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Guidelines for Considering New Performance Metric Development

The information below is for an old version of the document that is already published as an RFC.
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This is an older version of an Internet-Draft that was ultimately published as RFC 6390.
Authors Benoît Claise , Alan Clark
Last updated 2015-10-14 (Latest revision 2011-07-28)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Best Current Practice
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IESG IESG state Became RFC 6390 (Best Current Practice)
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Responsible AD Dan Romascanu
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Network Working Group                                           A. Clark
Internet-Draft                                     Telchemy Incorporated
Intended status: BCP                                           B. Claise
Expires: January 29, 2012                            Cisco Systems, Inc.
                                                           July 28, 2011

     Guidelines for Considering New Performance Metric Development


   This document describes a framework and a process for developing
   Performance Metrics of protocols and applications transported over
   IETF-specified protocols, and that can be used to characterize
   traffic on live networks and services.

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
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   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 29, 2012.

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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
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   Without obtaining an adequate license from the person(s) controlling
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   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Background and Motivation  . . . . . . . . . . . . . . . .  4
     1.2.  Organization of this document  . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Performance Metrics Directorate  . . . . . . . . . . . . .  5
     2.2.  Quality of Service . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Quality of Experience  . . . . . . . . . . . . . . . . . .  5
     2.4.  Performance Metric . . . . . . . . . . . . . . . . . . . .  6
   3.  Purpose and Scope  . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Relationship between QoS, QoE and Application-specific
       Performance Metrics  . . . . . . . . . . . . . . . . . . . . .  7
   5.  Performance Metrics Development  . . . . . . . . . . . . . . .  7
     5.1.  Identifying and Categorizing the Audience  . . . . . . . .  7
     5.2.  Definitions of a Performance Metric  . . . . . . . . . . .  8
     5.3.  Computed Performance Metrics . . . . . . . . . . . . . . .  9
       5.3.1.  Composed Performance Metrics . . . . . . . . . . . . .  9
       5.3.2.  Index  . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Performance Metric Specification . . . . . . . . . . . . . 10
       5.4.1.  Outline  . . . . . . . . . . . . . . . . . . . . . . . 10
       5.4.2.  Normative parts of Performance Metric definition . . . 10
       5.4.3.  Informative parts of Performance Metric definition . . 12
       5.4.4.  Performance Metric Definition Template . . . . . . . . 13
       5.4.5.  Example: Loss Rate . . . . . . . . . . . . . . . . . . 14
     5.5.  Dependencies . . . . . . . . . . . . . . . . . . . . . . . 15
       5.5.1.  Timing accuracy  . . . . . . . . . . . . . . . . . . . 15
       5.5.2.  Dependencies of Performance Metric definitions on
               related events or metrics  . . . . . . . . . . . . . . 16
       5.5.3.  Relationship between Performance Metric and lower
               layer Performance Metrics  . . . . . . . . . . . . . . 16
       5.5.4.  Middlebox presence . . . . . . . . . . . . . . . . . . 16
     5.6.  Organization of Results  . . . . . . . . . . . . . . . . . 16
     5.7.  Parameters, the variables of a Performance Metric  . . . . 17
   6.  Performance Metric Development Process . . . . . . . . . . . . 17
     6.1.  New Proposals for Performance Metrics  . . . . . . . . . . 17
     6.2.  Reviewing Metrics  . . . . . . . . . . . . . . . . . . . . 18
     6.3.  Performance Metrics Directorate Interaction with other
           WGs  . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     6.4.  Standards Track Performance Metrics  . . . . . . . . . . . 19
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
     10.2. Informative References . . . . . . . . . . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22

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1.  Introduction

   Many networking technologies, applications, or services, are
   distributed in nature, and their performance may be impacted by IP
   impairments, server capacity, congestion and other factors.  It is
   important to measure the performance of applications and services to
   ensure that quality objectives are being met and to support problem
   diagnosis.  Standardized metrics help to ensure that performance
   measurement is implemented consistently and facilitate 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

   During the development of metrics, it is often useful to define
   performance objectives and expected value ranges.  However, this is
   not defined as part of the metric specification.

