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Network Working Group                                          G. Mirsky
Internet-Draft                                                    X. Min
Intended status: Standards Track                               ZTE Corp.
Expires: January 14, 2021                                  July 13, 2020


       Error Performance Measurement in Packet-switched Networks
                        draft-mirsky-ippm-epm-00

Abstract

   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 PSN are defined, as well as
   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 analyzed.  All metrics and measurement
   methods are equally applicable to underlay and overlay networks.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 14, 2021.

Copyright Notice

   Copyright (c) 2020 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
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   to this document.  Code Components extracted from this document must



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   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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology and  Acronyms . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   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 . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Operations, Administration, and Maintenance (OAM) is a collection of
   methods to detect, characterize, localize failures in a network,
   monitor the network's performance by 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 for packet-switched networks (PSN) component
   of OAM.

   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
   [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



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   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
   methods of active OAM, per definition in [RFC7799].  This document
   identifies metrics that characterize error performance in PSN 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 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

2.2.  Requirements Language

   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.







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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:

   o  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.

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

   o  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
   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
   below:





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   o  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.

   o  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.

   o  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:

   o  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.

   o  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

   TBA

5.  Active OAM Protocol for EPM

   TBA

6.  IANA Considerations

   TBA








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7.  Security Considerations

   TBA

8.  Acknowledgments

   TBA

9.  References

9.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [ITU.G.826]
              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.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com


   Xiao Min
   ZTE Corp.

   Email: xiao.min2@zte.com.cn







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