Network Working Group                                          G. Mirsky
Internet-Draft                                                J. Halpern
Intended status: Standards Track                                Ericsson
Expires: 27 April 2022                                            X. Min
                                                               ZTE Corp.
                                                                  L. Han
                                                            China Mobile
                                                         24 October 2021

       Error Performance Measurement in Packet-switched Networks


   This document describes the use of the error performance metric to
   characterize a packet-switched network's conformance to the pre-
   defined set of performance objectives.  In this document, metrics
   that characterize error performance in a packet-switched network
   (PSN) are defined, as well as methods to measure and calculate them.
   Also, the requirements for an active Operation, Administration, and
   Maintenance protocol to support the error performance measurement in
   PSN are discussed, and potential candidate protocols are analyzed.
   All metrics and measurement methods are equally applicable to
   underlay and overlay networks.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 27 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology and Acronyms  . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Error Performance Metrics . . . . . . . . . . . . . . . . . .   4
     3.1.  Measure Error Performance Metrics . . . . . . . . . . . .   4
     3.2.  Calculate Error Performance Metrics . . . . . . . . . . .   5
   4.  Requirements to EPM . . . . . . . . . . . . . . . . . . . . .   5
   5.  Active OAM Protocol for EPM . . . . . . . . . . . . . . . . .   6
   6.  Availability of Anything-as-a-Service . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Operations, Administration, and Maintenance (OAM) is a collection of
   methods to detect, characterize, localize failures in a network, and
   monitor the network's performance using various measurement methods.
   Traditionally, the former set of OAM tools identified as Fault
   Management (FM) OAM.  The latter - Performance Monitoring (PM) OAM.
   Some OAM protocols can be used for both groups of tasks, while some
   serve one particular group.  But regardless of how many OAM protocols
   are in use, network operators and network users are faced with
   multiple metrics that characterize the network conditions.  This
   document describes a new component of packet-switched network (PSN)

   Error performance measurement (EPM) is a part of an OAM toolset that
   provides an operator with information related to network measurements
   for a uni-directional or a bidirectional connection between two
   systems.  In current technology, EPM has been defined only for data
   communication methods that have a constant bit-rate transmission

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   [ITU.G.826] and not for PSN, where transmissions are statistically
   random.  As a statistically multiplexed network in a PSN, a receiver
   node does not expect a packet to arrive from a sender node at a
   specific moment, less from a particular sender.  That is what
   differentiates PSN from networks built on a constant bit-rate
   transmission, where a stream of bits between two nodes is always
   present, whether it represents data or not.  That provides the
   receiver with a predictable number of measurements in a series of
   measurement intervals.  In PSN, on-path OAM methods, i.e.,
   measurement methods that use data flow, cannot provide such
   predictability and thus be used for EPM.  In PSN, EPM needs to use
   active OAM methods, per definition in [RFC7799].  This document
   identifies metrics that characterize PSN error performance and
   methods to measure and calculate them.  Also, the requirements for an
   active OAM protocol to support EPM in PSN are discussed, and
   potential candidate protocols are analyzed.

2.  Conventions used in this document

2.1.  Terminology and Acronyms

   OAM Operations, Administration, and Maintenance

   EP Error Performance

   EPM Error Performance Measurement

   ES Errored Second

   ESR Errored Second Ratio

   SES Severely Errored Second

   SESR Severely Errored Second Ratio

   EFS Error-Free Second

   PSN Packet-switched Network

   FM Fault Management

   PM Performance Monitoring

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2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

3.  Error Performance Metrics

   When analyzing the error performance of a path between two nodes, we
   need to select a time interval as the unit of EPM.  In [ITU.G.826], a
   time interval of one second is used.  It is reasonable to use the
   same time interval for EPM for PSNs.  Further, for the purpose of
   EPM, each time interval, i.e., second, is classified either as
   Errored Second (ES), Severely Errored Second (SES), or Error-Free
   Second (EFS).  These are defined as follows:

   *  An ES is a time interval during which at least one of the
      performance parameters degraded below its optimal level threshold
      or a defect was detected.

   *  An SES is a time interval during which at least one the
      performance parameters degraded below its critical threshold or a
      defect was detected.

   *  Consequently, an EFS is a time interval during which all
      performance objectives are at or above their respective optimal
      levels, and no defect has been detected.

   The definition of a state of a defect in the network is also
   necessary for understanding the EPM.  In this document, the defect is
   interpreted as the state of inability to communicate between a
   particular set of nodes.  It is important to note that it is being
   defined as a state, and thus, it has conditions that define entry
   into it and exit out of it.  Also, the state of defect exists only in
   connection to the particular group of nodes in the network, not the
   network as a domain.

3.1.  Measure Error Performance Metrics

   The definitions of ES, SES, and EFS allow for characterization of the
   communication between two nodes relative to the level of required and
   acceptable performance and when performance degrades below the
   acceptable level.  The former condition in this document referred to
   as network availability.  The latter - network unavailability.  Based
   on the definitions, SES is the one-second of network unavailability
   while ES and EFS present an interval of network availability.  But

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   since the conditions of network are everchanging periods of network
   availability and unavailability need to be defined with duration
   larger than one-second interval to reduce the number of state changes
   while correctly reflecting the network condition.  The method to
   determine the state of the network in terms of EPM OAM is described

   *  If ten consecutive SES intervals been detected, then the EPM state
      of the network determined as unavailability and the beginning of
      that period of unavailability state is at the start of the first
      SES in the sequence of the consecutive SES intervals.

