A YANG Data Model for Alarm Management
RFC 8632

Document Type RFC - Proposed Standard (September 2019; No errata)
Last updated 2019-09-11
Replaces draft-vallin-ccamp-alarm-module
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Internet Engineering Task Force (IETF)                         S. Vallin
Request for Comments: 8632                              Stefan Vallin AB
Category: Standards Track                                   M. Bjorklund
ISSN: 2070-1721                                                    Cisco
                                                          September 2019

                 A YANG Data Model for Alarm Management

Abstract

   This document defines a YANG module for alarm management.  It
   includes functions for alarm-list management, alarm shelving, and
   notifications to inform management systems.  There are also
   operations to manage the operator state of an alarm and
   administrative alarm procedures.  The module carefully maps to
   relevant alarm standards.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8632.

Copyright Notice

   Copyright (c) 2019 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
   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 and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.

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RFC 8632         A YANG Data Model for Alarm Management   September 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology and Notation  . . . . . . . . . . . . . . . .   3
   2.  Objectives  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Alarm Data Model Concepts . . . . . . . . . . . . . . . . . .   5
     3.1.  Alarm Definition  . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Alarm Type  . . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Identifying the Alarming Resource . . . . . . . . . . . .   8
     3.4.  Identifying Alarm Instances . . . . . . . . . . . . . . .   9
     3.5.  Alarm Lifecycle . . . . . . . . . . . . . . . . . . . . .   9
       3.5.1.  Resource Alarm Lifecycle  . . . . . . . . . . . . . .  10
       3.5.2.  Operator Alarm Lifecycle  . . . . . . . . . . . . . .  11
       3.5.3.  Administrative Alarm Lifecycle  . . . . . . . . . . .  11
     3.6.  Root Cause, Impacted Resources, and Related Alarms  . . .  11
     3.7.  Alarm Shelving  . . . . . . . . . . . . . . . . . . . . .  13
     3.8.  Alarm Profiles  . . . . . . . . . . . . . . . . . . . . .  13
   4.  Alarm Data Model  . . . . . . . . . . . . . . . . . . . . . .  13
     4.1.  Alarm Control . . . . . . . . . . . . . . . . . . . . . .  15
       4.1.1.  Alarm Shelving  . . . . . . . . . . . . . . . . . . .  15
     4.2.  Alarm Inventory . . . . . . . . . . . . . . . . . . . . .  16
     4.3.  Alarm Summary . . . . . . . . . . . . . . . . . . . . . .  16
     4.4.  The Alarm List  . . . . . . . . . . . . . . . . . . . . .  17
     4.5.  The Shelved-Alarm List  . . . . . . . . . . . . . . . . .  19
     4.6.  Alarm Profiles  . . . . . . . . . . . . . . . . . . . . .  19
     4.7.  Operations  . . . . . . . . . . . . . . . . . . . . . . .  20
     4.8.  Notifications . . . . . . . . . . . . . . . . . . . . . .  20
   5.  Relationship to the ietf-hardware YANG Module . . . . . . . .  20
   6.  Alarm YANG Module . . . . . . . . . . . . . . . . . . . . . .  21
   7.  The X.733 Mapping Module  . . . . . . . . . . . . . . . . . .  53
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  65
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  65
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  67
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  67
     10.2.  Informative References . . . . . . . . . . . . . . . . .  68
   Appendix A.  Vendor-Specific Alarm Types Example  . . . . . . . .  70
   Appendix B.  Alarm Inventory Example  . . . . . . . . . . . . . .  71
   Appendix C.  Alarm List Example . . . . . . . . . . . . . . . . .  71
   Appendix D.  Alarm Shelving Example . . . . . . . . . . . . . . .  73
   Appendix E.  X.733 Mapping Example  . . . . . . . . . . . . . . .  74
   Appendix F.  Relationship to Other Alarm Standards  . . . . . . .  74
     F.1.  Definition of "Alarm" . . . . . . . . . . . . . . . . . .  74
     F.2.  Data Model  . . . . . . . . . . . . . . . . . . . . . . .  76
       F.2.1.  X.733 . . . . . . . . . . . . . . . . . . . . . . . .  76
       F.2.2.  The Alarm MIB (RFC 3877)  . . . . . . . . . . . . . .  77
       F.2.3.  3GPP Alarm IRP  . . . . . . . . . . . . . . . . . . .  77
       F.2.4.  G.7710  . . . . . . . . . . . . . . . . . . . . . . .  78

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   Appendix G.  Alarm-Usability Requirements . . . . . . . . . . . .  78
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  82
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  82

1.  Introduction

   This document defines a YANG module [RFC7950] for alarm management.
   The purpose is to define a standardized alarm interface for network
   devices that can be easily integrated into management applications.
   The model is also applicable as a northbound alarm interface in the
   management applications.

   Alarm monitoring is a fundamental part of monitoring the network.
   Raw alarms from devices do not always tell the status of the network
   services or necessarily point to the root cause.  However, being able
   to feed alarms to the alarm-management application in a standardized
   format is a starting point for performing higher-level network
   assurance tasks.

   The design of the module is based on experience from using and
   implementing available alarm standards from ITU [X.733], 3GPP
   [ALARMIRP], and ANSI [ISA182].

1.1.  Terminology and Notation

   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.

   The following terms are defined in [RFC7950]:

   o  action

   o  client

   o  data tree

   o  server

   The following terms are used within this document:

   Alarm (the general concept):  An alarm signifies an undesirable state
      in a resource that requires corrective action.

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   Fault:  A fault is the underlying cause of an undesired behavior.
      There is no trivial one-to-one mapping between faults and alarms.
      One fault may result in several alarms in case the system lacks
      root-cause and correlation capabilities.  An alarm might not have
      an underlying fault as a cause.  For example, imagine a bad Mean
      Opinion Score (MOS) alarm from a Voice over IP (VOIP) probe and
      the cause being non-optimal QoS configuration.

   Alarm Type:  An alarm type identifies a possible unique alarm state
      for a resource.  Alarm types are names to identify the state like
      "link-alarm", "jitter-violation", and "high-disk-utilization".

   Resource:  A fine-grained identification of the alarming resource,
      for example, an interface and a process.

   Alarm Instance:  The alarm state for a specific resource and alarm
      type, for example, ("GigabitEthernet0/15", "link-alarm").  An
      entry in the alarm list.

   Cleared Alarm:  A cleared alarm is an alarm where the system
      considers the undesired state to be cleared.  Operators cannot
      clear alarms; clearance is managed by the system.  For example, a
      "linkUp" notification can be considered a clear condition for a
      "linkDown" state.

   Closed Alarm:  Operators can close alarms irrespective of the alarm
      being cleared or not.  A closed alarm indicates that the alarm
      does not need attention because either the corrective action has
      been taken or it can be ignored for other reasons.

   Alarm Inventory:  A list of all possible alarm types on a system.

   Alarm Shelving:  Blocking alarms according to specific criteria.

   Corrective Action:  An action taken by an operator or automation
      routine in order to minimize the impact of the alarm or resolve
      the root cause.

   Management System:  The alarm-management application that consumes
      the alarms, i.e., acts as a client.

   System:  The system that implements this YANG module, i.e., acts as a
      server.  This corresponds to a network device or a management
      application that provides a northbound alarm interface.

   Tree diagrams used in this document follow the notation defined in
   [RFC8340].

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2.  Objectives

   The objectives for the design of the alarm data model are:

   o  Users find it simple to use.  If a system supports this module, it
      shall be straightforward to integrate it into a YANG-based alarm
      manager.

   o  Alarms are viewed as states on resources and not as discrete
      notifications.

   o  A precise definition of "alarm" is provided in order to exclude
      general events that should not be forwarded as alarm
      notifications.

   o  Precise identification of alarm types and alarm instances is
      provided.

   o  A management system should be able to pull all available alarm
      types from a system, i.e., read the alarm inventory from a system.
      This makes it possible to prepare alarm operators with
      corresponding alarm instructions.

   o  Alarm-usability requirements are addressed; see Appendix G.  While
      IETF and telecom standards have addressed alarms mostly from a
      protocol perspective, the process industry has published several
      relevant standards addressing requirements for a useful alarm
      interface; see [EEMUA] and [ISA182].  This document defines
      usability requirements as well as a YANG data model.

   o  Mapping to [X.733], which is a requirement for some alarm systems,
      is achievable.  Still, keep some of the X.733 concepts out of the
      core model in order to make the model small and easy to
      understand.

3.  Alarm Data Model Concepts

   This section defines the fundamental concepts behind the data model.
   This section is rooted in the works of Vallin et. al [ALARMSEM].

3.1.  Alarm Definition

   An alarm signifies an undesirable state in a resource that requires
   corrective action.

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   There are two main things to remember from this definition:

   1.  It focuses on leaving out events and logging information in
       general.  Alarms should only be used for undesired states that
       require action.

   2.  It also focuses on alarms as a state on a resource, not the
       notifications that report the state changes.

   See Appendix F for information on how this definition relates to
   other alarm standards.

3.2.  Alarm Type

   This document defines an alarm type with an alarm-type id and an
   alarm-type qualifier.

   The alarm-type id is modeled as a YANG identity.  With YANG
   identities, new alarm types can be defined in a distributed fashion.
   YANG identities are hierarchical, which means that a hierarchy of
   alarm types can be defined.

   Standards and vendors should define their own alarm-type identities
   based on this definition.

   The use of YANG identities means that all possible alarms are
   identified at design time.  This explicit declaration of alarm types
   makes it easier to allow for alarm qualification reviews and
   preparation of alarm actions and documentation.

   There are occasions where the alarm types are not known at design
   time.  An example is a system with digital inputs that allows users
   to connect detectors, such as smoke detectors, to the inputs.  In
   this case, it is a configuration action that says certain connectors
   are fire alarms, for example.

   In order to allow for dynamic addition of alarm types, the alarm data
   model permits further qualification of the identity-based alarm type
   using a string.  A potential drawback of this is that there is a
   significant risk that alarm operators will receive alarm types as a
   surprise.  They do not know how to resolve the problem since a
   defined alarm procedure does not necessarily exist.  To avoid this
   risk, the system MUST publish all possible alarm types in the alarm
   inventory; see Section 4.2.

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   A vendor or standards organization can define their own alarm-type
   hierarchy.  The example below shows a hierarchy based on X.733 event
   types:

     import ietf-alarms {
       prefix al;
     }
     identity vendor-alarms {
       base al:alarm-type;
     }
     identity communications-alarm {
       base vendor-alarms;
     }
     identity link-alarm {
       base communications-alarm;
     }

   Alarm types can be abstract.  An abstract alarm type is used as a
   base for defining hierarchical alarm types.  Concrete alarm types are
   used for alarm states and appear in the alarm inventory.  There are
   two kinds of concrete alarm types:

   1.  The last subordinate identity in the "alarm-type-id" hierarchy is
       concrete, for example, "alarm-identity.environmental-
       alarm.smoke".  In this example, "alarm-identity" and
       "environmental-alarm" are abstract YANG identities, whereas
       "smoke" is a concrete YANG identity.

   2.  The YANG identity hierarchy is abstract, and the concrete alarm
       type is defined by the dynamic alarm-qualifier string, for
       example, "alarm-identity.environmental-alarm.external-detector"
       with alarm-type-qualifier "smoke".

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   For example:

     // Alternative 1: concrete alarm type identity
     import ietf-alarms {
       prefix al;
     }
     identity environmental-alarm {
       base al:alarm-type;
       description "Abstract alarm type";
     }
     identity smoke {
       base environmental-alarm;
       description "Concrete alarm type";
     }

     // Alternative 2: concrete alarm type qualifier
     import ietf-alarms {
       prefix al;
     }
     identity environmental-alarm {
       base al:alarm-type;
       description "Abstract alarm type";
     }
     identity external-detector {
       base environmental-alarm;
       description
         "Abstract alarm type; a runtime configuration
          procedure sets the type of alarm detected.  This will
          be reported in the alarm-type-qualifier.";
     }

   A server SHOULD strive to minimize the number of dynamically defined
   alarm types.

3.3.  Identifying the Alarming Resource

   It is of vital importance to be able to refer to the alarming
   resource.  This reference must be as fine-grained as possible.  If
   the alarming resource exists in the data tree, an instance-identifier
   MUST be used with the full path to the object.

   When the module is used in a controller/orchestrator/manager, the
   original device resource identification can be modified to include
   the device in the path.  The details depend on how devices are
   identified and are out of scope for this specification.

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   Example:

      The original device alarm might identify the resource as
      "/dev:interfaces/dev:interface[dev:name='FastEthernet1/0']".

      The resource identification in the manager could look something
      like: "/mgr:devices/mgr:device[mgr:name='xyz123']/dev:interfaces/
      dev:interface[dev:name='FastEthernet1/0']"

   This module also allows for alternate naming of the alarming resource
   if it is not available in the data tree.

3.4.  Identifying Alarm Instances

   A primary goal of the alarm data model is to remove any ambiguity in
   how alarm notifications are mapped to an update of an alarm instance.
   The X.733 [X.733] and 3GPP [ALARMIRP] documents were not clear on
   this point.  This alarm data model states that the tuple (resource,
   alarm-type identifier, and alarm-type qualifier) corresponds to a
   single alarm instance.  This means that alarm notifications for the
   same resource and same alarm type are matched to update the same
   alarm instance.  These three leafs are therefore used as the key in
   the alarm list:

     list alarm {
       key "resource alarm-type-id alarm-type-qualifier";
       ...
     }

3.5.  Alarm Lifecycle

   The alarm model clearly separates the resource alarm lifecycle from
   the operator and administrative lifecycles of an alarm.

   o  resource alarm lifecycle: the alarm instrumentation that controls
      alarm raise, clearance, and severity changes.

   o  operator alarm lifecycle: operators acting upon alarms with
      actions like acknowledging and closing.  Closing an alarm implies
      that the operator considers the corrective action performed.
      Operators can also shelve (block/filter) alarms in order to avoid
      nuisance alarms.

   o  administrative alarm lifecycle: purging (deleting) unwanted alarms
      and compressing the alarm status-change list.  This module exposes
      operations to manage the administrative lifecycle.  The server may
      also perform these operations based on other policies, but how
      that is done is out of scope for this document.

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   A server SHOULD describe how long it retains cleared/closed alarms
   until they are manually purged or if it has an automatic removal
   policy.  How this is done is outside the scope of this document.

