Some Key Terms for Network Fault and Problem Management
draft-ietf-nmop-terminology-07

Network Working Group                                      N. Davis, Ed.
Internet-Draft                                                     Ciena
Intended status: Informational                            A. Farrel, Ed.
Expires: 7 May 2025                                   Old Dog Consulting
                                                                 T. Graf
                                                                Swisscom
                                                                   Q. Wu
                                                                  Huawei
                                                                   C. Yu
                                                     Huawei Technologies
                                                         3 November 2024

        Some Key Terms for Network Fault and Problem Management
                     draft-ietf-nmop-terminology-07

Abstract

   This document sets out some terms that are fundamental to a common
   understanding of network fault and problem management within the
   IETF.

   The purpose of this document is to bring clarity to discussions and
   other work related to network fault and problem management in
   particular YANG models and management protocols that report, make
   visible, or manage network faults and problems.

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 7 May 2025.

Copyright Notice

   Copyright (c) 2024 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
   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
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Context Terminology . . . . . . . . . . . . . . . . . . .   3
     2.2.  Core Terms  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Other Terms . . . . . . . . . . . . . . . . . . . . . . .   8
   3.  Workflow Explanations . . . . . . . . . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  13
   Informative References  . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Successful operation of large or busy networks depends on network
   management.  Network management comprises a virtuous circle of
   network control, network observability, network analytics, network
   assurance, and back to network control.  Network fault and problem
   management is an important aspect of network management and control
   solutions.  It deals with the reporting, inspection, correlation, and
   management of events within the network.  The intention is to focus
   on those events have a negative effect on the network's ability to
   forward traffic in an optimal way.  Fault and problem management
   extends to include actions taken to determine the causes of problems
   and to work toward recovery of optimal network behavior.

   A number of work efforts within the IETF seek to provide components
   of a fault management system, such as YANG models or management
   protocols.  It is important that a common terminology is used so that
   there is a clear understanding of how the elements of the management
   and control solutions fit together, and how faults and problems will
   be handled.

   This document sets out some terms that are fundamental to a common
   understanding of network fault and problem management.  While
   "faults" and "problems" are concepts that apply at all levels of

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   technology in the Internet, the scope of this document is restricted
   to the network layer and below, hence this document is specifically
   about "network fault and problem management."

   The terms defined in this document are principally intended for
   consistent use within the IETF.  Where similar concepts are described
   in other bodies, an attempt has been made to harmonize with those
   other descriptions, but there is care needed where terms are not used
   consistently between bodies or where terms are applied outside the
   network layer.  If other bodies find the terminology defined in this
   document useful, they are free to use it.

   Note that some useful terms are defined in [RFC3877] and [RFC8632].
   The definitions in this document are informed by those documents, but
   they are not dependent on that prior work.

2.  Terminology

   This section contains key terms.  It is split into three subsections.

   *  Section 2.1 contains terms that help set the context for the
      incident and fault management systems.

   *  Section 2.2 includes specific and detailed core terms that will be
      used in other documents that describe elements of the fault
      management systems.

   *  Section 2.3 provides two further terms that may be helpful.

2.1.  Context Terminology

   This section includes some terminology that helps describe the
   context for the rest of this work.  The definitions are deliberately
   kept relatively terse.  Further documents may expand on these terms
   without loss of specificity.

   Network Telemetry:  This is defined in [RFC9232] and describes the
      process of collecting operational network data categorized into
      network planes.  Data collected through the Network Telemetry
      process does not contain network or device configuration
      information.  Nor does it contain any data related to service
      definition (i.e., intent per [RFC9315].

   Network Monitoring:  This is the process of keeping a continuous

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      record of a resource, function, or connectivity service.  The term
      'monitoring' focuses on one single dimension and measurement in
      dimensional data modelling ([wikipedia]).  This could be a
      measurement of the service state, a network function measurement,
      or the state of a network function of a resource as an example.

   Network Analytics:  Network analytics is the process of deriving
      analytical insights into or from operational network data.  A
      process, could be a software, a system, or a human that analyzes
      operational data and outputs new analytical data, ideally metadata
      (a symptom for example), which is related to the operational data.