   *  Similarly, ten consecutive non-SES intervals, i.e., either ES or
      EFS, indicate that the network is in the availability period,
      i.e., available.  The start of that period is at the beginning of
      the first non-SES interval.

   *  Resulting from these two definitions, a sequence of less than ten
      consecutive SES or non-SES intervals does not change the EPM state
      of the network.  For example, if the EPM state is determined as
      unavailability, a sequence of seven EFS intervals is not viewed as
      an availability period.

3.2.  Calculate Error Performance Metrics

   Determining the period in which the path is currently EP-wise is
   helpful.  But because switching between periods requires ten
   consecutive one-second intervals, conditions that last shorter
   intervals may not be adequately reflected.  Two additional EP OAM
   metrics can be used, and they are defined as follows:

   *  errored second ratio (ESR) is the ratio of ES to the total number
      of seconds in a time of the availability periods during a fixed
      measurement interval.

   *  severely errored second ratio (SESR) - is the ratio of SES to the
      total number of seconds in a time of the availability periods
      during a fixed measurement interval.

4.  Requirements to EPM


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5.  Active OAM Protocol for EPM

   Digital communication methods characterized as the constant-bit rate
   digital paths and connections allow measurement of the error
   performance without using an active OAM.  That is possible because a
   predictable flow of digital signals is expected at an egress system.
   That is not the case for packet-switched networks that are based on
   the principle of statistical multiplexing flows.  The latter usually
   improves the utilization of the communication network's resources,
   but it also makes the flow unpredictable for the egress system.  For
   that reason, an active OAM has to be used in measuring the error
   performance in a network.  A combination of OAM protocols can provide
   the necessary for EPM functionality.  For example, Bidirectional
   Forwarding Detection (BFD) [RFC5880] can be used to monitor the
   continuity of a path between the ingress and egress systems.  And
   STAMP [RFC8762] can be used to measure and calculate performance
   metrics that are used as Service Level Objectives.  But using two
   protocols and correlating the state of the network from them adds to
   the complexity in network operation.

6.  Availability of Anything-as-a-Service

   Anything as a service (XaaS) describes a general category of services
   related to cloud computing and remote access.  These services include
   the vast number of products, tools, and technologies that are
   delivered to users as a service over the Internet.  In this document,
   the availability of XaaS is viewed as the ability to access the
   service over a period of time with pre-defined performance
   objectives.  Among the advantages of the XaaS model are:

   *  Improving the expense model by purchasing services from providers
      on a subscription basis rather than buying individual products,
      e.g., software, hardware, servers, security, infrastructure, and
      install them on-site, and then link everything together to create

   *  Speeding new apps and business processes by quickly adapting to
      changing market conditions with new applications or solutions.

   *  Shifting IT resources to specialized higher-value projects that
      use the core expertise of the company.

   But XaaS model also has potential challenges:

   *  Possible downtime resulting from issues of internet reliability,
      resilience, provisioning, and managing the infrastructure

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   *  Performance issues caused by depleted resources like bandwidth,
      computing power, inefficiencies of virtualized environments,
      ongoing management and security of multi-cloud services.

   *  Complexity impacts enterprise IT team that must remain in the
      process of the continued learning of the provided services.

   The framework and metrics of the EPM defined in Section 3 allow a
   provider of XaaS and their customers to quantify, measure, monitor
   for conformance what is often referred to as an ephemeral -
   availability of the service to be delivered.  There are other
   definitions and methods of expressing availability.  For example,
   [HighAvailability-WP] uses the following equation:

   Availability Average = MTBF/(MTBF + MTRR),
   MTBF (Mean Time Between Failures) - mean time between
         individual component failures.  For example, a hard drive
         malfunction or hypervisor reboot.
   MTTR (Mean Time To Repair) - refers to how long it takes to fix
         the broken component or the application to come back online,

   While this approach estimates the expected availability of a XaaS,
   the EPM reflects near-real-time availability of a service as
   experienced by a user.  It also provides valuable data for more
   accurate and realistic MTBF and MTTR in the particular environment,
   and simplifies comparison of different solutions that may use
   redundant servers (web and database), load balancers.

   In another field of communication, mobile voice and data services,
   the definition of service availability is understood as "the
   probability of successful service reception: a given area is declared
   "in-coverage" if the service in that area is available with a pre-
   specified minimum rate of success.  Service availability has the
   advantage of being more easily understandable for consumers and is
   expressed as a percentage of the number of attempts to access a given
   service."  [BEREC-CP].  The definition of the availability used in
   the EPM throughout this document is close to the quoted above.  It
   might be considered as the extension that allows regulators,
   operators, and consumers to compare not only the rate of successfully
   establishing a connection but the quality of the connection during
   its lifetime.

7.  IANA Considerations


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8.  Security Considerations


9.  Acknowledgments


10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

10.2.  Informative References

   [BEREC-CP] Body of European Regulators for Electronic Communications,
              "BEREC Common Position on information to consumers on
              mobile coverage", Common Approaches/Positions BoR (18)
              237, June 2018, <

              Avi Freedman, Server Central, "High Availability in Cloud
              and Dedicated Infrastructure", <

              ITU-T, "End-to-end error performance parameters and
              objectives for international, constant bit-rate digital
              paths and connections", ITU-T G.826, December 2002.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

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   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <>.

   [RFC8762]  Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
              Two-Way Active Measurement Protocol", RFC 8762,
              DOI 10.17487/RFC8762, March 2020,

Authors' Addresses

   Greg Mirsky


   Joel Halpern


   Xiao Min
   ZTE Corp.


   Liuyan Han
   China Mobile
   32 XuanWuMenXi Street


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