Network Working Group M. Bagnulo
Internet-Draft UC3M
Intended status: Best Current Practice B. Claise
Expires: January 7, 2016 Cisco Systems, Inc.
P. Eardley
A. Morton
AT&T Labs
A. Akhter
July 6, 2015

Registry for Performance Metrics


This document defines the IANA Registry for Performance Metrics. This document also gives a set of guidelines for Registered Performance Metric requesters and reviewers.

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

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 January 7, 2016.

Copyright Notice

Copyright (c) 2015 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 ( 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.

Table of Contents

1. Open Issues

  1. Define the Filter column subcolumns, i.e. how filters are expressed.
  2. Need to include an example for a passive metric
  3. Shall we remove the definitions of active and passive? If we remove it, shall we keep all the related comments in the draft?
  4. URL: should we include a URL link in each registry entry with a URL specific to the entry that links to a different text page that contains all the details of the registry entry as in
  5. As discussed between Marcelo and Benoit, modify "defines" in the Parameter definition. Reasoning: the distinction between a new performance metric and a parameter is not clear. If it's defined as a variable, is it a new perf metric? "All Parameters must be known to measure using a metric": well, if it's a new perf metric, we don't have the problem. And state what the parameter is the example.
  6. As discussed between Marcelo and Benoit, can we find a Parameter for passive monitoring? The sampling distribution is a fixed Parameter, right? Because it's needed "to interpret the results", as mentioned in the Parameter definition.
  7. We miss a new Parameter section that explains the link between Parameters, Fixed Parameters, Run-time Parameters, and potentially stream parameters. We must also add in this section that "Differences in values for a fixed parameters implies a new registry entries"
  8. The double definitions are annoying: Registered Performance Metric = Registered Metric, and Performance Metrics Registry = Registry. I (Benoit) am in favor to only keep a single definition (the longest one), and be consistent

2. Introduction

The IETF specifies and uses Performance Metrics of protocols and applications transported over its protocols. Performance metrics are such an important part of the operations of IETF protocols that [RFC6390] specifies guidelines for their development.

The definition and use of Performance Metrics in the IETF happens in various working groups (WG), most notably:

It is expected that more Performance Metrics will be defined in the future, not only IP-based metrics, but also metrics which are protocol-specific and application-specific.

However, despite the importance of Performance Metrics, there are two related problems for the industry. First, how to ensure that when one party requests another party to measure (or report or in some way act on) a particular Performance Metric, then both parties have exactly the same understanding of what Performance Metric is being referred to. Second, how to discover which Performance Metrics have been specified, so as to avoid developing new Performance Metric that is very similar, but not quite inter-operable. The problems can be addressed by creating a registry of performance metrics. The usual way in which IETF organizes namespaces is with Internet Assigned Numbers Authority (IANA) registries, and there is currently no Performance Metrics Registry maintained by the IANA.

This document therefore creates an IANA-maintained Performance Metrics Registry. It also provides best practices on how to specify new entries or update ones in the Performance Metrics Registry.

3. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

Performance Metric:
A Performance Metric is a quantitative measure of performance, targeted to an IETF-specified protocol or targeted 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. This definition is consistent with the definition of metric in [RFC2330] and broader than the definition of performance metric in [RFC6390].
Registered Performance Metric:
A Registered Performance Metric (or Registered Metric) is a Performance Metric expressed as an entry in the Performance Metric Registry, administered by IANA. Such a performance metric has met all the registry review criteria defined in this document in order to included in the registry.
Performance Metrics Registry:
The IANA registry containing Registered Performance Metrics. In this document, it is also called simply "Registry".
Proprietary Registry:
A set of metrics that are registered in a proprietary registry, as opposed to Performance Metrics Registry.
Performance Metrics Experts:
The Performance Metrics Experts is a group of designated experts [RFC5226] selected by the IESG to validate the Performance Metrics before updating the Performance Metrics Registry. The Performance Metrics Experts work closely with IANA.
An input factor defined as a variable in the definition of a Performance Metric. A numerical or other specified factor forming one of a set that defines a metric or sets the conditions of its operation. All Parameters must be known to measure using a metric and interpret the results. Although Parameters do not change the fundamental nature of the Performance Metric's definition, some have substantial influence on the network property being assessed and interpretation of the results.
Note: Consider the case of packet loss in the following two Active Measurement Method cases. The first case is packet loss as background loss where the parameter set includes a very sparse Poisson stream, and only characterizes the times when packets were lost. Actual user streams likely see much higher loss at these times, due to tail drop or radio errors. The second case is packet loss as inverse of throughput where the parameter set includes a very dense, bursty stream, and characterizes the loss experienced by a stream that approximates a user stream. These are both "loss metrics", but the difference in interpretation of the results is highly dependent on the Parameters (at least), to the extreme where we are actually using loss to infer its compliment: delivered throughput.

