| Network Working Group | M. Bagnulo |
| Internet-Draft | UC3M |
| Intended status: Best Current Practice | B. Claise |
| Expires: September 12, 2019 | Cisco Systems, Inc. |
| P. Eardley | |
| BT | |
| A. Morton | |
| AT&T Labs | |
| A. Akhter | |
| Consultant | |
| March 11, 2019 |
Registry for Performance Metrics
draft-ietf-ippm-metric-registry-18
This document defines the format for the IANA Performance Metrics Registry. This document also gives a set of guidelines for Registered Performance Metric requesters and reviewers.
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 https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2019.
Copyright (c) 2019 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 (https://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.
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 a 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 requests that IANA create and maintain a Performance Metrics Registry, according to the maintenance procedures and the Performance Metrics Registry format defined in this memo. The resulting Performance Metrics Registry is for use by the IETF and others. Although the Registry formatting specifications herein are primarily for registry creation by IANA, any other organization that wishes to create a Performance Metrics Registry MAY use the same formatting specifications for their purposes. The authors make no guarantee of the registry format's applicability to any possible set of Performance Metrics envisaged by other organizations, but encourage others to apply it. In the remainder of this document, unless we explicitly say otherwise, we will refer to the IANA-maintained Performance Metrics Registry as simply the Performance Metrics Registry.
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 BCP 14[RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
This document is meant mainly for two different audiences. For those defining new Registered Performance Metrics, it provides specifications and best practices to be used in deciding which Registered Performance Metrics are useful for a measurement study, instructions for writing the text for each column of the Registered Performance Metrics, and information on the supporting documentation required for the new Performance Metrics 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 Metrics Registry, it defines a set of acceptance criteria against which these proposed Registered Performance Metrics should be evaluated. In addition, this document may be useful for other organizations who are defining a Performance Metric registry of their own, and may re-use the features of the Performance Metrics Registry defined in this document.
This Performance Metrics 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 Metrics 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 Performance Metrics Registry with initial entries.
Based on [RFC8126] Section 4.3, this document is processed as Best Current Practice (BCP) [RFC2026].
In this section, we detail several motivations for the Performance Metrics Registry.
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 Metrics Registry, there are two types of protocols that will use the Performance Metrics in the Performance Metrics Registry during their operation (by referring to the Index values):
It should be noted that the LMAP framework explicitly allows for using not only the IANA-maintained Performance Metrics Registry but also other registries containing Performance Metrics, either defined by other organizations or private ones. However, others who are creating Registries to be used in the context of an LMAP framework are encouraged to use the Registry format defined in this document, because this makes it easier for developers of LMAP Measurement Agents (MAs) to programmatically use information found in those other Registries' entries.
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.
There are a couple of side benefits of having such a registry. First, the Performance Metrics 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.
It is neither possible nor desirable to populate the Performance Metrics Registry with all combinations of Parameters of all Performance Metrics. The Registered Performance Metrics should be:
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.
There was a previous attempt to define a metric registry RFC 4148. However, it was obsoleted by RFC 6248 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.
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 Performance Metrics 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 Performance Metrics 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.
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 Performance Metrics Registry: the LMAP framework and protocol. Because the LMAP protocol will use the Performance Metrics 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 Metrics 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) allows implementation to be ambiguous.
This Performance Metrics Registry is applicable to Performance Metrics used for Active Measurement, Passive Measurement, and any other form of Performance Metric. Each category of measurement has unique properties, so some of the columns defined below are not applicable for a given metric category. In this 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 the future, a new category of metrics could require additional columns, and adding new columns is a recognized form of registry extension. The specification defining the new column(s) MUST give guidelines to populate the new column(s) for existing entries (in general).
The columns of the Performance Metrics Registry are defined below. The columns are grouped into "Categories" to facilitate the use of the registry. Categories are described at the 7.x heading level, and columns are at the 7.x.y heading level. The Figure below illustrates this organization. An entry (row) therefore gives a complete description of a Registered Performance Metric.
Registry Categories and Columns, shown as
Category
------------------
Column | Column |
Summary
------------------------------------------------------------------------
Identifier | Name | URIs | Desc. | Reference | Change Controller | Ver |
Metric Definition
-----------------------------------------
Reference Definition | Fixed Parameters |
Method of Measurement
---------------------------------------------------------------------
Reference | Packet | Traffic | Sampling | Run-time | Role |
Method | Stream | Filter | Distribution | Parameters | |
| Generation |
Output
-----------------------------------------
Type | Reference | Units | Calibration |
| 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.
A numeric identifier for the Registered Performance Metric. This identifier MUST be unique within the Performance Metrics Registry.
The Registered Performance Metric unique identifier is a 16-bit integer (range 0 to 65535).
