When one-way measurements cannot be obtained, or when
clocks cannot be expected to be synchronized, round-trip measurement
MAY be used.
5.1. One-Way Active Measurement
The default duration of the measurement interval is 10 seconds.
The default sending schedule is a Poisson stream.
The default sending rate is 10 packets/second on average. The
default sending schedule is a Poisson stream. When randomized
schedules, such as a Poisson stream, are used, the rate MUST be set
with the distribution parameter(s). With a randomized schedule, the
default sample size is 100 packets and the measurement window
duration can vary to some extent depending on the values of the
(pseudo-)random deviates.
The default packet size is the minimum necessary for the measurement.
Values other than the default ones MAY be used; if they are used,
their use, and specific values used, MUST be reported.
A one-way active measurement is characterized by the source IP
address, the destination IP address, the time when measurement was
taken, and the type of packets (e.g., UDP with given port numbers and
a given DSCP) used in the measurement. For the time, the middle of
the measurement interval MUST be reported.
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5.2. Round-Trip Active Measurement
The same default parameters and characterization apply to round-trip
measurement as to one-way measurement (Section 5.1).
5.3. Passive Measurement
Passive measurement use whatever data it is natural to use. For
example, an IP telephony application or a networked game would use
the data that it sends. An analysis of performance of a link might
use all the packets that traversed the link in the measurement
interval. An analysis of performance of an Internet service
provider's network might use all the packets that traversed the
network in the measurement interval. An analysis of performance of a
specific service from the point of view of a given site might use an
appropriate filter to select only the relevant packets. In any case,
the source needs to be reported.
The same default duration applies to passive measurement as to one-
way active measurement (Section 5.1).
When the passive measurement data is reported in real time, a sliding
window SHOULD be used as a measurement period, so that recent data
become more quickly reflected.
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6. 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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7. 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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8. IANA Considerations
This document requires no action from the IANA.
9. 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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Appendix A. Acknowledgments
The author gratefully acknowledges discussion with, encouragement
from, and contributions of Lawrence D. Dunn, Reza Fardid,
Ruediger Geib, Matt Mathis, Al Morton, Carsten Schmoll,
Henk Uijterwaal, and Matthew J. Zekauskas.
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Appendix B. TODO
FIXME: This section needs to be removed before publication.
o Add references
o Add non-normative code for illustration
o Add examples (code output)
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Appendix C. Revision History
FIXME: This section needs to be removed before publication.
$Log: draft-ietf-ippm-reporting.xml,v $
Revision 1.6 2006/06/02 21:21:57 shalunov
draft-ietf-ippm-reporting-00: Include a ``Scope'' section.
Change tags from draft-shalunov-ippm-reporting.
Revision 1.5 2006/05/02 20:25:44 shalunov
Version 03: Various refinements and clarifications based on feedback
from Reza Fardid, Ruediger Geib, and Al Morton.
Revision 1.4 2006/04/25 22:38:58 shalunov
Version 02: Address comments from Carsten Schmoll, sent in message
70524A4436C03E43A293958B505008B61B9CFB@EXCHSRV.fokus.fraunhofer.de.
My response, with clarifications and diffs, is in message
8664kxwazk.fsf@abel.internet2.edu.
Revision 1.3 2006/04/11 22:09:47 shalunov
Version 01: Wording changes based on discussion with Matt Zekauskas
(reordering, loss). Rewrite abstract a bit. Add TODO list.
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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