



NETCONF Working Group                                              Q. Wu
Internet-Draft                                                    Huawei
Intended status: Experimental                                     P. Liu
Expires: 15 March 2026                                      China Mobile
                                                                   Q. Ma
                                                                  Huawei
                                                                 W. Wang
                                                           China Telecom
                                                                  Z. Niu
                                                               Microsoft
                                                       11 September 2025


               Adaptive Subscription to YANG Notification
              draft-ietf-netconf-adaptive-subscription-11

Abstract

   This document defines a YANG data model and associated mechanism to
   enable adaptive subscriptions to YANG notifications.  The publisher
   can dynamically adjust the periodic update interval based on the
   evaluation of pre-configured conditions (e.g., thresholds or
   expressions).  This allows for finer-grained telemetry by increasing
   update frequency when certain criteria are met, and reducing it
   otherwise.

Editorial Note (To be removed by RFC Editor)

   Note to the RFC Editor: This section is to be removed prior to
   publication.  Please also remove Section 6.

   This document contains placeholder values that need to be replaced
   with finalized values at the time of publication.  This note
   summarizes all of the substitutions that are needed.  No other RFC
   Editor instructions are specified elsewhere in this document.

   Please apply the following replacements:

   *  XXXX --> the assigned RFC number for this document

   *  2025-05-21 --> the actual date of the publication of this document

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) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Provisions Relating to IETF Documents (https://trustee.ietf.org/
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Experimental Considerations . . . . . . . . . . . . . . .   5
   2.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Adaptive Subscription Parameters  . . . . . . . . . . . .   5
     2.2.  RPC Failures  . . . . . . . . . . . . . . . . . . . . . .   7
     2.3.  Subscription State Change Notifications . . . . . . . . .   8
     2.4.  Notifications for Adaptive Subscribed Content . . . . . .   9
   3.  Adaptive Subscription Data Model  . . . . . . . . . . . . . .  10
     3.1.  YANG Tree Diagram . . . . . . . . . . . . . . . . . . . .  10
     3.2.  The "ietf-adaptive-subscription" Module . . . . . . . . .  12
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
     4.1.  Updates to the IETF XML Registry for New YANG Module  . .  20
     4.2.  Updates to the YANG Module Names Registry for New YANG
           Module  . . . . . . . . . . . . . . . . . . . . . . . . .  20
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .  21
     5.1.  XPath Complexity Evaluation . . . . . . . . . . . . . . .  21
     5.2.  Threshold Selection for XPath Evaluation  . . . . . . . .  22
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  22
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  24



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   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  25
   9.  Acknowledges  . . . . . . . . . . . . . . . . . . . . . . . .  25
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     10.2.  Informative References . . . . . . . . . . . . . . . . .  27
   Appendix A.  Use Cases  . . . . . . . . . . . . . . . . . . . . .  28
     A.1.  Wireless Network Performance Monitoring . . . . . . . . .  28
     A.2.  Reducing Impact on High CPU Utilization . . . . . . . . .  28
   Appendix B.  Example YANG Module  . . . . . . . . . . . . . . . .  29
     B.1.  "example-wifi-network-diagnostic" YANG Module . . . . . .  29
   Appendix C.  Adaptive Subscription and Notification Example . . .  34
     C.1.  Configured Subscription Example . . . . . . . . . . . . .  34
     C.2.  Dynamic Subscription Example  . . . . . . . . . . . . . .  35
     C.3.  "xpath-evaluation-unsupported" error response example . .  36
     C.4.  "adaptive-period-update" notification example . . . . . .  37
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  38

1.  Introduction

   YANG-Push subscriptions [RFC8641] allow subscriber applications to
   request a continuous customized stream of updates from a YANG
   datastore without needing to poll.  It defines a mechanism (i.e.,
   update trigger) to determine when an update record needs to be
   generated.  Two types of subscription are introduced in [RFC8641],
   distinguished by how updates are triggered: periodic and on-change.

   *  Periodic subscription allows subscribed data to be streamed to the
      destination at a configured fixed time interval;

   *  On-change subscription allows update to be triggered whenever a
      change in the subscribed information is detected.

   However, in some deployments involving an increased data collection
   rate or "on-change" subscription to push updates that change
   frequently, it becomes more likely that both clients and servers
   could be temporarily overwhelmed with a burst of streamed data, and
   network and computation resources could be excessively consumed.
   Therefore, it may be expensive to continuously monitor operational
   data at a high collection rate, and on-change subscriptions are only
   suitable for data that changes infrequently and may not be supported
   by all implementations or every data object.  Conversely, if a stream
   of data is collected at a lower rate or some low priority data is
   allowed to be dropped, insufficient data might not be able to detect
   and diagnose service problems.

   A client might choose to monitor the operational state and send a
   request to modify the data collection rate on the server as needed.
   But how often the client evaluates if the modification of the data



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   collection rate is required highly depends on the current collection
   rate, collecting a stream of data at a low rate prevents the
   subscriber from capturing sufficient data for timely decision-making.
   In addition, when tens of thousands of network devices need to be
   managed, frequent follow-up modification requests are prone to
   errors.

   This document defines a YANG data model and associated mechanism that
   enable adaptive subscription to YANG notifications.  Servers can be
   configured with multiple different period intervals and corresponding
   period update conditions which allow servers/publishers to
   automatically switch to different period intervals according to the
   network condition changes without the interaction with the client for
   policy update instructions.  Applying adaptive subscription allows
   publishers to adjust the subscription period dynamically based on
   pre-defined threshold for finer-grained network telemetry data sent
   to receivers.

1.1.  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.

   The following terms are defined in [RFC5277], [RFC7950], [RFC8342],
   [RFC8639], [RFC8641] and are not redefined here:

   *  Event

   *  Client

   *  Configuration

   *  Configured subscription

   *  Configuration datastore

   *  Notification message

   *  Publisher

   *  Receiver

   *  Subscriber

   *  Subscription



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   *  On-change subscription

   *  Periodic subscription

   *  Selection filter

   This document defines the following term:

   Adaptive Subscription:  A subscription that specifies subscription
      period update policy on the servers when the subscription is
      initialized and allows servers/publishers to automatically switch
      to different period intervals according to network condition
      changes without interacting with the client for update policy
      instructions.

