draft-netana-nmop-network-anomaly-lifecycle-04.txt

NMOP                                                        V. Riccobene
Internet-Draft                                                A. Roberto
Intended status: Experimental                                     Huawei
Expires: 22 April 2025                                           T. Graf
                                                                   W. Du
                                                                Swisscom
                                                           A. Huang Feng
                                                               INSA-Lyon
                                                         19 October 2024


                 Experiment: Network Anomaly Lifecycle
             draft-netana-nmop-network-anomaly-lifecycle-04

Abstract

   Network Anomaly Detection is the act of detecting problems in the
   network.  Accurately detect problems is very challenging for network
   operators in production networks.  Good results require a lot of
   expertise and knowledge around both the implied network technologies
   and the connectivity services provided to customers, apart from a
   proper monitoring infrastructure.  In order to facilitate network
   anomaly detection, novel techniques are being introduced, including
   programmatical, rule-based and AI-based, with the promise of
   improving scalability and the hope to keep a high detection accuracy.
   To guarantee acceptable results, the process needs to be properly
   designed, adopting well-defined stages to accurately collect evidence
   of anomalies, validate their relevancy and improve the detection
   systems over time, iteratively.

   This document describes a well-defined approach on managing the
   lifecycle process of a network anomaly detection system, spanning
   across the recording of its output and its iterative refinement, in
   order to facilitate network engineers to interact with the network
   anomaly detection system, enable the "human-in-the-loop" paradigm and
   refine the detection abilities over time.  The major contributions of
   this document are: the definition of three key stages of the
   lifecycle process, the definition of a state machine for each anomaly
   annotation on the system and the definition of YANG data models
   describing a comprehensive format for the anomaly labels, allowing a
   well structured exchange of those between all the interested actors.

Status of This Memo

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





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Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Discussion Venues . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Status of this document . . . . . . . . . . . . . . . . . . .   3
   3.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Defining Desired States . . . . . . . . . . . . . . . . . . .   5
   6.  Lifecycle of a Network Anomaly  . . . . . . . . . . . . . . .   6
     6.1.  Network Anomaly Detection . . . . . . . . . . . . . . . .   7
     6.2.  Network Anomaly Validation  . . . . . . . . . . . . . . .   8
     6.3.  Network Anomaly Refinement  . . . . . . . . . . . . . . .   8
   7.  Network Anomaly State Machine . . . . . . . . . . . . . . . .   9
   8.  Network Anomaly Data Model  . . . . . . . . . . . . . . . . .  10
     8.1.  Overview of the Data Model for the Relevant State and all
           the related entities  . . . . . . . . . . . . . . . . . .  10
   9.  Implementation status . . . . . . . . . . . . . . . . . . . .  20
     9.1.  Antagonist  . . . . . . . . . . . . . . . . . . . . . . .  20
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  20
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   12. Normative References  . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22




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1.  Discussion Venues

   This note is to be removed before publishing as an RFC.

   Discussion of this document takes place on the Operations and
   Management Area Working Group Working Group mailing list
   (nmop@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/nmop/.

   Source for this draft and an issue tracker can be found at
   https://github.com/network-analytics/draft-netana-nmop-network-
   anomaly-lifecycle.

2.  Status of this document

   This document is experimental.  The main goal of this document is to
   propose an iterative lifecycle process to network anomaly detection
   by proposing a data model for metadata to be addressed at different
   lifecycle stages.

   The experiment consists of verifying whether the approach is usable
   in real use case scenarios to support proper refinement and
   adjustments of network anomaly detection algorithms.  The experiment
   can be deemed successful if validated at least with an open-source
   implementation sucessfully applied with real networks.

3.  Introduction

   In [I-D.ietf-nmop-terminology] A network anomaly is defined as "an
   unusual or unexpected event or pattern in network data in the
   forwarding plane, control plane, or management plane that deviates
   from the normal, expected behavior".

   A network problem is defined as "A state regarded as undesirable and
   may require remedial action" (see [I-D.ietf-nmop-terminology]).

   The main objective of a network anomaly detection system is to
   identify Relevant States of the network (defined as states that have
   relevancy for network operators, according to
   [I-D.ietf-nmop-terminology] ), as they could lead to problems or
   might be clear indications of problem already happening.

   That said, it is still remarkably difficult to gain a full
   understanding and a complete perspective of "if" and "how" a relevant
   state is actually an indication of a problem or it is just
   unexpected, but has no impact on end users.  Anomaly detection
   providers should aim at increasing accuracy, by minimizing false
   positives and false negatives.  Moreover, the behaviour of the



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   network naturally changes over time, when more connectivity services
   are deployed, more customers on-boarded, devices are upgraded or
   replaced, and therefore it is almost impossible to build an anomaly
   detection system that remains accurate over time.

   This opens up to the necessity of further validating notified
   relevant states to check if the detected Symptoms are actually
   impacting connectivity services: this might require different actors
   (both human and algorithmic) to act during the process and refine
   their understanding across the network anomaly lifecycle.

   Finally, once validation has happened, this might lead to refinements
   to the logic that is used by the detection, so that this process can
   improve the detection accuracy over time.

   Performing network anomaly detection is a process that requires a
   continuous learning and continuous improvement.  Relevant states are
   detected by aggregating and understanding Symptoms, then validated,
   confirming that Symptoms actually impacted connectivity services
   impacting and eventually need to be further analyzed by performing
   postmortem analysis to identify any potential adjustment to improve
   the detection capability.  Each of these steps represents an
   opportunity to learn and refine the process, and since
   implementations of these steps might also be provided by different
   parties and/or products, this document also contributes a formal data
   model to capture and exchange Symptom information across the
   lifecycle.

4.  Terminology

   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.

   This document makes use of the terms defined in
   [I-D.ietf-nmop-terminology].

   *  State

   *  Problem

   *  Event

   *  Alarm

   *  Symptom



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   The following terms are used as defined in [RFC9417].

   *  Metric

   *  Intent

   The following terms are defined in this document.

   *  Annotator: Is a human or an algorithm which produces metadata by
      describing anomalies with Symptoms.

   *  False Positive: Is a detected anomaly which has been identified
      during the postmortem to be not anomalous.

   *  False Negative: Is anomalous but has been not been identified by
      the anomaly detection system.

5.  Defining Desired States

   The above definitions of network problem provide the scope for what
   to be looking for when detecting network anomalies.  Concepts like
   "desirable state" and "required state" are introduced.  This poses
   the attention on a significant problem that network operators have to
   face: the definition of what is to be considered "desirable" or
   "undesirable".  It is not always easy to detect if a network is
   operating in an undesired state at a given point in time.  To
   approach this, network operators can rely on different methodologies,
   more or less deterministic and more or less sensitive: on the one
   side, the definition of intents (including Service Level Objectives
   and Service Level Agreements) which approaches the problem top-down;
   on the other side, the definition of Symptoms, by mean of solutions
   like SAIN [RFC9417], [RFC9418] and
   [I-D.netana-nmop-network-anomaly-architecture], which approaches the
   problem bottom-up.  At the center of these approaches, there are the
   so-called Symptoms, explaining what is not working as expected in the
   network, sometimes also providing hints towards issues and their
   causes.

   One of the more deterministic approaches is to rely on Symptoms based
   on measurable service-based KPIs, for example, by using Service Level
   Indicators, Objectives and Agreements:

   Service Level Agreement (SLA)  An SLA is an agreement between parties
      that a service provider makes to its customers on the behavior of
      the provided service.  SLAs are a tool to define exactly what
      customers can expect out of the service provided to them.  In many
      cases, SLA breaches also come with contractual penalties.




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   Service Level Objectives (SLOs)  An SLO is a threshold above which
      the service provider acts to prevent a breach of an SLA.  SLOs are
      a tool for service providers to know when they should start
      becoming concerned about a service not behaving as expected.  SLOs
      are rarely connected to penalties as they usually are internal
      metrics for the service providers.

   Service Level Indicators (SLIs)  An SLI is an observable metric that
      describes the state of a monitored subsystem.  SLIs are a tool to
      gain measurable visibility about the behavior of a subsystem in
      the network.  SLIs usually differ from SLOs as SLOs are usually
      expressed as thresholds, while SLIs would often be expressed e.g.
      as percentages.

   However, the definition of these KPIs turns out to be very
   challenging in some cases, as accurate KPIs could require
   computationally expensive techniques to be collected or substantial
   modifications to existing network protocols.

   Alternative methodologies rely on Symptoms as the way to generate
   analytical data out of operational data.  For instance:

   SAIN  introduces the definition and exposure of Symptoms as a
      mechanism for detecting those concerning behaviors in more
      deterministic ways.  Moreover, the concept of "impact score" has
      been introduced by SAIN, to indicate what is the expected degree
      of impact that a given Symptom will have on the services relying
      on the related subservice to which the Symptom is attached.

   Daisy  introduces the concept of concern score to indicate what is
      the degree of concern that a given Symptom could cause a
      degradation for a connectivity service.

   In general, defining boundaries between desirable vs. undesirable in
   an accurate fashion requires continuous iterations and improvements
   coming from all the stages of the network anomaly detection
   lifecycle, by which network engineers can transfer what they learn
   through the process into new Symptom definitions and, ultimately,
   into refinements of the detection algorithms.

6.  Lifecycle of a Network Anomaly

   The lifecycle of a network anomaly can be articulated in three
   phases, structured as a loop: Detection, Validation, Refinement.







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                               +-------------+
                    +--------> |  Detection  | ---------+
        Adjustments |          +-------------+          | Symptoms
                    |                                   |
                    |                                   v
            +------------+                       +------------+
            | Refinement |<--------------------- | Validation |
            +------------+        Problem        +------------+
                                Confirmation


              Figure 1: Anomaly Detection Refinement Lifecycle

   Each of these phases can either be performed by a network expert or
   an algorithm or complementing each other.

   The network anomaly metadata is generated by an annotator, which can
   be either a human expert or an algorithm.  The annotator can produce
   the metadata for a network anomaly, for each stage of the cycle and
   even multiple versions for the same stage.  In each version of the
   network anomaly metadata, the annotator indicates the list of
   Symptoms that are part of the network anomaly taken into account.
   The iterative process is about the identification of the right set of
   Symptoms.

6.1.  Network Anomaly Detection

   The Network Anomaly Detection stage is about the continuous
   monitoring of the network through Network Telemetry [RFC9232] and the
   identification of Symptoms.  One of the main requirements that
   operator have on network anomaly detection systems is the high
   accuracy.  This means having a small number of false negatives,
   Symptoms causing connectivity service impact are not missed, and
   false positives, Symptoms that are actually innocuous are not picked
   up.

   As the detection stage is becoming more and more automated for
   production networks, the identified Symptoms might point towards
   three potential kinds of behaviors:

   i. those that are surely corresponding to an impact on connectivity
   services, (e.g. the breach of an SLO),

   ii. those that will cause problems in the future (e.g. rising trends
   on a timeseries metric hitting towards saturation),






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   iii. those or which the impact to connectivuty services cannot be
   confirmed (e.g. sudden increase/decrease of timeseries metrics,
   anomalous amounts of log entries, etc.).

   The first category requires immediate intervention (a.k.a. the
   problem is "confirmed"), the second one provides pointers towards
   early signs of an problem potentially happening in the near future
   (a.k.a. the problem is "forecasted"), and the third one requires some
   analysis to confirm if the detected Symptom requires any attention or
   immediate intervention (a.k.a. the problem is "potential").  As part
   of the iterative improvement required in this stage, one that is very
   relevant is the gradual conversion of the third category into one of
   the first two, which would make the network anomaly detection system
   more deterministic.  The main objective is to reduce uncertainty
   around the raised alarms by refining the detection algorithms.  This
   can be achieved by either generating new Symptom definitions,
   adjusting the weights of automated algorithms or other similar
   approaches.

6.2.  Network Anomaly Validation

   The key objective for the validation stage is clearly to decide if
   the detected Symptoms are signaling a real problem (a.k.a. requires
   action) or if they are to be treated as false positives (a.k.a.
   suppressing the alarm).  For those Symptoms surely having impact on
   connectivity services, 100% confidence on the fact that a network
   problem is happening can be assumed.  For the other two categories,
   "forecasted" and "potential", further analysis and validation is
   required.

6.3.  Network Anomaly Refinement

   After validation of a problem, the service provider performs
   troubleshooting and resolution of the problem.  Although the network
   might be back in a desired state at this point, network operators can
   perform detailed postmortem analysis of network problems with the
   objective to identify useful adjustments to the prevention and
   detection mechanisms (for instance improving or extending the
   definition of SLIs and SLOs, refining concern/impact scores, etc.),
   and improving the accuracy of the validation stage (e.g. automating
   parts of the validation, implementing automated root cause analysis
   and automation for remediation actions).  In this stage of the
   lifecycle it is assumed that the problem is under analysis.

   After the adjustments are performed to the network anomaly detection
   methods, the cycle starts again, by "replaying" the network anomaly
   and checking if there is any measurable improvement in the ability to
   detect problems by using the updated method.



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7.  Network Anomaly State Machine

   In the context of this document, from a network anomaly detection
   point of view a network problem is defined as a collection of
   interrelated Symptoms, as specified in
   [I-D.netana-nmop-network-anomaly-semantics].

   The understanding of a network problem can change over time.
   Moreover, multiple actors are involved in the process of refining
   this understanding in the different phases.

   From this perspective, a problem can be refined according to the
   following states (Figure 2).






































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                                             +---------+
                                             | Initial |-----------------+
                                             +---------+                 |
                                                  |                      |
                                            +-----+---------+            |
                                   +--------|---------------|------+     |
                                   | +------v-----+  +------v----+ |     |
                                   | |  Problem   |  |  Problem  | |     |
                             +---->| | Forecasted |  | Potential | |     |
                             |     | +------------+  +-----------+ |     |
                             |     +--------|--Detection---|-------+     |
                             |              |              |             |
        +-------+            |              +------- ----- +             |
        | Final |            |                      |                    |
        +---^---+            |                      |                    |
            |                |                      |                    |
            |                |                      v                    |
            |                |     +-----------Validation------------+   |
+-----------------------+    |     |  +-----------+                  |   |
|           |           |    |     |  |  Problem  |   |  Problem  |  |   |
|  +-----------------+  |    |     |  | Discarded |   | Confirmed |<-|---+
|  |    Detection    |  |    |     |  +-----|-----+   +-----------+  |
|  |     Adjusted    |-------+     +---------------------------------+
|  +--------^--------+  |                   |               |
|           |           |                   |               |
|           |           |               +---v---+           |
|           |           |               | Final |           |
|           |           |               +-------+           |
| +---------|--------+  |                                   |
| |     Problem      |  |                                   |
| |     Analyzed     |<-|-----------------------------------+
| +------------------+  |
+-------Refinement------+


               Figure 2: Network Anomaly State Machine

   The knowledge gained at each stage is codified as a list of anomaly
   labels that can be stored on a Label Store ( see Section 9.1 for a
   reference).

8.  Network Anomaly Data Model

   In this section, the proposed data model is described.

8.1.  Overview of the Data Model for the Relevant State and all the
      related entities




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            module: ietf-relevant-state
            +--rw relevant-state
              +--rw id                          yang:uuid
              +--rw description?                string
              +--rw start-time                  yang:date-and-time
              +--rw end-time?                   yang:date-and-time
              +--rw anomalies* [id version]
                  +--rw id                              yang:uuid
                  +--rw version                 yang:counter32
                  +--rw state                   identityref
                  +--rw description?              string
                  +--rw start-time                yang:date-and-time
                  +--rw end-time?                 yang:date-and-time
                  +--rw confidence-score          score
                  +--rw (pattern)?
                  |  +--:(drop)
                  |  |  +--rw drop?               empty
                  |  +--:(spike)
                  |  |  +--rw spike?              empty
                  |  +--:(mean-shift)
                  |  |  +--rw mean-shift?         empty
                  |  +--:(seasonality-shift)
                  |  |  +--rw seasonality-shift?        empty
                  |  +--:(trend)
                  |  |  +--rw trend?              empty
                  |  +--:(other)
                  |     +--rw other?              string
                  +--rw annotator!
                  |  +--rw name                 string
                  |  +--rw (annotator-type)?
                  |     +--:(human)
                  |     |  +--rw human?         empty
                  |     +--:(algorithm)
                  |        +--rw algorithm?     empty
                  +--rw symptom!
                  |  +--rw id                     yang:uuid
                  |  +--rw concern-score          score
                  +--rw service!
                    +--rw id                    yang:uuid

            notifications:
              +---n relevant-state-notification
                +--ro id                        yang:uuid
                +--ro description?              string
                +--ro start-time                yang:date-and-time
                +--ro end-time?                 yang:date-and-time
                +--ro anomalies* [id version]
                    +--ro id                    yang:uuid



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                    +--ro version                 yang:counter32
                    +--ro state                   identityref
                    +--ro description?            string
                    +--ro start-time              yang:date-and-time
                    +--ro end-time?               yang:date-and-time
                    +--ro confidence-score        score
                    +--ro (pattern)?
                    |  +--:(drop)
                    |  |  +--ro drop?                   empty
                    |  +--:(spike)
                    |  |  +--ro spike?                  empty
                    |  +--:(mean-shift)
                    |  |  +--ro mean-shift?                     empty
                    |  +--:(seasonality-shift)
                    |  |  +--ro seasonality-shift?      empty
                    |  +--:(trend)
                    |  |  +--ro trend?                  empty
                    |  +--:(other)
                    |     +--ro other?                  string
                    +--ro annotator!
                    |  +--ro name                               string
                    |  +--ro (annotator-type)?
                    |     +--:(human)
                    |     |  +--ro human?                       empty
                    |     +--:(algorithm)
                    |        +--ro algorithm?                   empty
                    +--ro symptom!
                    |  +--ro id                                 yang:uuid
                    |  +--ro concern-score                      score
                    +--ro service!
                      +--ro id                                   yang:uuid


         Figure 3: YANG tree diagram for ietf-relevant-state

   <CODE BEGINS> file "ietf-relevant-state@2024-10-18.yang"
     module ietf-relevant-state {
       yang-version 1.1;
       namespace "urn:ietf:params:xml:ns:yang:ietf-relevant-state";
       prefix rsn;

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

       organization
         "IETF NMOP Working Group";



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       contact
         "WG Web:   <https://datatracker.ietf.org/wg/nmop/>
         WG List:  <mailto:nmop@ietf.org>

         Authors:  Vincenzo Riccobene
                   <mailto:vincenzo.riccobene@huawei-partners.com>
                   Antonio Roberto
                   <mailto:antonio.roberto@huawei.com>
                   Thomas Graf
                   <mailto:thomas.graf@swisscom.com>
                   Wanting Du
                   <mailto:wanting.du@swisscom.com>
                   Alex Huang Feng
                   <mailto:alex.huang-feng@insa-lyon.fr>";
       description
           "This module defines the relevant-state container and
               notifications to be used by a network anomaly detection
               system. The defined objects can be used to augment
               operational network collected observability data and
           analytical problem data equally. Describing the relevant-state
                   of observed symptoms.

           Copyright (c) 2024 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 Revised 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 XXXX; see the RFC
           itself for full legal notices.";

       revision 2024-10-18 {
         description
           "Initial version";
         reference
           "RFCXXXX: Experiment: Network Anomaly Postmortem Lifecycle";
       }

       typedef score {
           type uint8 {
               range "0 .. 100";
           }
       }
       identity network-anomaly-state {



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         description
           "Base identity for representing the state of the network anomaly";
       }
       identity network-anomaly-detection {
         base network-anomaly-state;
         description
         "A problem reached detection state";
       }
       identity network-anomaly-validation {
         base network-anomaly-state;
         description
         "A problem reached validation state";
       }
       identity network-anomaly-refinement {
         base network-anomaly-state;
         description
         "A problem reached refinement state";
       }
         identity problem-forecasted {
         base network-anomaly-detection;
         description
         "A problem has been forecasted, as it is expected that
         the indicated list of symptoms will impact a
             connectivity service in the near future";
       }
       identity problem-potential {
         base network-anomaly-detection;
         description
         "A problem has been detected with a confidence
         lower than 100%. In order to confirm that this set of
         symptoms are generating connectivity service impact, it
             requires further validation";
       }
       identity problem-confirmed {
         base network-anomaly-validation;
         description
         "After validation, the problem has been confirmed";
       }
       identity discarded {
         base network-anomaly-validation;
         description
         "After validation, the network anomaly has been
         discarded, as there is no evindence that it is causing an
         problem";
       }
       identity analyzed {
         base network-anomaly-refinement;
         description



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         "The anomaly detection went through analysis to identify
         potential ways to further improve the detection process in
         for future anomalies";
       }
       identity adjusted {
         base network-anomaly-refinement;
         description
         "The network anomaly has been solved and analysed.
         No further action is required.";
       }

       grouping relevant-state-grouping {
           leaf id {
               mandatory true;
               type yang:uuid;
               description
                   "Unique ID of the fault";
           }
           leaf description {
               type string;
               description
                   "Textual description of the fault";
           }
           leaf start-time {
               type yang:date-and-time;
               mandatory true;
               description
                   "Date and time indicating the beginning of the fault";
           }
           leaf end-time {
               type yang:date-and-time;
               description
                   "Date and time indicating the end of the fault";
           }
       }

       grouping annotator-grouping {
           leaf name {
               mandatory true;
               type string;
           }
           choice annotator-type {
               case human {
                   leaf human {
                       type empty;
                   }
               }
               case algorithm {



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                   leaf algorithm {
                       type empty;
                   }
               }
           }
       }

       grouping symptom-grouping {
           leaf id {
               type yang:uuid;
               mandatory true;
               description
                   "Unique ID of the symptom type";
           }
           leaf concern-score {
               type score;
               mandatory true;
           }
       }

       grouping service-grouping {
           leaf id {
               type yang:uuid;
               mandatory true;
               description
                   "Unique ID of the connectivity service (or monitored entity)";
           }
       }

       grouping anomaly-grouping {
           list anomalies {
               key "id version";
               leaf id {
                   type yang:uuid;
                   description
                       "Unique ID of the anomaly";
               }
               leaf version {
                   type yang:counter32;
                   description
                           "Version of the problem metadata object.
                           It allows multiple versions of the metadata to be
                           generated in order to support the definition of
                           multiple problem objects from the same source to
                           facilitate improvements overtime";
               }
               leaf state {
                   type identityref {



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                       base network-anomaly-state;
                   }
                   mandatory true;
                   description "State of the anomaly.";
               }
               leaf description {
                   type string;
                   description
                       "Textual description of the anomaly";
               }
               leaf start-time {
                   type yang:date-and-time;
                   mandatory true;
                   description
                       "Date and time indicating the beginning of the anomaly";
               }
               leaf end-time {
                   type yang:date-and-time;
                   description
                       "Date and time indicating the end of the anomaly";
               }
               leaf confidence-score {
                   type score;
                   mandatory true;
               }
               choice pattern {
                   description
                       "Network Plane affected by the symptom";
                   case drop {
                       leaf drop {
                           type empty;
                       }
                   }
                   case spike {
                       leaf spike {
                           type empty;
                       }
                   }
                   case mean-shift {
                       leaf mean-shift {
                           type empty;
                       }
                   }
                   case seasonality-shift {
                       leaf seasonality-shift {
                           type empty;
                       }
                   }



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                   case trend {
                       leaf trend {
                           type empty;
                       }
                   }
                   case other {
                       leaf other {
                           type string;
                           description "specify the type";
                       }
                   }
               }
               container annotator {
                   presence "It specifies an annotator for the anomaly";
                   uses annotator-grouping;
               }
               container symptom {
                   presence "It specifies the symptom for the anomaly";
                   uses symptom-grouping;
               }
               container service {
                   presence "It specifies the connectivity service (or the monitored entity) affected by the anomaly";
                   uses service-grouping;
               }
           }
       }

       notification relevant-state-notification {
           uses relevant-state-grouping;
           uses anomaly-grouping;
       }

       container relevant-state {
           uses relevant-state-grouping;
           uses anomaly-grouping;
       }
     }
   <CODE ENDS>

               Figure 4: YANG module for ietf-relevant-state

   The model has been defined based on a list of requirements, defined
   in the following.  The data model:

      must be semantically consistent from a networking point of view;

      must be both human and machine readable;




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      must allow different detection, validation and refinement
      solutions to interoperate;

      must provide support the "human-in-the-loop" paradigm, allowing
      for network experts to validate and adjust network anomaly labels
      and detection systems.

   The base for the modules is the relevant-state data model.  Relevant
   state is at the root of the data model, with its parameters (ID,
   description, start-time, end-time) and a collection of anomalies.
   This allows the relevant state to be considered as a container of
   anomalies.

   Each anomaly is characterized by some intrinsic fields (such as id,
   version, state, description, start-time, end-time, confidence score
   and pattern) Particularly the confidence score is a measure of how
   confident was the detector in considering the given anomaly as an
   anomalous behaviour.

   Each anomaly also include the symptom and the service container.
   These containers are placeholders to represent the information about
   the symptom (what is exaclty happening as anomalous behaviour) and
   the connectivity service (what entity is affected by the anomaly).
   In particular, for what concerns the symptom, a concern score is
   defined, which has the meaning of expressing how much the anomaly is
   impacting connectivity services.  Based on the intentions of the
   authors of this data model, the correct use of the symptom and
   service containers is to augment the model by providing a more
   accurate implementation of both of them.  An example of this is
   provided in [I-D.netana-nmop-network-anomaly-semantics], where an
   augmentation of Symptom for connectivity services is proposed.

   Also a list of various actors that can be involved in the process is
   presented as following:

   In the detection stage:  the detectors can be Network Engineers and/
      or Automatic detectors (including Rule-based detectors and ML-
      based detectors)

   In the validation stage:  the validators can be Network Engineers
      manually validating the labels

   In the refinement stage:  the refiners can be Data Scientists and/or
      Automatic Refiners (including systems that automatically refine
      the detection systems, based on the validated labels).






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   The data model that has been defined is used in two YANG modules: the
   relevant-state-notification and the ietf-relevant-state: the
   notification is primarily used by the Network Anomaly Detector, to
   notify the "Alarm and Problem Management System" and the "Post-mortem
   System" (see [I-D.netana-nmop-network-anomaly-architecture]); the
   container instead is used inside the Post-mortem system to exhance
   anomaly detection lables between the anomaly detection stages defined
   above (valdation, refinement, detection).

9.  Implementation status

   This section provides pointers to existing open source
   implementations of this draft.  Note to the RFC-editor: Please remove
   this before publishing.

9.1.  Antagonist

   An open source implementation for this draft is called AnTagOnIst
   (Anomaly Tagging On hIstorical data), and it has been implemented in
   order to validate the application of the YANG model defined in this
   draft.  Antagonist provides visual support for two important use
   cases in the scope of this document:

   *  the generation of a ground truth in relation to symptoms and
      problems in timeseries data

   *  the visual validation of results produced by automated network
      anomaly detection tools.

   The open source code can be found here: [Antagonist]

   As part of the experiment that was conducted with AnTagOnIst, Some
   main Use Case scenarios have been validated so far:

      Exposure of a GUI for human validation of the labels.

      Integration with Rule Based anomaly detection systems.  In
      particular the integration with SAIN and Cosmos Bright Lights is
      on going.

      Integration with ML-based detection systems.

10.  Security Considerations

   The security considerations will have to be updated according to
   "https://wiki.ietf.org/group/ops/yang-security-guidelines".





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11.  Acknowledgements

   The authors would like to thank xxx for their review and valuable
   comments.

12.  Normative References

   [Antagonist]
              Riccobene, V., Roberto, A., Du, W., Graf, T., and H. Huang
              Feng, "Antagonist: Anomaly tagging on historical data",
              <https://github.com/vriccobene/antagonist>.

   [I-D.ietf-nmop-terminology]
              Davis, N., Farrel, A., Graf, T., Wu, Q., and C. Yu, "Some
              Key Terms for Network Fault and Problem Management", Work
              in Progress, Internet-Draft, draft-ietf-nmop-terminology-
              06, 17 October 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
              terminology-06>.

   [I-D.netana-nmop-network-anomaly-architecture]
              Graf, T., Du, W., and P. Francois, "An Architecture for a
              Network Anomaly Detection Framework", Work in Progress,
              Internet-Draft, draft-netana-nmop-network-anomaly-
              architecture-00, 8 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-netana-nmop-
              network-anomaly-architecture-00>.

   [I-D.netana-nmop-network-anomaly-semantics]
              Graf, T., Du, W., Feng, A. H., Riccobene, V., and A.
              Roberto, "Semantic Metadata Annotation for Network Anomaly
              Detection", Work in Progress, Internet-Draft, draft-
              netana-nmop-network-anomaly-semantics-02, 8 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-netana-nmop-
              network-anomaly-semantics-02>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [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>.



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

   [RFC9417]  Claise, B., Quilbeuf, J., Lopez, D., Voyer, D., and T.
              Arumugam, "Service Assurance for Intent-Based Networking
              Architecture", RFC 9417, DOI 10.17487/RFC9417, July 2023,
              <https://www.rfc-editor.org/info/rfc9417>.

   [RFC9418]  Claise, B., Quilbeuf, J., Lucente, P., Fasano, P., and T.
              Arumugam, "A YANG Data Model for Service Assurance",
              RFC 9418, DOI 10.17487/RFC9418, July 2023,
              <https://www.rfc-editor.org/info/rfc9418>.

Authors' Addresses

   Vincenzo Riccobene
   Huawei
   Dublin
   Ireland
   Email: vincenzo.riccobene@huawei-partners.com


   Antonio Roberto
   Huawei
   Dublin
   Ireland
   Email: antonio.roberto@huawei.com


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


   Wanting Du
   Swisscom
   Binzring 17
   CH-8045 Zurich
   Switzerland
   Email: wanting.du@swisscom.com






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   Alex Huang Feng
   INSA-Lyon
   Lyon
   France
   Email: alex.huang-feng@insa-lyon.fr














































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