   Network Observability:  This is the enablement of network behavioral
      assessment through analysis of observed operational network data
      (logs, alarms, traces, etc.) with the aim of detecting symptoms
      of, and to identify, anomalies and their causes.  Network
      observability begins with information gathered using conventional
      network monitoring tools and enriched with other operational data
      (e.g., change records).  The expected outcome of the observability
      processes is identification and analysis of deviations in observed
      state versus the expected state of a network.

   Thus, there is a cascaded sequence where:

   *  Telemetry: the process of collecting operational data from the
      network.

   *  Network Monitoring: the process of creating/keeping a record of
      data gathered in Network Telemetry.

   *  Network Analytics: the process of deriving insight through the
      data recorded in Network Monitoring.

   *  Network Observability: the process of enabling behavioral
      assessment of the network through Network Analytics.

2.2.  Core Terms

   The terms are presented below in an order that is intended to flow
   such that it is possible to gain understanding reading top to bottom.
   The figures and explanations in Section 3 may aid understanding the
   terms set out here.

   System:  An assembly of components that exhibits some behavior.

   External System:  A system that includes elements that are beyond the
      scope of the control system.

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   Controlled External System:  An external system that is of interest
      to and is influenced by the control system.  Viewed as a
      collection of resources.

   Resource:  A component, commodity, service, or capability that can be
      used to support the delivery of some function.  Such function can
      be local (e.g., within a node) or distributed (e.g., at the level
      of a network).

      Resource is a recursive concept so that a resource may be a
      collection of other resources (for example, a network node is a
      collection of interfaces).

   Characteristic:  Observable or measurable aspect or behavior
      associated with a resource.

      *  A characteristic may be considered with respect to the concept
         of dimensional that is built on facts (see 'value', below) and
         dimensions (the contexts and descriptors that identify and give
         meaning to the facts).

      *  The term "Metric" is another word for "Characteristic".

   Value:  A measurable amount which may be in the form of an integer
      (e.g., a count) or on a continuous variable (e.g., an analogue
      measurement) associated with a characteristic.

   Condition:  The interpretation of the values of a set of
      characteristics of the resource (with respect to working order or
      some other aspect relevant to the resource purpose/application).

   Change:  In the context of monitoring network resources, the
      variation in values associated with a characteristic of a resource
      at a specific time or over time.

      *  Most changes are not noteworthy (i.e., are not relevant).

      *  Perception of change depends upon detection, the sampling
         rate/accuracy/detail, and perspective.

   Detect:  To notice the presence of something (state, change,
      activity, form, etc.).

      *  Hence also to notice a change (from the perspective of the
         viewer).

   Event:  The change in value (of a characteristic of a resource) at a
      measurable instant in time (i.e., the period is negligible).

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      *  Compared with a change, which is over a period of time, an
         event happens at a measurable instant.

   State:  A particular condition that something (e.g., a resource) is
      in (at a specific time).

      *  While a state may be observed at a specific moment in time, it
         is actually achieved by summarizing the measurement over time
         in a process sometimes called state compression.

   Relevance:  Consideration of an event, state, or value (through the
      application of policy, relative to a specific viewpoint/
      perspective, intent, and in relation to other events, states, and
      values) to determine whether it is of note to the control system.

   Occurrence:  A relevant event.

      A particular relevant change.

      *  An occurrence may be an aggregation or abstraction of smaller
         occurrences.

      *  Applies to all scales and scopes, i.e., is essentially fractal
         (can recurse indefinitely).

      *  Note that occurrence is used here with respect to the temporal
         dimension.

   Fault:  An occurrence that is not desired/required (as it may be
      indicative of a current or future undesired State).  A fault can
      generally be associated with a known cause.  See [RFC8632] for a
      more detailed discussion of network faults.

   Problem:  A state regarded as undesirable and may require remedial
      action.  A problem cannot necessarily be associated with a cause.
      The resolution of a problem does not necessarily act on the thing
      that has the problem.