Active Measurement Method:
Methods of Measurement conducted on traffic which serves only the purpose of measurement and is generated for that reason alone, and whose traffic characteristics are known a priori. Examples of Active Measurement Methods are the measurement methods for the One way delay metric defined in [RFC2679] and the one for round trip delay defined in [RFC2681].
Passive Measurement Method:
Methods of Measurement conducted on network traffic, generated either from the end users or from network elements. One characteristic of Passive Measurement Methods is that sensitive information may be observed, and as a consequence, stored in the measurement system.

4. Scope

This document is meant for two different audiences. For those defining new Registered Performance Metrics, it provides specifications and best practices to be used in deciding which Registered Metrics are useful for a measurement study, instructions for writing the text for each column of the Registered Metrics, and information on the supporting documentation required for the new Registry entry (up to and including the publication of one or more RFCs or I-Ds describing it). For the appointed Performance Metrics Experts and for IANA personnel administering the new IANA Performance Metric Registry, it defines a set of acceptance criteria against which these proposed Registered Performance Metrics should be evaluated.

This Performance Metric Registry is applicable to Performance Metrics issued from Active Measurement, Passive Measurement, and any other form of Performance Metric. This registry is designed to encompass Performance Metrics developed throughout the IETF and especially for the technologies specified in the following working groups: IPPM, XRBLOCK, IPFIX, and BMWG. This document analyzes an prior attempt to set up a Performance Metric Registry, and the reasons why this design was inadequate [RFC6248]. Finally, this document gives a set of guidelines for requesters and expert reviewers of candidate Registered Performance Metrics.

This document makes no attempt to populate the Registry with initial entries. It does provides a few examples that are merely illustrations and should not be included in the registry at this point in time.

Based on [RFC5226] Section 4.3, this document is processed as Best Current Practice (BCP) [RFC2026].

5. Motivation for a Performance Metrics Registry

In this section, we detail several motivations for the Performance Metric Registry.

5.1. Interoperability

As any IETF registry, the primary use for a registry is to manage a namespace for its use within one or more protocols. In the particular case of the Performance Metric Registry, there are two types of protocols that will use the Performance Metrics in the Registry during their operation (by referring to the Index values):

5.2. Single point of reference for Performance Metrics

A Performance Metrics Registry serves as a single point of reference for Performance Metrics defined in different working groups in the IETF. As we mentioned earlier, there are several WGs that define Performance Metrics in the IETF and it is hard to keep track of all them. This results in multiple definitions of similar Performance Metrics that attempt to measure the same phenomena but in slightly different (and incompatible) ways. Having a Registry would allow both the IETF community and external people to have a single list of relevant Performance Metrics defined by the IETF (and others, where appropriate). The single list is also an essential aspect of communication about Performance Metrics, where different entities that request measurements, execute measurements, and report the results can benefit from a common understanding of the referenced Performance Metric.