The Identifier 0 should be Reserved. The Identifier values from 64512 to 65536 are reserved for private use.
When adding newly Registered Performance Metrics to the Performance Metrics Registry, IANA SHOULD assign the lowest available identifier to the new Registered Performance Metric.
If a Performance Metrics Expert providing review determines that there is a reason to assign a specific numeric identifier, possibly leaving a temporary gap in the numbering, then the Performance Expert SHALL inform IANA of this decision.
As the name of a Registered Performance Metric is the first thing a potential human implementor will use when determining whether it is suitable for their measurement study, it is important to be as precise and descriptive as possible. In future, users will review the names to determine if the metric they want to measure has already been registered, or if a similar entry is available as a basis for creating a new entry.
Names are composed of the following elements, separated by an underscore character "_":
MetricType_Method_SubTypeMethod_... Spec_Units_Output
SubTypeMethod values are separated by a hyphen "-" character, which indicates that they belong to this element, and that their order is unimportant when considering name uniqueness.
An example is:
RTDelay_Active_IP-UDP-Periodic_RFCXXXXsecY_Seconds_95Percentile
as described in section 4 of [I-D.ietf-ippm-initial-registry].
Note that private registries following the format described here SHOULD use the prefix "Priv_" on any name to avoid unintended conflicts (further considerations are described in section 10). Private registry entries usually have no specifying RFC, thus the Spec: element has no clear interpretation.
The URIs column MUST contain a URI [RFC3986] that uniquely identifies the metric. This URI is a URN [RFC2141]. The URI is automatically generated by prepending the prefix
urn:ietf:metrics:perf:
to the metric name. The resulting URI is globally unique.
The URIs column MUST contain a second URI which is a URL [RFC3986] and uniquely identifies and locates the metric entry so it is accessible through the Internet. The URL points to a file containing all the human-readable information for one registry entry. The URL SHALL reference a target file that is HTML-formated and contains URLs to referenced sections of HTML-ized RFCs. These target files for different entries can be more easily edited and re-used when preparing new entries. The exact form of the URL for each target file will be determined by IANA and reside on "iana.org". The major sections of [I-D.ietf-ippm-initial-registry] provide an example of a target file in HTML form (sections 4 and higher).
A Registered Performance Metric description is a written representation of a particular Performance Metrics Registry entry. It supplements the Registered Performance Metric name to help Performance Metrics Registry users select relevant Registered Performance Metrics.
This entry gives the specification containing the candidate registry entry which was reviewed and agreed, if such an RFC or other specification exists.
This entry names the entity responsible for approving revisions to the registry entry, and SHALL provide contact information (for an individual, where appropriate).
This entry gives the version number for the registry format used. Formats complying with this memo MUST use 1.0. The version number SHALL not change unless a new RFC is published that changes the registry format.
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.
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.
Fixed Parameters are Parameters whose value must be specified in the Performance Metrics 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. As an 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.
Parameters MUST have well-defined names. For human readers, the hanging indent style is preferred, and any Parameter names and definitions that do not appear in the Reference Method Specification MUST appear in this column (or Run-time Parameters column).
Parameters MUST have a well-specified data format.
A Parameter which is a Fixed Parameter for one Performance Metrics Registry entry may be designated as a Run-time Parameter for another Performance Metrics Registry entry.
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.
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.
This column applies to Performance Metrics that generate traffic as part of their Measurement Method, including but not necessarily limited to Active metrics. The generated traffic is referred as a stream and this column describes its characteristics.
Each entry for this column contains the following information:
The packet generation stream may require parameters such as the the average packet rate and distribution truncation value for streams with Poisson-distributed inter-packet sending times. In case such parameters are needed, they should be included either in the Fixed parameter column or in the run time parameter column, depending on wether they will be fixed or will be an input for the metric.
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 parameters names and values should be included either in the Fixed Parameters column or in the Run-time parameter column.
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 192.0.2.0/24 would be "dst net 192.0.2.0/24 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.
The traffic filter includes the following information:
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:
The sampling distribution may require parameters. In case such parameters are needed, they should be included either in the Fixed parameter column or in the run time parameter column, depending on whether they will be fixed or will be an input for the metric.
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].
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 Performance Metrics 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.
Parameters MUST have well defined names. For human readers, the hanging indent style is preferred, and the names and definitions that do not appear in the Reference Method Specification MUST appear in this column.
A Data Format for each Run-time Parameter MUST be specified in this column, to simplify the control and implementation of measurement devices. For example, parameters that include an IPv4 address can be encoded as a 32 bit integer (i.e. binary base64 encoded value) or ip-address as defined in [RFC6991]. The actual encoding(s) used must be explicitly defined for each Run-time parameter. IPv6 addresses and options MUST be accomodated, allowing Registered Metrics to be used in either address family.
