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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
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This Internet-Draft will expire on January 14, 2021.
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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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