      *  Note that there is a historic aspect to the concept of a
         problem.  The current state may be operational, but there could
         have been a failure that is unexplained, and the fact of that
         unexplained recent failure is a problem.

      *  Note that whilst a problem is unresolved it may continue to
         require attention.  A record of resolved problems may be
         maintained in a log.

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      *  Note that there may be a state which is considered to be a
         problem from several perspectives (e.g., a loss of light state
         may cause multiple services to fail).  A state change (so that
         the light recovers) may cause the problem to be resolved from
         one perspective (the services are operational once more), but
         may leave the problem as unresolved (because the loss of light
         has not been explained).  There could be a further development
         (the reason for the temporary loss of light is traced to a
         microbend in the fiber that is repaired) resulting in that
         unresolved problem is now resolved.  But this leaves a further
         problem still unresolved (why did the microbend occur in the
         first place?).

   Incident:  A network incident is an undesired occurrence such as an
      unexpected interruption of a network service, degradation of the
      quality of a network service, or the below-target health of a
      network service.  An incident results from one or more problems,
      and a problem may give rise to or contribute to one or more
      incidents.  Greater discussion of network incidents, including
      incident management, can be found in
      [I-D.ietf-nmop-network-incident-yang].

   Anomaly:  A (network) anomaly is an unusual or unexpected event or
      pattern in network data in the forwarding plane, control plane, or
      management plane that deviates from the normal, expected behavior.
      See [I-D.ietf-nmop-network-anomaly-architecture] for more details.

   Symptom:  An observable characteristic/state/condition considered as
      an indication of a problem or potential problem.

   Cause:  The events (detected or otherwise) that gave rise to a fault/
      problem.

   Consolidation:  The process of considering multiple problems,
      symptoms, and their causes to determine the underlying causes.

   Alert:  The indication of a fault.

   Alarm:  Per [RFC8632], an alarm signifies an undesirable state in a
      resource that requires corrective action.  From a management point
      of view, an alarm can be as a state in its own right and the
      transition to this state is a fault and may result in an alert
      being issued.  The receipt of this alert may give rise to a
      continuous indication (to a human operator) highlighting the
      potential or actual presence of a problem.

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2.3.  Other Terms

   Two other terms may be helpful:

   Transient:  A state, considered as a problem, that persists for a
      limited amount of time before becoming resolved without direct
      action by an operator or control system.

   Intermittent:  A state that is not maintained, but keeps occurring in
      some meaningfully short time frame.

3.  Workflow Explanations

   The relationship between system, resource, and characteristics is
   shown in Figure 1.  A Controlled External System is comprised of
   Resources, and Resources have Characteristics.

                                   Characteristics
                                          ^
                                          |
                                       Resource
                                          ^
                                          |
                              Controlled External System
                                          ^
                                          |
                                   External System

            Figure 1: Relationship Between Elements of a System

   The Value of a Characteristic of a Resource is expected to change
   over time.  Specific changes in value may be noticed at a specific
   time (as digital changes), Detected, and treated as Events.  This is
   shown on the left of Figure 2.

   The center of Figure 2 shows how the Value of a Characteristic may
   change over time.  The value may be Detected at specific times or
   periodically and give rise to States (and consequently State
   changes).

   In practice, the Characteristic may vary in an analog manner over
   time as shown on the right hand side of Figure 2.  The Value can be
   read or reported (i.e., Detected) periodically leading to Analogue
   Values that may be deemed Relevant Values, or may be evaluated over
   time as shown in Figure 6.

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              Event                State                  Value

                ^                    ^                      ^
         Detect :             Detect :               Detect :
                :                    :                      :

           ^        ^          ^     ^     ^                   /\
           :        :          :     :     :                  /  \
           :        :          :     :     :             /\  /    \
            __    __               _____                /  \/
           |        |             |     |            /\/
         __|        |__       ____|     |____       /

        Change at a time     Change over time      Change over time

                   Figure 2: Characteristics and Changes

   Figure 3 shows the workflow progress for Events.  As noted above, an
   Event is a Change in the Value of a Characteristic at a time.  The
   Event may be evaluated (considering policy, relative to a specific
   viewpoint/perspective, with a view to intent, and in relation to
   other Events, States, and Values) to determine if it is an Occurrence
   and possibly to indicate a change of State.  An Occurrence may be
   undesirable (a Fault) and that can cause an Alert to be generated,
   may be evidence of a Problem and could directly indicate a Cause.