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.
In some methods of measurement, there may be several roles defined, e.g., for a one-way packet delay active measurement there is one measurement agent that generates the packets and another agent that receives the packets. This column contains the name of the Role(s) for this particular entry. In the one-way delay example above, there should be two entries in the Role registry column, one for each Role (Source and Destination). When a measurement agent is instructed to perform the "Source" Role for one-way delay metric, the agent knows that it is required to generate packets. The values for this field are defined in the reference method of measurement (and this frequently results in abbreviated role names such as "Src").
When the Role column of a registry entry defines more than one Role, then the Role SHALL be treated as a Run-time Parameter and supplied for execution. It should be noted that the LMAP framework [RFC7594] distinguishes the Role from other Run-time Parameters, and defines a special parameter "Roles" inside the registry-grouping function list in the LMAP YANG model[RFC8194].
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.
This column contains the name of the output type. The output type defines a single type of result that the metric produces. It can be the raw results (packet send times and singleton metrics), or it can be a summary 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"). See the Naming section above for a list of Output Types.
This column contains a pointer to the specification(s) where the output type and format are defined.
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 Section 11 of[RFC2330] for definitions of these terms) is collected, this entry will specify the units for each measured value.
Some specifications for Methods of Measurement include the possibility to perform an error calibration. Section 3.7.3 of [RFC7679] is one example. In the registry entry, this field will identify a method of calibration for the metric, and when available, the measurement system SHOULD perform the calibration when requested and produce the output with an indication that it is the result of a calbration method. In-situ calibration could be enabled with an internal loopback that includes as much of the measurement system as possible, performs address manipulation as needed, and provides some form of isolation (e.g., deterministic delay) to avoid send-receive interface contention. Some portion of the random and systematic error can be characterized this way.
For one-way delay measurements, the error calibration must include an assessment of the internal clock synchronization with its external reference (this internal clock is supplying timestamps for measurement). In practice, the time offsets of clocks at both the source and destination are needed to estimate the systematic error due to imperfect clock synchronization (the time offsets are smoothed, thus the random variation is not usually represented in the results).
Both internal loopback calibration and clock synchronization can be used to estimate the *available accuracy* of the Output Metric Units. For example, repeated loopback delay measurements will reveal the portion of the Output result resolution which is the result of system noise, and thus inaccurate.
The status of the specification of this Registered Performance Metric. Allowed values are 'current' and 'deprecated'. All newly defined Information Elements have 'current' status.
The requester for the Registered Performance Metric. The requester MAY be a document, such as RFC, or person.
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.
The date of acceptance or the most recent revision for the Registered Performance Metric. The date SHALL be determined by the reviewing Performance Metrics Expert in the case of Expert Review, or by IANA in the case of Standards Action.
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.
Once a Performance Metric or set of Performance Metrics has been identified for a given application, candidate Performance Metrics Registry entry specifications prepared in accordance with Section 7 should be 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 Metrics Registry, such as deprecation or revision, as described later in this section.
It is also desirable that the author(s) of a candidate Performance Metrics Registry entry seek review in the relevant IETF working group, or offer the opportunity for review on the working group mailing list.
Requests to add Registered Performance Metrics in the Performance Metrics 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 [RFC8126]policy defined for the Performance Metrics 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.
At least one Performance Metric Expert should endeavor to complete referred reviews in a timely manner. If the request is acceptable, the Performance Metric Experts signify their approval to IANA, and IANA updates the Performance Metrics Registry. If the request is not acceptable, the Performance Metric Experts MAY coordinate with the requester to change the request to be compliant, otherwise IANA SHALL coordinate resolution of issues on behalf of the expert. The Performance Metric Experts MAY choose to reject clearly frivolous or inappropriate change requests outright, but such exceptional circumstances should be rare.
This process should not in any way be construed as allowing the Performance Metric Experts to overrule IETF consensus. Specifically, any Registered Performance Metrics that were added to the Performance Metrics Registry with IETF consensus require IETF consensus for revision or deprecation.
Decisions by the Performance Metric Experts may be appealed as in Section 7 of [RFC8126].
A request for Revision is only permissible when the changes maintain backward-compatibility with implementations of the prior Performance Metrics Registry entry describing a Registered Performance Metric (entries with lower revision numbers, but the same Identifier and Name).
The purpose of the Status field in the Performance Metrics Registry is to indicate whether the entry for a Registered Performance Metric is 'current' or 'deprecated'.
In addition, no policy is defined for revising the Performance Metric entries in the IANA Regsirty or addressing errors therein. To be certain, changes and deprecations within the Performance Metrics 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 Performance Metrics 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 Performance Metric and possibly the deprecation of the earlier metric.