3.5.1.  Resource Alarm Lifecycle

   From a resource perspective, an alarm can, for example, have the
   following lifecycle: raise, change severity, change severity, clear,
   being raised again, etc.  All of these status changes can have
   different alarm texts generated by the instrumentation.  Two
   important things to note:

   1.  Alarms are not deleted when they are cleared.  Deleting alarms is
       an administrative process.  The "ietf-alarms" YANG module defines
       an action "purge-alarms" that deletes alarms.

   2.  Alarms are not cleared by operators; only the underlying
       instrumentation can clear an alarm.  Operators can close alarms.

   The YANG tree representation below illustrates the resource-oriented
   lifecycle:

     +--ro alarm* [resource alarm-type-id alarm-type-qualifier]
        ...
        +--ro is-cleared                 boolean
        +--ro last-raised                yang:date-and-time
        +--ro last-changed               yang:date-and-time
        +--ro perceived-severity         severity
        +--ro alarm-text                 alarm-text
        +--ro status-change* [time] {alarm-history}?
           +--ro time                    yang:date-and-time
           +--ro perceived-severity      severity-with-clear
           +--ro alarm-text              alarm-text

   For every status change from the resource perspective, a row is added
   to the "status-change" list, if the server implements the feature
   "alarm-history".  The feature "alarm-history" is optional to
   implement, since keeping the alarm history may have an impact on the
   server's memory resources.

   The last status values are also represented as leafs for the alarm.
   Note well that the alarm severity does not include "cleared"; alarm
   clearance is a boolean flag.

   Therefore, an alarm can look like this: (("GigabitEthernet0/25",
   "link-alarm",""), false, 2018-04-08T08:20:10.00Z,
   2018-04-08T08:20:10.00Z, major, "Interface GigabitEthernet0/25
   down").

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3.5.2.  Operator Alarm Lifecycle

   Operators can act upon alarms using the set-operator-state action:

     +--ro alarm* [resource alarm-type-id alarm-type-qualifier]
        ...
        +--ro operator-state-change* [time] {operator-actions}?
        |  +--ro time        yang:date-and-time
        |  +--ro operator    string
        |  +--ro state       operator-state
        |  +--ro text?       string
        +---x set-operator-state {operator-actions}?
           +---w input
              +---w state    writable-operator-state
              +---w text?    string

   The operator state for an alarm can be "none", "ack", "shelved", and
   "closed".  Alarm deletion (using the action "purge-alarms") can use
   this state as a criterion.  For example, a closed alarm is an alarm
   where the operator has performed any required corrective actions.
   Closed alarms are good candidates for being purged.

3.5.3.  Administrative Alarm Lifecycle

   Deleting alarms from the alarm list is considered an administrative
   action.  This is supported by the "purge-alarms" action.  The "purge-
   alarms" action takes a filter as input.  The filter selects alarms
   based on the operator and resource alarm lifecycle such as "all
   closed cleared alarms older than a time specification".  The server
   may also perform these operations based on other policies, but how
   that is done is out of scope for this document.

   Purged alarms are removed from the alarm list.  Note well that if the
   alarm resource state changes after a purge, the alarm will reappear
   in the alarm list.

   Alarms can be compressed.  Compressing an alarm deletes all entries
   in the alarm's "status-change" list except for the last status
   change.  A client can perform this using the "compress-alarms"
   action.  The server may also perform these operations based on other
   policies, but how that is done is out of scope for this document.

3.6.  Root Cause, Impacted Resources, and Related Alarms

   The alarm data model does not mandate any requirements for the system
   to support alarm correlation or root-cause and service-impact
   analysis.  However, if such features are supported, this section
   describes how the results of such analysis are represented in the

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   data model.  These parts of the model are optional.  The module
   supports three scenarios:

   Root-cause analysis:  An alarm can indicate candidate root-cause
      resources, for example, a database issue alarm referring to a
      full-disk partition.

   Service-impact analysis:  An alarm can refer to potential impacted
      resources, for example, an interface alarm referring to impacted
      network services.

   Alarm correlation:  Dependencies between alarms; several alarms can
      be grouped as relating to each other, for example, a streaming
      media alarm relating to a high-jitter alarm.

   Different systems have varying degrees of alarm correlation and
   analysis capabilities, and the intent of the alarm data model is to
   enable any capability, including none.

   The general principle of this alarm data model is to limit the amount
   of alarms.  In many cases, several resources are affected for a given
   underlying problem.  A full disk will of course impact databases and
   applications as well.  The recommendation is to have a single alarm
   for the underlying problem and list the affected resources in the
   alarm rather than having separate alarms for each resource.

   The alarm has one leaf-list to identify a possible "impacted-
   resource" and a leaf-list to identify a possible "root-cause-
   resource".  These serve as hints only.  It is up to the client
   application to use this information to present the overall status.
   Using the disk-full example, a good alarm would be to use the hard-
   disk partition as the alarming resource and add the database and
   applications into the "impacted-resource" leaf-list.

   A system should always strive to identify the resource that can be
   acted upon as the "resource" leaf.  The "impacted-resource" leaf-list
   shall be used to identify any side effects of the alarm.  The
   impacted resources cannot be acted upon to fix the problem.  The disk
   full example above illustrates the principle; you cannot fix the
   underlying issue by database operations.  However, you need to pay
   attention to the database to perform any operations that limit the
   impact of the problem.

   On some occasions, the system might not be capable of detecting the
   root cause, the resource that can be acted upon.  The instrumentation
   in this case only monitors the side effect and raises an alarm to
   indicate a situation requiring attention.  The instrumentation still
   might identify possible candidates for the root-cause resource.  In

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   this case, the "root-cause-resource" leaf-list can be used to
   indicate the candidate root-cause resources.  An example of this kind
   of alarm might be an active test tool that detects a Service Level
   Agreement (SLA) violation on a VPN connection and identifies the
   devices along the chain as candidate root causes.

   The alarm data model also supports a way to associate different
   alarms with each other using the "related-alarm" list.  This list
   enables the server to inform the client that certain alarms are
   related to other alarms.

   Note well that this module does not prescribe any dependencies or
   preference between the above alarm correlation mechanisms.  Different
   systems have different capabilities, and the above described
   mechanisms are available to support the instrumentation features.

3.7.  Alarm Shelving

   Alarm shelving is an important function in order for alarm-management
   applications and operators to stop superfluous alarms.  A shelved
   alarm implies that any alarms fulfilling these criteria are ignored
   (blocked/filtered).  Shelved alarms appear in a dedicated shelved-
   alarm list; thus, they can be filtered out so that the main alarm
   list only contains entries of interest.  Shelved alarms do not
   generate notifications, but the shelved-alarm list is updated with
   any alarm-state changes.

   Alarm shelving is optional to implement, since matching alarms
   against shelf criteria may have an impact on the server's processing
   resources.

3.8.  Alarm Profiles

   Alarm profiles are used to configure further information to an alarm
   type.  This module supports configuring severity levels overriding
   the system-default levels.  This corresponds to the Alarm Severity
   Assignment Profile (ASAP) functionality in M.3100 [M.3100] and M.3160
   [M.3160].  Other standard or enterprise modules can augment this list
   with further alarm-type information.

4.  Alarm Data Model

   The fundamental parts of the data model are the "alarm-list" with
   associated notifications and the "alarm-inventory" list of all
   possible alarm types.  These MUST be implemented by a system.  The
   rest of the data model is made conditional with these YANG features:
   "operator-actions", "alarm-shelving", "alarm-history", "alarm-
   summary", "alarm-profile", and "severity-assignment".

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   The data model has the following overall structure:

     +--rw control
     |  +--rw max-alarm-status-changes?   union
     |  +--rw notify-status-changes?      enumeration
     |  +--rw notify-severity-level?      severity
     |  +--rw alarm-shelving {alarm-shelving}?
     |        ...
     +--ro alarm-inventory
     |  +--ro alarm-type* [alarm-type-id alarm-type-qualifier]
     |        ...
     +--ro summary {alarm-summary}?
     |  +--ro alarm-summary* [severity]
     |  |     ...
     |  +--ro shelves-active?   empty {alarm-shelving}?
     +--ro alarm-list
     |  +--ro number-of-alarms?   yang:gauge32
     |  +--ro last-changed?       yang:date-and-time
     |  +--ro alarm* [resource alarm-type-id alarm-type-qualifier]
     |  |     ...
     |  +---x purge-alarms
     |  |     ...
     |  +---x compress-alarms {alarm-history}?
     |        ...
     +--ro shelved-alarms {alarm-shelving}?
     |  +--ro number-of-shelved-alarms?      yang:gauge32
     |  +--ro shelved-alarms-last-changed?   yang:date-and-time
     |  +--ro shelved-alarm*
     |  |       [resource alarm-type-id alarm-type-qualifier]
     |  |     ...
     |  +---x purge-shelved-alarms
     |  |     ...
     |  +---x compress-shelved-alarms {alarm-history}?
     |        ...
     +--rw alarm-profile*
             [alarm-type-id alarm-type-qualifier-match resource]
             {alarm-profile}?
        +--rw alarm-type-id                        alarm-type-id
        +--rw alarm-type-qualifier-match           string
        +--rw resource                             resource-match
        +--rw description                          string
        +--rw alarm-severity-assignment-profile
                {severity-assignment}?
              ...

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4.1.  Alarm Control

   The "/alarms/control/notify-status-changes" leaf controls whether
   notifications are sent for all state changes, only raise and clear,
   or only notifications more severe than a configured level.  This
   feature, in combination with alarm shelving, corresponds to the ITU
   Alarm Report Control functionality; see Appendix F.2.4.

   Every alarm has a list of status changes.  The length of this list is
   controlled by "/alarms/control/max-alarm-status-changes".  When the
   list is full and a new entry created, the oldest entry is removed.

4.1.1.  Alarm Shelving

   The shelving control tree is shown below:

     +--rw control
        +--rw alarm-shelving {alarm-shelving}?
           +--rw shelf* [name]
              +--rw name           string
              +--rw resource*      resource-match
              +--rw alarm-type*
              |       [alarm-type-id alarm-type-qualifier-match]
              |  +--rw alarm-type-id                 alarm-type-id
              |  +--rw alarm-type-qualifier-match    string
              +--rw description?   string

   Shelved alarms are shown in a dedicated shelved-alarm list.  Matching
   alarms MUST appear in the "/alarms/shelved-alarms/shelved-alarm"
   list, and non-matching alarms MUST appear in the "/alarms/alarm-list/
   alarm" list.  The server does not send any notifications for shelved
   alarms.

   Shelving and unshelving can only be performed by editing the shelf
   configuration.  It cannot be performed on individual alarms.  The
   server will add an operator state indicating that the alarm was
   shelved/unshelved.

   A leaf, "/alarms/summary/shelves-active", in the alarm summary
   indicates if there are shelved alarms.

   A system can select not to support the shelving feature.

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4.2.  Alarm Inventory

   The alarm inventory represents all possible alarm types that may
   occur in the system.  A management system may use this to build alarm
   procedures.  The alarm inventory is relevant for the following
   reasons:

      The system might not implement all defined alarm type identities,
      and some alarm identities are abstract.

      The system has configured dynamic alarm types using the alarm
      qualifier.  The inventory makes it possible for the management
      system to discover these.

   Note that the mechanism whereby dynamic alarm types are added using
   the alarm-type qualifier MUST populate this list.

   The optional leaf-list "resource" in the alarm inventory enables the
   system to publish for which resources a given alarm type may appear.

   A server MUST implement the alarm inventory in order to enable
   controlled alarm procedures in the client.

   A server implementer may want to document the alarm inventory for
   offline processing by clients.  The file format defined in
   [YANG-INSTANCE] can be used for this purpose.

   The alarm inventory tree is shown below:

     +--ro alarm-inventory
        +--ro alarm-type* [alarm-type-id alarm-type-qualifier]
           +--ro alarm-type-id           alarm-type-id
           +--ro alarm-type-qualifier    alarm-type-qualifier
           +--ro resource*               resource-match
           +--ro will-clear              boolean
           +--ro severity-level*         severity
           +--ro description             string

4.3.  Alarm Summary

   The alarm summary list summarizes alarms per severity: how many
   cleared, cleared and closed, and closed.  It also gives an indication
   if there are shelved alarms.

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   The alarm summary tree is shown below:

     +--ro summary {alarm-summary}?
        +--ro alarm-summary* [severity]
        |  +--ro severity                  severity
        |  +--ro total?                    yang:gauge32
        |  +--ro not-cleared?              yang:gauge32
        |  +--ro cleared?                  yang:gauge32
        |  +--ro cleared-not-closed?       yang:gauge32
        |  |       {operator-actions}?
        |  +--ro cleared-closed?           yang:gauge32
        |  |       {operator-actions}?
        |  +--ro not-cleared-closed?       yang:gauge32
        |  |       {operator-actions}?
        |  +--ro not-cleared-not-closed?   yang:gauge32
        |          {operator-actions}?
        +--ro shelves-active?   empty {alarm-shelving}?

4.4.  The Alarm List

   The alarm list, "/alarms/alarm-list", is a function from the tuple
   (resource, alarm type, alarm-type qualifier) to the current composite
   alarm state.  The composite state includes states for the resource
   alarm lifecycle such as severity, clearance flag, and operator states
   such as acknowledged.  This means that for a given resource and alarm
   type, the alarm list shows the current states of the alarm such as
   acknowledged and cleared.