5.3. Side benefits

There are a couple of side benefits of having such a Registry. First, the Registry could serve as an inventory of useful and used Performance Metrics, that are normally supported by different implementations of measurement agents. Second, the results of measurements using the Performance Metrics would be comparable even if they are performed by different implementations and in different networks, as the Performance Metric is properly defined. BCP 176 [RFC6576] examines whether the results produced by independent implementations are equivalent in the context of evaluating the completeness and clarity of metric specifications. This BCP defines the standards track advancement testing for (active) IPPM metrics, and the same process will likely suffice to determine whether Registered Performance Metrics are sufficiently well specified to result in comparable (or equivalent) results. Registered Performance Metrics which have undergone such testing SHOULD be noted, with a reference to the test results.

6. Criteria for Performance Metrics Registration

It is neither possible nor desirable to populate the Registry with all combinations of Parameters of all Performance Metrics. The Registered Performance Metrics should be:

  1. interpretable by the user.
  2. implementable by the software designer,
  3. deployable by network operators,
  4. accurate, for interoperability and deployment across vendors,
  5. Operationally useful, so that it has significant industry interest and/or has seen deployment,
  6. Sufficiently tightly defined, so that different values for the Run-time Parameters does not change the fundamental nature of the measurement, nor change the practicality of its implementation.

In essence, there needs to be evidence that a candidate Registered Performance Metric has significant industry interest, or has seen deployment, and there is agreement that the candidate Registered Performance Metric serves its intended purpose.

7. Performance Metric Registry: Prior attempt

There was a previous attempt to define a metric registry RFC 4148 [RFC4148]. However, it was obsoleted by RFC 6248 [RFC6248] because it was "found to be insufficiently detailed to uniquely identify IPPM metrics... [there was too much] variability possible when characterizing a metric exactly" which led to the RFC4148 registry having "very few users, if any".

A couple of interesting additional quotes from RFC 6248 might help understand the issues related to that registry.

  1. "It is not believed to be feasible or even useful to register every possible combination of Type P, metric parameters, and Stream parameters using the current structure of the IPPM Metrics Registry."
  2. "The registry structure has been found to be insufficiently detailed to uniquely identify IPPM metrics."
  3. "Despite apparent efforts to find current or even future users, no one responded to the call for interest in the RFC 4148 registry during the second half of 2010."

The current approach learns from this by tightly defining each Registered Performance Metric with only a few variable (Run-time) Parameters to be specified by the measurement designer, if any. The idea is that entries in the Registry stem from different measurement methods which require input (Run-time) parameters to set factors like source and destination addresses (which do not change the fundamental nature of the measurement). The downside of this approach is that it could result in a large number of entries in the Registry. There is agreement that less is more in this context - it is better to have a reduced set of useful metrics rather than a large set of metrics, some with with questionable usefulness.

7.1. Why this Attempt Will Succeed

As mentioned in the previous section, one of the main issues with the previous registry was that the metrics contained in the registry were too generic to be useful. This document specifies stricter criteria for performance metric registration (see section 6), and imposes a group of Performance Metrics Experts that will provide guidelines to assess if a Performance Metric is properly specified.

Another key difference between this attempt and the previous one is that in this case there is at least one clear user for the Registry: the LMAP framework and protocol. Because the LMAP protocol will use the Registry values in its operation, this actually helps to determine if a metric is properly defined. In particular, since we expect that the LMAP control protocol will enable a controller to request a measurement agent to perform a measurement using a given metric by embedding the Performance Metric Registry value in the protocol, a metric is properly specified if it is defined well-enough so that it is possible (and practical) to implement the metric in the measurement agent. This was the failure of the previous attempt: a registry entry with an undefined Type-P (section 13 of RFC 2330 [RFC2330]) allows implementation to be ambiguous.

8. Definition of the Performance Metric Registry

In this section we define the columns of the Performance Metric Registry. This Performance Metric Registry is applicable to Performance Metrics issued from Active Measurement, Passive Measurement, and any other form of Performance Metric. Because of that, it may be the case that some of the columns defined are not applicable for a given type of metric. If this is the case, the column(s) SHOULD be populated with the "NA" value (Non Applicable). However, the "NA" value MUST NOT be used by any metric in the following columns: Identifier, Name, URI, Status, Requester, Revision, Revision Date, Description. In addition, it may be possible that, in the future, a new type of metric requires additional columns. Should that be the case, it is possible to add new columns to the registry. The specification defining the new column(s) must define how to populate the new column(s) for existing entries.