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                              Alert- - - - > Alarm
                                ^
                                |
                                |     -----> Cause
                                |    |
                                |----------> Problem
                                |
                                |
                              Fault
                                ^
                                |
                                |
                                |
                           Occurrence
                                ^
                                |
                                |----------> State
                                |
                                |
                              Event

                    Figure 3: Events and Dependent Terms

   Parallel to the workflow for Events, Figure 4 shows the workflow
   progress for States.  As shown in Figure 2, Change noted at a
   particular time gives rise to State.  The State may be deemed
   relevant (via Relevance) considering policy, relative to a specific
   viewpoint/perspective, with a view to intent, and in relation to
   other Events, States, and Values.  A Relevant State may be deemed a
   Problem, or may indicate a Problem.

   Problems may be considered as Symptoms and may map directly or
   indirectly to Causes.  An Alarm may be raised as the result of a
   Problem.  An Incident results from one or more Problems.

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                             Alarm
                               ^
                               |     ------> Incident
                               |    |
                               |    |   ---> Cause
                               |    |  |
                           Problem---------> Symptom
                               ^
                               |
                               |
                               |
                         Relevant State
                               ^
                               |
                               |
                               |
                             State

                    Figure 4: States and Dependent Terms

   Figure 5 shows how Faults and Problems may be consolidated to
   determine the Causes.

   A Cause can be indicated by or determined from Faults, Problems and
   Symptoms.  It may be that one Cause points to another, and can also
   be considered as a Symptom.  The determination of Causes can consider
   multiple inputs.  An Incident results from one or more Problems.

                                          ---------
                           ------------- |         |
                          |  ----------> | Symptom |
                          | |            |         |
                          | |             ---------
                          v |                 ^
                       ---------              |
              ------->|  Cause  |<---------   |
             |         ---------           |  |
             |           ^   |             |  |
             |           |   |             |  |
             |            ---              |  |
             |                             |  |
         ---------                      ---------          ----------
        |  Fault  |------------------->| Problem |------->| Incident |
         ---------                      ---------          ----------

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               Figure 5: Consolidation of Symptoms and Causes

   The final figure in this section (Figure 6) shows how thresholds are
   important in the consideration of Analogue Values and Events.  The
   use of threshold-driven events and states (and the alerts that they
   might give rise to) must be treated with caution to dampen any
   "flapping" (so that consistent states may be observed) and to avoid
   overwhelming management processes or systems.  Analogue Values may be
   read or notified from the Resource and could transition a threshold,
   be deemed Relevant Values, or evaluated over time.  Events may be
   counted, and the Count may cross a threshold or reach a Relevant
   Value.

   The Threshold Process may be implementation-specific and subject to
   policies.  When a threshold is crossed and any other conditions are
   matched, an Event may be determined, and treated like any other
   Event.

     Occurrence
          ^
          |
          |---------------------> State
          |
          |        -------
          |------>| Count |-------------------------> Relevant Value
          |        -------          |                       ^
          |           |             |                       |
          |           |             |                       |
          |           |             v                       |
          |           |        -----------           ----------------
        Event         |       | Evaluated |         |                |
          ^           |       | over time |<--------| Analogue Value |
          |           v        -----------          |                |
          |      -----------        |               |                |
          |     | Threshold |       |               |                |
          |<----|  Process  |<------                |                |
          |     |           |<----------------------|                |
          |      -----------                         ----------------
          |                                                 ^
          |                                                 |
          | Detect                                   Detect |
          |                                                 |
     Change at a Time                                Change over Time

                  Figure 6: Counts, Thresholds, and Values

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4.  Security Considerations

   This document specifies terminology and has no direct effect on the
   security of implementations or deployments.  However, protocol
   solutions and management models need to be aware of several aspects:

   *  The exposure of information pertaining to faults may make
      available knowledge of the internal workings of a network (in
      particular its vulnerabilities) that may be of use to an attacker.