A change to a Registered Performance Metric SHALL be determined to be backward-compatible only when:
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 Metrics Registry. The requester of the change is appended to the requester in the Performance Metrics Registry.
Each Registered Performance Metric in the Performance Metrics 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 Metrics 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 SHALL be changed to "Deprecated".
Changes that are not permissible by the above criteria for Registered Performance Metric's revision may only be handled by deprecation. A Registered Performance Metric MAY be deprecated and replaced when:
A request for deprecation is sent to IANA, which passes it to the Performance Metric Experts for review. When deprecating an Performance Metric, the Performance Metric description in the Performance Metrics 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 Performance Metrics should result in a log entry or human-readable warning by the respective application.
Names and Metric IDs of deprecated Registered Performance 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").
This draft defines a registry structure, and does not itself introduce any new security considerations for the Internet. The definition of Performance Metrics for this registry may introduce some security concerns, but the mandatory references should have their own considerations for secuity, and such definitions should be reviewed with security in mind if the security considerations are not covered by one or more reference standards.
This document requests the following IANA Actions.
This document requests the allocation of the URI prefix urn:ietf:metrics for the purpose of generating URIs for metrics in general. The registration procedure for the new "metrics" URN sub-namespace is IETF Review.
This document requests the allocation of the URI prefix urn:ietf:metrics:perf for the purpose of generating URIs for Registered Performance Metrics. The registration procedures for the new "perf" URN sub-namespace are Expert Review or IETF Standards Action, and coordinated with the entries added to the New Performance Metrics Registry (see below).
This document specifies the procedure for Performance Metrics Name Element Registry setup. IANA is requested to create a new set of registries for Performance Metric Name Elements called "IETF URN Sub-namespace for Registered Performance Metric Name Elements" (urn:ietf:metrics:perf). Each Registry, whose names are listed below:
will contain the current set of possibilities for Performance Metrics Registry Entry Names.
To populate the IETF URN Sub-namespace for Registered Performance Metric Name Elements at creation, the IANA is asked to use the lists of values for each name element listed in Section 7.1.2. The Name Elements in each registry are case-sensitive.
When preparing a Metric entry for Registration, the developer SHOULD choose Name elements from among the registered elements. However, if the proposed metric is unique in a significant way, it may be necessary to propose a new Name element to properly describe the metric, as described below.
A candidate Metric Entry RFC or document for Expert Review would propose one or more new element values required to describe the unique entry, and the new name element(s) would be reviewed along with the metric entry. New assignments for IETF URN Sub-namespace for Registered Performance Metric Name Elements will be administered by IANA through Expert Review [RFC8126], i.e., review by one of a group of experts, the Performance Metric Experts, who are appointed by the IESG upon recommendation of the Transport Area Directors.
This document specifies the procedure for Performance Metrics Registry setup. IANA is requested to create a new registry for Performance Metrics called "Performance Metrics Registry". This Registry will contain the following Summary columns:
Descriptions of these columns and additional information found in the template for registry entries (categories and columns) are further defined in section
The "Identifier" 0 should be Reserved. "The Identifier" values from 64512 to 65536 are reserved for private use.
Names starting with the prefix Priv_ are reserved for private use, and are not considered for registration. The "Name" column entries are further defined in section Section 7.
The "URIs" column will have a URL to the full template of each registry entry, and the linked text may be the URN itself. The template shall be HTML-ized to aid the reader, with links to reference RFCs (similar to the way that Internet Drafts are HTML-ized, the same tool can perform the function).
The “Reference” column will include an RFC, an approved specification from another standards body, or the contact person.
New assignments for Performance Metrics Registry will be administered by IANA through Expert Review [RFC8126], i.e., review by one of a group of experts, the Performance Metric Experts, who are appointed by the IESG upon recommendation of the Transport Area Directors, or by Standards Action. The experts can be initially drawn from the Working Group Chairs, document editors, and members of the Performance Metrics Directorate, among other sources of experts.
Extensions of the Performance Metrics Registry require IETF Standards Action. Only one form of registry extension is envisaged:
If the Performance Metrics Registry is extended in this way, the Version number of future entries complying with the extension SHALL be incremented (either in the unit or tenths digit, depending on the degree of extension.
Thanks to Brian Trammell and Bill Cerveny, IPPM chairs, for leading some brainstorming sessions on this topic. Thanks to Barbara Stark and Juergen Schoenwaelder for the detailed feedback and suggestions. Thanks to Andrew McGregor for suggestions on metric naming. Thanks to Michelle Cotton for her early IANA review, and to Amanda Barber for answering questions related to the presentation of the registry and accessibility of the complete template via URL.