1.2.  Experimental Considerations

   The YANG data model and associated mechanism detailed in this
   document are designated as experimental.  The experiment aims to
   explore the use of XPath condition expressions as defined in "eval-
   expression" parameter to determine the period interval with which to
   report updates.  Some RPC failures specified in Section 2.2 may serve
   as safeguards against the experiment inadvertently "leaking out" into
   the unexpected operational environment.  Additional implementations
   would be necessary in the future to assess the scalability,
   stability, and effectiveness of the proposed solution in the
   document.  Feedback garnered from deployments will be crucial in
   determining whether this specification merits progression from
   Experimental to the IETF Standards Track.

2.  Solution Overview

2.1.  Adaptive Subscription Parameters

   Adaptive subscription can be implemented using either dynamic or
   configured subscription.  Regardless of the type of adaptive
   subscription, triggered updates always occur at the boundaries of
   specified time intervals when the corresponding trigger condition is
   evaluated to be satisfied.  These boundaries can be calculated from
   the following parameters:

   *  "name": represents the unique name of each adaptive period.

   *  "eval-expression": represents a standard XPath evaluation
      expression (Section 6.4 of [RFC7950]) that is applied against the
      targeted data node, which is used to trigger/control the update
      interval switching within the server.  It follows the rules
      defined in Section 3.4 of [XPATH1.0] and contains a comparison of



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      a targeted node instance to the specific threshold in the XPath
      format.  Different from selection filter defined in [RFC8641], it
      monitors a specific data node instance change and evaluates the
      trigger condition associated with the specified threshold value to
      be true or false using XPath rules and does not affect the event/
      update record output generation from a publisher.  The updates are
      only pushed as the corresponding period interval when the XPath
      expression is evaluated to "true".

      The represented expression defined in "eval-expression" is
      evaluated in the following XPath context:

      -  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 the leaf is encoded in XML, all namespace declarations in
         scope on the "eval-expression" 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.

      -  The set of variable bindings is empty.

      -  The function library is the core function library defined in
         [XPATH1.0] and the function defined in Section 10 of [RFC7950].

      -  The context node is the root node in the accessible tree which
         is the operational state data in the server.

      When specified, multiple XPath evaluation criteria inside
      "adaptive-periodic" container MUST be mutually exclusive.  For the
      cases where the "eval-expression" parameter refers to multiple
      list/leaf-list instances, XPath abbreviated syntax can be used to
      identify a particular instance, e.g., to represent a comparison
      for a leaf in a list entry:

        /if:interfaces/if:interface[if:name="eth0"]/if:in-errors>1000.

      The server MUST convert the XPath evaluation expression defined in
      "eval-expression" to a boolean value and internally apply the
      "boolean" function defined in Section 4.3 in [XPATH1.0] if the
      evaluated result is not a boolean value.  It MUST evaluates to
      "false" if the target node instance to be compared is deleted.
      Only if the XPath expression is evaluated to "true", does the
      publisher switch to the corresponding period with which push
      updates are reported.



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   *  "eval-interval": defines how often the XPath condition expression
      as defined in "eval-expression" is evaluated to decide whether to
      switch to another period interval.  If an "eval-interval" is not
      provided, then the "eval-interval" is set with the minimum time
      interval that the server is able to detect wherever changes to the
      targeted data node occur.

   *  "period": defines the duration between push updates, in units of
      0.01 seconds.  The "period" has the same definition as the
      yp:period for periodic subscription defined in [RFC8641], while it
      must be present with the "eval-expression" parameter so that
      update interval can be switched based on trigger conditions
      indicated by the "eval-expression" parameter;

   *  "anchor-time": update intervals fall on the points in time that
      are a multiple of a "period" from an "anchor-time".  If an
      "anchor-time" is not provided, then the "anchor-time" MUST be set
      with the creation time of the initial update record inside each
      periodic timeframe.  The "anchor-time" parameter, together with
      the "eval-interval" value, specifies when the initial update is to
      be pushed within each adaptive periodic timeframe.

   Note that the adaptive subscription may not be supported by every
   YANG datastore node.  The solution presented in this document
   augments the "ietf-notification-capabilities" YANG module defined in
   [RFC9196] to enable a subscriber to discover adaptive subscription
   capabilities.  A publisher MAY decide to simply reject an adaptive
   subscription with "adaptive-unsupported" (defined in Section 2.2) if
   the subscription contains selected data nodes for which adaptive
   subscription is not supported.

2.2.  RPC Failures

   RPC error responses from the publisher are used to indicate a
   rejection of an RPC for any reason.  In addition to the RPC failures
   defined in [RFC8639] and [RFC8641], this document introduces
   following RPC errors for "establish-subscription" and "modify-
   subscription" RPCs.













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   establish-subscription
   -----------------------------
   adaptive-unsupported
   xpath-evaluation-unsupported
   evaluation-interval-unsupported
   multi-xpath-criteria-conflict

   modify-subscription
   -----------------------------
   xpath-evaluation-unsupported
   evaluation-interval-unsupported
   multi-xpath-criteria-conflict

   The "adaptive-unsupported" RPC error is used to indicate that the
   adaptive subscription is not supported for the targeted set of data
   nodes that are selected by the filter.

   The "xpath-evaluation-unsupported" RPC error is used to indicate that
   a server failed to parse syntax defined in "eval-expression".  The
   failure can be caused by either a syntax error or some XPath 1.0
   syntax not supported against the specific data node.

   The "evaluation-interval-unsupported" RPC error is used to indicate
   that the requested XPath evaluation interval represented by "eval-
   interval" is too short.  Hints suggesting alternative intervals may
   be returned as supplemental information.

   The "multi-xpath-criteria-conflict" error is used to indicate that
   the multiple XPath evaluation criteria represented by "eval-
   expression" are evaluated as conflicting, i.e., more than one
   condition expressions may be evaluated to "true" at the same time.

   For an example of how the above RPC errors can be returned, see the
   "xpath-evaluation-unsupported" error response illustrated in
   Appendix C.3.

   Note that existing RPC errors defined in [RFC8639] and [RFC8641] are
   still supported by this document.  For example, if any configured
   period for adaptive subscription is not supported by the publisher, a
   "period-unsupported" error response could be used.

2.3.  Subscription State Change Notifications

   This document reuses subscription state change notifications and
   mechanisms from [RFC8639] and [RFC8641].  Notifications
   "subscription-started" and "subscription-modified" have been
   augmented to include the adaptive subscription specific parameters.