   The intended audience for this document includes, but is not limited
   to, IETF participants who write Performance Metrics documents in the
   IETF, reviewers of such documents, and members of the Performance
   Metrics Directorate.

1.1.  Background and Motivation

   Previous IETF work related to reporting of application Performance
   Metrics includes the "Real-time Application Quality-of-Service
   Monitoring (RAQMON) Framework" [RFC4710], which extends the remote
   network monitoring (RMON) family of specifications to allow real-time
   quality-of-service (QoS) monitoring of various applications that run
   on devices such as IP phones, pagers, Instant Messaging clients,
   mobile phones, and various other handheld computing devices.
   Furthermore, the "RTP Control Protocol Extended Reports (RTCP XR)"
   [RFC3611] and the "SIP RTCP Summary Report Protocol" [RFC6035] are
   protocols that support the real-time reporting of Voice over IP and
   other applications running on devices such as IP phones and mobile

   The IETF is also actively involved in the development of reliable
   transport protocols, such as TCP [RFC0793] or SCTP [RFC4960], which
   would affect the relationship between IP performance and application

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   Thus there is a gap in the currently chartered coverage of IETF
   Working Groups (WG): development of Performance Metrics for protocols
   above and below the IP-layer that can be used to characterize
   performance on live networks.

   Similarly to the "Guidelines for Considering Operations and
   Management of New Protocols and Protocol Extensions" [RFC5706], which
   is the reference document for the IETF Operations Directorate, this
   document should be consulted as part of the new Performance Metric
   review by the members of the Performance Metrics Directorate.

1.2.  Organization of this document

   This document 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.  Terminology

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.1.  Performance Metrics Directorate

   The Performance Metrics Directorate is a directorate provides
   guidance for Performance Metrics development in the IETF.

   The Performance Metrics Directorate should be composed of experts in
   the performance community, potentially selected from the IPPM, BMWG,
   and PMOL WGs.

2.2.  Quality of Service

   Quality of Service (QoS) is defined similarly to the ITU "QoS
   experienced/perceived by customer/user (QoE)" E.800 [E.800], i.e.:
   "Totality of characteristics of a telecommunications service that
   bear on its ability to satisfy stated and implied needs of the user
   of the service."

2.3.  Quality of Experience

   Quality of Experience (QoE) is defined in a similar way to the ITU
   "QoS experienced/perceived by customer/user (QoE)" E.800 [E.800],

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   i.e.: "a statement expressing the level of quality that customers/
   users believe they have experienced."

   NOTE 1 - The level of QoS experienced and/or perceived by the
   customer/user may be expressed by an opinion rating.

   NOTE 2 - QoE has two main components: quantitative and qualitative.
   The quantitative component can be influenced by the complete end-to-
   end system effects (including user devices and network

   NOTE 3 - The qualitative component can be influenced by user
   expectations, ambient conditions, psychological factors, application
   context, etc.

   NOTE 4 - QoE may also be considered as QoS delivered, received, and
   interpreted by a user with the pertinent qualitative factors
   influencing his/her perception of the service.

2.4.  Performance Metric

   A quantitative measure of performance, specific to an IETF-specified
   protocol or specific to an application transported over an IETF-
   specified protocol.  Examples of Performance Metrics are: the FTP
   response time for a complete file download, the DNS response time to
   resolve the IP address, a database logging time, etc.

3.  Purpose and Scope

   The purpose of this document is to define a framework and a process
   for developing Performance Metrics for protocols above and below the
   IP-layer (such as IP-based applications that operate over reliable or
   datagram transport protocols), that can be used to characterize
   traffic on live networks and services.  As such, this document does
   not define any Performance Metrics.

   The scope of this document covers guidelines for the Performance
   Metrics Directorate members for considering new Performance Metrics,
   and suggests how the Performance Metrics Directorate will interact
   with the rest of the IETF.  However this document is not intended to
   supersede existing working methods within WGs that have existing
   chartered work in this area.