   *  Systems that generate management information (messages,
      notifications, etc.) when faults occur, may be attacked by causing
      them to generate so much information that the management system is
      swamped an unable to properly manage the network.

   *  Reporting false information about faults (or masking reports of
      faults) may cause the management system to function incorrectly.

5.  Privacy Considerations

   In general, Fault Management should not expose information about end-
   user activities or user data.  The main privacy concern is for a
   network operator to keep control of all information about faults to
   protect their privacy and the details of how they operate their
   network.

6.  IANA Considerations

   This document makes no requests for IANA action.

Acknowledgments

   The authors would like to thank Med Boucadair, Wanting Du, Joe
   Clarke, Javier Antich, Benoit Claise, Christopher Janz, Sherif
   Mostafa, and Kristian Larsson for their helpful comments.

   Special thanks to the team that met at a side meeting at IETF-120 to
   discuss some of the thorny issues:

   *  Benoit Claise

   *  Watson Ladd

   *  Brad Peters

   *  Bo Wu

   *  Georgios Karagiannis

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   *  Olga Havel

   *  Vincenzo Riccobene

   *  Yi Lin

   *  Jie Dong

   *  Aihua Guo

   *  Thomas Graf

   *  Qin Wu

   *  Chaode Yu

   *  Adrian Farrel

Informative References

   [I-D.ietf-nmop-network-anomaly-architecture]
              Graf, T., Du, W., and P. Francois, "An Architecture for a
              Network Anomaly Detection Framework", Work in Progress,
              Internet-Draft, draft-ietf-nmop-network-anomaly-
              architecture-01, 20 October 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
              network-anomaly-architecture-01>.

   [I-D.ietf-nmop-network-incident-yang]
              Hu, T., Contreras, L. M., Wu, Q., Davis, N., and C. Feng,
              "A YANG Data Model for Network Incident Management", Work
              in Progress, Internet-Draft, draft-ietf-nmop-network-
              incident-yang-02, 10 October 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
              network-incident-yang-02>.

   [RFC3877]  Chisholm, S. and D. Romascanu, "Alarm Management
              Information Base (MIB)", RFC 3877, DOI 10.17487/RFC3877,
              September 2004, <https://www.rfc-editor.org/info/rfc3877>.

   [RFC8632]  Vallin, S. and M. Bjorklund, "A YANG Data Model for Alarm
              Management", RFC 8632, DOI 10.17487/RFC8632, September
              2019, <https://www.rfc-editor.org/info/rfc8632>.

   [RFC9232]  Song, H., Qin, F., Martinez-Julia, P., Ciavaglia, L., and
              A. Wang, "Network Telemetry Framework", RFC 9232,
              DOI 10.17487/RFC9232, May 2022,
              <https://www.rfc-editor.org/info/rfc9232>.

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   [RFC9315]  Clemm, A., Ciavaglia, L., Granville, L. Z., and J.
              Tantsura, "Intent-Based Networking - Concepts and
              Definitions", RFC 9315, DOI 10.17487/RFC9315, October
              2022, <https://www.rfc-editor.org/info/rfc9315>.

   [wikipedia]
              Wikipedia, "Dimensional Modeling", Web page Wikipedia,
              <https://en.wikipedia.org/wiki/Dimensional_modeling>.

Authors' Addresses

   Nigel Davis (editor)
   Ciena
   United Kingdom
   Email: ndavis@ciena.com

   Adrian Farrel (editor)
   Old Dog Consulting
   United Kingdom
   Email: adrian@olddog.co.uk

   Thomas Graf
   Swisscom
   Binzring 17
   CH-8045 Zurich
   Switzerland
   Email: thomas.graf@swisscom.com

   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: bill.wu@huawei.com

   Chaode Yu
   Huawei Technologies
   Email: yuchaode@huawei.com

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