The columns of the Performance Metric Registry are defined next. The columns are grouped into "Categories" to facilitate the use of the registry. Categories are described at the 8.x heading level, and columns are at the 8.x.y heading level. The Figure below illustrates this organization. An entry (row) therefore gives a complete description of a Registered Metric.

 Registry Categories and Columns, shown as
    Column |  Column |
	Identifier  | Name | URI | Description | 

	Metric Definition
	Reference Definition | Fixed Parameters |

	Method of Measurement
    Reference | Packet     | Traffic | Sampling     | Run-time   | Role |
    Method    | Generation | Filter  | Distribution | Parameters |      |
              | Stream     |
    | Type | Reference  | Units | 
    |      | Definition |       |

    Administrative Information
    Status |Request | Rev | Rev.Date |

    Comments and Remarks


Each column serves as a check-list item and helps to avoid omissions during registration and expert review.

8.1. Summary Category

8.1.1. Identifier

A numeric identifier for the Registered Performance Metric. This identifier MUST be unique within the Performance Metric Registry.

The Registered Performance Metric unique identifier is a 16-bit integer (range 0 to 65535). When adding newly Registered Performance Metrics to the Performance Metric Registry, IANA should assign the lowest available identifier to the next Registered Performance Metric.

8.1.2. Name

As the name of a Registered Performance Metric is the first thing a potential implementor will use when determining whether it is suitable for a given application, it is important to be as precise and descriptive as possible.

New names of Registered Performance Metrics:

  1. "MUST be chosen carefully to describe the Registered Performance Metric and the context in which it will be used."
  2. "MUST be unique within the Performance Metric Registry."
  3. "MUST use capital letters for the first letter of each component. All other letters MUST be lowercase, even for acronyms. Exceptions are made for acronyms containing a mixture of lowercase and capital letters, such as 'IPv4' and 'IPv6'."
  4. MUST use '_' between each component of the Registered Performance Metric name.
  5. MUST start with prefix Act_ for active measurement Registered Performance Metric.
  6. MUST start with prefix Pas_ for passive monitoring Registered Performance Metric.
  7. Other types of Performance Metric should define a proper prefix for identifying the type.
  8. Some examples of names of passive metrics might be: Pas_L3_L4_Octets (Layer 3 and 4 level accounting of bytes observed), Pas_DNS_RTT (Round Trip Time of in DNS query response of observed traffic), and Pas_L3_TCP_RTT (Passively observed round trip time in TCP handshake organized with L3 addresses)
  9. The remaining rules for naming are left for the Performance Metric Experts to determine as they gather experience, so this is an area of planned update by a future RFC

An example is "Act_UDP_Latency_Poisson_99mean" for a active monitoring UDP latency metric using a Poisson stream of packets and producing the 99th percentile mean as output.

8.1.3. URI

The URI column MUST contain a URI [RFC3986] that uniquely identified the Registered Performance Metric. The URI is a URN [RFC2141]. The URI is automatically generated by prepending the prefix urn:ietf:params:ippm:metric: to the metric name. The resulting URI is globally unique.

8.1.4. Description

A Registered Performance Metric description is a written representation of a particular Registry entry. It supplements the Registered Performance Metric name to help Registry users select relevant Registered Performance Metrics.

8.2. Metric Definition Category

This category includes columns to prompt all necessary details related to the metric definition, including the RFC reference and values of input factors, called fixed parameters, which are left open in the RFC but have a particular value defined by the performance metric.

8.2.1. Reference Definition

This entry provides a reference (or references) to the relevant section(s) of the document(s) that define the metric, as well as any supplemental information needed to ensure an unambiguous definition for implementations. The reference needs to be an immutable document, such as an RFC; for other standards bodies, it is likely to be necessary to reference a specific, dated version of a specification.