   This process is not intended to govern Performance Metric development
   in existing IETF WG that are focused on metrics development, such as
   IPPM and BMWG.  However, this guidelines document may be useful in
   these activities, and MAY be applied where appropriate.  A typical

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   example is the development of Performance Metrics to be exported with
   the IPFIX protocol RFC 5101 [RFC5101], with specific IPFIX
   information elements RFC 5102 [RFC5102], which would benefit from the
   framework in this document.

   The framework in this document applies to Performance Metrics derived
   from both active and passive measurements.

4.  Relationship between QoS, QoE and Application-specific Performance

   Network QoS deals with network and network protocol performance,
   while QoE deals with the assessment of a user's experience in a
   context of a task or a service.  As a result, the topic of
   application-specific Performance Metrics includes the measurement of
   performance at layers between IP and the user.  For example, network
   QoS metrics (packet loss, delay, and delay variation [RFC5481]) can
   be used to estimate application-specific Performance Metrics (de-
   jitter buffer size and RTP-layer packet loss), then combined with
   other known aspects of a VoIP application (such as codec type) to
   estimate a Mean Opinion Score (MOS) [P.800].  However, the QoE for a
   particular VoIP user depends on the specific context, such as a
   casual conversation, a business conference call, or an emergency
   call.  Finally, QoS and application-specific Performance Metrics are
   quantitative, while QoE is qualitative.  Also network QoS and
   application-specific Performance Metrics can be directly or
   indirectly evident to the user, while the QoE is directly evident.

5.  Performance Metrics Development

   This section provides key definitions and qualifications of
   Performance Metrics.

5.1.  Identifying and Categorizing the Audience

   Many of the aspects of metric definition and reporting, even the
   selection or determination of the essential metrics, depend on who
   will use the results, and for what purpose.  For example, the metric
   description SHOULD include use cases and example reports that
   illustrate service quality monitoring and maintenance or
   identification and quantification of problems.

   All documents defining Performance Metrics SHOULD identify the
   primary audience and its associated requirements.  The audience can
   influence both the definition of metrics and the methods of

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   The key areas of variation between different metric users include:

   o  Suitability of passive measurements of live traffic, or active
      measurements using dedicated traffic

   o  Measurement in laboratory environment, or on a network of deployed

   o  Accuracy of the results

   o  Access to measurement points and configuration information

   o  Measurement topology (point-to-point, point-to-multipoint)

   o  Scale of the measurement system

   o  Measurements conducted on-demand, or continuously

   o  Required reporting formats and periods

   o  Sampling criteria, such systematic or probabilistic

   o  Period (and duration) of measurement, as the live traffic can have

5.2.  Definitions of a Performance Metric

   A Performance Metric is a measure of an observable behavior of a
   networking technology, an application, or a service.  Most of the
   time, the Performance Metric can be directly measured however,
   sometimes, the Performance Metric value is computed.  The process for
   determining the value of a metric may assume some implicit or
   explicit underlying statistical process, in this case, the
   Performance Metric is an estimate of a parameter of this process,
   assuming that the statistical process closely models the behavior of
   the system.

   A Performance 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 Performance Metric may also be an input to some
   other process, for example the computation of a composite Performance
   Metric or a model or simulation of a system.  Tests of the
   "usefulness" of a Performance Metric include:

      (i) the degree to which its absence would cause significant loss
      of information on the behavior or performance of the application
      or system being measured

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      (ii) the correlation between the Performance Metric, the QoS
      [G.1000] and QoE delivered to the user (person or other

      (iii) the degree to which the Performance Metric is able to
      support the identification and location of problems affecting
      service quality.

      (iv) the requirement to develop policies (Service Level Agreement,
      and potentially Service Level Contract) based on the Performance

   For example, consider a distributed application operating over a
   network connection that is subject to packet loss.  A Packet Loss
   Rate (PLR) Performance Metric is defined as the mean packet loss
   ratio over some time period.  If the application performs poorly over
   network connections with high packet loss ratio and always performs
   well when the packet loss ratio is zero then the PLR Performance
   Metric is useful to some degree.  Some applications are sensitive to
   short periods of high loss (bursty loss) and are relatively
   insensitive to isolated packet loss events; for this type of
   application there would be very weak correlation between PLR and
   application performance.  A "better" Performance Metric would
   consider both the packet loss ratio and the distribution of loss
   events.  If application performance is degraded when the PLR exceeds
   some rate then a useful Performance Metric may be a measure of the
   duration and frequency of periods during which the PLR exceeds that
   rate (as for example in RFC3611).