   +--ro alarm-list
      +--ro number-of-alarms?   yang:gauge32
      +--ro last-changed?       yang:date-and-time
      +--ro alarm* [resource alarm-type-id alarm-type-qualifier]
      |  +--ro resource                 resource
      |  +--ro alarm-type-id            alarm-type-id
      |  +--ro alarm-type-qualifier     alarm-type-qualifier
      |  +--ro alt-resource*            resource
      |  +--ro related-alarm*
      |  |       [resource alarm-type-id alarm-type-qualifier]
      |  |       {alarm-correlation}?
      |  |  +--ro resource
      |  |  |       -> /alarms/alarm-list/alarm/resource
      |  |  +--ro alarm-type-id           leafref
      |  |  +--ro alarm-type-qualifier    leafref
      |  +--ro impacted-resource*       resource
      |  |       {service-impact-analysis}?
      |  +--ro root-cause-resource*     resource
      |  |       {root-cause-analysis}?
      |  +--ro time-created             yang:date-and-time

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      |  +--ro is-cleared               boolean
      |  +--ro last-raised              yang:date-and-time
      |  +--ro last-changed             yang:date-and-time
      |  +--ro perceived-severity       severity
      |  +--ro alarm-text               alarm-text
      |  +--ro status-change* [time] {alarm-history}?
      |  |  +--ro time                  yang:date-and-time
      |  |  +--ro perceived-severity    severity-with-clear
      |  |  +--ro alarm-text            alarm-text
      |  +--ro operator-state-change* [time] {operator-actions}?
      |  |  +--ro time        yang:date-and-time
      |  |  +--ro operator    string
      |  |  +--ro state       operator-state
      |  |  +--ro text?       string
      |  +---x set-operator-state {operator-actions}?
      |  |  +---w input
      |  |     +---w state    writable-operator-state
      |  |     +---w text?    string
      |  +---n operator-action {operator-actions}?
      |     +-- time        yang:date-and-time
      |     +-- operator    string
      |     +-- state       operator-state
      |     +-- text?       string
      +---x purge-alarms
      |  +---w input
      |  |  +---w alarm-clearance-status    enumeration
      |  |  +---w older-than!
      |  |  |  +---w (age-spec)?
      |  |  |     +--:(seconds)
      |  |  |     |  +---w seconds?   uint16
      |  |  |     +--:(minutes)
      |  |  |     |  +---w minutes?   uint16
      |  |  |     +--:(hours)
      |  |  |     |  +---w hours?     uint16
      |  |  |     +--:(days)
      |  |  |     |  +---w days?      uint16
      |  |  |     +--:(weeks)
      |  |  |        +---w weeks?     uint16
      |  |  +---w severity!
      |  |  |  +---w (sev-spec)?
      |  |  |     +--:(below)
      |  |  |     |  +---w below?   severity
      |  |  |     +--:(is)
      |  |  |     |  +---w is?      severity
      |  |  |     +--:(above)
      |  |  |        +---w above?   severity
      |  |  +---w operator-state-filter! {operator-actions}?

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      |  |     +---w state?   operator-state
      |  |     +---w user?    string
      |  +--ro output
      |     +--ro purged-alarms?   uint32
      +---x compress-alarms {alarm-history}?
         +---w input
         |  +---w resource?               resource-match
         |  +---w alarm-type-id?
         |  |       -> /alarms/alarm-list/alarm/alarm-type-id
         |  +---w alarm-type-qualifier?   leafref
         +--ro output
            +--ro compressed-alarms?   uint32

   Every alarm has three important states: the resource clearance state
   "is-cleared", the severity "perceived-severity", and the operator
   state available in the operator-state change list.

   In order to see the alarm history, the resource state changes are
   available in the "status-change" list, and the operator history is
   available in the "operator-state-change" list.

4.5.  The Shelved-Alarm List

   The shelved-alarm list has the same structure as the alarm list
   above.  It shows all the alarms that match the shelving criteria
   "/alarms/control/alarm-shelving".

4.6.  Alarm Profiles

   Alarm profiles, "/alarms/alarm-profile", is a list of configurable
   alarm types.  The list supports configurable alarm severity levels in
   the container "alarm-severity-assignment-profile".  If an alarm
   matches the configured alarm type, it MUST use the configured
   severity level(s) instead of the system default.  This configuration
   MUST also be represented in the alarm inventory.

     +--rw alarm-profile*
             [alarm-type-id alarm-type-qualifier-match resource]
             {alarm-profile}?
        +--rw alarm-type-id                        alarm-type-id
        +--rw alarm-type-qualifier-match           string
        +--rw resource                             resource-match
        +--rw description                          string
        +--rw alarm-severity-assignment-profile
                {severity-assignment}?
           +--rw severity-level*    severity

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4.7.  Operations

   The alarm data model supports the following actions to manage the
   alarms:

   "/alarms/alarm-list/purge-alarms":  Delete alarms from the "alarm-
      list" according to specific criteria, for example, all cleared
      alarms older than a specific date.

   "/alarms/alarm-list/compress-alarms":  Compress the "status-change"
      list for the alarms.

   "/alarms/alarm-list/alarm/set-operator-state":  Change the operator
      state for an alarm.  For example, an alarm can be acknowledged by
      setting the operator state to "ack".

   "/alarms/shelved-alarm-list/purge-shelved-alarms":  Delete alarms
      from the "shelved-alarm-list" according to specific criteria, for
      example, all alarms older than a specific date.

   "/alarms/shelved-alarm-list/compress-shelved-alarms":  Compress the
      "status-change" list for the alarms.

4.8.  Notifications

   The alarm data model supports a general notification to report alarm-
   state changes.  It carries all relevant parameters for the alarm-
   management application.

   There is also a notification to report that an operator changed the
   operator state on an alarm, like acknowledged.

   If the alarm inventory is changed, for example, a new card type is
   inserted, a notification will tell the management application that
   new alarm types are available.

5.  Relationship to the ietf-hardware YANG Module

   RFC 8348 [RFC8348] defines the "ietf-hardware" YANG data model for
   the management of hardware.  The "alarm-state" in RFC 8348 is a
   summary of the alarm severity levels that may be active on the
   specific hardware component.  It does not say anything about how
   alarms are reported, and it doesn't provide any details of the
   alarms.

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   The mapping between the alarm YANG data model, prefix "al", and the
   "alarm-state" in RFC 8348, prefix "hw", is as follows:

   "al:resource":  Corresponds to an entry in the list
      "/hw:hardware/hw:component/".

   "al:is-cleared":  No bit set in "/hw:hardware/hw:component/hw:state/
      hw:alarm-state".

   "al:perceived-severity":  Corresponding bit set in
      "/hw:hardware/hw:component/hw:state/hw:alarm-state".

   "al:operator-state-change/al:state":  If the alarm is acknowledged by
      the operator, the bit "hw:under-repair" is set in
      "/hw:hardware/hw:component/hw:state/hw:alarm-state".

6.  Alarm YANG Module

   This YANG module references [RFC6991] and [XSD-TYPES].

  <CODE BEGINS> file "ietf-alarms@2019-09-11.yang"
  module ietf-alarms {
    yang-version 1.1;
    namespace "urn:ietf:params:xml:ns:yang:ietf-alarms";
    prefix al;

    import ietf-yang-types {
      prefix yang;
      reference
        "RFC 6991: Common YANG Data Types.";
    }

    organization
      "IETF CCAMP Working Group";
    contact
      "WG Web:   <https://trac.ietf.org/trac/ccamp>
       WG List:  <mailto:ccamp@ietf.org>

       Editor:   Stefan Vallin
                 <mailto:stefan@wallan.se>

       Editor:   Martin Bjorklund
                 <mailto:mbj@tail-f.com>";
    description
      "This module defines an interface for managing alarms.  Main
       inputs to the module design are the 3GPP Alarm Integration
       Reference Point (IRP), ITU-T X.733, and ANSI/ISA-18.2 alarm
       standards.

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       Main features of this module include:

         * Alarm list:
                   A list of all alarms.  Cleared alarms stay in
                   the list until explicitly purged.

         * Operator actions on alarms:
                   Acknowledging and closing alarms.

         * Administrative actions on alarms:
                   Purging alarms from the list according to specific
                   criteria.

         * Alarm inventory:
                   A management application can read all
                   alarm types implemented by the system.

         * Alarm shelving:
                   Shelving (blocking) alarms according
                   to specific criteria.

         * Alarm profiles:
                   A management system can attach further
                   information to alarm types, for example,
                   overriding system-default severity
                   levels.

       This module uses a stateful view on alarms.  An alarm is a state
       for a specific resource (note that an alarm is not a
       notification).  An alarm type is a possible alarm state for a
       resource.  For example, the tuple:

         ('link-alarm', 'GigabitEthernet0/25')

       is an alarm of type 'link-alarm' on the resource
       'GigabitEthernet0/25'.

       Alarm types are identified using YANG identities and an optional
       string-based qualifier.  The string-based qualifier allows for
       dynamic extension of the statically defined alarm types.  Alarm
       types identify a possible alarm state and not the individual
       notifications.  For example, the traditional 'link-down' and
       'link-up' notifications are two notifications referring to the
       same alarm type 'link-alarm'.

       With this design, there is no ambiguity about how alarm and
       alarm clear correlation should be performed; notifications that
       report the same resource and alarm type are considered updates

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       of the same alarm, e.g., clearing an active alarm or changing
       the severity of an alarm.  The instrumentation can update the
       severity and alarm text on an existing alarm.  The above alarm
       example can therefore look like the following:

         (('link-alarm', 'GigabitEthernet0/25'),
          warning,
          'interface down while interface admin state is up')

       There is a clear separation between updates on the alarm from
       the underlying resource, like clear, and updates from an
       operator, like acknowledging or closing an alarm:

         (('link-alarm', 'GigabitEthernet0/25'),
          warning,
          'interface down while interface admin state is up',
          cleared,
          closed)

       Administrative actions like removing closed alarms older than a
       given time is supported.

       This YANG module does not define how the underlying
       instrumentation detects and clears the specific alarms.  That
       belongs to the Standards Development Organization (SDO) or
       enterprise that owns that specific technology.

       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 (RFC 2119) (RFC 8174) when, and only when,
       they appear in all capitals, as shown here.

       Copyright (c) 2019 IETF Trust and the persons identified as
       authors of the code.  All rights reserved.

       Redistribution and use in source and binary forms, with or
       without modification, is permitted pursuant to, and subject to
       the license terms contained in, the Simplified BSD License set
       forth in Section 4.c of the IETF Trust's Legal Provisions
       Relating to IETF Documents
       (https://trustee.ietf.org/license-info).

       This version of this YANG module is part of RFC 8632; see
       the RFC itself for full legal notices.";

    revision 2019-09-11 {
      description

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        "Initial revision.";
      reference
        "RFC 8632: A YANG Data Model for Alarm Management";
    }

    /*
     * Features
     */

    feature operator-actions {
      description
        "This feature indicates that the system supports operator
         states on alarms.";
    }

    feature alarm-shelving {
      description
        "This feature indicates that the system supports shelving
         (blocking) alarms.

         Alarm shelving may have an impact on server processing
         resources in order to match alarms against shelf
         criteria.";
    }

    feature alarm-history {
      description
        "This feature indicates that the server maintains a history
         of state changes for each alarm.  For example, if an alarm
         toggles between cleared and active 10 times, these state
         changes are present in a separate list in the alarm.

         Keeping the alarm history may have an impact on server
         memory resources.";
    }

    feature alarm-summary {
      description
        "This feature indicates that the server summarizes the number
         of alarms per severity and operator state.";
    }

    feature alarm-profile {
      description
        "The system enables clients to configure further information
         to each alarm type.";
    }

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    feature severity-assignment {
      description
        "The system supports configurable alarm severity levels.";
      reference
        "ITU-T Recommendation M.3100:
           Generic network information model
         ITU-T Recommendation M.3160:
           Generic, protocol-neutral management information model";
    }

    feature root-cause-analysis {
      description
        "The system supports identifying candidate root-cause
         resources for an alarm, for example, a disk partition
         root cause for a logger failure alarm.";
    }

    feature service-impact-analysis {
      description
        "The system supports identifying candidate-impacted
         resources for an alarm, for example, an interface state change
         resulting in a link alarm, which can refer to a link as being
         impacted.";
    }

    feature alarm-correlation {
      description
        "The system supports correlating/grouping alarms
         that belong together.";
    }

    /*
     * Identities
     */

    identity alarm-type-id {
      description
        "Base identity for alarm types.  A unique identification of
         the alarm, not including the resource.  Different resources
         can share alarm types.  If the resource reports the same
         alarm type, it is considered to be the same alarm.  The alarm
         type is a simplification of the different X.733 and 3GPP Alarm
         IRP correlation mechanisms, and it allows for
         hierarchical extensions.

         A string-based qualifier can be used in addition to the
         identity in order to have different alarm types based on
         information not known at design time, such as values in

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         textual SNMP Notification varbinds.

         Standards and vendors can define sub-identities to clearly
         identify specific alarm types.

         This identity is abstract and MUST NOT be used for alarms.";
    }

    /*
     * Common types
     */

    typedef resource {
      type union {
        type instance-identifier {
          require-instance false;
        }
        type yang:object-identifier;
        type string;
        type yang:uuid;
      }
      description
        "This is an identification of the alarming resource, such as an
         interface.  It should be as fine-grained as possible to both
         guide the operator and guarantee uniqueness of the alarms.

         If the alarming resource is modeled in YANG, this type will
         be an instance-identifier.

         If the resource is an SNMP object, the type will be an
         'object-identifier'.

         If the resource is anything else, for example, a distinguished
         name or a Common Information Model (CIM) path, this type will
         be a string.

         If the alarming object is identified by a Universally Unique
         Identifier (UUID), use the uuid type.  Be cautious when using
         this type, since a UUID is hard to use for an operator.

         If the server supports several models, the precedence should
         be in the order as given in the union definition.";
    }

    typedef resource-match {
      type union {
        type yang:xpath1.0;
        type yang:object-identifier;

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        type string;
      }
      description
        "This type is used to match resources of type 'resource'.
         Since the type 'resource' is a union of different types, the
         'resource-match' type is also a union of corresponding types.

         If the type is given as an XPath 1.0 expression, a resource
         of type 'instance-identifier' matches if the instance is part
         of the node set that is the result of evaluating the XPath 1.0
         expression.  For example, the XPath 1.0 expression:

          /ietf-interfaces:interfaces/ietf-interfaces:interface
              [ietf-interfaces:type='ianaift:ethernetCsmacd']

         would match the resource instance-identifier:

          /if:interfaces/if:interface[if:name='eth1'],

         assuming that the interface 'eth1' is of type
         'ianaift:ethernetCsmacd'.

         If the type is given as an object identifier, a resource of
         type 'object-identifier' matches if the match object
         identifier is a prefix of the resource's object identifier.
         For example, the value:

          1.3.6.1.2.1.2.2

         would match the resource object identifier:

          1.3.6.1.2.1.2.2.1.1.5

         If the type is given as an UUID or a string, it is interpreted
         as an XML Schema regular expression, which matches a resource
         of type 'yang:uuid' or 'string' if the given regular
         expression matches the resource string.

         If the type is given as an XPath expression, it is evaluated
         in the following XPath context:

           o  The set of namespace declarations is the set of prefix
              and namespace pairs for all YANG modules implemented by
              the server, where the prefix is the YANG module name and
              the namespace is as defined by the 'namespace' statement
              in the YANG module.