8.2.2. Fixed Parameters

Fixed Parameters are Paremeters whose value must be specified in the Registry. The measurement system uses these values.

Where referenced metrics supply a list of Parameters as part of their descriptive template, a sub-set of the Parameters will be designated as Fixed Parameters. For example, for active metrics, Fixed Parameters determine most or all of the IPPM Framework convention "packets of Type-P" as described in [RFC2330], such as transport protocol, payload length, TTL, etc. An example for passive metrics is for RTP packet loss calculation that relies on the validation of a packet as RTP which is a multi-packet validation controlled by MIN_SEQUENTIAL as defined by [RFC3550]. Varying MIN_SEQUENTIAL values can alter the loss report and this value could be set as a Fixed Parameter

A Parameter which is a Fixed Parameter for one Registry entry may be designated as a Run-time Parameter for another Registry entry.

8.3. Method of Measurement Category

This category includes columns for references to relevant sections of the RFC(s) and any supplemental information needed to ensure an unambiguous method for implementations.

8.3.1. Reference Method

This entry provides references to relevant sections of the RFC(s) describing the method of measurement, as well as any supplemental information needed to ensure unambiguous interpretation for implementations referring to the RFC text.

Specifically, this section should include pointers to pseudocode or actual code that could be used for an unambigious implementation.

8.3.2. Packet Generation Stream

This column applies to Performance Metrics that generate traffic for a part of their Measurement Method purposes including but not necessarily limited to Active metrics. The generated traffic is referred as stream and this columns describe its characteristics.

Each entry for this column contains the following information:

The simplest example of stream specification is Singleton scheduling (see [RFC2330]), where a single atomic measurement is conducted. Each atomic measurement could consist of sending a single packet (such as a DNS request) or sending several packets (for example, to request a webpage). Other streams support a series of atomic measurements in a "sample", with a schedule defining the timing between each transmitted packet and subsequent measurement. Principally, two different streams are used in IPPM metrics, Poisson distributed as described in [RFC2330] and Periodic as described in [RFC3432]. Both Poisson and Periodic have their own unique parameters, and the relevant set of values is specified in this column.

8.3.3. Traffic Filter

This column applies to Performance Metrics that observe packets flowing through (the device with) the measurement agent i.e. that is not necessarily addressed to the measurement agent. This includes but is not limited to Passive Metrics. The filter specifies the traffic that is measured. This includes protocol field values/ranges, such as address ranges, and flow or session identifiers.

The traffic filter itself depends on needs of the metric itself and a balance of operators measurement needs and user's need for privacy. Mechanics for conveying the filter criteria might be the BPF (Berkley Packet Filter) or PSAMP [RFC5475] Property Match Filtering which reuses IPFIX [RFC7012]. An example BPF string for matching TCP/80 traffic to remote destination net would be "dst net and tcp dst port 80". More complex filter engines might be supported by the implementation that might allow for matching using Deep Packet Inspection (DPI) technology.

8.3.4. Sampling Distribution

The sampling distribution defines out of all the packets that match the traffic filter, which one of those are actually used for the measurement. One possibility is "all" which implies that all packets matching the Traffic filter are considered, but there may be other sampling strategies. It includes the following information:

Sampling and Filtering Techniques for IP Packet Selection are documented in the PSAMP (Packet Sampling) [RFC5475], while the Framework for Packet Selection and Reporting, [RFC5474] provides more background information. The sampling distribution parameters might be expressed in terms of the Information Model for Packet Sampling Exports, [RFC5477], and the Flow Selection Techniques, [RFC7014].

8.3.5. Run-time Parameters

Run-Time Parameters are Parameters that must be determined, configured into the measurement system, and reported with the results for the context to be complete. However, the values of these parameters is not specified in the Registry (like the Fixed Parameters), rather these parameters are listed as an aid to the measurement system implementer or user (they must be left as variables, and supplied on execution).

Where metrics supply a list of Parameters as part of their descriptive template, a sub-set of the Parameters will be designated as Run-Time Parameters.