5.3.  Computed Performance Metrics

5.3.1.  Composed Performance Metrics

   Some Performance Metrics may not be measured directly, but can be
   composed from base metrics that have been measured.  A composed
   Performance Metric is derived from other metrics by applying a
   deterministic process or function (e.g., a composition function).
   The process may use metrics that are identical to the metric being
   composed, or metrics that are dissimilar, or some combination of both
   types.  Usually the base metrics have a limited scope in time or
   space, and they can be combined to estimate the performance of some
   larger entities.

   Some examples of composed Performance Metrics and composed
   Performance Metric definitions are:

      Spatial composition is defined as the composition of metrics of
      the same type with differing spatial domains [RFC5835] [RFC6049].

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      Ideally, for spatially composed metrics to be meaningful, the
      spatial domains should be non-overlapping and contiguous, and the
      composition operation should be mathematically appropriate for the
      type of metric.

      Temporal composition is defined as the composition of sets of
      metrics of the same type with differing time spans [RFC5835].  For
      temporally composed metrics to be meaningful, the time spans
      should be non-overlapping and contiguous, and the composition
      operation should be mathematically appropriate for the type of

      Temporal aggregation is a summarization of metrics into a smaller
      number of metrics that relate to the total time span covered by
      the original metrics.  An example would be to compute the minimum,
      maximum and average values of a series of time sampled values of a

   In the context of flow records in IP Flow Information eXport (IPFIX),
   the IPFIX Mediation: Framework [RFC6183] also discusses some aspects
   of the temporal and spatial composition.

5.3.2.  Index

   An Index is a metric for which the output value range has been
   selected for convenience or clarity, and the behavior of which is
   selected to support ease of understanding; for example the R Factor
   [G.107].  The deterministic function for an index is often developed
   after the index range and behavior have been determined.

5.4.  Performance Metric Specification

5.4.1.  Outline

   A Performance Metric definition MUST have a normative part that
   defines what the metric is and how it is measured or computed and
   SHOULD have an informative part that describes the Performance Metric
   and its application.

5.4.2.  Normative parts of Performance Metric definition

   The normative part of a Performance Metric definition MUST define at
   least the following:

   (i) Metric Name

   Performance Metric names are RECOMMENDED to be unique within the set
   of metrics being defined for the protocol layer and context.  While

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   strict uniqueness may not be attainable (See the IPPM registry
   [RFC6248] for an example of IANA metric registry failing to provide
   sufficient specificity), broad review must be sought to avoid naming
   overlap.  Note that the Performance Metrics Directorate can help with
   suggestions for IANA metric registration for unique naming.  The
   Performance Metric name MAY be descriptive.

   (ii) Metric Description

   The Performance Metric description MUST explain what the metric is,
   what is being measured and how this relates to the performance of the
   system being measured.

   (iii) Method of Measurement or Calculation

   The method of measurement or calculation MUST define what is being
   measured or computed and the specific algorithm to be used.  Does the
   measurement involve active or only passive measurements?  Terms such
   as "average" should be qualified (e.g. running average or average
   over some interval).  Exception cases SHOULD also be defined with the
   appropriate handling method.  For example, there are a number of
   commonly used metrics related to packet loss; these often don't
   define the criteria by which a packet is determined to be lost (vs
   very delayed) or how duplicate packets are handled.  For example, if
   the average packet loss rate during a time interval is reported, and
   a packet's arrival is delayed from one interval to the next then was
   it "lost" during the interval during which it should have arrived or
   should it be counted as received?

   Some methods of calculation might require discarding some data
   collected (due to outliers) so as to make the measurement parameters
   meaningful.  One example is burstable billing that sorts the 5-min
   samples, and discard the top 5 percentile.

