Internet DRAFT - draft-morton-ippm-active-passive
draft-morton-ippm-active-passive
Network Working Group A. Morton
Internet-Draft AT&T Labs
Intended status: Informational February 23, 2015
Expires: August 27, 2015
Active and Passive Metrics and Methods (and everything in-between)
draft-morton-ippm-active-passive-01
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
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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 and Metrics . . . . . . . . . . . . . . . 5
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Discussion of PDM . . . . . . . . . . . . . . . . . . . . 7
4.2. Discussion of "Coloring" Method . . . . . . . . . . . . . 7
5. Security considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
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
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definitions and discusses means to evaluate new techniques as they
emerge.
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 [RFC7011] 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 (or are
augmented or modified to include 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 those
performing tests 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 undisturbed
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
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packet transfer across a network path between two Observation Points.
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 [RFC7011]).
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, so the metrics are agnostic to the distinction between active
and passive when packet correspondence can be derived from the
observed stream when required.
3.8. Hybrid Methods and Metrics
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. ITU-T Recommendation Y.1540
defines metrics are applicable to the hybrid category, since packet
correspondence at different observation/reference points could be
derived from "fields which are dedicated to measurement", but
otherwise the methods are passive.
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 (initially chosen) are:
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1. The degree to which the measured stream effects overall network
conditions. There is also the notion of time averages - a
measurement stream may have significant effect while it is
present, but the stream is only generated 0.1% of the time. On
the other hand, observations alone have no effect on network
performance. To keep things simple, we consider the stream
effect 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 protocol first packet observed will use or
how many packets will comprise the flow, but once the standard
protocol of a flow is known the possibilities narrow (for some
compliant flows).
There are a few examples we can plot on a two-dimensional space. We
can anchor the dimensions with reference point descriptions.
Effect of the measured 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
We recognize that method categorization could be based on additional
dimensions, but this would require a different graphical approach.
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For example, "effect of measured stream on network conditions" could
easily be further qualified into:
1. effect on the performance of the measured stream itself: for
example, choosing a packet marking or DSCP resulting in domain
treatment as a real-time stream (as opposed to default/best-
effort marking.
2. effect on unmeasured flows that share the path and/or
bottlenecks: for example, an extremely sparse measured stream of
minimal size packets typically has little effect on other flows
(and itself), while a stream designed to characterize path
capacity may effect all other flows passing through the capacity
bottleneck (including itself).
3. effect on network conditions, resulting in network adaptation:
for example, a network monitoring load and congestion conditions
might change routing, placing some flows to alternate paths to
mitigate the congestion.
As suggestions emerge we will examine the possibilities.
4.1. Discussion of PDM
In [I-D.elkins-ippm-pdm-option], an IPv6 Option Header is described
which (when added to the stream at strategic interfaces) supports
performance measurements. This method processes a user traffic
stream and adds "fields which are dedicated to measurement". Thus:
o The method may have a small effect on the measured stream and
other streams in the network.
o The measured stream has unknown characteristics until it is
processed to add the PDM Option header.
We conclude that this is a Hybrid method, having at least one
characteristic of both active and passive methods.
4.2. Discussion of "Coloring" Method
Draft [I-D.tempia-opsawg-p3m], proposed to color packets by re-
writing a field of the stream at strategic interfaces to support
performance measurements. This method processes a user traffic
stream and inserts "fields which are dedicated to measurement".
Thus:
o The method may have a small effect on the measured stream and
other streams in the network (smaller than PDM above).
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o The measured stream has unknown characteristics until it is
processed to add the coloring in the header, and the stream could
be measured and time-stamped during that process.
We note that [I-D.chen-ippm-coloring-based-ipfpm-framework] proposes
a method similar to [I-D.tempia-opsawg-p3m], and ippm-list discussion
indicates [I-D.chen-ippm-coloring-based-ipfpm-framework] may be
covered by the same IPR as [I-D.tempia-opsawg-p3m].
We conclude that this is a Hybrid method, having at least one
characteristic of both active and passive methods.
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
(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. Tiziano Ionta
reviewed the draft and suggested the classification for the
"coloring" method of measurement. Nalini Elkins identified several
areas for clarification following her review. Bill Jouris reviewed
01 editorially and suggested several improvements.
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.
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[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.
[RFC7011] Claise, B., Trammell, B., and P. Aitken, "Specification of
the IP Flow Information Export (IPFIX) Protocol for the
Exchange of Flow Information", STD 77, RFC 7011, September
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 of Broadband Performance (LMAP)", draft-ietf-
lmap-framework-11 (work in progress), February 2015.
[I-D.elkins-ippm-pdm-option]
Elkins, N. and M. Ackermann, "IPPM Considerations for the
IPv6 PDM Destination Option", draft-elkins-ippm-pdm-
option-03 (work in progress), February 2015.
[I-D.tempia-opsawg-p3m]
Capello, A., Cociglio, M., Castaldelli, L., and A. Bonda,
"A packet based method for passive performance
monitoring", draft-tempia-opsawg-p3m-04 (work in
progress), February 2014.
[I-D.chen-ippm-coloring-based-ipfpm-framework]
Chen, M., Zheng, L., Mirsky, G., and G. Fioccola, "IP Flow
Performance Measurement Framework", draft-chen-ippm-
coloring-based-ipfpm-framework-03 (work in progress),
February 2015.
Author's Address
Al Morton
AT&T Labs
200 Laurel Avenue South
Middletown, NJ
USA
Email: acmorton@att.com
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