Examples of Run-time Parameters include IP addresses, measurement point designations, start times and end times for measurement, and other information essential to the method of measurement.

8.3.6. Role

In some method of measurements, there may be several roles defined e.g. on a one-way packet delay active measurement, there is one measurement agent that generates the packets and the other one that receives the packets. This column contains the name of the role for this particular entry. In the previous example, there should be two entries in the registry, one for each role, so that when a measurement agent is instructed to perform the one way delay source metric know that it is supposed to generate packets. The values for this field are defined in the reference method of measurement.

8.4. Output Category

For entries which involve a stream and many singleton measurements, a statistic may be specified in this column to summarize the results to a single value. If the complete set of measured singletons is output, this will be specified here.

Some metrics embed one specific statistic in the reference metric definition, while others allow several output types or statistics.

8.4.1. Type

This column contain the name of the output type. The output type defines the type of result that the metric produces. It can be the raw results or it can be some form of statistic. The specification of the output type must define the format of the output. In some systems, format specifications will simplify both measurement implementation and collection/storage tasks. Note that if two different statistics are required from a single measurement (for example, both "Xth percentile mean" and "Raw"), then a new output type must be defined ("Xth percentile mean AND Raw").

8.4.2. Reference Definition

This column contains a pointer to the specification where the output type is defined

8.4.3. Metric Units

The measured results must be expressed using some standard dimension or units of measure. This column provides the units.

When a sample of singletons (see [RFC2330] for definitions of these terms) is collected, this entry will specify the units for each measured value.

8.5. Administrative information

8.5.1. Status

The status of the specification of this Registered Performance Metric. Allowed values are 'current' and 'deprecated'. All newly defined Information Elements have 'current' status.

8.5.2. Requester

The requester for the Registered Performance Metric. The requester MAY be a document, such as RFC, or person.

8.5.3. Revision

The revision number of a Registered Performance Metric, starting at 0 for Registered Performance Metrics at time of definition and incremented by one for each revision.

8.5.4. Revision Date

The date of acceptance or the most recent revision for the Registered Performance Metric.

8.6. Comments and Remarks

Besides providing additional details which do not appear in other categories, this open Category (single column) allows for unforeseen issues to be addressed by simply updating this informational entry.

9. The Life-Cycle of Registered Metrics

Once a Performance Metric or set of Performance Metrics has been identified for a given application, candidate Registry entry specifications in accordance with Section 8 are submitted to IANA to follow the process for review by the Performance Metric Experts, as defined below. This process is also used for other changes to the Performance Metric Registry, such as deprecation or revision, as described later in this section.

It is also desirable that the author(s) of a candidate Registry entry seek review in the relevant IETF working group, or offer the opportunity for review on the WG mailing list.

9.1. Adding new Performance Metrics to the Registry

Requests to change Registered Metrics in the Performance Metric Registry are submitted to IANA, which forwards the request to a designated group of experts (Performance Metric Experts) appointed by the IESG; these are the reviewers called for by the Expert Review RFC5226 policy defined for the Performance Metric Registry. The Performance Metric Experts review the request for such things as compliance with this document, compliance with other applicable Performance Metric-related RFCs, and consistency with the currently defined set of Registered Performance Metrics.

Authors are expected to review compliance with the specifications in this document to check their submissions before sending them to IANA.

The Performance Metric Experts should endeavor to complete referred reviews in a timely manner. If the request is acceptable, the Performance Metric Experts signify their approval to IANA, which updates the Performance Metric Registry. If the request is not acceptable, the Performance Metric Experts can coordinate with the requester to change the request to be compliant. The Performance Metric Experts may also choose in exceptional circumstances to reject clearly frivolous or inappropriate change requests outright.

This process should not in any way be construed as allowing the Performance Metric Experts to overrule IETF consensus. Specifically, any Registered Metrics that were added with IETF consensus require IETF consensus for revision or deprecation.

Decisions by the Performance Metric Experts may be appealed as in Section 7 of RFC5226.