   Some parameters linked to the method MAY also be reported, in order
   to fully interpret the Performance Metric.  For example, the time
   interval, the load, the minimum packet loss, the potential
   measurement errors and their sources, the attainable accuracy of the
   metric (e.g. +/-0,1), the method of caluclation, etc...

   (iv) Units of measurement

   The units of measurement MUST be clearly stated.

   (v) Measurement Point(s)

   If the measurement is specific to a measurement point, this SHOULD be
   defined.  The measurement domain MAY also be defined.  Specifically,

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   if measurement points are spread across domains, the measurement
   domain (intra-, inter-) is another factor to consider.

   The Performance Metric definition should discuss how the Performance
   Metric value might vary depending which measurement point is chosen.
   For example, the time between a SIP request [RFC3261] and the final
   response can be significantly different at the User Agent Client
   (UAC) or User Agent Server (UAS).

   In some cases, the measurement requires multiple measurement points:
   all measurement points SHOULD be defined, including the measurement

   (vi) Measurement timing

   The acceptable range of timing intervals or sampling intervals for a
   measurement and the timing accuracy required for such intervals MUST
   be specified.  Short sampling intervals or frequent samples provide a
   rich source of information that can help to assess application
   performance but may lead to excessive measurement data.  Long
   measurement or sampling intervals reduce the amount of reported and
   collected data such that it may be insufficient to understand
   application performance or service quality insofar as the measured
   quantity may vary significantly with time.

   In case of multiple measurement points, the potential requirement for
   synchronized clocks must be clearly specified.  In the specific
   example of the IP delay variation application metric, the different
   aspects of synchronized clocks are discussed in [RFC5481].

5.4.3.  Informative parts of Performance Metric definition

   The informative part of a Performance Metric specification is
   intended to support the implementation and use of the metric.  This
   part SHOULD provide the following data:

   (i) Implementation

   The implementation description MAY be in the form of text, algorithm
   or example software.  The objective of this part of the metric
   definition is to assist implementers to achieve consistent results.

   (ii) Verification

   The Performance Metric definition SHOULD provide guidance on
   verification testing.  This may be in the form of test vectors, a
   formal verification test method or informal advice.

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   (iii) Use and Applications

   The use and applications description is intended to assist the "user"
   to understand how, when and where the metric can be applied, and what
   significance the value range for the metric may have.  This MAY
   include a definition of the "typical" and "abnormal" range of the
   Performance Metric, if this was not apparent from the nature of the
   metric.  The description MAY include information about the influence
   of extreme measurement values, i.e. if the Performance Metric is
   sensitive to outliers.  The Use and Application section SHOULD also
   include the security implications in the description.

   For example:

   (a) it is fairly intuitive that a lower packet loss ratio would
   equate to better performance.  However the user may not know the
   significance of some given packet loss ratio,

   (b) the speech level of a telephone signal is commonly expressed in
   dBm0.  If the user is presented with:

   Speech level = -7 dBm0

   this is not intuitively understandable, unless the user is a
   telephony expert.  If the metric definition explains that the typical
   range is -18 to -28 dBm0, a value higher than -18 means the signal
   may be too high (loud) and less than -28 means that the signal may be
   too low (quiet), it is much easier to interpret the metric.

   (iv) Reporting Model

   The reporting model definition is intended to make any relationship
   between the metric and the reporting model clear.  There are often
   implied relationships between the method of reporting metrics and the
   metric itself, however these are often not made apparent to the
   implementor.  For example, if the metric is a short term running
   average packet delay variation (e.g. the interarrival jitter in
   [RFC3550]) and this value is reported at intervals of 6-10 seconds,
   the resulting measurement may have limited accuracy when packet delay
   variation is non-stationary.

5.4.4.  Performance Metric Definition Template


   o  Metric Name

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   o  Metric Description

   o  Method of Measurement or Calculation

   o  Units of Measurement

   o  Measurement Point(s) with potential Measurement Domain

   o  Measurement Timing


   o  Implementation

   o  Verification

   o  Use and Applications

   o  Reporting Model

5.4.5.  Example: Loss Rate

   The example used is the loss rate metric as specified in RFC 3611

   Metric Name: LossRate

   Metric Description: The fraction of RTP data packets from the source
   lost since the beginning of reception.