              If a leaf of this type is encoded in XML, all namespace

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              declarations in scope on the leaf element are added to
              the set of namespace declarations.  If a prefix found in
              the XML is already present in the set of namespace
              declarations, the namespace in the XML is used.

           o  The set of variable bindings is empty.

           o  The function library is the core function library, and
              the functions are defined in Section 10 of RFC 7950.

           o  The context node is the root node in the data tree.";
      reference
        "XML Schema Part 2: Datatypes Second Edition,
           World Wide Web Consortium Recommendation
           REC-xmlschema-2-20041028";
    }

    typedef alarm-text {
      type string;
      description
        "The string used to inform operators about the alarm.  This
         MUST contain enough information for an operator to be able to
         understand the problem and how to resolve it.  If this string
         contains structure, this format should be clearly documented
         for programs to be able to parse that information.";
    }

    typedef severity {
      type enumeration {
        enum indeterminate {
          value 2;
          description
            "Indicates that the severity level could not be
             determined.  This level SHOULD be avoided.";
        }
        enum warning {
          value 3;
          description
            "The 'warning' severity level indicates the detection of a
             potential or impending service-affecting fault, before any
             significant effects have been felt.  Action should be
             taken to further diagnose (if necessary) and correct the
             problem in order to prevent it from becoming a more
             serious service-affecting fault.";
        }
        enum minor {
          value 4;
          description

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            "The 'minor' severity level indicates the existence of a
             non-service-affecting fault condition and that corrective
             action should be taken in order to prevent a more serious
             (for example, service-affecting) fault.  Such a severity
             can be reported, for example, when the detected alarm
             condition is not currently degrading the capacity of the
             resource.";
        }
        enum major {
          value 5;
          description
            "The 'major' severity level indicates that a service-
             affecting condition has developed and an urgent corrective
             action is required.  Such a severity can be reported, for
             example, when there is a severe degradation in the
             capability of the resource and its full capability must be
             restored.";
        }
        enum critical {
          value 6;
          description
            "The 'critical' severity level indicates that a service-
             affecting condition has occurred and an immediate
             corrective action is required.  Such a severity can be
             reported, for example, when a resource becomes totally out
             of service and its capability must be restored.";
        }
      }
      description
        "The severity level of the alarm.  Note well that the value
         'clear' is not included.  Whether or not an alarm is cleared
         is a separate boolean flag.";
      reference
        "ITU-T Recommendation X.733: Information Technology
           - Open Systems Interconnection
           - System Management: Alarm Reporting Function";
    }

    typedef severity-with-clear {
      type union {
        type enumeration {
          enum cleared {
            value 1;
            description
              "The alarm is cleared by the instrumentation.";
          }
        }
        type severity;

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      }
      description
        "The severity level of the alarm including clear.  This is used
         only in notifications reporting state changes for an alarm.";
    }

    typedef writable-operator-state {
      type enumeration {
        enum none {
          value 1;
          description
            "The alarm is not being taken care of.";
        }
        enum ack {
          value 2;
          description
            "The alarm is being taken care of.  Corrective action not
             taken yet or has failed";
        }
        enum closed {
          value 3;
          description
            "Corrective action taken successfully.";
        }
      }
      description
        "Operator states on an alarm.  The 'closed' state indicates
         that an operator considers the alarm being resolved.  This is
         separate from the alarm's 'is-cleared' leaf.";
    }

    typedef operator-state {
      type union {
        type writable-operator-state;
        type enumeration {
          enum shelved {
            value 4;
            description
              "The alarm is shelved.  Alarms in /alarms/shelved-alarms/
               MUST be assigned this operator state by the server as
               the last entry in the 'operator-state-change' list.  The
               text for that entry SHOULD include the shelf name.";
          }
          enum un-shelved {
            value 5;
            description
              "The alarm is moved back to 'alarm-list' from a shelf.
               Alarms that are moved from /alarms/shelved-alarms/ to

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               /alarms/alarm-list MUST be assigned this state by the
               server as the last entry in the 'operator-state-change'
               list.  The text for that entry SHOULD include the shelf
               name.";
          }
        }
      }
      description
        "Operator states on an alarm.  The 'closed' state indicates
         that an operator considers the alarm being resolved.  This is
         separate from the alarm's 'is-cleared' leaf.";
    }

    /* Alarm type */

    typedef alarm-type-id {
      type identityref {
        base alarm-type-id;
      }
      description
        "Identifies an alarm type.  The description of the alarm type
         id MUST indicate whether or not the alarm type is abstract.
         An abstract alarm type is used as a base for other alarm type
         ids and will not be used as a value for an alarm or be present
         in the alarm inventory.";
    }

    typedef alarm-type-qualifier {
      type string;
      description
        "If an alarm type cannot be fully specified at design time by
         'alarm-type-id', this string qualifier is used in addition to
         fully define a unique alarm type.

         The definition of alarm qualifiers is considered to be part of
         the instrumentation and is out of scope for this module.  An
         empty string is used when this is part of a key.";
    }

    /*
     * Groupings
     */

    grouping common-alarm-parameters {
      description
        "Common parameters for an alarm.

         This grouping is used both in the alarm list and in the

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         notification representing an alarm-state change.";
      leaf resource {
        type resource;
        mandatory true;
        description
          "The alarming resource.  See also 'alt-resource'.  This could
           be, for example, a reference to the alarming interface";
      }
      leaf alarm-type-id {
        type alarm-type-id;
        mandatory true;
        description
          "This leaf and the leaf 'alarm-type-qualifier' together
           provide a unique identification of the alarm type.";
      }
      leaf alarm-type-qualifier {
        type alarm-type-qualifier;
        description
          "This leaf is used when the 'alarm-type-id' leaf cannot
           uniquely identify the alarm type.  Normally, this is not the
           case, and this leaf is the empty string.";
      }
      leaf-list alt-resource {
        type resource;
        description
          "Used if the alarming resource is available over other
           interfaces.  This field can contain SNMP OIDs, CIM paths, or
           3GPP distinguished names, for example.";
      }
      list related-alarm {
        if-feature "alarm-correlation";
        key "resource alarm-type-id alarm-type-qualifier";
        description
          "References to related alarms.  Note that the related alarm
           might have been purged from the alarm list.";
        leaf resource {
          type leafref {
            path "/alarms/alarm-list/alarm/resource";
            require-instance false;
          }
          description
            "The alarming resource for the related alarm.";
        }
        leaf alarm-type-id {
          type leafref {
            path "/alarms/alarm-list/alarm"
               + "[resource=current()/../resource]"
               + "/alarm-type-id";

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            require-instance false;
          }
          description
            "The alarm type identifier for the related alarm.";
        }
        leaf alarm-type-qualifier {
          type leafref {
            path "/alarms/alarm-list/alarm"
               + "[resource=current()/../resource]"
               + "[alarm-type-id=current()/../alarm-type-id]"
               + "/alarm-type-qualifier";
            require-instance false;
          }
          description
            "The alarm qualifier for the related alarm.";
        }
      }
      leaf-list impacted-resource {
        if-feature "service-impact-analysis";
        type resource;
        description
          "Resources that might be affected by this alarm.  If the
           system creates an alarm on a resource and also has a mapping
           to other resources that might be impacted, these resources
           can be listed in this leaf-list.  In this way, the system
           can create one alarm instead of several.  For example, if an
           interface has an alarm, the 'impacted-resource' can
           reference the aggregated port channels.";
      }
      leaf-list root-cause-resource {
        if-feature "root-cause-analysis";
        type resource;
        description
          "Resources that are candidates for causing the alarm.  If the
           system has a mechanism to understand the candidate root
           causes of an alarm, this leaf-list can be used to list the
           root-cause candidate resources.  In this way, the system can
           create one alarm instead of several.  An example might be a
           logging system (alarm resource) that fails; the alarm can
           reference the file system in the 'root-cause-resource'
           leaf-list.  Note that the intended use is not to also send
           an alarm with the 'root-cause-resource' as an alarming
           resource.  The 'root-cause-resource' leaf-list is a hint and
           should not also generate an alarm for the same problem.";
      }
    }

    grouping alarm-state-change-parameters {

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      description
        "Parameters for an alarm-state change.

         This grouping is used both in the alarm list's status-change
         list and in the notification representing an alarm-state
         change.";
      leaf time {
        type yang:date-and-time;
        mandatory true;
        description
          "The time the status of the alarm changed.  The value
           represents the time the real alarm-state change appeared in
           the resource and not when it was added to the alarm
           list.  The /alarm-list/alarm/last-changed MUST be set to the
           same value.";
      }
      leaf perceived-severity {
        type severity-with-clear;
        mandatory true;
        description
          "The severity of the alarm as defined by X.733.  Note that
           this may not be the original severity since the alarm may
           have changed severity.";
        reference
          "ITU-T Recommendation X.733: Information Technology
             - Open Systems Interconnection
             - System Management: Alarm Reporting Function";
      }
      leaf alarm-text {
        type alarm-text;
        mandatory true;
        description
          "A user-friendly text describing the alarm-state change.";
        reference
          "ITU-T Recommendation X.733: Information Technology
             - Open Systems Interconnection
             - System Management: Alarm Reporting Function";
      }
    }

    grouping operator-parameters {
      description
        "This grouping defines parameters that can be changed by an
         operator.";
      leaf time {
        type yang:date-and-time;
        mandatory true;
        description

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          "Timestamp for operator action on the alarm.";
      }
      leaf operator {
        type string;
        mandatory true;
        description
          "The name of the operator that has acted on this alarm.";
      }
      leaf state {
        type operator-state;
        mandatory true;
        description
          "The operator's view of the alarm state.";
      }
      leaf text {
        type string;
        description
          "Additional optional textual information provided by the
           operator.";
      }
    }

    grouping resource-alarm-parameters {
      description
        "Alarm parameters that originate from the resource view.";
      leaf is-cleared {
        type boolean;
        mandatory true;
        description
          "Indicates the current clearance state of the alarm.  An
           alarm might toggle from active alarm to cleared alarm and
           back to active again.";
      }
      leaf last-raised {
        type yang:date-and-time;
        mandatory true;
        description
          "An alarm may change severity level and toggle between
           active and cleared during its lifetime.  This leaf indicates
           the last time it was raised ('is-cleared' = 'false').";
      }
      leaf last-changed {
        type yang:date-and-time;
        mandatory true;
        description
          "A timestamp when the 'status-change' or
           'operator-state-change' list was last changed.";
      }

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      leaf perceived-severity {
        type severity;
        mandatory true;
        description
          "The last severity of the alarm.

           If an alarm was raised with severity 'warning' but later
           changed to 'major', this leaf will show 'major'.";
      }
      leaf alarm-text {
        type alarm-text;
        mandatory true;
        description
          "The last reported alarm text.  This text should contain
           information for an operator to be able to understand the
           problem and how to resolve it.";
      }
      list status-change {
        if-feature "alarm-history";
        key "time";
        min-elements 1;
        description
          "A list of status-change events for this alarm.

           The entry with latest timestamp in this list MUST
           correspond to the leafs 'is-cleared', 'perceived-severity',
           and 'alarm-text' for the alarm.

           This list is ordered according to the timestamps of alarm
           state changes.  The first item corresponds to the latest
           state change.

           The following state changes create an entry in this
           list:
           - changed severity (warning, minor, major, critical)
           - clearance status; this also updates the 'is-cleared'
             leaf
           - alarm-text update";
        uses alarm-state-change-parameters;
      }
    }

    grouping filter-input {
      description
        "Grouping to specify a filter construct on alarm information.";
      leaf alarm-clearance-status {
        type enumeration {
          enum any {

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            description
              "Ignore alarm-clearance status.";
          }
          enum cleared {
            description
              "Filter cleared alarms.";
          }
          enum not-cleared {
            description
              "Filter not-cleared alarms.";
          }
        }
        mandatory true;
        description
          "The clearance status of the alarm.";
      }
      container older-than {
        presence "Age specification";
        description
          "Matches the 'last-status-change' leaf in the alarm.";
        choice age-spec {
          description
            "Filter using date and time age.";
          case seconds {
            leaf seconds {
              type uint16;
              description
                "Age expressed in seconds.";
            }
          }
          case minutes {
            leaf minutes {
              type uint16;
              description
                "Age expressed in minutes.";
            }
          }
          case hours {
            leaf hours {
              type uint16;
              description
                "Age expressed in hours.";
            }
          }
          case days {
            leaf days {
              type uint16;
              description

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                "Age expressed in days.";
            }
          }
          case weeks {
            leaf weeks {
              type uint16;
              description
                "Age expressed in weeks.";
            }
          }
        }
      }
      container severity {
        presence "Severity filter";
        choice sev-spec {
          description
            "Filter based on severity level.";
          leaf below {
            type severity;
            description
              "Severity less than this leaf.";
          }
          leaf is {
            type severity;
            description
              "Severity level equal to this leaf.";
          }
          leaf above {
            type severity;
            description
              "Severity level higher than this leaf.";
          }
        }
        description
          "Filter based on severity.";
      }
      container operator-state-filter {
        if-feature "operator-actions";
        presence "Operator state filter";
        leaf state {
          type operator-state;
          description
            "Filter on operator state.";
        }
        leaf user {
          type string;
          description
            "Filter based on which operator.";

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        }
        description
          "Filter based on operator state.";
      }
    }

    /*
     * The /alarms data tree
     */

    container alarms {
      description
        "The top container for this module.";
      container control {
        description
          "Configuration to control the alarm behavior.";
        leaf max-alarm-status-changes {
          type union {
            type uint16;
            type enumeration {
              enum infinite {
                description
                  "The status-change entries are accumulated
                   infinitely.";
              }
            }
          }
          default "32";
          description
            "The 'status-change' entries are kept in a circular list
             per alarm.  When this number is exceeded, the oldest
             status change entry is automatically removed.  If the
             value is 'infinite', the status-change entries are
             accumulated infinitely.";
        }
        leaf notify-status-changes {
          type enumeration {
            enum all-state-changes {
              description
                "Send notifications for all status changes.";
            }
            enum raise-and-clear {
              description
                "Send notifications only for raise, clear, and
                 re-raise.  Notifications for severity-level changes or
                 alarm-text changes are not sent.";
            }
            enum severity-level {

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              description
                "Only send notifications for alarm-state changes
                 crossing the level specified in
                 'notify-severity-level'.  Always send clear
                 notifications.";
            }
          }
          must '. != "severity-level" or ../notify-severity-level' {
            description
              "When notify-status-changes is 'severity-level', a value
               must be given for 'notify-severity-level'.";
          }
          default "all-state-changes";
          description
            "This leaf controls the notifications sent for alarm status
             updates.  There are three options:

             1.  Notifications are sent for all updates, severity-level
                 changes, and alarm-text changes.

             2.  Notifications are only sent for alarm raise and clear.

             3.  Notifications are sent for status changes equal to or
                 above the specified severity level.  Clear
                 notifications shall always be sent.  Notifications
                 shall also be sent for state changes that make an
                 alarm less severe than the specified level.