9.2. Revising Registered Performance Metrics

A request for Revision is only permissible when the changes maintain backward-compatibility with implementations of the prior Registry entry describing a Registered Metric (entries with lower revision numbers, but the same Identifier and Name).

The purpose of the Status field in the Performance Metric Registry is to indicate whether the entry for a Registered Metric is 'current' or 'deprecated'.

In addition, no policy is defined for revising IANA Performance Metric entries or addressing errors therein. To be certain, changes and deprecations within the Performance Metric Registry are not encouraged, and should be avoided to the extent possible. However, in recognition that change is inevitable, the provisions of this section address the need for revisions.

Revisions are initiated by sending a candidate Registered Performance Metric definition to IANA, as in Section 8, identifying the existing Registry entry.

The primary requirement in the definition of a policy for managing changes to existing Registered Performance Metrics is avoidance of interoperability problems; Performance Metric Experts must work to maintain interoperability above all else. Changes to Registered Performance Metrics may only be done in an inter-operable way; necessary changes that cannot be done in a way to allow interoperability with unchanged implementations must result in the creation of a new Registered Metric and possibly the deprecation of the earlier metric.

A change to a Registered Performance Metric is held to be backward-compatible only when:

  1. "it involves the correction of an error that is obviously only editorial; or"
  2. "it corrects an ambiguity in the Registered Performance Metric's definition, which itself leads to issues severe enough to prevent the Registered Performance Metric's usage as originally defined; or"
  3. "it corrects missing information in the metric definition without changing its meaning (e.g., the explicit definition of 'quantity' semantics for numeric fields without a Data Type Semantics value); or"
  4. "it harmonizes with an external reference that was itself corrected."

If an Performance Metric revision is deemed permissible by the Performance Metric Experts, according to the rules in this document, IANA makes the change in the Performance Metric Registry. The requester of the change is appended to the requester in the Registry.

Each Registered Performance Metric in the Registry has a revision number, starting at zero. Each change to a Registered Performance Metric following this process increments the revision number by one.

When a revised Registered Performance Metric is accepted into the Performance Metric Registry, the date of acceptance of the most recent revision is placed into the revision Date column of the Registry for that Registered Performance Metric.

Where applicable, additions to Registered Performance Metrics in the form of text Comments or Remarks should include the date, but such additions may not constitute a revision according to this process.

Older version(s) of the updated metric entries are kept in the registry for archival purposes. The older entries are kept with all fields unmodified (version, revision date) except for the status field that is changed to "Deprecated".

9.3. Deprecating Registered Performance Metrics

Changes that are not permissible by the above criteria for Registered Metric's revision may only be handled by deprecation. A Registered Performance Metric MAY be deprecated and replaced when:

  1. "the Registered Performance Metric definition has an error or shortcoming that cannot be permissibly changed as in Section Revising Registered Performance Metrics; or"
  2. "the deprecation harmonizes with an external reference that was itself deprecated through that reference's accepted deprecation method; or"

A request for deprecation is sent to IANA, which passes it to the Performance Metric Expert for review. When deprecating an Performance Metric, the Performance Metric description in the Performance Metric Registry must be updated to explain the deprecation, as well as to refer to any new Performance Metrics created to replace the deprecated Performance Metric.

The revision number of a Registered Performance Metric is incremented upon deprecation, and the revision Date updated, as with any revision.

The use of deprecated Registered Metrics should result in a log entry or human-readable warning by the respective application.

Names and Metric ID of deprecated Registered Metrics must not be reused.

The deprecated entries are kept with all fields unmodified, except the version, revision date, and the status field (changed to "Deprecated").

10. Security considerations

This draft doesn't introduce any new security considerations for the Internet. However, the definition of Performance Metrics may introduce some security concerns, and should be reviewed with security in mind.

11. IANA Considerations

This document specifies the procedure for Performance Metrics Registry setup. IANA is requested to create a new Registry for Performance Metrics called "Registered Performance Metrics" with the columns defined in Section 8.