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2.4.  Notifications for Adaptive Subscribed Content

   This document also defines a new subscription state change
   notification called "adaptive-period-update", to indicate that an
   adaptive subscription period interval has been switched based on its
   trigger condition.  Similar to subscription state change
   notifications defined in [RFC8639], the adaptive period update
   notification cannot be dropped or filtered out, it cannot be stored
   in replay buffers, and it is delivered only to impacted receivers of
   a subscription.  The identification of the adaptive update
   notification is easy to separate from other notification messages
   using the YANG extension "subscription-state-notification" defined in
   [RFC8639].  This extension tags a notification as a subscription
   state change notification.

   The elements in the "adaptive-period-update" notification include:

   *  A subscription ID of the subscription for which the update record
      was generated.

   *  A "period" that defines the duration between push updates, the
      period can be changed based on trigger conditions.

   *  A "period-update-time" that designates a timestamp when the server
      starts to switch to another period interval because the evaluated
      "eval-expression" result changed.

   *  A chunk of data defined as an anydata node [RFC7950] called
      "satisfied-criteria-data" to include the instance nodes and values
      specified in "eval-expression" that satisfy the condition and thus
      trigger the period interval switching within the server.  This
      node could be useful for troubleshooting.

   *  A selection filter to identify YANG nodes of interest in a
      datastore.  Filter contents are specified via a reference to an
      existing filter or via an in-line definition for only that
      subscription based on XPath Section 6.4 of [RFC7950] evaluation
      criteria.  Referenced filters allow an implementation to avoid
      evaluating filter acceptability during a dynamic subscription
      request.  The "case" statement differentiates the options.  Note
      that filter contents are not affected by the "eval-expression"
      parameter defined by the update trigger.









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3.  Adaptive Subscription Data Model

   This document defines a YANG data model named "ietf-adaptive-
   subscription" which augments the "update-trigger" choice defined in
   the "ietf-yang-push" module [RFC8641] with subscription configuration
   parameters that are specific to a subscriber's adaptive subscription.

   In addition to subscription state notifications defined in [RFC8639]
   and notifications for subscribed content defined in [RFC8641], "ietf-
   adaptive-subscription" module also defines "adaptive-period-update"
   notification to report the update interval change.

   Additionally, it augments the "ietf-notification-capabilities" data
   model defined in [RFC9196] so that the adaptive subscription
   capabilities could be discovered beforehand.

   The YANG module specified in this document is compliant with Network
   Management Datastore Architecture (NMDA) [RFC8342].

3.1.  YANG Tree Diagram

   The following tree diagrams [RFC8340] provide an overview of the data
   model for "ietf-adaptive-subscription" module.

   module: ietf-adaptive-subscription
     augment /sn:subscriptions/sn:subscription/yp:update-trigger:
       +--:(adaptive-periodic) {adaptive-subscription}?
          +--rw adaptive-periodic
             +--rw periodic* [name]
                +--rw name               string
                +--rw eval-expression    yang:xpath1.0
                +--rw eval-interval?     yp:centiseconds
                +--rw period             yp:centiseconds
                +--rw anchor-time?       yang:date-and-time
     augment /sn:establish-subscription/sn:input/yp:update-trigger:
       +--:(adaptive-periodic) {adaptive-subscription}?
          +-- adaptive-periodic
             +-- periodic* [name]
                +-- name               string
                +-- eval-expression    yang:xpath1.0
                +-- eval-interval?     yp:centiseconds
                +-- period             yp:centiseconds
                +-- anchor-time?       yang:date-and-time
     augment /sn:modify-subscription/sn:input/yp:update-trigger:
       +--:(adaptive-periodic) {adaptive-subscription}?
          +-- adaptive-periodic
             +-- periodic* [name]
                +-- name               string



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                +-- eval-expression    yang:xpath1.0
                +-- eval-interval?     yp:centiseconds
                +-- period             yp:centiseconds
                +-- anchor-time?       yang:date-and-time
     augment /sn:subscription-started/yp:update-trigger:
       +--:(adaptive-periodic) {adaptive-subscription}?
          +-- adaptive-periodic
             +-- periodic* [name]
                +-- name               string
                +-- eval-expression    yang:xpath1.0
                +-- eval-interval?     yp:centiseconds
                +-- period             yp:centiseconds
                +-- anchor-time?       yang:date-and-time
     augment /sn:subscription-modified/yp:update-trigger:
       +--:(adaptive-periodic) {adaptive-subscription}?
          +-- adaptive-periodic
             +-- periodic* [name]
                +-- name               string
                +-- eval-expression    yang:xpath1.0
                +-- eval-interval?     yp:centiseconds
                +-- period             yp:centiseconds
                +-- anchor-time?       yang:date-and-time
     augment /sysc:system-capabilities/notc:subscription-capabilities:
       +--ro adaptive-notifications-supported?   notification-support
     augment /sysc:system-capabilities/sysc:datastore-capabilities
               /sysc:per-node-capabilities
               /notc:subscription-capabilities:
       +--ro adaptive-notifications-supported?   notification-support

     notifications:
       +---n adaptive-period-update {adaptive-subscription}?
          +--ro id?
          |       sn:subscription-id
          +--ro period                                  yp:centiseconds
          +--ro period-update-time?
          |       yang:date-and-time
          +--ro satisfied-criteria-data?                <anydata>
          +--ro datastore                               identityref
          +--ro (selection-filter)?
             +--:(by-reference)
             |  +--ro selection-filter-ref
             |          selection-filter-ref
             +--:(within-subscription)
                +--ro (filter-spec)?
                   +--:(datastore-subtree-filter)
                   |  +--ro datastore-subtree-filter?   <anydata>
                   |          {sn:subtree}?
                   +--:(datastore-xpath-filter)



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                      +--ro datastore-xpath-filter?     yang:xpath1.0
                              {sn:xpath}?

3.2.  The "ietf-adaptive-subscription" Module

   This YANG module imports modules from [RFC6991],[RFC8639], [RFC8641],
   and [RFC9196].

   <CODE BEGINS> file "ietf-adaptive-subscription@2025-05-21.yang"
   module ietf-adaptive-subscription {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription";
     prefix as;

     import ietf-subscribed-notifications {
       prefix sn;
       reference
         "RFC 8639: Subscription to YANG Notifications";
     }
     import ietf-yang-push {
       prefix yp;
       reference
         "RFC 8641: Subscription to YANG Notifications for Datastore
          Updates";
     }
     import ietf-yang-types {
       prefix yang;
       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-system-capabilities {
       prefix sysc;
       reference
         "RFC 9196: YANG Modules Describing Capabilities for
          Systems and Datastore Update Notifications";
     }
     import ietf-notification-capabilities {
       prefix notc;
       reference
         "RFC 9196: YANG Modules Describing Capabilities for
          Systems and Datastore Update Notifications";
     }

     organization
       "IETF NETCONF (Network Configuration) Working Group";
     contact
       "WG Web:   <http://tools.ietf.org/wg/netconf>
        WG List:  <netconf@ietf.org>



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        Author: Qin Wu
              <mailto:bill.wu@huawei.com>
        Author: Peng Liu
              <mailto: liupengyjy@chinamobile.com>
        Author: Qiufang Ma
              <mailto: maqiufang1@huawei.com>
        Author: Wei Wang
             <mailto: wangw36@chinatelecom.cn>
        Author: Zhixiong Niu
             <mailto: Zhixiong.Niu@microsoft.com>";
     description
       "This module extends the YANG data module defined in
        YANG-push to enable the subscriber's adaptive
        subscriptions to a publisher's event streams with various
        different period intervals to report updates.

        Copyright (c) 2025 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
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC
        itself for full legal notices.

        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.";

     revision 2025-05-21 {
       description
         "Initial revision";
       reference
         "RFC XXXX: Adaptive Subscription to YANG Notification.";
     }

     feature adaptive-subscription {
       description
         "This feature indicates that adaptive-subscriptions are
          supported.";



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     }

     identity adaptive-unsupported {
       base sn:establish-subscription-error;
       description
         "Adaptive-subscription is not supported for the targeted set
          of objects that are selectable by the filter.";
     }

     identity xpath-evaluation-unsupported {
       base sn:establish-subscription-error;
       base sn:modify-subscription-error;
       description
         "Unable to parse the XPath evaluation criteria defined in
          'eval-expression' because of a syntax error or some XPath
          1.0 syntax not supported against the specific data node.";
     }

     identity evaluation-interval-unsupported {
       base sn:establish-subscription-error;
       base sn:modify-subscription-error;
       description
         "The requested XPath evaluation interval represented by
          'eval-interval' is too short. Hints suggesting alternative
          intervals may be returned as supplemental information.";
     }

     identity multi-xpath-criteria-conflict {
       base sn:establish-subscription-error;
       base sn:modify-subscription-error;
       description
         "Multiple XPath evaluation criteria represented by
          'eval-expression' are evaluated as a conflict. I.e.,
          more than one condition expression is evaluated to
          'true'.";
     }

     grouping adaptive-subscription-modifiable {
       description
         "This grouping describes the datastore-specific adaptive
          subscription conditions that can be changed during the
          lifetime of the subscription.";
       container adaptive-periodic {
         description
           "The publisher is requested to periodically notify the
            receiver regarding the current values of the datastore
            as defined by the selection filter. The publisher supports
            to switch to different period intervals adaptively based



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            on pre-defined condition expressions.";
         list periodic {
           key "name";
           description
             "A list of adaptive period which defines a push update
              interval and trigger conditions to switch to the update
              interval for sending an event record to the subscriber.";
           leaf name {
             type string {
               length "1..64";
             }
             description
               "The unique name of adaptive period.";
           }
           leaf eval-expression {
             type yang:xpath1.0;
             mandatory true;
             description
               "A standard XPath evaluation expression that is applied
                against the targeted data node, which is used to
                trigger/control the update interval switching within
                the server. The updates are only pushed as the
                corresponding period interval when the XPath expression
                is evaluated to 'true'.

                The expression is evaluated in the following XPath
                context:
                -  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 the leaf is encoded in XML, all namespace
                   declarations in scope on the 'eval-expression' 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.

                -  The set of variable bindings is empty.

                -  The function library is the core function library
                   defined in XPath1.0 and the functions defined in
                   Section 10 in RFC 7950.

                -  The context node is the root node in the accessible
                   tree which is the operational state data in the



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                   server.";
             reference
               "XML Path Language (XPath) Version 1.0
                (https://www.w3.org/TR/1999/REC-xpath-19991116)
                RFC 7950: The YANG 1.1 Data Modeling Language,
                          Section 10";
           }
           leaf eval-interval {
             type yp:centiseconds;
             description
               "How often the Xpath condition expression is evaluated
                to decide whether to switch to another period
                interval.";
           }
           leaf period {
             type yp:centiseconds;
             mandatory true;
             description
               "Duration of time that should occur between periodic
                push updates, in units of 0.01 seconds.";
           }
           leaf anchor-time {
             type yang:date-and-time;
             description
               "Designates a timestamp before or after which a series
                of periodic push updates is determined.  The next
                update will take place at a point in time that is a
                multiple of a period from the 'anchor-time'.
                For example, for an 'anchor-time' that is set for the
                top of a particular minute and a period interval of a
                minute, updates will be sent at the top of every
                minute that this subscription is active.";
           }
         }
       }
     }

     augment "/sn:subscriptions/sn:subscription/yp:update-trigger" {
       description
         "This augmentation adds additional subscription parameters
          that apply specifically to adaptive subscription.";
       case adaptive-periodic {
         if-feature "adaptive-subscription";
         description
           "The publisher is requested to periodically notify the
            receiver regarding the current values of the datastore
            as defined by the selection filter. The periodicity of
            these notifications are determined by adaptive criteria.";



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         uses adaptive-subscription-modifiable;
       }
     }

     augment "/sn:establish-subscription/sn:input/yp:update-trigger" {
       description
         "This augmentation adds additional establish-subscription
          parameters that apply specifically to datastore updates to
          RPC input.";
       case adaptive-periodic {
         if-feature "adaptive-subscription";
         description
           "The publisher is requested to periodically notify the
            receiver regarding the current values of the datastore
            as defined by the selection filter. The periodicity of
            these notifications are determined by adaptive criteria.";
         uses adaptive-subscription-modifiable;
       }
     }

     augment "/sn:modify-subscription/sn:input/yp:update-trigger" {
       description
         "This augmentation adds additional modify-subscription
          parameters that apply specifically to datastore updates to
          RPC input.";
       case adaptive-periodic {
         if-feature "adaptive-subscription";
         description
           "The publisher is requested to periodically notify the
            receiver regarding the current values of the datastore
            as defined by the selection filter. The periodicity of
            these notifications are determined by adaptive criteria.";
         uses adaptive-subscription-modifiable;
       }
     }

     augment "/sn:subscription-started/yp:update-trigger" {
       description
         "This augmentation adds additional adaptive subscription
          parameters to the notification that a subscription has
          started.";
       case adaptive-periodic {
         if-feature "adaptive-subscription";
         description
           "The publisher is requested to periodically notify the
            receiver regarding the current values of the datastore
            as defined by the selection filter. The periodicity of
            these notifications are determined by adaptive criteria.";



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         uses adaptive-subscription-modifiable;
       }
     }

     augment "/sn:subscription-modified/yp:update-trigger" {
       description
         "This augmentation adds additional adaptive subscription
          parameters to the notification that a subscription has been
          modified.";
       case adaptive-periodic {
         if-feature "adaptive-subscription";
         description
           "The publisher is requested to periodically notify the
            receiver regarding the current values of the datastore
            as defined by the selection filter. The periodicity of
            these notifications are determined by adaptive criteria.";
         uses adaptive-subscription-modifiable;
       }
     }

     notification adaptive-period-update {
       if-feature "adaptive-subscription";
       sn:subscription-state-notification;
       description
         "This notification is sent to indicate that an adaptive
          subscription period interval has been switched based its
          triggered condition.";
       leaf id {
         type sn:subscription-id;
         description
           "This references the subscription that drove the
            notification to be sent.";
       }
       leaf period {
         type yp:centiseconds;
         mandatory true;
         description
           "New duration of time that should occur between periodic
            push updates, in units of 0.01 seconds.";
       }
       leaf period-update-time {
         type yang:date-and-time;
         description
           "Designates a timestamp when the server starts to switch
            to another period interval because the evaluated
            'eval-expression' expression result changed.";
       }
       anydata satisfied-criteria-data {



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         description
           "The corresponding instance nodes and values specified in
            'eval-expression' that satisfy the condition and thus
            trigger the update interval switching within the server.";
       }
       uses yp:datastore-criteria {
         refine "selection-filter/within-subscription" {
           description
             "Specifies the selection filter and where it originated
              from.  If the 'selection-filter-ref' is populated, the
              filter in the subscription came from the 'filters'
              container.  Otherwise, it is populated in-line as part
              of the subscription itself.";
         }
       }
     }

     grouping adaptive-subscription-capabilities {
       description
         "Capabilities related to adaptive subscription and
          notification.";
       typedef notification-support {
         type bits {
           bit config-changes {
             description
               "The publisher is capable of sending
                notifications for 'config true' nodes for the
                relevant scope and subscription type.";
           }
           bit state-changes {
             description
               "The publisher is capable of sending
                notifications for 'config false' nodes for the
                relevant scope and subscription type.";
           }
         }
         description
           "Type for defining whether 'on-change' or
            'periodic' notifications are supported for all data nodes,
            'config false' data nodes, 'config true' data nodes, or
            no data nodes.

            The bits config-changes or state-changes have no effect
            when they are set for a datastore or for a set of nodes
            that does not contain nodes with the indicated config
            value.  In those cases, the effect is the same as if no
            support was declared.  One example of this is indicating
            support for state-changes for a candidate datastore that



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            has no effect.";
       }

       leaf adaptive-notifications-supported {
         type notification-support;
         description
           "Specifies whether the publisher is capable of sending
            'adaptive' notifications for the selected data nodes,
            including any subtrees that may exist below them.";
       }
     }

     augment "/sysc:system-capabilities"
           + "/notc:subscription-capabilities" {
       description
         "Add system level capabilities of adaptive subscription.";
       uses adaptive-subscription-capabilities;
     }

     augment
       "/sysc:system-capabilities/sysc:datastore-capabilities/"
     + "sysc:per-node-capabilities/notc:subscription-capabilities" {
       description
         "Add node-level capabilities of adaptive subscription.";
       uses adaptive-subscription-capabilities;
     }
   }
   <CODE ENDS>

4.  IANA Considerations

4.1.  Updates to the IETF XML Registry for New YANG Module

   IANA is requested to register the following URI in the "ns" registry
   within the "IETF XML Registry" group [RFC3688].

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

4.2.  Updates to the YANG Module Names Registry for New YANG Module

   IANA is requested to register the following YANG module in the "YANG
   Module Names" registry [RFC6020] within the "YANG Parameters"
   registry group.




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   ---------------------------------------------------------------------
      Name:       ietf-adaptive-subscription
      Maintained by IANA? N
      Namespace:  urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription
      Prefix:     as
      Reference:  RFC XXXX
   ---------------------------------------------------------------------

5.  Operational Considerations

5.1.  XPath Complexity Evaluation

   YANG-Push subscriptions [RFC8641] specify selection filters to
   identify targeted YANG datastore nodes and/or datastore subtrees for
   which updates are to be pushed.  In addition, it specifies update
   policies which contain conditions that trigger generation and pushing
   of new update records.  To support a subscriber's adaptive
   subscription defined in this document, the trigger condition also
   uses similar selection filters to express a standard XPath evaluation
   criterion that is applied against the targeted data node(s).

   The subscriber must take care about the following complex XPath
   evaluation criteria design and usage, although they have already been
   well supported by the Section 3.4 of [XPATH1.0]:

   *  Apply XPath evaluation criteria on any arbitrary "config true" and
      "config false" data nodes;

   *  Have more than one target data node selection and operation (e.g.,
      addition, subtraction, division and multiplication) in a single
      XPath evaluation criterion;

   *  Target any type of node value in the XPath evaluation criterion,
      e.g., string, int64, uint64, and decimal64 types;

   *  Both objects in the XPath evaluation criterion to be compared are
      node-sets;

   *  Targeted data to be compared are in different data types, e.g.,
      one is an integer, the other is a string.

   As described in Section 6.4 of [RFC7950], Numbers in XPath 1.0 are
   IEEE 754 [IEEE754-2008] double-precision floating-point values; some
   values of int64, uint64, and decimal64 types cannot be exactly
   represented in XPath expressions.






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   If targeted data to be compared are in different data types, a
   conversion function is needed to convert different data types into
   numbers.