             For example, in option 3, assume that the severity level
             is set to major and that the alarm has the following state
             changes:

             [(Time, severity, clear)]:
             [(T1, major, -), (T2, minor, -), (T3, warning, -),
              (T4, minor, -), (T5, major, -), (T6, critical, -),
              (T7, major.  -), (T8, major, clear)]

             In that case, notifications will be sent at times
             T1, T2, T5, T6, T7, and T8.";
        }
        leaf notify-severity-level {
          when '../notify-status-changes = "severity-level"';
          type severity;
          description
            "Only send notifications for alarm-state changes crossing
             the specified level.  Always send clear notifications.";
        }
        container alarm-shelving {

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          if-feature "alarm-shelving";
          description
            "The 'alarm-shelving/shelf' list is used to shelve
             (block/filter) alarms.  The conditions in the shelf
             criteria are logically ANDed.  The first matching shelf is
             used, and an alarm is shelved only for this first match.
             Matching alarms MUST appear in the
             /alarms/shelved-alarms/shelved-alarm list, and
             non-matching /alarms MUST appear in the
             /alarms/alarm-list/alarm list.  The server does not send
             any notifications for shelved alarms.

             The server MUST maintain states (e.g., severity
             changes) for the shelved alarms.

             Alarms that match the criteria shall have an
             operator state 'shelved'.  When the shelf
             configuration removes an alarm from the shelf, the server
             shall add the operator state 'un-shelved'.";
          list shelf {
            key "name";
            ordered-by user;
            leaf name {
              type string;
              description
                "An arbitrary name for the alarm shelf.";
            }
            description
              "Each entry defines the criteria for shelving alarms.
               Criteria are ANDed.  If no criteria are specified,
               all alarms will be shelved.";
            leaf-list resource {
              type resource-match;
              description
                "Shelve alarms for matching resources.";
            }
            list alarm-type {
              key "alarm-type-id alarm-type-qualifier-match";
              description
                "Any alarm matching the combined criteria of
                 'alarm-type-id' and 'alarm-type-qualifier-match'
                 MUST be matched.";
              leaf alarm-type-id {
                type alarm-type-id;
                description
                  "Shelve all alarms that have an 'alarm-type-id' that
                   is equal to or derived from the given
                   'alarm-type-id'.";

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              }
              leaf alarm-type-qualifier-match {
                type string;
                description
                  "An XML Schema regular expression that is used to
                   match an alarm type qualifier.  Shelve all alarms
                   that match this regular expression for the alarm
                   type qualifier.";
                reference
                  "XML Schema Part 2: Datatypes Second Edition,
                     World Wide Web Consortium Recommendation
                     REC-xmlschema-2-20041028";
              }
            }
            leaf description {
              type string;
              description
                "An optional textual description of the shelf.  This
                 description should include the reason for shelving
                 these alarms.";
            }
          }
        }
      }
      container alarm-inventory {
        config false;
        description
          "The 'alarm-inventory/alarm-type' list contains all possible
           alarm types for the system.

           If the system knows for which resources a specific alarm
           type can appear, it is also identified in the inventory.
           The list also tells if each alarm type has a corresponding
           clear state.  The inventory shall only contain concrete
           alarm types.

           The alarm inventory MUST be updated by the system when new
           alarms can appear.  This can be the case when installing new
           software modules or inserting new card types.  A
           notification 'alarm-inventory-changed' is sent when the
           inventory is changed.";
        list alarm-type {
          key "alarm-type-id alarm-type-qualifier";
          description
            "An entry in this list defines a possible alarm.";
          leaf alarm-type-id {
            type alarm-type-id;
            description

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              "The statically defined alarm type identifier for this
               possible alarm.";
          }
          leaf alarm-type-qualifier {
            type alarm-type-qualifier;
            description
              "The optionally dynamically defined alarm type identifier
               for this possible alarm.";
          }
          leaf-list resource {
            type resource-match;
            description
              "Optionally, specifies for which resources the alarm type
               is valid.";
          }
          leaf will-clear {
            type boolean;
            mandatory true;
            description
              "This leaf tells the operator if the alarm will be
               cleared when the correct corrective action has been
               taken.  Implementations SHOULD strive for detecting the
               cleared state for all alarm types.

               If this leaf is 'true', the operator can monitor the
               alarm until it becomes cleared after the corrective
               action has been taken.

               If this leaf is 'false', the operator needs to validate
               that the alarm is no longer active using other
               mechanisms.  Alarms can lack a corresponding clear due
               to missing instrumentation or no logical
               corresponding clear state.";
          }
          leaf-list severity-level {
            type severity;
            description
              "This leaf-list indicates the possible severity levels of
               this alarm type.  Note well that 'clear' is not part of
               the severity type.  In general, the severity level
               should be defined by the instrumentation based on the
               dynamic state, rather than being defined statically by
               the alarm type, in order to provide a relevant severity
               level based on dynamic state and context.  However, most
               alarm types have a defined set of possible severity
               levels, and this should be provided here.";
          }
          leaf description {

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            type string;
            mandatory true;
            description
              "A description of the possible alarm.  It SHOULD include
               information on possible underlying root causes and
               corrective actions.";
          }
        }
      }
      container summary {
        if-feature "alarm-summary";
        config false;
        description
          "This container gives a summary of the number of alarms.";
        list alarm-summary {
          key "severity";
          description
            "A global summary of all alarms in the system.  The summary
             does not include shelved alarms.";
          leaf severity {
            type severity;
            description
              "Alarm summary for this severity level.";
          }
          leaf total {
            type yang:gauge32;
            description
              "Total number of alarms of this severity level.";
          }
          leaf not-cleared {
            type yang:gauge32;
            description
              "Total number of alarms of this severity level
               that are not cleared.";
          }
          leaf cleared {
            type yang:gauge32;
            description
              "For this severity level, the number of alarms that are
               cleared.";
          }
          leaf cleared-not-closed {
            if-feature "operator-actions";
            type yang:gauge32;
            description
              "For this severity level, the number of alarms that are
               cleared but not closed.";
          }

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          leaf cleared-closed {
            if-feature "operator-actions";
            type yang:gauge32;
            description
              "For this severity level, the number of alarms that are
               cleared and closed.";
          }
          leaf not-cleared-closed {
            if-feature "operator-actions";
            type yang:gauge32;
            description
              "For this severity level, the number of alarms that are
               not cleared but closed.";
          }
          leaf not-cleared-not-closed {
            if-feature "operator-actions";
            type yang:gauge32;
            description
              "For this severity level, the number of alarms that are
               not cleared and not closed.";
          }
        }
        leaf shelves-active {
          if-feature "alarm-shelving";
          type empty;
          description
            "This is a hint to the operator that there are active
             alarm shelves.  This leaf MUST exist if the
             /alarms/shelved-alarms/number-of-shelved-alarms is > 0.";
        }
      }
      container alarm-list {
        config false;
        description
          "The alarms in the system.";
        leaf number-of-alarms {
          type yang:gauge32;
          description
            "This object shows the total number of
             alarms in the system, i.e., the total number
             of entries in the alarm list.";
        }
        leaf last-changed {
          type yang:date-and-time;
          description
            "A timestamp when the alarm list was last
             changed.  The value can be used by a manager to
             initiate an alarm resynchronization procedure.";

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        }
        list alarm {
          key "resource alarm-type-id alarm-type-qualifier";
          description
            "The list of alarms.  Each entry in the list holds one
             alarm for a given alarm type and resource.  An alarm can
             be updated from the underlying resource or by the user.
             The following leafs are maintained by the resource:
             'is-cleared', 'last-change', 'perceived-severity', and
             'alarm-text'.  An operator can change 'operator-state' and
             'operator-text'.

             Entries appear in the alarm list the first time an alarm
             becomes active for a given alarm type and resource.
             Entries do not get deleted when the alarm is cleared.
             Clear status is represented as a boolean flag.

             Alarm entries are removed, i.e., purged, from the list by
             an explicit purge action.  For example, purge all alarms
             that are cleared and in closed operator state that are
             older than 24 hours.  Purged alarms are removed from the
             alarm list.  If the alarm resource state changes after a
             purge, the alarm will reappear in the alarm list.

             Systems may also remove alarms based on locally configured
             policies; this is out of scope for this module.";
          uses common-alarm-parameters;
          leaf time-created {
            type yang:date-and-time;
            mandatory true;
            description
              "The timestamp when this alarm entry was created.  This
               represents the first time the alarm appeared; it can
               also represent that the alarm reappeared after a purge.
               Further state changes of the same alarm do not change
               this leaf; these changes will update the 'last-changed'
               leaf.";
          }
          uses resource-alarm-parameters;
          list operator-state-change {
            if-feature "operator-actions";
            key "time";
            description
              "This list is used by operators to indicate the state of
               human intervention on an alarm.  For example, if an
               operator has seen an alarm, the operator can add a new
               item to this list indicating that the alarm is
               acknowledged.";

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            uses operator-parameters;
          }
          action set-operator-state {
            if-feature "operator-actions";
            description
              "This is a means for the operator to indicate the level
               of human intervention on an alarm.";
            input {
              leaf state {
                type writable-operator-state;
                mandatory true;
                description
                  "Set this operator state.";
              }
              leaf text {
                type string;
                description
                  "Additional optional textual information.";
              }
            }
          }
          notification operator-action {
            if-feature "operator-actions";
            description
              "This notification is used to report that an operator
               acted upon an alarm.";
            uses operator-parameters;
          }
        }
        action purge-alarms {
          description
            "This operation requests that the server delete entries
             from the alarm list according to the supplied criteria.

             Typically, this operation is used to delete alarms that
             are in closed operator state and older than a specified
             time.

             The number of purged alarms is returned as an output
             parameter.";
          input {
            uses filter-input;
          }
          output {
            leaf purged-alarms {
              type uint32;
              description
                "Number of purged alarms.";

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            }
          }
        }
        action compress-alarms {
          if-feature "alarm-history";
          description
            "This operation requests that the server compress
             entries in the alarm list by removing all but the
             latest 'status-change' entry for all matching alarms.
             Conditions in the input are logically ANDed.  If no
             input condition is given, all alarms are compressed.";
          input {
            leaf resource {
              type resource-match;
              description
                "Compress the alarms matching this resource.";
            }
            leaf alarm-type-id {
              type leafref {
                path "/alarms/alarm-list/alarm/alarm-type-id";
                require-instance false;
              }
              description
                "Compress alarms with this 'alarm-type-id'.";
            }
            leaf alarm-type-qualifier {
              type leafref {
                path "/alarms/alarm-list/alarm/alarm-type-qualifier";
                require-instance false;
              }
              description
                "Compress the alarms with this
                 'alarm-type-qualifier'.";
            }
          }
          output {
            leaf compressed-alarms {
              type uint32;
              description
                "Number of compressed alarm entries.";
            }
          }
        }
      }
      container shelved-alarms {
        if-feature "alarm-shelving";
        config false;
        description

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          "The shelved alarms.  Alarms appear here if they match the
           criteria in /alarms/control/alarm-shelving.  This list does
           not generate any notifications.  The list represents alarms
           that are considered not relevant by the operator.  Alarms in
           this list have an 'operator-state' of 'shelved'.  This
           cannot be changed.";
        leaf number-of-shelved-alarms {
          type yang:gauge32;
          description
            "This object shows the total number of current
             alarms, i.e., the total number of entries
             in the alarm list.";
        }
        leaf shelved-alarms-last-changed {
          type yang:date-and-time;
          description
            "A timestamp when the shelved-alarm list was last changed.
             The value can be used by a manager to initiate an alarm
             resynchronization procedure.";
        }
        list shelved-alarm {
          key "resource alarm-type-id alarm-type-qualifier";
          description
            "The list of shelved alarms.  Shelved alarms can only be
             updated from the underlying resource; no operator actions
             are supported.";
          uses common-alarm-parameters;
          leaf shelf-name {
            type leafref {
              path "/alarms/control/alarm-shelving/shelf/name";
              require-instance false;
            }
            description
              "The name of the shelf.";
          }
          uses resource-alarm-parameters;
          list operator-state-change {
            if-feature "operator-actions";
            key "time";
            description
              "This list is used by operators to indicate the state of
               human intervention on an alarm.  For shelved alarms, the
               system has set the list item in the list to 'shelved'.";
            uses operator-parameters;
          }
        }
        action purge-shelved-alarms {
          description

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            "This operation requests that the server delete entries from
             the shelved-alarm list according to the supplied criteria.
             In the shelved-alarm list, it makes sense to delete alarms
             that are not relevant anymore.

             The number of purged alarms is returned as an output
             parameter.";
          input {
            uses filter-input;
          }
          output {
            leaf purged-alarms {
              type uint32;
              description
                "Number of purged alarms.";
            }
          }
        }
        action compress-shelved-alarms {
          if-feature "alarm-history";
          description
            "This operation requests that the server compress entries
             in the shelved-alarm list by removing all but the latest
             'status-change' entry for all matching shelved alarms.
             Conditions in the input are logically ANDed.  If no input
             condition is given, all alarms are compressed.";
          input {
            leaf resource {
              type leafref {
                path "/alarms/shelved-alarms/shelved-alarm/resource";
                require-instance false;
              }
              description
                "Compress the alarms with this resource.";
            }
            leaf alarm-type-id {
              type leafref {
                path "/alarms/shelved-alarms/shelved-alarm"
                   + "/alarm-type-id";
                require-instance false;
              }
              description
                "Compress alarms with this 'alarm-type-id'.";
            }
            leaf alarm-type-qualifier {
              type leafref {
                path "/alarms/shelved-alarms/shelved-alarm"
                   + "/alarm-type-qualifier";

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                require-instance false;
              }
              description
                "Compress the alarms with this
                 'alarm-type-qualifier'.";
            }
          }
          output {
            leaf compressed-alarms {
              type uint32;
              description
                "Number of compressed alarm entries.";
            }
          }
        }
      }
      list alarm-profile {
        if-feature "alarm-profile";
        key "alarm-type-id alarm-type-qualifier-match resource";
        ordered-by user;
        description
          "This list is used to assign further information or
           configuration for each alarm type.  This module supports a
           mechanism where the client can override the system-default
           alarm severity levels.  The 'alarm-profile' is also a useful
           augmentation point for specific additions to alarm types.";
        leaf alarm-type-id {
          type alarm-type-id;
          description
            "The alarm type identifier to match.";
        }
        leaf alarm-type-qualifier-match {
          type string;
          description
            "An XML Schema regular expression that is used to match the
             alarm type qualifier.";
          reference
            "XML Schema Part 2: Datatypes Second Edition,
               World Wide Web Consortium Recommendation
               REC-xmlschema-2-20041028";
        }
        leaf resource {
          type resource-match;
          description
            "Specifies which resources to match.";
        }
        leaf description {
          type string;

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          mandatory true;
          description
            "A description of the alarm profile.";
        }
        container alarm-severity-assignment-profile {
          if-feature "severity-assignment";
          description
            "The client can override the system-default severity
             level.";
          reference
            "ITU-T Recommendation M.3100:
               Generic network information model
             ITU-T Recommendation M.3160:
               Generic, protocol-neutral management information model";
          leaf-list severity-level {
            type severity;
            ordered-by user;
            description
              "Specifies the configured severity level(s) for the
               matching alarm.  If the alarm has several severity
               levels, the leaf-list shall be given in rising severity
               order.  The original M3100/M3160 ASAP function only
               allows for a one-to-one mapping between alarm type and
               severity, but since YANG module supports stateful
               alarms, the mapping must allow for several severity
               levels.

               Assume a high-utilization alarm type with two thresholds
               with the system-default severity levels of threshold1 =
               warning and threshold2 = minor.  Setting this leaf-list
               to (minor, major) will assign the severity levels as
               threshold1 = minor and threshold2 = major";
          }
        }
      }
    }

    /*
     * Notifications
     */

    notification alarm-notification {
      description
        "This notification is used to report a state change for an
         alarm.  The same notification is used for reporting a newly
         raised alarm, a cleared alarm, or changing the text and/or
         severity of an existing alarm.";
      uses common-alarm-parameters;

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      uses alarm-state-change-parameters;
    }

    notification alarm-inventory-changed {
      description
        "This notification is used to report that the list of possible
         alarms has changed.  This can happen when, for example, a new
         software module is installed or a new physical card is
         inserted.";
    }
  }
  <CODE ENDS>

7.  The X.733 Mapping Module

   Many alarm systems are based on the X.733 [X.733] and X.736 [X.736]
   alarm standards.  This module "ietf-alarms-x733" augments the alarm
   inventory, the alarm lists, and the alarm notification with X.733 and
   X.736 parameters.

   The module also supports a feature whereby the alarm manager can
   configure the mapping from alarm types to X.733 "event-type" and
   "probable-cause" parameters.  This might be needed when the default
   mapping provided by the system is in conflict with other management
   systems or not considered correct.

   Note that the term "resource" in this document is synonymous to the
   ITU term "managed object".

   This YANG module references [RFC6991], [X.721], [X.733], and [X.736].

   <CODE BEGINS> file "ietf-alarms-x733@2019-09-11.yang"
   module ietf-alarms-x733 {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-alarms-x733";
     prefix x733;

     import ietf-alarms {
       prefix al;
     }
     import ietf-yang-types {
       prefix yang;
       reference
         "RFC 6991: Common YANG Data Types";
     }

     organization
       "IETF CCAMP Working Group";

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     contact
       "WG Web:   <https://trac.ietf.org/trac/ccamp>
        WG List:  <mailto:ccamp@ietf.org>

        Editor:   Stefan Vallin
                  <mailto:stefan@wallan.se>

        Editor:   Martin Bjorklund
                  <mailto:mbj@tail-f.com>";
     description
       "This module augments the ietf-alarms module with X.733 alarm
        parameters.

        The following structures are augmented with the X.733 event type
        and probable cause:

         1) alarms/alarm-inventory: all possible alarm types
         2) alarms/alarm-list: every alarm in the system
         3) alarm-notification: notifications indicating alarm-state
            changes
         4) alarms/shelved-alarms

        The module also optionally allows the alarm-management system
        to configure the mapping from the ietf-alarms' alarm keys
        to the ITU tuple (event-type, probable-cause).

        The mapping does not include a corresponding problem value
        specific to X.733.  The recommendation is to use the
        'alarm-type-qualifier' leaf, which serves the same purpose.

        The module uses an integer and a corresponding string for
        probable cause instead of a globally defined enumeration, in
        order to be able to manage conflicting enumeration definitions.
        A single globally defined enumeration is challenging to
        maintain.

        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 (RFC 2119) (RFC 8174) when, and only when,
        they appear in all capitals, as shown here.

        Copyright (c) 2019 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Simplified BSD License set

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        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC 8632; see
        the RFC itself for full legal notices.";
     reference
       "ITU-T Recommendation X.733: Information Technology
          - Open Systems Interconnection
          - System Management: Alarm Reporting Function";

     revision 2019-09-11 {
       description
         "Initial revision.";
       reference
         "RFC 8632: A YANG Data Model for Alarm Management";
     }

     /*
      * Features
      */

     feature configure-x733-mapping {
       description
         "The system supports configurable X733 mapping from
          the ietf-alarms' alarm-type to X733 event-type
          and probable-cause.";
     }

     /*
      * Typedefs
      */

     typedef event-type {
       type enumeration {
         enum other {
           value 1;
           description
             "None of the below.";
         }
         enum communications-alarm {
           value 2;
           description
             "An alarm of this type is principally associated with the
              procedures and/or processes required to convey
              information from one point to another.";
         }
         enum quality-of-service-alarm {

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           value 3;
           description
             "An alarm of this type is principally associated with a
              degradation in the quality of a service.";
         }
         enum processing-error-alarm {
           value 4;
           description
             "An alarm of this type is principally associated with a
              software or processing fault.";
         }
         enum equipment-alarm {
           value 5;
           description
             "An alarm of this type is principally associated with an
              equipment fault.";
         }
         enum environmental-alarm {
           value 6;
           description
             "An alarm of this type is principally associated with a
              condition relating to an enclosure in which the equipment
              resides.";
         }
         enum integrity-violation {
           value 7;
           description
             "An indication that information may have been illegally
              modified, inserted, or deleted.";
         }
         enum operational-violation {
           value 8;
           description
             "An indication that the provision of the requested service
              was not possible due to the unavailability, malfunction,
              or incorrect invocation of the service.";
         }
         enum physical-violation {
           value 9;
           description
             "An indication that a physical resource has been violated
              in a way that suggests a security attack.";
         }
         enum security-service-or-mechanism-violation {
           value 10;
           description
             "An indication that a security attack has been detected by
              a security service or mechanism.";

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         }
         enum time-domain-violation {
           value 11;
           description
             "An indication that an event has occurred at an unexpected
              or prohibited time.";
         }
       }
       description
         "The event types as defined by X.733 and X.736.";
       reference
         "ITU-T Recommendation X.733: Information Technology
            - Open Systems Interconnection
            - System Management: Alarm Reporting Function
          ITU-T Recommendation X.736: Information Technology
            - Open Systems Interconnection
            - System Management: Security Alarm Reporting Function";
     }

     typedef trend {
       type enumeration {
         enum less-severe {
           description
             "There is at least one outstanding alarm of a
              severity higher (more severe) than that in the
              current alarm.";
         }
         enum no-change {
           description
             "The Perceived severity reported in the current
              alarm is the same as the highest (most severe)
              of any of the outstanding alarms";
         }
         enum more-severe {
           description
             "The Perceived severity in the current alarm is
              higher (more severe) than that reported in any
              of the outstanding alarms.";
         }
       }
       description
         "This type is used to describe the
          severity trend of the alarming resource.";
       reference
         "ITU-T Recommendation X.721: Information Technology
             - Open Systems Interconnection
             - Structure of management information:
               Definition of management information

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               Module Attribute-ASN1Module";
     }

     typedef value-type {
       type union {
         type int64;
         type uint64;
         type decimal64 {
           fraction-digits 2;
         }
       }
       description
         "A generic union type to match the ITU choice of
          integer and real.";
     }

     /*
      * Groupings
      */

     grouping x733-alarm-parameters {
       description
         "Common X.733 parameters for alarms.";
       leaf event-type {
         type event-type;
         description
           "The X.733/X.736 event type for this alarm.";
       }
       leaf probable-cause {
         type uint32;
         description
           "The X.733 probable cause for this alarm.";
       }
       leaf probable-cause-string {
         type string;
         description
           "The user-friendly string matching
            the probable cause integer value.  The string
            SHOULD match the X.733 enumeration.  For example,
            value 27 is 'localNodeTransmissionError'.";
       }
       container threshold-information {
         description
           "This parameter shall be present when the alarm
            is a result of crossing a threshold. ";
         leaf triggered-threshold {
           type string;
           description

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             "The identifier of the threshold attribute that
              caused the notification.";
         }
         leaf observed-value {
           type value-type;
           description
             "The value of the gauge or counter that crossed
              the threshold.  This may be different from the
              threshold value if, for example, the gauge may
              only take on discrete values.";
         }
         choice threshold-level {
           description
             "In the case of a gauge, the threshold level specifies
              a pair of threshold values: the first is the value
              of the crossed threshold, and the second is its
              corresponding hysteresis; in the case of a counter,
              the threshold level specifies only the threshold
              value.";
           case up {
             leaf up-high {
               type value-type;
               description
                 "The going-up threshold for raising the alarm.";
             }
             leaf up-low {
               type value-type;
               description
                 "The going-down threshold for clearing the alarm.
                  This is used for hysteresis functions for gauges.";
             }
           }
           case down {
             leaf down-low {
               type value-type;
               description
                 "The going-down threshold for raising the alarm.";
             }
             leaf down-high {
               type value-type;
               description
                 "The going-up threshold for clearing the alarm.
                  This is used for hysteresis functions for gauges.";
             }
           }
         }
         leaf arm-time {
           type yang:date-and-time;

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           description
             "For a gauge threshold, it's the time at which the
              threshold was last re-armed; namely, it's the time after
              the previous threshold crossing at which the hysteresis
              value of the threshold was exceeded, thus again permitting
              the generation of notifications when the threshold is
              crossed.  For a counter threshold, it's the later of the
              time at which the threshold offset was last applied or the
              counter was last initialized (for resettable counters).";
         }
       }
       list monitored-attributes {
         uses attribute;
         key "id";
         description
           "The Monitored attributes parameter, when present, defines
            one or more attributes of the resource and their
            corresponding values at the time of the alarm.";
       }
       leaf-list proposed-repair-actions {
         type string;
         description
           "This parameter, when present, is used if the cause is
            known and the system being managed can suggest one or
            more solutions (such as switch in standby equipment,
            retry, and replace media).";
       }
       leaf trend-indication {
         type trend;
         description
           "This parameter specifies the current severity
            trend of the resource.  If present, it indicates
            that there are one or more alarms ('outstanding
            alarms') that have not been cleared and that
            pertain to the same resource as this alarm
            ('current alarm') does.  The possible values are:

              more-severe: The Perceived severity in the current
                alarm is higher (more severe) than that reported in
                any of the outstanding alarms.

              no-change: The Perceived severity reported in the
                current alarm is the same as the highest (most severe)
                of any of the outstanding alarms.

              less-severe: There is at least one outstanding alarm
                of a severity higher (more severe) than that in the
                current alarm.";

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       }
       leaf backedup-status {
         type boolean;
         description
           "This parameter, when present, specifies whether or not the
            object emitting the alarm has been backed up; therefore, it
            is possible to know whether or not services provided to the
            user have been disrupted when this parameter is included.
            The use of this field in conjunction with the
            'perceived-severity' field provides information in an
            independent form to qualify the seriousness of the alarm and
            the ability of the system as a whole to continue to provide
            services.  If the value of this parameter is true, it
            indicates that the object emitting the alarm has been backed
            up; if false, the object has not been backed up.";
       }
       leaf backup-object {
         type al:resource;
         description
           "This parameter SHALL be present when the 'backedup-status'
            parameter is present and has the value 'true'.  This
            parameter specifies the managed object instance that is
            providing back-up services for the managed object to which
            the notification pertains.  This parameter is useful, for
            example, when the back-up object is from a pool of objects,
            any of which may be dynamically allocated to replace a
            faulty object.";
       }
       list additional-information {
         key "identifier";
         description
           "This parameter allows the inclusion of an additional
            information set in the alarm.  It is a series of data
            structures, each of which contains three items of
            information: an identifier, a significance indicator,
            and the problem information.";
         leaf identifier {
           type string;
           description
             "Identifies the data type of the information parameter.";
         }
         leaf significant {
           type boolean;
           description
             "Set to 'true' if the receiving system must be able to
              parse the contents of the information subparameter
              for the event report to be fully understood.";
         }

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         leaf information {
           type string;
           description
             "Additional information about the alarm.";
         }
       }
       leaf security-alarm-detector {
         type al:resource;
         description
           "This parameter identifies the detector of the security
            alarm.";
       }
       leaf service-user {
         type al:resource;
         description
           "This parameter identifies the service-user whose request
            for service led to the generation of the security alarm.";
       }
       leaf service-provider {
         type al:resource;
         description
           "This parameter identifies the intended service-provider
            of the service that led to the generation of the security
            alarm.";
       }
       reference
         "ITU-T Recommendation X.733: Information Technology
            - Open Systems Interconnection
            - System Management: Alarm Reporting Function
          ITU-T Recommendation X.736: Information Technology
            - Open Systems Interconnection
            - System Management: Security Alarm Reporting Function";
     }

     grouping x733-alarm-definition-parameters {
       description
         "Common X.733 parameters for alarm definitions.
          This grouping is used to define those alarm
          attributes that can be mapped from the alarm-type
          mechanism in the ietf-alarms module.";
       leaf event-type {
         type event-type;
         description
           "The alarm type has this X.733/X.736 event type.";
       }
       leaf probable-cause {
         type uint32;
         description

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           "The alarm type has this X.733 probable cause value.
            This module defines probable cause as an integer
            and not as an enumeration.  The reason being that the
            primary use of probable cause is in the management
            application if it is based on the X.733 standard.
            However, most management applications have their own
            defined enum definitions and merging enums from
            different systems might create conflicts.  By using
            a configurable uint32, the system can be configured
            to match the enum values in the management application.";
       }
       leaf probable-cause-string {
         type string;
         description
           "This string can be used to give a user-friendly string
            to the probable cause value.";
       }
     }

     grouping attribute {
       description
         "A grouping to match the ITU generic reference to
          an attribute.";
       leaf id {
         type al:resource;
         description
           "The resource representing the attribute.";
       }
       leaf value {
         type string;
         description
           "The value represented as a string since it could
            be of any type.";
       }
       reference
         "ITU-T Recommendation X.721: Information Technology
             - Open Systems Interconnection
             - Structure of management information:
               Definition of management information
          Module Attribute-ASN1Module";
     }

     /*
      * Add X.733 parameters to the alarm definitions, alarms,
      * and notification.
      */

     augment "/al:alarms/al:alarm-inventory/al:alarm-type" {

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       description
         "Augment X.733 mapping information to the alarm inventory.";
       uses x733-alarm-definition-parameters;
     }

     /*
      * Add X.733 configurable mapping.
      */

     augment "/al:alarms/al:control" {
       description
         "Add X.733 mapping capabilities. ";
       list x733-mapping {
         if-feature "configure-x733-mapping";
         key "alarm-type-id alarm-type-qualifier-match";
         description
           "This list allows a management application to control the
            X.733 mapping for all alarm types in the system.  Any entry
            in this list will allow the alarm manager to override the
            default X.733 mapping in the system, and the final mapping
            will be shown in the alarm inventory.";
         leaf alarm-type-id {
           type al:alarm-type-id;
           description
             "Map the alarm type with this alarm type identifier.";
         }
         leaf alarm-type-qualifier-match {
           type string;
           description
             "A W3C regular expression that is used when mapping an
              alarm type and alarm-type-qualifier to X.733 parameters.";
         }
         uses x733-alarm-definition-parameters;
       }
     }

     augment "/al:alarms/al:alarm-list/al:alarm" {
       description
         "Augment X.733 information to the alarm.";
       uses x733-alarm-parameters;
     }

     augment "/al:alarms/al:shelved-alarms/al:shelved-alarm" {
       description
         "Augment X.733 information to the alarm.";
       uses x733-alarm-parameters;
     }

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     augment "/al:alarm-notification" {
       description
         "Augment X.733 information to the alarm notification.";
       uses x733-alarm-parameters;
     }
   }
   <CODE ENDS>

8.  IANA Considerations

   This document registers two URIs in the "IETF XML Registry"
   [RFC3688].  Following the format in RFC 3688, the following
   registrations have been made.

       URI: urn:ietf:params:xml:ns:yang:ietf-alarms
       Registrant Contact: The IESG.
       XML: N/A; the requested URI is an XML namespace.

       URI: urn:ietf:params:xml:ns:yang:ietf-alarms-x733
       Registrant Contact: The IESG.
       XML: N/A; the requested URI is an XML namespace.

   This document registers two YANG modules in the "YANG Module Names"
   registry [RFC6020].

       name:        ietf-alarms
       namespace:   urn:ietf:params:xml:ns:yang:ietf-alarms
       prefix:      al
       reference:   RFC 8632

       name:        ietf-alarms-x733
       namespace:   urn:ietf:params:xml:ns:yang:ietf-alarms-x733
       prefix:      x733
       reference:   RFC 8632

9.  Security Considerations

   The YANG modules specified in this document define a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

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   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   The list of alarms itself may be potentially sensitive from a
   security perspective, in that it potentially gives an attacker an
   authoritative picture of the (broken) state of the network.

   There are a number of data nodes defined in the YANG modules that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   in the "ietf-alarms" module and their sensitivity/vulnerability:

   "/alarms/control/notify-status-changes":  This leaf controls whether
      an alarm should notify based on various state changes.
      Unauthorized access to this leaf could have a negative impact on
      operational procedures relying on fine-grained alarm-state change
      reporting.

   "/alarms/control/alarm-shelving/shelf":  This list controls the
      shelving (blocking) of alarms.  Unauthorized access to this list
      could jeopardize the alarm-management procedures, since these
      alarms will not be notified or be part of the alarm list.

   "/alarms/control/alarm-profile/alarm-severity-assignment-profile":
      This list controls the severity levels of an alarm.  Unauthorized
      access to this could, for example, downgrade the severity of an
      alarm and thereby have a negative impact on the alarm-monitoring
      process.

   Some of the RPC operations in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control access to these operations.  These are the
   operations and their sensitivity/vulnerability:

   "/alarms/alarm-list/purge-alarms":  This action deletes alarms from
      the alarm list.  Unauthorized use of this action could jeopardize
      the alarm-management procedures since the deleted alarms may be
      vital for the alarm-management application.

   "/alarms/alarm-list/alarm/set-operator-state":  This action can be
      used by the operator to indicate the level of human intervention
      on an alarm.  Unauthorized use of this action could result in
      alarms being ignored by operators.

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10.  References

10.1.  Normative References

   [M.3100]   International Telecommunication Union, "Generic network
              information model", ITU-T Recommendation M.3100, April
              2005, <https://www.itu.int/rec/T-REC-M.3100-200504-I/en>.

   [M.3160]   International Telecommunication Union, "Generic,
              protocol-neutral management information model",
              ITU-T Recommendation M.3100, November 2008,
              <https://www.itu.int/rec/T-REC-M.3160-200811-I>.

   [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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

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   [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>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8348]  Bierman, A., Bjorklund, M., Dong, J., and D. Romascanu, "A
              YANG Data Model for Hardware Management", RFC 8348,
              DOI 10.17487/RFC8348, March 2018,
              <https://www.rfc-editor.org/info/rfc8348>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [X.721]    International Telecommunication Union, "Information
              technology - Open Systems Interconnection - Structure of
              management information: Definition of management
              information", ITU-T Recommendation X.721, February 1992,
              <https://www.itu.int/rec/T-REC-X.721-199202-I/en>.

   [X.733]    International Telecommunication Union, "Information
              technology - Open Systems Interconnection - Systems
              Management: Alarm reporting function",
              ITU-T Recommendation X.733, February 1992,
              <https://www.itu.int/rec/T-REC-X.733-199202-I/en>.

   [XSD-TYPES]
              Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
              Second Edition", World Wide Web Consortium Recommendation
              REC-xmlschema-2-20041028, October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.

10.2.  Informative References

   [ALARMIRP] 3GPP, "Telecommunication management; Fault Management;
              Part 2: Alarm Integration Reference Point (IRP):
              Information Service (IS)", 3GPP TS 32.111-2, March 2005,
              <http://www.3gpp.org/ftp/Specs/html-info/32111-2.htm>.

   [ALARMSEM] Wallin, S., Leijon, V., Nordlander, J., and N. Bystedt,
              "The semantics of alarm definitions: enabling systematic
              reasoning about alarms", International Journal of Network
              Management, Volume 22, Issue 3, May 2012,
              <http://dx.doi.org/10.1002/nem.800>.

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   [EEMUA]    "Alarm systems: a guide to design, management and
              procurement", EEMUA Publication No. 191, Engineering
              Equipment and Materials Users Association, Second Edition,
              2007.

   [G.7710]   International Telecommunication Union, "SERIES G:
              TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND
              NETWORKS - Data over Transport - Generic aspects -
              Transport network control aspects; Common equipment
              management function requirements", ITU-T
              Recommendation G.7710/Y.1701, Amendment 1, November 2012.

   [ISA182]   International Society of Automation, "Management of Alarm
              Systems for the Process Industries", ANSI/ISA - 18.2-2016,
              March 2016.

   [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>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [X.736]    International Telecommunication Union, "Information
              technology - Open Systems Interconnection - Systems
              Management: Security alarm reporting function",
              ITU-T Recommendation X.736, January 1992,
              <https://www.itu.int/rec/T-REC-X.736-199201-I/en>.

   [YANG-INSTANCE]
              Lengyel, B. and B. Claise, "YANG Instance Data File
              Format", Work in Progress, draft-ietf-netmod-yang-
              instance-file-format-02, August 2019.

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Appendix A.  Vendor-Specific Alarm Types Example

   This example shows how to define alarm types in a vendor-specific
   module.  In this case, the vendor "xyz" has chosen to define top-
   level identities according to X.733 event types.

   module example-xyz-alarms {
     namespace "urn:example:xyz-alarms";
     prefix xyz-al;

     import ietf-alarms {
       prefix al;
     }

     identity xyz-alarms {
       base al:alarm-type-id;
     }

     identity communications-alarm {
       base xyz-alarms;
     }
     identity quality-of-service-alarm {
       base xyz-alarms;
     }
     identity processing-error-alarm {
       base xyz-alarms;
     }
     identity equipment-alarm {
       base xyz-alarms;
     }
     identity environmental-alarm {
       base xyz-alarms;
     }

     // communications alarms
     identity link-alarm {
       base communications-alarm;
     }

     // QoS alarms
     identity high-jitter-alarm {
       base quality-of-service-alarm;
     }
   }

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Appendix B.  Alarm Inventory Example

   This shows an alarm inventory: one alarm type is defined only with
   the identifier and another is dynamically configured.  In the latter
   case, a digital input has been connected to a smoke detector;
   therefore, the "alarm-type-qualifier" is set to "smoke-detector" and
   the "alarm-type-id" to "environmental-alarm".

   <alarms xmlns="urn:ietf:params:xml:ns:yang:ietf-alarms"
           xmlns:xyz-al="urn:example:xyz-alarms"
           xmlns:dev="urn:example:device">
     <alarm-inventory>
       <alarm-type>
         <alarm-type-id>xyz-al:link-alarm</alarm-type-id>
         <alarm-type-qualifier/>
         <resource>
           /dev:interfaces/dev:interface
         </resource>
         <will-clear>true</will-clear>
         <description>
           Link failure; operational state down but admin state up
         </description>
       </alarm-type>
       <alarm-type>
         <alarm-type-id>xyz-al:environmental-alarm</alarm-type-id>
         <alarm-type-qualifier>smoke-alarm</alarm-type-qualifier>
         <will-clear>true</will-clear>
         <description>
           Connected smoke detector to digital input
         </description>
       </alarm-type>
     </alarm-inventory>
   </alarms>

Appendix C.  Alarm List Example

   In this example, we show an alarm that has toggled [major, clear,
   major].  An operator has acknowledged the alarm.

   <alarms xmlns="urn:ietf:params:xml:ns:yang:ietf-alarms"
           xmlns:xyz-al="urn:example:xyz-alarms"
           xmlns:dev="urn:example:device">
     <alarm-list>
       <number-of-alarms>1</number-of-alarms>
       <last-changed>2018-04-08T08:39:50.00Z</last-changed>
       <alarm>

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         <resource>
           /dev:interfaces/dev:interface[name='FastEthernet1/0']
         </resource>
         <alarm-type-id>xyz-al:link-alarm</alarm-type-id>
         <alarm-type-qualifier></alarm-type-qualifier>
         <time-created>2018-04-08T08:20:10.00Z</time-created>
         <is-cleared>false</is-cleared>
         <alt-resource>1.3.6.1.2.1.2.2.1.1.17</alt-resource>
         <last-raised>2018-04-08T08:39:40.00Z</last-raised>
         <last-changed>2018-04-08T08:39:50.00Z</last-changed>
         <perceived-severity>major</perceived-severity>
         <alarm-text>
           Link operationally down but administratively up
         </alarm-text>
         <status-change>
           <time>2018-04-08T08:39:40.00Z</time>
           <perceived-severity>major</perceived-severity>
           <alarm-text>
             Link operationally down but administratively up
           </alarm-text>
         </status-change>
         <status-change>
           <time>2018-04-08T08:30:00.00Z</time>
           <perceived-severity>cleared</perceived-severity>
           <alarm-text>
             Link operationally up and administratively up
           </alarm-text>
         </status-change>
         <status-change>
           <time>2018-04-08T08:20:10.00Z</time>
           <perceived-severity>major</perceived-severity>
           <alarm-text>
             Link operationally down but administratively up
           </alarm-text>
         </status-change>
         <operator-state-change>
           <time>2018-04-08T08:39:50.00Z</time>
           <state>ack</state>
           <operator>joe</operator>
           <text>Will investigate, ticket TR764999</text>
         </operator-state-change>
       </alarm>
     </alarm-list>
   </alarms>

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Appendix D.  Alarm Shelving Example

   This example shows how to shelve alarms.  We shelve alarms related to
   the smoke detectors, since they are being installed and tested.  We
   also shelve all alarms from FastEthernet1/0.

   <alarms xmlns="urn:ietf:params:xml:ns:yang:ietf-alarms"
           xmlns:xyz-al="urn:example:xyz-alarms"
           xmlns:dev="urn:example:device">
     <control>
       <alarm-shelving>
         <shelf>
           <name>FE10</name>
           <resource>
             /dev:interfaces/dev:interface[name='FastEthernet1/0']
           </resource>
         </shelf>
         <shelf>
           <name>detectortest</name>
           <alarm-type>
             <alarm-type-id>
               xyz-al:environmental-alarm
             </alarm-type-id>
             <alarm-type-qualifier-match>
               smoke-alarm
             </alarm-type-qualifier-match>
           </alarm-type>
         </shelf>
       </alarm-shelving>
     </control>
   </alarms>

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Appendix E.  X.733 Mapping Example

   This example shows how to map a dynamic alarm type (alarm-type-
   id=environmental-alarm, alarm-type-qualifier=smoke-alarm) to the
   corresponding X.733 "event-type" and "probable-cause" parameters.

   <alarms xmlns="urn:ietf:params:xml:ns:yang:ietf-alarms"
           xmlns:xyz-al="urn:example:xyz-alarms">
     <control>
       <x733-mapping
          xmlns="urn:ietf:params:xml:ns:yang:ietf-alarms-x733">
         <alarm-type-id>xyz-al:environmental-alarm</alarm-type-id>
         <alarm-type-qualifier-match>
           smoke-alarm
         </alarm-type-qualifier-match>
         <event-type>quality-of-service-alarm</event-type>
         <probable-cause>777</probable-cause>
       </x733-mapping>
     </control>
   </alarms>

Appendix F.  Relationship to Other Alarm Standards

   This section briefly describes how this alarm data model relates to
   other relevant standards.

F.1.  Definition of "Alarm"

   The table below summarizes relevant definitions of the term "alarm"
   in other alarm standards.

   +------------+---------------------------+--------------------------+
   | Standard   | Definition                | Comment                  |
   +------------+---------------------------+--------------------------+
   | X.733      | error: A deviation of a   | The X.733 alarm          |
   | [X.733]    | system from normal        | definition is focused on |
   |            | operation.  fault: The    | the notification as such |
   |            | physical or algorithmic   | and not the state.       |
   |            | cause of a malfunction.   | X.733 defines an alarm   |
   |            | Faults manifest           | as a deviation from a    |
   |            | themselves as errors.     | normal condition but     |
   |            | alarm: A notification, of | without the requirement  |
   |            | the form defined by this  | that it needs corrective |
   |            | function, of a specific   | actions.                 |
   |            | event.  An alarm may or   |                          |
   |            | may not represent an      |                          |
   |            | error.                    |                          |
   |            |                           |                          |

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   | G.7710     | Alarms are indications    | The G.7710 definition is |
   | [G.7710]   | that are automatically    | close to the original    |
   |            | generated by a device as  | X.733 definition.        |
   |            | a result of the           |                          |
   |            | declaration of a failure. |                          |
   |            |                           |                          |
   | Alarm MIB  | Alarm: Persistent         | RFC 3877 defines the     |
   | [RFC3877]  | indication of a fault.    | term alarm as referring  |
   |            | Fault: Lasting error or   | back to "a deviation     |
   |            | warning condition.        | from normal operation".  |
   |            | Error: A deviation of a   | The Alarm YANG data      |
   |            | system from normal        | model adds the           |
   |            | operation.                | requirement that it      |
   |            |                           | should require a         |
   |            |                           | corrective action and    |
   |            |                           | should be undesired, not |
   |            |                           | only a deviation from    |
   |            |                           | normal.  The alarm MIB   |
   |            |                           | is state oriented in the |
   |            |                           | same way as the Alarm    |
   |            |                           | YANG module; it focuses  |
   |            |                           | on the  "lasting         |
   |            |                           | condition", not the      |
   |            |                           | individual               |
   |            |                           | notifications.           |
   |            |                           |                          |
   | ISA        | Alarm: An audible and/or  | The ISA standard adds an |
   | [ISA182]   | visible means of          | important requirement to |
   |            | indicating to the         | the "deviation from      |
   |            | operator an equipment     | normal condition state": |
   |            | malfunction, process      | requiring a response.    |
   |            | deviation, or abnormal    |                          |
   |            | condition requiring a     |                          |
   |            | response.                 |                          |
   |            |                           |                          |
   | EEMUA      | An alarm is an event to   | This is the foundation   |
   | [EEMUA]    | which an operator must    | for the definition of    |
   |            | knowingly react, respond, | alarm in this document.  |
   |            | and acknowledge -- not    | It focuses on the core   |
   |            | simply acknowledge and    | criterion that an action |
   |            | ignore.                   | is really needed.        |
   |            |                           |                          |

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   | 3GPP Alarm | 3GPP v15: An alarm        | The latest 3GPP Alarm    |
   | IRP        | signifies an undesired    | IRP version uses         |
   | [ALARMIRP] | condition of a resource   | literally the same alarm |
   |            | (e.g., device, link) for  | definition as this alarm |
   |            | which an operator action  | data model.  It is worth |
   |            | is required.  It          | noting that earlier      |
   |            | emphasizes a key          | versions used a          |
   |            | requirement that          | definition not requiring |
   |            | operators [...] should    | an operator action and   |
   |            | not be informed about an  | the more-broad           |
   |            | undesired condition       | definition of deviation  |
   |            | unless it requires        | from normal condition.   |
   |            | operator action.          | The earlier version also |
   |            | 3GPP v12: alarm: abnormal | defined an alarm as a    |
   |            | network entity condition, | special case of "event". |
   |            | which categorizes an      |                          |
   |            | event as a fault.         |                          |
   |            | fault: a deviation of a   |                          |
   |            | system from normal        |                          |
   |            | operation, which may      |                          |
   |            | result in the loss of     |                          |
   |            | operational capabilities  |                          |
   |            | [...]                     |                          |
   +------------+---------------------------+--------------------------+

           Table 1: Definition of the Term "Alarm" in Standards

   The evolution of the definition of alarm moves from focused on events
   reporting a deviation from normal operation towards a definition to a
   undesired *state* that *requires an operator action*.

F.2.  Data Model

   This section describes how this YANG alarm data model relates to
   other standard data models.  Note well that we cover other data
   models for alarm interfaces but not other standards such as SDO-
   specific alarms.

F.2.1.  X.733

   X.733 has acted as a base for several alarm data models over the
   years.  The YANG alarm data model differs in the following ways:

      X.733 models the alarm list as a list of notifications.  The YANG
      alarm data model defines the alarm list as the current alarm
      states for the resources, which is generated from the state change
      reporting notifications.

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      In X.733, an alarm can have the severity level "clear".  In the
      YANG alarm data model, "clear" is not a severity level; it is a
      separate state of the alarm.  An alarm can have the following
      states, for example, (major, cleared) and (minor, not cleared).

      X.733 uses a flat, globally defined enumerated "probable-cause" to
      identify alarm types.  This alarm data model uses a hierarchical
      YANG identity: "alarm-type".  This enables delegation of alarm
      types within organizations.  It also enables management to reason
      about abstract alarm types corresponding to base identities; see
      Section 3.2.

      The YANG alarm data model has not included the majority of the
      X.733 alarm attributes.  Rather, these are defined in an
      augmenting module [X.733] if "strict" X.733 compliance is needed.

F.2.2.  The Alarm MIB (RFC 3877)

   The MIB in RFC 3877 takes a different approach; rather than defining
   a concrete data model for alarms, it defines a model to map existing
   SNMP-managed objects and notifications into alarm states and alarm
   notifications.  This was necessary since MIBs were already defined
   with both managed objects and notifications indicating alarms, for
   example, "linkUp" and "linkDown" notifications in combination with
   "ifAdminState" and "ifOperState".  So, RFC 3877 cannot really be
   compared to the alarm YANG module in that sense.

   The Alarm MIB maps existing MIB definitions into alarms, such as
   "alarmModelTable".  The upside of that is that an SNMP Manager can,
   at runtime, read the possible alarm types.  This corresponds to the
   "alarmInventory" in the alarm YANG module.

F.2.3.  3GPP Alarm IRP

   The 3GPP Alarm IRP is an evolution of X.733.  Main differences
   between the alarm YANG module and 3GPP are as follows:

      3GPP keeps the majority of the X.733 attributes, but the alarm
      YANG module does not.

      3GPP introduced overlapping and possibly conflicting keys for
      alarms, alarmId, and (managed object, event type, probable cause,
      specific problem).  (See Example 3 in Annex C of [ALARMIRP]).  In
      the YANG alarm data model, the key for identifying an alarm
      instance is clearly defined by ("resource", "alarm-type-id",
      "alarm-type-qualifier").  See also Section 3.4 for more
      information.

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      The alarm YANG module clearly separates the resource/
      instrumentation lifecycle from the operator lifecycle. 3GPP allows
      operators to set the alarm severity to clear; this is not allowed
      by this module.  Rather, an operator closes an alarm, which does
      not affect the severity.

F.2.4.  G.7710

   G.7710 is different than the previously referenced alarm standards.
   It does not define a data model for alarm reporting.  It defines
   common equipment management function requirements including alarm
   instrumentation.  The scope is transport networks.

   The requirements in G.7710 correspond to features in the alarm YANG
   module in the following way:

      Alarm Severity Assignment Profile (ASAP): the alarm profile
      "/alarms/alarm-profile/".

      Alarm Reporting Control (ARC): alarm shelving "/alarms/control/
      alarm-shelving/" and the ability to control alarm notifications
      "/alarms/control/notify-status-changes".  Alarm shelving
      corresponds to the use case of turning off alarm reporting for a
      specific resource, which is the NALM (No ALarM) state in M.3100.

Appendix G.  Alarm-Usability Requirements

   This section defines usability requirements for alarms.  Alarm
   usability is important for an alarm interface.  A data model will
   help in defining the format, but if the actual alarms are of low
   value, we have not gained the goal of alarm management.

   Common alarm problems and their causes are summarized in Table 2.
   This summary is adopted to networking based on the ISA [ISA182] and
   Engineering Equipment Materials Users Association (EEMUA) [EEMUA]
   standards.

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   +-----------------+--------------------------------+----------------+
   | Problem         | Cause                          | How this       |
   |                 |                                | module         |
   |                 |                                | addresses the  |
   |                 |                                | cause          |
   +-----------------+--------------------------------+----------------+
   | Alarms are      | "Nuisance" alarms (chattering  | Strict         |
   | generated, but  | alarms and fleeting alarms),   | definition of  |
   | they are        | faulty hardware, redundant     | alarms         |
   | ignored by the  | alarms, cascading alarms,      | requiring      |
   | operator.       | incorrect alarm settings, and  | corrective     |
   |                 | alarms that have not been      | response.  See |
   |                 | rationalized; the alarms       | alarm          |
   |                 | represent log information      | requirements   |
   |                 | rather than true alarms.       | in Table 3.    |
   |                 |                                |                |
   | When alarms     | Insufficient alarm-response    | The alarm      |
   | occur,          | procedures and not well-       | inventory      |
   | operators do    | defined alarm types.           | lists all      |
   | not know how to |                                | alarm types    |
   | respond.        |                                | and corrective |
   |                 |                                | actions.  See  |
   |                 |                                | alarm          |
   |                 |                                | requirements   |
   |                 |                                | in Table 3.    |
   |                 |                                |                |
   | The alarm       | Nuisance alarms, stale alarms, | The alarm      |
   | display is full | and alarms from equipment not  | definition and |
   | of alarms, even | in service.                    | alarm          |
   | when there is   |                                | shelving.      |
   | nothing wrong.  |                                |                |
   |                 |                                |                |
   | During a        | Incorrect prioritization of    | State-based    |
   | failure,        | alarms.  Not using advanced    | alarm model    |
   | operators are   | alarm techniques (e.g., state- | and alarm-rate |
   | flooded with so | based alarming).               | requirements;  |
   | many alarms     |                                | see Tables 4   |
   | that they do    |                                | and 5,         |
   | not know which  |                                | respectively.  |
   | ones are the    |                                |                |
   | most important. |                                |                |
   +-----------------+--------------------------------+----------------+

                    Table 2: Alarm Problems and Causes

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   Based upon the above problems, EEMUA gives the following definition
   of a good alarm:

   +----------------+--------------------------------------------------+
   | Characteristic | Explanation                                      |
   +----------------+--------------------------------------------------+
   | Relevant       | Not spurious or of low operational value.        |
   |                |                                                  |
   | Unique         | Not duplicating another alarm.                   |
   |                |                                                  |
   | Timely         | Not long before any response is needed or too    |
   |                | late to do anything.                             |
   |                |                                                  |
   | Prioritized    | Indicating the importance that the operator      |
   |                | deals with the problem.                          |
   |                |                                                  |
   | Understandable | Having a message that is clear and easy to       |
   |                | understand.                                      |
   |                |                                                  |
   | Diagnostic     | Identifying the problem that has occurred.       |
   |                |                                                  |
   | Advisory       | Indicative of the action to be taken.            |
   |                |                                                  |
   | Focusing       | Drawing attention to the most important issues.  |
   +----------------+--------------------------------------------------+

                    Table 3: Definition of a Good Alarm

   Vendors SHOULD rationalize all alarms according to the table above.
   Another crucial requirement is acceptable alarm notification rates.
   Vendors SHOULD make sure that they do not exceed the recommendations
   from EEMUA below:

   +-----------------------------------+-------------------------------+
   | Long-Term Alarm Rate in Steady    | Acceptability                 |
   | Operation                         |                               |
   +-----------------------------------+-------------------------------+
   | More than one per minute          | Very likely to be             |
   |                                   | unacceptable.                 |
   |                                   |                               |
   | One per 2 minutes                 | Likely to be overdemanding.   |
   |                                   |                               |
   | One per 5 minutes                 | Manageable.                   |
   |                                   |                               |
   | Less than one per 10 minutes      | Very likely to be acceptable. |
   +-----------------------------------+-------------------------------+

              Table 4: Acceptable Alarm Rates -- Steady State

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   +----------------------------+--------------------------------------+
   | Number of alarms displayed | Acceptability                        |
   | in 10 minutes following a  |                                      |
   | major network problem      |                                      |
   +----------------------------+--------------------------------------+
   | More than 100              | Definitely excessive and very likely |
   |                            | to lead to the operator abandoning   |
   |                            | the use of the alarm system.         |
   |                            |                                      |
   | 20-100                     | Hard to cope with.                   |
   |                            |                                      |
   | Under 10                   | Should be manageable, but it may be  |
   |                            | difficult if several of the alarms   |
   |                            | require a complex operator response. |
   +----------------------------+--------------------------------------+

                 Table 5: Acceptable Alarm Rates -- Burst

   The numbers in Tables 4 and 5 are the sum of all alarms for a network
   being managed from one alarm console.  So every individual system or
   Network Management System (NMS) contributes to these numbers.

   Vendors SHOULD make sure that the following rules are used in
   designing the alarm interface:

   1.  Rationalize the alarms in the system to ensure that every alarm
       is necessary, has a purpose, and follows the cardinal rule that
       it requires an operator response.  Adheres to the rules of
       Table 3.

   2.  Audit the quality of the alarms.  Talk with the operators about
       how well the alarm information supports them.  Do they know what
       to do in the event of an alarm?  Are they able to quickly
       diagnose the problem and determine the corrective action?  Does
       the alarm text adhere to the requirements in Table 3?

   3.  Analyze and benchmark the performance of the system and compare
       it to the recommended metrics in Tables 4 and 5.  Start by
       identifying nuisance alarms, as well as standing alarms at normal
       state and startup.

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Acknowledgements

   The authors wish to thank Viktor Leijon and Johan Nordlander for
   their valuable input on forming the alarm model.

   The authors also wish to thank Nick Hancock, Joey Boyd, Tom Petch,
   and Balazs Lengyel for their extensive reviews and contributions to
   this document.

Authors' Addresses

   Stefan Vallin
   Stefan Vallin AB

   Email: stefan@wallan.se

   Martin Bjorklund
   Cisco

   Email: mbj@tail-f.com

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