New assignments for Performance Metric Registry will be administered by IANA through Expert Review [RFC5226], i.e., review by one of a group of experts, the Performance Metric Experts, appointed by the IESG upon recommendation of the Transport Area Directors. The experts can be initially drawn from the Working Group Chairs and document editors of the Performance Metrics Directorate among other sources of experts.

The Identifier values from 64512 to 65536 are reserved for private use. The name starting with the prefix Priv- are reserved for private use.

This document requests the allocation of the URI prefix urn:ietf:params:ippm:metric for the purpose of generating URIs for registered metrics.

12. Acknowledgments

Thanks to Brian Trammell and Bill Cerveny, IPPM chairs, for leading some brainstorming sessions on this topic.

13. References

13.1. 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.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J. and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998.
[RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005.
[RFC4148] Stephan, E., "IP Performance Metrics (IPPM) Metrics Registry", BCP 108, RFC 4148, August 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[RFC6248] Morton, A., "RFC 4148 and the IP Performance Metrics (IPPM) Registry of Metrics Are Obsolete", RFC 6248, April 2011.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New Performance Metric Development", BCP 170, RFC 6390, October 2011.
[RFC6576] Geib, R., Morton, A., Fardid, R. and A. Steinmitz, "IP Performance Metrics (IPPM) Standard Advancement Testing", BCP 176, RFC 6576, March 2012.

13.2. Informative References

[RFC2679] Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2681] Almes, G., Kalidindi, S. and M. Zekauskas, "A Round-trip Delay Metric for IPPM", RFC 2681, September 1999.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation Metric for IP Performance Metrics (IPPM)", RFC 3393, November 2002.
[RFC3432] Raisanen, V., Grotefeld, G. and A. Morton, "Network performance measurement with periodic streams", RFC 3432, November 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.
[RFC4566] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006.
[RFC5474] Duffield, N., 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.
[RFC5477] Dietz, T., Claise, B., Aitken, P., Dressler, F. and G. Carle, "Information Model for Packet Sampling Exports", RFC 5477, March 2009.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation Applicability Statement", RFC 5481, March 2009.
[RFC5905] Mills, D., Martin, J., Burbank, J. and W. Kasch, "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, June 2010.
[RFC6035] Pendleton, A., Clark, A., Johnston, A. and H. Sinnreich, "Session Initiation Protocol Event Package for Voice Quality Reporting", RFC 6035, November 2010.
[RFC6776] Clark, A. and Q. Wu, "Measurement Identity and Information Reporting Using a Source Description (SDES) Item and an RTCP Extended Report (XR) Block", RFC 6776, October 2012.
[RFC6792] Wu, Q., Hunt, G. and P. Arden, "Guidelines for Use of the RTP Monitoring Framework", RFC 6792, November 2012.
[RFC7003] Clark, A., Huang, R. and Q. Wu, "RTP Control Protocol (RTCP) Extended Report (XR) Block for Burst/Gap Discard Metric Reporting", RFC 7003, September 2013.
[RFC7012] Claise, B. and B. Trammell, "Information Model for IP Flow Information Export (IPFIX)", RFC 7012, September 2013.
[RFC7014] D'Antonio, S., Zseby, T., Henke, C. and L. Peluso, "Flow Selection Techniques", RFC 7014, September 2013.
[I-D.ietf-lmap-framework] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T., Aitken, P. and A. Akhter, "A framework for Large-Scale Measurement of Broadband Performance (LMAP)", Internet-Draft draft-ietf-lmap-framework-14, April 2015.

Authors' Addresses

Marcelo Bagnulo Universidad Carlos III de Madrid Av. Universidad 30 Leganes, Madrid 28911 SPAIN Phone: 34 91 6249500 EMail: URI:
Benoit Claise Cisco Systems, Inc. De Kleetlaan 6a b1 1831 Diegem, Belgium EMail:
Philip Eardley BT Adastral Park, Martlesham Heath Ipswich, ENGLAND EMail:
Al Morton AT&T Labs 200 Laurel Avenue South Middletown, NJ, USA EMail:
Aamer Akhter Consultant 118 Timber Hitch Cary, NC USA EMail: