Internet DRAFT - draft-mirsky-ippm-epm
draft-mirsky-ippm-epm
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
draft-mirsky-ippm-epm-04
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 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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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . 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)
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
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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",
"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.
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
below:
* 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
TBA
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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
networks.
* 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
resources.
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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),
where:
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
TBA
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8. Security Considerations
TBA
9. Acknowledgments
TBA
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,
<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>.
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, <https://berec.europa.eu/eng/document_regi
ster/subject_matter/berec/regulatory_best_practices/
common_approaches_positions/8315-berec-common-position-on-
information-to-consumers-on-mobile-coverage>.
[HighAvailability-WP]
Avi Freedman, Server Central, "High Availability in Cloud
and Dedicated Infrastructure", <https://www.deft.com/wp-
content/uploads/pdf/SCTG-High-Availability-White-Paper-
Part-2.pdf>.
[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.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
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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, <https://www.rfc-editor.org/info/rfc7799>.
[RFC8762] Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
Two-Way Active Measurement Protocol", RFC 8762,
DOI 10.17487/RFC8762, March 2020,
<https://www.rfc-editor.org/info/rfc8762>.
Authors' Addresses
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
Joel Halpern
Ericsson
Email: joel.halpern@ericsson.com
Xiao Min
ZTE Corp.
Email: xiao.min2@zte.com.cn
Liuyan Han
China Mobile
32 XuanWuMenXi Street
Beijing
100053
China
Email: hanliuyan@chinamobile.com
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