   If both objects in XPath evaluation criteria to be compared are node-
   sets, more computation resources are required which add complexity.

   To reduce these complexities, the following implementation and use
   principles are RECOMMENDED:

   *  XPath evaluation criteria are applied against a minimal set of
      data nodes in the data model, the minimal set of data nodes can be
      advertised using "ietf-notification-capabilities" module defined
      in [RFC9196];

   *  Both targets in the XPath evaluation criterion to be compared are
      in the same data type;

   *  One target to be compared in the XPath evaluation criterion is a
      leaf/leaf-list data node with numerical data type (e.g., signed/
      unsigned integer) and the other is a numerical threshold value.

   If a server receives an XPath evaluation criterion with some XPath
   syntax unsupported against the specific targeted data node, an RPC
   error with "xpath-evaluation-unsupported" MUST be returned.

5.2.  Threshold Selection for XPath Evaluation

   Determining the threshold used in an XPath expression criterion can
   be challenging for subscribers sometimes.  Generally, the selection
   of a threshold should be based on the impact of the targeted node on
   monitored service/application and experience from deployments.  In
   extreme cases, setting a too high or low threshold may make adaptive
   subscription degenerated to periodic subscription.  Sometimes the
   threshold needs to be adjusted during the lifecycle of an adaptive
   subscription, depending on factors like historical fluctuation range,
   how rapid the targeted value of the node changes, distribution
   characteristics of the targeted node value and even the generated
   volume of telemetry traffic.

6.  Implementation Status

   Note to the RFC Editor: Please remove this section before
   publication, as well as the reference to [RFC7942].

   This section records the status of known implementations of the
   mechanism defined by this specification at the time of posting of
   this Internet-Draft, and is based on a proposal described in



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   [RFC7942].  The description of implementations in this section is
   intended to assist the IETF in its decision processes in progressing
   drafts to RFCs.  Please note that the listing of any individual
   implementation here does not imply endorsement by the IETF.
   Furthermore, no effort has been spent to verify the information
   presented here that was supplied by IETF contributors.  This is not
   intended as, and must not be construed to be, a catalog of available
   implementations or their features.  Readers are advised to note that
   other implementations may exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   There is at least one known implementation, the details of which are
   as follows.

   *  Organization: Huawei Technologies Co.,Ltd.

   *  Implementation: https://github.com/IETF-Hackathon/ietf113-project-
      presentations/blob/main/ietf-hackathon-adaptive-subscription.pdf

   *  Description: gRPC-based adaptive telemetry to collect data from
      Access Points (APs) in a campus network.

   *  Level of maturity: prototype.

   *  Coverage: The "ietf-adaptive-subscription" module with the
      evaluation criteria supporting a comparison of a limited set of
      targeted node instances to the threshold in the XPath format.

   *  Contact: maqiufang1@huawei.com

   *  Test Scenario: The radio signals of an AP can cover only a limited
      area, Wi-Fi roaming is what happens when a wireless client
      disconnects from one AP because it receives weak signals (i.e.,
      the Received Signal Strength Indicator (RSSI) lower than the
      threshold) and connects to another as the client moves from the
      coverage area of an AP to that of another AP.  One objective of
      telemetry in this scenario is to collect the RSSI values of a
      specific client as it moves and detect real-time Wi-Fi roaming
      events.  We also collect the bytes sent from the AP uplink (which
      is also identified as "upbytes") so as to detect the possible
      uplink congestion.  Three data collection ways are evaluated:




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      -  Periodic subscriptions with periods of 2 seconds for RSSI
         collection and 1 minute for upbytes collection.

      -  Periodic subscriptions with periods of 30 seconds for RSSI
         collection and 10 minutes for upbytes collection.

      -  Adaptive subscriptions:

         o  For the RSSI collection, if the RSSI value is greater than
            or equal to -65 dB, switch to 30 seconds for publication;
            otherwise, switch to 2 seconds for publication; threshold
            detection occurs every 2 seconds.

         o  For the upbytes collection, if the upbytes value is greater
            than or equal to 60000 bytes, switch to 1 minute for
            publication; otherwise, switch to 10 minutes for
            publication; threshold detection occurs every minute.

   *  Implementation experience: The results show adaptive telemetry can
      greatly reduce the data volume but still ensure network events can
      be captured at the same time.  When the specific value does not
      reach the threshold, a lower frequency data publication can
      greatly reduce the amount of collected data; when it does exceed
      the threshold, the device detects the change and switches to a
      higher frequency data publication so that sufficient data will not
      be missed to diagnose network events.  Adaptive subscription can
      be served as a compromise between data management resource cost
      and data fidelity for network diagnosis.  However, the selection
      of threshold is crucial to adaptive subscription and should be
      based on operational experience and adjusted as needed.

7.  Security Considerations

   This section is modeled after the template described in Section 3.7
   of [I-D.ietf-netmod-rfc8407bis].

   The "ietf-adaptive-subscription" YANG module defines a data model
   that is designed to be accessed via YANG-based management protocols,
   such as NETCONF [RFC6241] and RESTCONF [RFC8040].  These YANG-based
   management protocols (1) have to use a secure transport layer (e.g.,
   SSH [RFC4252], TLS [RFC8446], and QUIC [RFC9000]) and (2) have to use
   mutual authentication.

   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.




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   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., "config true", which is the
   default).  All writable data nodes are likely to be reasonably
   sensitive or vulnerable in some network environments.  Write
   operations (e.g., edit-config) and delete operations to these nodes
   without proper protection or authentication can have a negative
   effect on network operations.  The following subtrees and data nodes
   have particular sensitivities/vulnerabilities:

   *  "periodic": By modifying this list, an attacker might alter the
      updates that are being sent in order to confuse a receiver,
      withhold certain updates to be sent to the receiver, and/or
      overwhelm a receiver.  For example, an attacker might modify the
      period with which updates are reported and/or the XPath evaluation
      expression, resulting in certain updates not being published or a
      high volume of updates being published to exhaust receiver
      resources.

   This YANG module uses groupings from other YANG modules that define
   nodes that may be considered sensitive or vulnerable in network
   environments.  Refer to the Security Considerations of [RFC8641] for
   information as to which nodes may be considered sensitive or
   vulnerable in network environments.