   Method of measurement or calculation: This value is calculated by
   dividing the total number of packets lost (after the effects of
   applying any error protection such as FEC) by the total number of
   packets expected, multiplying the result of the division by 256,
   limiting the maximum value to 255 (to avoid overflow), and taking the
   integer part.

   Units of Measurement: This metric is expressed as a fixed point
   number with the binary point at the left edge of the field.  For
   example, a metric value of 12 means a loss rate of approximately 5%.

   Measurement Point(s): This metric is made at the receiving end of the
   RTP stream sent during a Voice over IP call.

   Measurement Timing: This metric can be used over a wide range of time
   intervals.  Using time intervals of longer than one hour may prevent
   the detection of variations in the value of this metric due to time-
   of-day changes in network load.  Timing intervals should not vary in

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   duration by more than +/- 2%.

   Implementation: The numbers of duplicated packets and discarded
   packets do not enter into this calculation.  Since receivers cannot
   be required to maintain unlimited buffers, a receiver MAY categorize
   late-arriving packets as lost.  The degree of lateness that triggers
   a loss SHOULD be significantly greater than that which triggers a

   Verification: The metric value ranges between 0 and 255.

   Use and Applications: This metric is useful for monitoring VoIP
   calls.  More precisely, to detect the VoIP loss rate in the network.
   This loss rate, along with the rate of packets discarded due to
   jitter, has some effect on the quality of the voice stream.

   Reporting Model: This metric needs to be associated with a defined
   time interval, which could be defined by fixed intervals or by a
   sliding window.  In the context of RFC3611 the metric is measured
   continuously from the start of the RTP stream, the value of the
   metric is sampled and reported in RTCP XR VoIP Metrics reports

5.5.  Dependencies

   This section introduces several Performance Metrics dependencies,
   which the Performance Metric designer should keep in mind during the
   Performance Metric development.  These dependencies, and any others
   not listed here, SHOULD be documented in the Performance Metric

5.5.1.  Timing accuracy

   The accuracy of the timing of a measurement may affect the accuracy
   of the Performance Metric.  This may not materially affect a sampled
   value metric however would affect an interval based metric.  Some
   metrics, for example the number of events per time interval, would be
   directly affected; for example a 10% variation in time interval would
   lead directly to a 10% variation in the measured value.  Other
   metrics, such as the average packet loss ratio during some time
   interval, would be affected to a lesser extent.

   If it is necessary to correlate sampled values or intervals then it
   is essential that the accuracy of sampling time and interval start/
   stop times is sufficient for the application (for example +/- 2%).

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5.5.2.  Dependencies of Performance Metric definitions on related events
        or metrics

   Performance Metric definitions may explicitly or implicitly rely on
   factors that may not be obvious.  For example, the recognition of a
   packet as being "lost" relies on having some method to know the
   packet was actually lost (e.g.  RTP sequence number), and some time
   threshold after which a non-received packet is declared as lost.  It
   is important that any such dependencies are recognized and
   incorporated into the metric definition.

5.5.3.  Relationship between Performance Metric and lower layer
        Performance Metrics

   Lower layer Performance Metrics may be used to compute or infer the
   performance of higher layer applications, potentially using an
   application performance model.  The accuracy of this will depend on
   many factors including:

   (i) The completeness of the set of metrics - i.e. are there metrics
   for all the input values to the application performance model?

   (ii) Correlation between input variables (being measured) and
   application performance

   (iii) Variability in the measured metrics and how this variability
   affects application performance

5.5.4.  Middlebox presence

   Presence of a middlebox [RFC3303], e.g., proxy, network address
   translation (NAT), redirect server, session border controller (SBC,
   [RFC5853]), and application layer gateway (ALG) may add variability
   to or restrict the scope of measurements of a metric.  For example,
   an SBC that does not process RTP loopback packets may block or
   locally terminate this traffic rather then pass it through to its

5.6.  Organization of Results

   The IPPM Framework [RFC2330] organizes the results of metrics into
   three related notions:

   o  singleton, an elementary instance, or "atomic" value.

   o  sample, a set of singletons with some common properties and some
      varying properties.

