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Network Working Group A. Clark
Internet-Draft Telchemy Incorporated
Intended status: Informational November 18, 2007
Expires: May 21, 2008
Framework for Performance Metric Development
draft-morton-perf-metrics-framework-01
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This memo describes a framework and guidelines for the development of
performance metrics that are beyond the scope of existing working
group charters in the IETF. In this version, the memo refers to a
Performance Metrics Entity, or PM Entity, which may in future be a
working group or directorate or a combination of these two.
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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].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Background and Motivation . . . . . . . . . . . . . . . . 3
1.2. Organization of this memo . . . . . . . . . . . . . . . . 4
2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 4
3. Metrics Development . . . . . . . . . . . . . . . . . . . . . 4
3.1. Audience for Metrics . . . . . . . . . . . . . . . . . . . 5
3.2. Definitions of a Metric . . . . . . . . . . . . . . . . . 5
3.3. Composed Metrics . . . . . . . . . . . . . . . . . . . . . 6
3.4. Metric Specification . . . . . . . . . . . . . . . . . . . 6
3.5. Classes of Metrics . . . . . . . . . . . . . . . . . . . . 6
3.6. Qualifying Metrics . . . . . . . . . . . . . . . . . . . . 6
3.7. Reporting Models . . . . . . . . . . . . . . . . . . . . . 7
3.8. Dependencies . . . . . . . . . . . . . . . . . . . . . . . 7
4. Performance Metric Development Process . . . . . . . . . . . . 7
4.1. New Proposals for Metrics . . . . . . . . . . . . . . . . 7
4.2. Proposal Approval . . . . . . . . . . . . . . . . . . . . 8
4.3. PM Entity Interaction with other WGs . . . . . . . . . . . 8
4.4. Standards Track Performance Metrics . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
There have always been some uncertainties about the performance and
suitability of new technologies and applications for their intended
audience, and the Internet is no exception. Most uncertainties are
effectively addressed through quantified assessment of key
performance indicators. Standardized performance metrics add the
desirable features of consistent implementation, interpretation, and
comparison.
There are at least three phases in the development of performance
standards. They are:
1. Definition of a Performance Metric and its units of measure
2. Specification of a Method of Measurement
3. Specification of the Reporting Format
In some metric development activites, there are additional steps,
such as setting numerical requirements or objectives. This memo will
focus on metric definition, but it is worth noting that the products
of this phase benefit when the challenges of measurement are
considered.
In this version, the memo refers to a Performance Metrics Entity, or
PM Entity, which may in future be a working group or directorate or a
combination of these two.
1.1. Background and Motivation
Although the IETF has two Working Groups dedicated to the development
of performance metrics, they each have strict limitations in their
charters:
- The Benchmarking Methodology WG has addressed a range of networking
technologies and protocols in their long history (such as IEEE 802.3,
ATM, Frame Relay, and Routing Protocols), but the charter strictly
limits their performance characterizations to the laboratory
environment.
- The IP Performance Metrics WG has the mandate to develop metrics
applicable to live IP networks, but it is specifically prohibited
from developing metrics that characterize traffic (such as a VoIP
stream).
A BOF held at IETF-69 introduced the IETF community to the
possibility of a generalized activity to define standardized
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performance metrics. The existence of a growing list of Internet-
Drafts on performance metrics (with community interest in
development, but in un-chartered areas) illustrates the need for
additional performance work. The majority of people present at the
BOF supported the proposition that IETF should be working in these
areas, and no one objected to any of the proposals.
The IETF does have current and completed activities related to the
reporting of application performance metrics (e.g. RAQMON) and is
also actively involved in the development of reliable transport
protocols which would affect the relationship between IP performance
and application performance.
Thus there is a gap in the currently chartered coverage of IETF WGs:
development of performance metrics for non-IP-layer protocols that
can be used to characterize performance on live networks.
1.2. Organization of this memo
This memo is divided in two major sections beyond the Purpose and
Scope section. The first is a definition and description of a
performance metric and its key aspects. The second defines a process
to develop these metrics that is applicable to the IETF environment.
2. Purpose and Scope
The purpose of this memo is to define a framework and a process for
developing performance metrics in the IETF.
The scope includes metric definition for any protocol developed by
the IETF. However, other frameworks exist for IETF chartered work
[RFC2330], and this memo is not intended to superceed the existing
working methods.
Question: How do we write this scope so as not to conflict with IPPM
and BMWG? Can we say that this framework may be useful to those
activities as well, and leave it at that? Perhaps this will do:
This process is not intended to govern performance metric development
in existing IETF WG, such as IPPM and BMWG. However, the framework
and guidelines may be useful in these activities, and MAY be applied
where appropriate.
3. Metrics Development
This section provides key definitions and qualifications of
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performance metrics.
3.1. Audience for Metrics
Leen Mak's comment: In order to limit the set of metrics to what is
really useful, the approach should be the other way. The first
question to be answered should be: which metrics are needed by the
network operators to properly maintain the network?
3.2. Definitions of a Metric
A metric is a measure of an observable behavior of an application,
protocol or other system. The definition of a metric often assumes
some implicit or explicit underlying statistical process, and a
metric is an estimate of a parameter of this process. If the assumed
statistical process closely models the behavior of the system then
the metric is "better" in the sense that it more accurately
characterizes the state or behavior of the system.
A metric should serve some defined purpose. This may include the
measurement of capacity, quantifying how bad some problem is,
measurement of service level, problem diagnosis or location and other
such uses. A metric may also be an input to some other process, for
example the computation of a composite metric or a model or
simulation of a system. Tests of the "usefulness" of a metric
include:
(i) the degree to which its absence would cause significant loss
of information on the behavior or state of the application or
system being measured
(ii) the correlation between the metric and the quality of service
/ experience delivered to the user (person or other application)
(iii) the degree to which the metric is able to support the
identification and location of problems affecting service quality.