8.  Contributors

      Wei Song
      Email: songwei80@huawei.com

      Michael Wang
      Email: wangzitao@huawei.com

9.  Acknowledges

   We would like to thank Rob Wilton, Thomas Graf, Andy Bierman, Michael
   Richardson, Henk Birkholz, Chong Feng, Adrian Farrel, Joe Clarke, and
   Dhruv Dhody for valuable review on this document, special thanks to
   Thomas and Michael for organizing the discussion on several relevant
   drafts and reach the common understanding on the concept and ideas.
   Thanks Michael for providing CHIP/Matter WI-FI statistics reference.

10.  References

10.1.  Normative References







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   [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>.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
              <https://www.rfc-editor.org/info/rfc5277>.

   [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>.

   [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>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

   [RFC9196]  Lengyel, B., Clemm, A., and B. Claise, "YANG Modules
              Describing Capabilities for Systems and Datastore Update
              Notifications", RFC 9196, DOI 10.17487/RFC9196, February
              2022, <https://www.rfc-editor.org/info/rfc9196>.



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10.2.  Informative References

   [CHIP]     CSA, "Connected Home over IP Specification", April 2021,
              <https://csa-iot.org/all-solutions/matter>.

   [I-D.ietf-netmod-rfc8407bis]
              Bierman, A., Boucadair, M., and Q. Wu, "Guidelines for
              Authors and Reviewers of Documents Containing YANG Data
              Models", Work in Progress, Internet-Draft, draft-ietf-
              netmod-rfc8407bis-28, 5 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              rfc8407bis-28>.

   [IEEE754-2008]
              IEEE, "IEEE Standard for Floating-Point Arithmetic",  DOI
              10.1109/IEEESTD.2008.4610935, 2008,
              <http://standards.ieee.org/findstds/
              standard/754-2008.html>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

   [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>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [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>.

   [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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   [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>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

   [XPATH1.0] W3C, "https://www.w3.org/TR/1999/REC-xpath-19991116/", 11
              November 1999.

Appendix A.  Use Cases

A.1.  Wireless Network Performance Monitoring

   Wireless signal strength is a critical factor in determining the
   quality and reliability of a wireless network connection.  In
   practical scenarios, when the wireless signal strength drops below a
   specific threshold, the network may experience issues such as
   increased latency, packet loss, or even disconnections, which would
   require more frequent monitoring of network and service performance
   metrics to detect anomalies in a timely manner.  Conversely, when the
   wireless signal strength exceeds a specific threshold, indicating a
   stable and strong connection, the data streaming rate can be reduced
   to a reasonable value to help conserve network bandwidth and
   computational resources.

   To optimize the process, adaptive subscription can be employed.  When
   the wireless signal strength falls below a configured threshold, the
   subscribed data can be streamed at a higher rate to capture
   potentially important data and events that might indicate continuous
   service degeneration or anomalies; while when the wireless signal
   strength crosses a configured threshold, the subscribed data can be
   streamed at a lower rate to maintain efficient resource utilization.

A.2.  Reducing Impact on High CPU Utilization

   Continuous monitoring of some metrics is essential for maintaining
   network and service health, however, this can place a significant
   burden on the device's CPU utilization, especially when the device is
   running resource-intensive tasks and is overloaded.  When the CPU
   utilization on the device exceeds a certain high-level value, it is
   crucial to manage the network monitoring process in a way that
   minimizes its impact on overall system performance.






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   In such cases, adaptive subscription can dynamically adjust the
   period interval with which to report streaming update and help
   balance monitoring needs with computational demands.  When the CPU
   utilization on the device exceeds a certain high-level value, the
   subscriber can specify a longer period interval for some less
   critical statistics to make room and save more resources.
   Conversely, When the CPU utilization falls below a specified
   threshold, indicating the device has sufficient idle resources, the
   subscriber can revert to a shorter period interval for streaming data
   without exhausting the CPU resources at the same time.

Appendix B.  Example YANG Module

   This section presents an example YANG module so that Appendix C can
   give examples of how the YANG module defined in Section 3.2 is used
   to perform adaptive subscription.  The example YANG module used in
   this section represents a Wi-Fi Network Diagnostics data specified in
   [CHIP] which can be used by a Node to assist a user or Administrative
   Node in diagnosing potential problems.

   YANG tree diagram for the "example-wifi-network-diagnostic" module:

   module: example-wifi-network-diagnostic
     +--ro server
     |  +--ro bssid?                       yang:mac-address
     |  +--ro security-type?               enumeration
     |  +--ro wifi-version?                enumeration
     |  +--ro channel-num?                 int8
     |  +--ro rssi?                        int8
     |  +--ro beacon-lost-count?           int8
     |  +--ro beacon-rx-count?             int8
     |  +--ro packet-multicast-rx-count?   int8
     |  +--ro packet-multicast-tx-count?   int8
     |  +--ro packet-unicast-rx-count?     int8
     |  +--ro packet-unicast-tx-count?     int8
     |  +--ro current-max-rate?            int8
     |  +--ro overrun-count?               int8
     +--ro events
        +--ro event* [name]
           +--ro name                   string
           +--ro disconnection?         enumeration
           +--ro association-failure?   enumeration
           +--ro connection-status?     enumeration

B.1.  "example-wifi-network-diagnostic" YANG Module






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   module example-wifi-network-diagnostic {
     yang-version 1;
     namespace "http://example.com/yang/wifi-network-diagnostic";
     prefix wnd;

     import ietf-yang-types {
       prefix yang;
     }

     container server {
       config false;
       description
         "Configuration of the Wi-Fi Server logical entity.";
       leaf bssid {
         type yang:mac-address;
         description
           "The MAC address of a wireless access point.";
       }
       leaf security-type {
         type enumeration {
           enum unspecified {
             value 0;
           }
           enum none {
             value 1;
           }
           enum wep {
             value 2;
           }
           enum wpa {
             value 3;
           }
           enum wpa2 {
             value 4;
           }
           enum wpa3 {
             value 5;
           }
         }
         description
           "The type of Wi-Fi security used. A value of 0
            indicate that the interface is not currently
            configured or operational.";
       }
       leaf wifi-version {
         type enumeration {
           enum 80211a {
             value 0;