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   o  statistic, a value derived from a sample through deterministic
      calculation, such as the mean.

   Performance Metrics MAY use this organization for the results, with
   or without the term names used by IPPM WG.  Section 11 of RFC 2330
   [RFC2330] should consulted for further details.

5.7.  Parameters, the variables of a Performance Metric

   Metrics are completely defined when all options and input variables
   have been identified and considered.  These variables are sometimes
   left unspecified in a metric definition, and their general name
   indicates that the user must set them and report them with the
   results.  Such variables are called "parameters" in the IPPM metric
   template.  The scope of the metric, the time at which it was
   conducted, the length interval of the sliding window measurement, the
   settings for timers and the thresholds for counters are all examples
   of parameters.

   All documents defining Performance Metric SHOULD identify all key
   parameters for each Performance Metric.

6.  Performance Metric Development Process

6.1.  New Proposals for Performance Metrics

   This process is intended to add additional considerations to the
   processes for adopting new work as described in RFC 2026 [RFC2026]
   and RFC 2418 [RFC2418].  Note that new Performance Metrics work item
   proposals SHALL be approved using the existing IETF process.  The
   following entry criteria will be considered for each proposal.

   Proposals SHOULD be prepared as Internet Drafts, describing the
   Performance Metric and conforming to the qualifications above as much
   as possible.  Proposals SHOULD be deliverables of the corresponding
   protocol development WG charters.  As such, the Proposals SHOULD be
   vetted by that WG prior to discussion by the Performance Metrics
   Directorate.  This aspect of the process includes an assessment of
   the need for the Performance Metric 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 identify additional expertise that might be consulted.

   Proposals SHOULD specify the intended audience and users of the
   Performance Metrics.  The development process encourages

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   participation by members of the intended audience.

   Proposals SHOULD identify any security and IANA requirements.
   Security issues could potentially involve revealing of user
   identifying data or the potential misuse of active test tools.  IANA
   considerations may involve the need for a Performance Metrics

6.2.  Reviewing Metrics

   Each Performance Metric SHOULD be assessed according to the following
   list of qualifications:

   o  Are the performance metrics unambiguously defined?

   o  Are the units of measure specified?

   o  Does the metric clearly define the measurement interval where

   o  Are significant sources of measurement errors identified and

   o  Does the method of measurement ensure that results are repeatable?

   o  Do the metric or method of measurement appear to be implement-
      able, (or offer evidence of working implementation)?

   o  Are there any undocumented assumptions concerning the underlying
      process that would affect an implementation or interpretation of
      the metric?

   o  Can the metric results related to application performance or user
      experience, when such a relationship is of value?

   o  Relationship to metrics defined elsewhere within IETF or within
      other SDO's

   o  Do the Security Considerations adequately address denial of
      service attacks, unwanted interference with the metric/
      measurement, and user data confidentiality (when measuring live

6.3.  Performance Metrics Directorate Interaction with other WGs

   The Performance Metrics Directorate SHALL provide guidance to the related
   protocol development WG when considering an Internet Draft that
   specifies Performance Metrics for a protocol.  A sufficient number of

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   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.

   A formal review is recommended by the time the document is reviewed
   by the Area Directors, or an IETF Last Call is being conducted - same
   as expert reviews are being performed by other directorates.

   Existing mailing lists SHOULD be used, however a dedicated mailing
   list MAY be initiated if necessary to facilitate work on a draft.

   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.

6.4.  Standards Track Performance Metrics

   The Performance Metrics Directorate will assist with the progression
   of 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

7.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC EDITOR: this section may be removed on publication as an

8.  Security Considerations

   In general, the existence of a framework for Performance Metric
   development does not constitute a security issue for the Internet.
   Performance Metric definitions may introduce security issues and this
   framework recommends that those defining Performance Metrics should
   identify any such risk factors.

