Active and Passive Metrics and Methods (and everything in-between)
draft-morton-ippm-active-passive-00

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
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 27, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Morton                   Expires April 27, 2015                 [Page 1]
Internet-Draft             Active and Passive               October 2014

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.

Morton                   Expires April 27, 2015                 [Page 2]
Internet-Draft             Active and Passive               October 2014

   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.

Morton                   Expires April 27, 2015                 [Page 3]
Internet-Draft             Active and Passive               October 2014

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.

Morton                   Expires April 27, 2015                 [Page 4]
Internet-Draft             Active and Passive               October 2014

   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

Morton                   Expires April 27, 2015                 [Page 5]
Internet-Draft             Active and Passive               October 2014

       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

Morton                   Expires April 27, 2015                 [Page 6]
Internet-Draft             Active and Passive               October 2014

   (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.

Morton                   Expires April 27, 2015                 [Page 7]
Internet-Draft             Active and Passive               October 2014

   [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

Morton                   Expires April 27, 2015                 [Page 8]