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RFC 6390

Guidelines for Considering New Performance Metric Development

Pages: 23
Best Current Practice: 170

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Internet Engineering Task Force (IETF)                          A. Clark
Request for Comments: 6390                         Telchemy Incorporated
BCP: 170                                                       B. Claise
Category: Best Current Practice                      Cisco Systems, Inc.
ISSN: 2070-1721                                             October 2011


     Guidelines for Considering New Performance Metric Development

Abstract

This document describes a framework and a process for developing Performance Metrics of protocols and applications transported over IETF-specified protocols. These metrics can be used to characterize traffic on live networks and services. Status of This Memo This memo documents an Internet Best Current Practice. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6390. Copyright Notice Copyright (c) 2011 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.
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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
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   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. Requirements Language ......................................5 2.2. Performance Metrics Directorate ............................5 2.3. Quality of Service .........................................5 2.4. Quality of Experience ......................................6 2.5. 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 ...11 5.4.3. Informative Parts of Performance Metric Definition .........................................13 5.4.4. Performance Metric Definition Template .............14 5.4.5. Example: Loss Rate .................................15 5.5. Dependencies ..............................................16 5.5.1. Timing Accuracy ....................................16 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 ....................17 5.5.4. Middlebox Presence .................................17 5.6. Organization of Results ...................................17 5.7. Parameters: The Variables of a Performance Metric .........18 6. Performance Metric Development Process .........................18 6.1. New Proposals for Performance Metrics .....................18 6.2. Reviewing Metrics .........................................19 6.3. Performance Metrics Directorate Interaction with Other WGs .................................................19 6.4. Standards Track Performance Metrics .......................20 7. Security Considerations ........................................20 8. Acknowledgements ...............................................20 9. References .....................................................21 9.1. Normative References ......................................21 9.2. Informative References ....................................21
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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 ensure that performance measurement is implemented consistently, and they facilitate interpretation and comparison. There are at least three phases in the development of performance standards. They are as follows: 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. This additional information is typically not part of the formal specification of the metric but does provide useful background for implementers and users of the metric. 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 the reporting of application Performance Metrics includes "Real-time Application Quality-of- Service Monitoring (RAQMON) Framework" [RFC4710]. This framework 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, "RTP Control Protocol Extended Reports (RTCP XR)" [RFC3611] and "Session Initiation Protocol Event Package for Voice Quality Reporting" [RFC6035] define protocols that support real-time Quality of Experience (QoE) reporting for Voice over IP (VoIP) and other applications running on devices such as IP phones and mobile handsets.
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   The IETF is also actively involved in the development of reliable
   transport protocols, such as TCP [RFC0793] or the Stream Control
   Transmission Protocol (SCTP) [RFC4960], which would affect the
   relationship between IP performance and application performance.

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

   Similar to "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 into 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

2.1. 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].

2.2. Performance Metrics Directorate

The Performance Metrics Directorate is a directorate that 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 IP Performance Metrics (IPPM), Benchmarking Methodology (BMWG), and Performance Metrics for Other Layers (PMOL) WGs.

2.3. Quality of Service

Quality of Service (QoS) is defined in a way similar to the ITU "Quality of Service (QoS)" section of [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".
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2.4. Quality of Experience

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

2.5. Performance Metric

A Performance Metric is 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). These metrics 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.
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   This process is not intended to govern Performance Metric development
   in existing IETF WGs that are focused on metrics development, such as
   the IPPM and BMWG WGs.  However, this guidelines document may be
   useful in these activities and MAY be applied where appropriate.  A
   typical example is the development of Performance Metrics to be
   exported with the IP Flow Information eXport (IPFIX) protocol
   [RFC5101], with specific IPFIX information elements [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 Metrics

Network QoS deals with network and network protocol performance, while QoE deals with the assessment of a user's experience in the context of a task or a service. 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), and then combined with other known aspects of a VoIP application (such as codec type) using an algorithm compliant with ITU-T P.564 [P.564] 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.
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   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
   measurement.

   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
      devices

   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 [RFC5474], such as systematic or probabilistic

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

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 an 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 purposes. This may include the measurement of capacity, quantifying how bad some problems are, measurement of service level, problem diagnosis or location, and other such uses. A Performance Metric may also be an input to some other processes, 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:
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      (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

      (ii) the correlation between the Performance Metric, the QoS, and
      the QoE delivered to the user (person or other application)

      (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
      Metric

   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 a 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 RFC 3611).

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.
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   Some examples of composed Performance Metrics and composed
   Performance Metric definitions are as follows:

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

      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 metric.