   The security considerations that apply to any active measurement of
   live networks are relevant here.  See [RFC4656].

   The security considerations that apply to any passive measurement of
   specific packets in live networks are relevant here as well.  See the
   security considerations in [RFC5475].

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9.  Acknowledgements

   The authors would like to thank Al Morton, Dan Romascanu, Daryl Malas
   and Loki Jorgenson for their comments and contributions.  The authors
   would like to thank Aamer Akhter, Yaakov Stein, Carsten Schmoll, and
   Jan Novak for their reviews.

10.  References

10.1.  Normative References

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2418]  Bradner, S., "IETF Working Group Guidelines and
              Procedures", BCP 25, RFC 2418, September 1998.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

10.2.  Informative References

   [E.800]    "ITU-T Recommendation E.800. SERIES E: OVERALL NETWORK

   [G.1000]   "ITU-T Recommendation G.1000. Communications Quality of
              Service: A framework and definitions".

   [G.107]    "ITU-T Recommendation G.107. : The E-model, a
              computational model for use in transmission planning.".

              Bradner, S. and V. Paxson, "Advancement of metrics
              specifications on the IETF Standards Track",
              draft-bradner-metricstest-03 (work in progress),
              August 2007.

   [P.800]    "ITU-T Recommendation P.800. : Methods for subjective
              determination of transmission quality".

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

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   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
              "Framework for IP Performance Metrics", RFC 2330,
              May 1998.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3303]  Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A., and
              A. Rayhan, "Middlebox communication architecture and
              framework", RFC 3303, August 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3611]  Friedman, T., Caceres, R., and A. Clark, "RTP Control
              Protocol Extended Reports (RTCP XR)", RFC 3611,
              November 2003.

   [RFC4710]  Siddiqui, A., Romascanu, D., and E. Golovinsky, "Real-time
              Application Quality-of-Service Monitoring (RAQMON)
              Framework", RFC 4710, October 2006.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [RFC5101]  Claise, B., "Specification of the IP Flow Information
              Export (IPFIX) Protocol for the Exchange of IP Traffic
              Flow Information", RFC 5101, January 2008.

   [RFC5102]  Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
              Meyer, "Information Model for IP Flow Information Export",
              RFC 5102, January 2008.

   [RFC5475]  Zseby, T., Molina, M., Duffield, N., Niccolini, S., and F.
              Raspall, "Sampling and Filtering Techniques for IP Packet
              Selection", RFC 5475, March 2009.

   [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation
              Applicability Statement", RFC 5481, March 2009.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions",
              RFC 5706, November 2009.

   [RFC5835]  Morton, A. and S. Van den Berghe, "Framework for Metric

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              Composition", RFC 5835, April 2010.

   [RFC5853]  Hautakorpi, J., Camarillo, G., Penfield, R., Hawrylyshen,
              A., and M. Bhatia, "Requirements from Session Initiation
              Protocol (SIP) Session Border Control (SBC) Deployments",
              RFC 5853, April 2010.

   [RFC6035]  Pendleton, A., Clark, A., Johnston, A., and H. Sinnreich,
              "Session Initiation Protocol Event Package for Voice
              Quality Reporting", RFC 6035, November 2010.

   [RFC6049]  Morton, A. and E. Stephan, "Spatial Composition of
              Metrics", RFC 6049, January 2011.

   [RFC6183]  Kobayashi, A., Claise, B., Muenz, G., and K. Ishibashi,
              "IP Flow Information Export (IPFIX) Mediation: Framework",
              RFC 6183, April 2011.

   [RFC6248]  Morton, A., "RFC 4148 and the IP Performance Metrics
              (IPPM) Registry of Metrics Are Obsolete", RFC 6248,
              April 2011.

Authors' Addresses

   Alan Clark
   Telchemy Incorporated
   2905 Premiere Parkway, Suite 280
   Duluth, Georgia  30097


   Benoit Claise
   Cisco Systems, Inc.
   De Kleetlaan 6a b1
   Diegem  1831

   Phone: +32 2 704 5622

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