One document matched: draft-morton-ippm-active-passive-00.txt
Network Working Group A. Morton
Internet-Draft AT&T Labs
Intended status: Informational October 24, 2014
Expires: April 27, 2015
Active and Passive Metrics and Methods (and everything in-between)
draft-morton-ippm-active-passive-00
Abstract
This memo provides clear definitions for Active and Passive
performance assessment. The construction of Metrics and Methods can
be described as Active or Passive. Methods can take on some of the
attributes of both, and we refer to these as Hybrid Methods.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on April 27, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 3
3. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3
3.1. Performance Metric . . . . . . . . . . . . . . . . . . . 3
3.2. Method of Measurement . . . . . . . . . . . . . . . . . . 3
3.3. Observation Point . . . . . . . . . . . . . . . . . . . . 3
3.4. Active Methods . . . . . . . . . . . . . . . . . . . . . 4
3.5. Active Metric . . . . . . . . . . . . . . . . . . . . . . 4
3.6. Passive Methods . . . . . . . . . . . . . . . . . . . . . 4
3.7. Passive Metric . . . . . . . . . . . . . . . . . . . . . 5
3.8. Hybrid Methods . . . . . . . . . . . . . . . . . . . . . 5
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The adjectives "active" and "passive" have been used for many years
to distinguish two different classes of Internet performance
assessment. The first Passive and Active Measurement (PAM)
Conference was held in 2000, but the earliest proceedings available
on-line are from the second PAM conference in 2001
[https://www.ripe.net/ripe/meetings/pam-2001].
The notions of "active" and "passive" are well-established. In
general:
An Active metric or method depends on a dedicated measurement
packet stream.
A Passive metric or method depends solely on observation of one or
more packet streams. The streams only serve measurement when they
are observed for that purpose, and are present whether
measurements take place or not.
As new techniques for assessment emerge it is helpful to have clear
definitions of these notions. This memo provides more detailed
definitions and discusses means to evaluate new techniques as they
emerge.
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This memo provides definitions for Active and Passive Metrics and
Methods based on long usage in the Internet measurement community,
and especially the Internet Engineering Task Force.
1.1. 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].
2. Purpose and Scope
The scope of this memo is to define and describe Active and Passive
versions of metrics and methods which are consistent with the long-
time usage of these adjectives in the Internet measurement community
and especially the Internet Engineering Task Force.
Further, this memo's purpose includes describing multiple dimensions
in which to evaluate methods as they emerge.
3. Terms and Definitions
This section defines the key terms of the memo.
3.1. Performance Metric
The standard definition of a quantity, produced in an assessment of
performance and/or reliability of the network, which has an intended
utility and is carefully specified to convey the exact meaning of a
measured value. (This definition is consistent with that of
Performance Metric in RFC 2330 and RFC 6390).
3.2. Method of Measurement
The procedure or set of operations having the object of determining a
Measured Value or Measurement Result.
3.3. Observation Point
See section 2 of [RFC7101] for this definition (a location in the
network where packets can be observed), and related definitions. The
comparable term defined in IETF literature on Active measurement is
Measurement Point, see section 4.1 of [RFC5835]. Two terms have come
into use describing somewhat actions at the identified point in the
network path.
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3.4. Active Methods
Active measurement methods have the following attributes:
1. Commonly, the packet stream of interest is generated as the basis
of measurement. A packet stream may be generated to increase
traffic load, but the loading stream itself may not be measured.
2. The packets in the stream of interest have fields which are
dedicated to measurement. Since measurement usually requires
determining the corresponding packets at multiple measurement
points, a sequence number is the most common information
dedicated to measurement.
3. The Source and Destination of the packet stream are usually known
a' priori.
4. Packet stream characteristics are known at the Source at least,
and may be communicated to Destination as part of the method.
When adding traffic to the network for measurement, Active Methods
influence the quantities measured to some degree, and should take
steps to quantify the effect(s) and/or minimize such effects.
3.5. Active Metric
An Active Metric incorporates one or more of the aspects of Active
Methods in the metric definition.
For example, IETF metrics for IP performance (developed according to
the [RFC2330] framework) include the Source packet stream
characteristics as metric input parameters, and also specify the
packet characteristics (Type-P) and Source and Destination IP
addresses (with their implications on both stream treatment and
interfaces associated with measurement points).
3.6. Passive Methods
Passive measurement methods are based on observations of un-disturbed
packet traffic. Some passive methods simply observe and collect
information on all packets that pass Observation Point(s), while
others filter the packets as a first step and only collect
information on packets that match the filter criteria.