For example, consider a distributed application operating over a
network connection that is subject to packet loss. A Packet Loss
Rate (PLR) metric is defined as the mean packet loss rate over some
time period. If the application performs poorly over network
connections with high packet loss rate and always performs well when
the packet loss rate is zero then the PLR metric is useful to some
degree. Some applications are sensitive to short periods of high
loss (bursty loss). If both bursty and independent loss occur, it is
possible that there may be periods during which the PLR metric would
be the same however the application performance would be different -
i.e. PLR is weakly correlated with application performance - which
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would suggest that the metric is weak.
3.3. Composed Metrics
Some metrics may not be measured directly, but may be composed from
metrics that have been measured. Usually the contribution metrics
have a limited scope in time or space, and they can be combined to
estimate the performance of some larger entity.
[I-D.ietf-ippm-framework-compagg] gives the framework for three types
of composed metrics: Temporal Aggregation, Spatial Aggregation, and
Spatial Composition.
Spatial Composition is described in
[I-D.ietf-ippm-spatial-composition]. Other memos in this framework
are TBD.
>>>Not sure what's intended in this next one >>>
- Derivative / Composite metrics (e.g. combined effect of several
different metrics)
3.4. Metric Specification
Process for specifying a metric
3.5. Classes of Metrics
Simplify process by identifying classes of metric
3.6. Qualifying Metrics
Each metric SHOULD be assessed according to the following list of
qualifications:
o Unambiguously defined?
o Units of Measure Specified?
o Measurement Errors Identified?
o Repeatable?
o Implementable?
o Assumptions concerning underlying process?
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o Use cases?
o Correlation with application performance/ user experience?
(not sure that the last one is essential, it can be useful to
characterize a network attribute without linking it to application
performance/user experience)
3.7. Reporting Models
A metric, or some set of metrics, may be measured over some time
period, measured continuously, sampled, aggregated and/or combined
into composite metrics and then reported using a "push" or "pull"
model. Reporting protocols typically introduce some limitations and
assumptions with regard to the definition of a metric.
3.8. Dependencies
Brian Carpenter's follow-up comment: My thought is that the variance
in the "upper" metric will be very hard to understand if there is a
large variance in the "lower" metrics. There seem likely to be non-
linear effects at work. If the upper metric is being used only as an
observation (e.g. to check SLA conformance) that is one thing, but if
it's being used to make any kind of prediction or to analyze the
behaviour of the upper layer protocol, I think describing it as
unreliable is justified.
4. Performance Metric Development Process
4.1. New Proposals for Metrics
The following entry criteria will be considered for each proposal.
Proposals SHOULD be prepared as Internet Drafts, describing the
metrics and conforming to the qualifications above as much as
possible.
Proposals SHOULD be vetted by the corresponding protocol development
Working Group prior to discussion by the PM Entity. This aspect of
the process includes an assessment of the need for the metrics
proposed and assessment of the support for their development in IETF.
Proposals SHOULD include an assessment of interaction and/or overlap
with work in other Standards Development Organizations.
Proposals SHOULD specify the intended audience and users of the
metrics. The development process encourages participation by members
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of the intended audience.
Proposals SHOULD survey the existing standards work in the area and
identify additional expertise that might be consulted, or possible
overlap with other standards development orgs.
4.2. Proposal Approval
Who does this???
The IETF/IESG/Relevant ADs/Relevant WG/PM Entity ???
This section depends on the direction of the solution, or form that
the PM Entity takes.
4.3. PM Entity Interaction with other WGs
The PM Entity SHALL work in partnership with the related protocol
development WG when considering an Internet Draft that specifies
performance metrics for a protocol. A sufficient number of
individuals with expertise must be willing to consult on the draft.
If the related WG has concluded, comments on the proposal should
still be sought from key RFC authors and former chairs, or from the
WG mailing list if it was not closed.
A dedicated mailing list MAY be initiated for each work area, so that
protocol experts can subscribe to and receive the message traffic
that is relevant to their work.
In some cases, it will be appropriate to have the IETF session
discussion during the related protocol WG session, to maximize
visibility of the effort to that WG and expand the review.
4.4. Standards Track Performance Metrics
The PM Entity will manage the progression of PM RFCs along the
Standards Track. See [I-D.bradner-metricstest]. This may include
the preparation of test plans to examine different implementations of
the metrics to ensure that the metric definitions are clear and
unambiguous (depending on the final form of the draft above).
5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
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6. Security Considerations
In general, the existence of framework for performance metric
development does not constitute a security issue for the Internet.
The security considerations that apply to any active measurement of
live networks are relevant here as well. See [RFC4656].
7. Acknowledgements
The authors would like to thank Al Morton
8. References
8.1. Normative References
[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.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
8.2. Informative References
[Casner] "A Fine-Grained View of High Performance Networking, NANOG
22 Conf.; http://www.nanog.org/mtg-0105/agenda.html", May
20-22 2001.
[I-D.bradner-metricstest]
Bradner, S. and V. Paxson, "Advancement of metrics
specifications on the IETF Standards Track",
draft-bradner-metricstest-03 (work in progress),
August 2007.
[I-D.ietf-ippm-framework-compagg]
Morton, A., "Framework for Metric Composition",
draft-ietf-ippm-framework-compagg-05 (work in progress),
November 2007.
[I-D.ietf-ippm-spatial-composition]
Morton, A. and E. Stephan, "Spatial Composition of
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Metrics", draft-ietf-ippm-spatial-composition-05 (work in
progress), November 2007.
Author's Address
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, Georgia 30097
USA
Phone:
Fax:
Email: alan.d.clark@telchemy.com
URI:
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