   In the context of flow records in IP Flow Information eXport (IPFIX),
   the IPFIX Mediation Framework [RFC6183], based on "IP Flow
   Information Export (IPFIX) Mediation: Problem Statement" [RFC5982],
   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 it SHOULD have an informative part that describes the Performance Metric and its application.
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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 strict uniqueness may not be attainable (see the IPPM registry [RFC6248] for an example of an 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 (versus very delayed) or how duplicate packets are handled. For example, if the average PLR 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 discards the top 5 percentile.
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      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 calculation, etc.

   (iv) Units of Measurement

      The units of measurement MUST be clearly stated.

   (v) Measurement Point(s) with Potential Measurement Domain

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

   (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 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 the 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].
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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, an algorithm, or example software. The objective of this part of the metric definition is to help implementers 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. (iii) Use and Applications The use and applications description is intended to help the "user" 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.
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      (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
      inter-arrival 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

Normative o Metric Name o Metric Description o Method of Measurement or Calculation o Units of Measurement o Measurement Point(s) with Potential Measurement Domain o Measurement Timing
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   Informative

      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 [RFC3611]. 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 Forward Error Correction (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) with Potential Measurement Domain: 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 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 discard.
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   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 RFC 3611, the metric is
      measured continuously from the start of the RTP stream, and 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 Performance Metric development. These dependencies, and any others not listed here, SHOULD be documented in the Performance Metric specifications.

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, it 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%).

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 of knowing the packet was actually lost (e.g., RTP sequence number), and some time threshold after which a non-received packet is declared lost. It is important that any such dependencies are recognized and incorporated into the metric definition.
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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 than pass it through to its target.

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. 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 the IPPM WG. Section 11 of RFC 2330 [RFC2330] should be consulted for further details.
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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 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 Metrics 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 more 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 its development in the IETF. Proposals SHOULD include an assessment of interaction and/or overlap with work in other Standards Development Organizations (SDOs). 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 participation by members of the intended audience. Proposals SHOULD identify any security and IANA requirements. Security issues could potentially involve revealing data identifying a user, or the potential misuse of active test tools. IANA considerations may involve the need for a Performance Metrics registry.
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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 applicable? o Are significant sources of measurement errors identified and discussed? o Does the method of measurement ensure that results are repeatable? o Does the metric or method of measurement appear to be implementable (or offer evidence of a 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 be related to application performance or user experience, when such a relationship is of value? o Is there an existing relationship to metrics defined elsewhere within the IETF or within other SDOs? o Do the security considerations adequately address denial-of- service attacks, unwanted interference with the metric/ measurement, and user data confidentiality (when measuring live traffic)?

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 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. As with expert reviews performed by other directorates, a formal review is recommended by the time the document is reviewed by the Area Directors or an IETF Last Call is being conducted.
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   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 [IPPM-STANDARD-ADV-TESTING]. 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 mentioned above).

7. 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, however, may introduce security issues, and this framework recommends that persons 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].

8. Acknowledgements

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

9.1. 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.

9.2. Informative References

[E.800] "ITU-T Recommendation E.800. E SERIES: OVERALL NETWORK OPERATION, TELEPHONE SERVICE, SERVICE OPERATION AND HUMAN FACTORS", September 2008. [G.107] "ITU-T Recommendation G.107. The E-model: a computational model for use in transmission planning", April 2009. [IPPM-STANDARD-ADV-TESTING] Geib, R., Ed., Morton, A., Fardid, R., and A. Steinmitz, "IPPM standard advancement testing", Work in Progress, June 2011. [P.564] "ITU-T Recommendation P.564. Conformance Testing for Voice over IP Transmission Quality Assessment Models", November 2007. [P.800] "ITU-T Recommendation P.800. Methods for subjective determination of transmission quality", August 1996. [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998.
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   [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., Ed., Caceres, R., Ed., and A. Clark, Ed.,
              "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., Ed., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [RFC5101]  Claise, B., Ed., "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.

   [RFC5474]  Duffield, N., Ed., Chiou, D., Claise, B., Greenberg, A.,
              Grossglauser, M., and J. Rexford, "A Framework for Packet
              Selection and Reporting", RFC 5474, March 2009.

   [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.
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   [RFC5835]  Morton, A., Ed., and S. Van den Berghe, Ed., "Framework
              for Metric Composition", RFC 5835, April 2010.

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

   [RFC5982]  Kobayashi, A., Ed., and B. Claise, Ed., "IP Flow
              Information Export (IPFIX) Mediation: Problem Statement",
              RFC 5982, August 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 USA EMail: alan.d.clark@telchemy.com Benoit Claise Cisco Systems, Inc. De Kleetlaan 6a b1 Diegem 1831 Belgium Phone: +32 2 704 5622 EMail: bclaise@cisco.com