It is common that passive methods are conducted at one or more
Observation Points. Passive methods to assess Performance Metrics
often require multiple observation points, e.g., to assess latency of
packet transfer across a network path between two Observation Points.
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In this case, the observed packets must include enough information to
determine the corresponding packets at different Observation Points.
Communication of the observations (in some form) to a collector is an
essential aspect of Passive Methods. In some configurations, the
traffic load associated with results export to a collector may
influence the network performance. However, the collection of
results is not unique to Passive Methods, and the load from
management and operations of measurement systems must always be
considered for potential effects on the measured values.
3.7. Passive Metric
Passive Metrics apply to observations of packet traffic (traffic
flows in [RFC7101]).
Passive performance metrics are assessed independent of the packets
or traffic flows, and solely through observation. Some refer to such
assessments as "out-of-band".
One example of passive performance metrics for IP packet transfer can
be found in ITU-T Recommendation Y.1540 (where the metrics are
defined on the basis of reference events as packet pass reference
points, and the metrics are therefore agnostic to the distinction
between active and passive).
3.8. Hybrid Methods
Methods of Measurement which use a combination of Active Methods and
Passive Methods, to assess Active Metrics, Passive Metrics, or a new
metrics derived from the observations.
4. Discussion
If we compare the Active and Passive Methods, there are at least two
dimensions on which methods can be evaluated. This evaluation space
may be useful when a method is a combination of the two alternative
methods.
The two dimensions are:
1. The degree to which the measurement stream affects network
conditions. For example, an extremely sparse stream of minimal
size packets typically has little effect, while a stream designed
to characterize path capacity may affect all other flows passing
through the capacity bottleneck. There is also the notion of
time averages - a measurement stream may have significant affect
while it is present, but the stream is only generated 0.1% of the
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time. On the other hand, observations alone have no affect on
network performance. To keep things simple, we consider the
stream affect only when it is present.
2. The methodological advantages of knowing the source stream
characteristics, and having complete control of the stream
characteristics. For example, knowing the number of packets in a
stream allows more efficient operation of the measurement
receiver, and so is an asset for active measurement methods.
Passive methods (with no sample filter) have few clues available
to anticipate what the first packet observed will be, but once
the standard protocol of a flow is known the possibilities narrow
(for compliant flows).
There are a few examples we can plot on a two-dimensional space. We
can anchor the dimensions with reference point descriptions.
Affect of the measurement stream on network conditions
^ Max
|* Active using max capacity stream
|
|
|
|
|* Active using stream with load of typical user
|
|
|
|* Active using extremely sparse, randomized stream
| * PDM Passive
| Min *
+----------------------------------------------------------------|
| |
Stream None
Characteristics
completely
known
5. Security considerations
When considering privacy of those involved in measurement or those
whose traffic is measured, there is sensitive information
communicated and observed at observation and measurement points
described above. We refer the reader to the privacy considerations
described in the Large Scale Measurement of Broadband Performance
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(LMAP) Framework [I-D.ietf-lmap-framework], which covers active and
passive measurement techniques and supporting material on measurement
context.
6. IANA Considerations
This memo makes no requests for IANA consideration.
7. Acknowledgements
Thanks to Mike Ackermann for asking the right question, and for
several suggestions on terminology. Brian Trammell provided key
terms and references for the passive category.
8. References
8.1. Normative References
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, May
1998.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432,
November 2002.
[RFC5835] Morton, A. and S. Van den Berghe, "Framework for Metric
Composition", RFC 5835, April 2010.
[RFC7101] Ginoza, S., "List of Internet Official Protocol Standards:
Replaced by a Web Page", RFC 7101, December 2013.
8.2. Informative References
[I-D.ietf-lmap-framework]
Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A framework for large-scale
measurement platforms (LMAP)", draft-ietf-lmap-
framework-08 (work in progress), August 2014.
[SK] Crawford, Sam., "Test Methodology White Paper", SamKnows
Whitebox Briefing Note
http://www.samknows.com/broadband/index.php, July 2011.
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[Q1741] Q.1741.7, , "IMT-2000 references to Release 9 of GSM-
evolved UMTS core network",
http://www.itu.int/rec/T-REC-Q.1741.7/en, November 2011.
Author's Address
Al Morton
AT&T Labs
200 Laurel Avenue South
Middletown, NJ
USA
Email: acmorton@att.com
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