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           }
           enum 80211b {
             value 1;
           }
           enum 80211g {
             value 2;
           }
           enum 80211n {
             value 3;
           }
           enum 80211ac {
             value 4;
           }
           enum 80211ax {
             value 5;
           }
         }
         description
           "The highest 802.11 standard version usable
            by the Node.";
       }
       leaf channel-num {
         type int8;
         description
           "The channel that Wi-Fi communication is currently
            operating on. A value of 0 indicates that the interface
            is not currently configured or operational.";
       }
       leaf rssi {
         type int8;
         description
           "The RSSI of the Node's Wi-Fi radio in dBm.";
       }
       leaf beacon-lost-count {
         type int8;
         description
           "The count of the number of missed beacons the
            Node has detected.";
       }
       leaf beacon-rx-count {
         type int8;
         description
           "The count of the number of received beacons. The
            total number of expected beacons that could have been
            received during the interval since association matches
            the sum of BeaconRxCount and BeaconLostCount. ";
       }
       leaf packet-multicast-rx-count {



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         type int8;
         description
           "The number of multicast packets received by
            the Node.";
       }
       leaf packet-multicast-tx-count {
         type int8;
         description
           "The number of multicast packets transmitted by
            the Node.";
       }
       leaf packet-unicast-rx-count {
         type int8;
         description
           "The number of multicast packets received by
            the Node.";
       }
       leaf packet-unicast-tx-count {
         type int8;
         description
           "The number of multicast packets transmitted by
            the Node.";
       }
       leaf current-max-rate {
         type int8;
         description
           "The current maximum PHY rate of transfer of
            data in bytes-per-second.";
       }
       leaf overrun-count {
         type int8;
         description
           "The number of packets dropped either at ingress or
            egress, due to lack of buffer memory to retain all
            packets on the ethernet network interface. The
            OverrunCount attribute is reset to 0 upon a
            reboot of the Node.";
       }
     }
     container events {
       config false;
       description
         "Configuration of WI-FI Network Diagnostic events.";
       list event {
         key "name";
         description
           "The list of event sources configured on the
            server.";



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         leaf name {
           type string;
           description
             "The unique name of an event source.";
         }
         leaf disconnection {
           type enumeration {
             enum de-authenticated {
               value 1;
             }
             enum dis-association {
               value 2;
             }
           }
           description
             "A Node's Wi-Fi connection has been disconnected as a
              result of de-authenticated or dis-association and
              indicates the reason.";
         }
         leaf association-failure {
           type enumeration {
             enum unknown {
               value 0;
             }
             enum association-failed {
               value 1;
             }
             enum authentication-failed {
               value 2;
             }
             enum ssid-not-found {
               value 3;
             }
           }
           description
             "A Node has attempted to connect, or reconnect, to
              a Wi-Fi access point, but is unable to successfully
              associate or authenticate, after exhausting all
              internal retries of its supplicant.";
         }
         leaf connection-status {
           type enumeration {
             enum connected {
               value 1;
             }
             enum notconnected {
               value 2;
             }



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           }
           description
             "A Node's connection status to a Wi-Fi network has
              changed. Connected, in this context, means that
              a Node acting as a Wi-Fi station is successfully
              associated to a Wi-Fi Access Point.";
         }
       }
     }
   }

Appendix C.  Adaptive Subscription and Notification Example

   The examples within this document use the normative YANG module
   "ietf-adaptive-subscription" defined in Section 3.2 and the non-
   normative example YANG module "example-wifi-network-diagnostic"
   defined in Appendix B.1.

   This section shows some typical adaptive subscription and
   notification message exchanges.

C.1.  Configured Subscription Example

   The client configures adaptive subscription policy parameters on the
   server.  The adaptive subscription configuration parameters require
   the server to support two update intervals (i.e., 5 seconds, 20
   seconds) and report updates every 20 seconds if the RSSI value is
   greater than or equal to -65 dB; If the RSSI value is less than -65
   dB, switch to 5 seconds period value to report updates.  The server
   compares the rssi value with -65 dB every 2 seconds.  Figure 1
   specifies an example of configured subscription with the <edit-
   config> operation.

 <rpc xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" message-id="101">
  <edit-config>
   <target>
    <running/>
   </target>
   <config>
    <subscriptions
     xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
     xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
     <subscription>
      <id>1011</id>
      <yp:datastore
       xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
       ds:operational
      </yp:datastore>



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      <yp:datastore-xpath-filter
       xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
       /wnd:server
      </yp:datastore-xpath-filter>
      <as:adaptive-periodic
      xmlns:as="urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription">
       <as:periodic>
        <as:name>adaptive-period-1</as:name>
        <as:eval-expression>
         /wnd:server/wnd:rssi&lt;-65
        </as:eval-expression>
        <as:eval-interval>200</as:eval-interval>
        <as:period>500</as:period>
        <as:anchor-time>2025-04-11T08:00:00Z</as:anchor-time>
       </as:periodic>
       <as:periodic>
        <as:name>adaptive-period-2</as:name>
        <as:eval-expression>
         /wnd:server/wnd:rssi&gt;=-65
        </as:eval-expression>
        <as:eval-interval>200</as:eval-interval>
        <as:period>2000</as:period>
        <as:anchor-time>2025-04-11T08:00:00Z</as:anchor-time>
       </as:periodic>
      </as:adaptive-periodic>
      <receivers>
       <receiver>
        <name>host.example.com</name>
       </receiver>
      </receivers>
     </subscription>
    </subscriptions>
   </config>
  </edit-config>
 </rpc>

            Figure 1: An Example of Configured Subscription

C.2.  Dynamic Subscription Example

   Alternatively, the subscriber may send an "establish-subscription"
   RPC with the parameters listed in Section 2.1 to request the creation
   of an adaptive subscription.  The adaptive subscription configuration
   parameters require the server to report updates every 5 seconds if
   the RSSI value is less than -65 dB; If the RSSI value is greater than
   or equal to -65 dB, switch to 20 seconds period value.  The server
   compares the RSSI value with -65 dB every 2 seconds.  Figure 2
   specifies an example of the "establish-subscription" RPC request.



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   <netconf:rpc message-id="101"
    xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
    <establish-subscription
     xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
     xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
     <yp:datastore
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
      ds:operational
     </yp:datastore>
     <yp:datastore-xpath-filter
      xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
      /wnd:server
     </yp:datastore-xpath-filter>
     <as:adaptive-periodic
      xmlns:as="urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription">
      <as:periodic>
       <as:name>adaptive-period-1</as:name>
       <as:eval-expression>
        /wnd:server/wnd:rssi&lt;-65
       </as:eval-expression>
       <as:eval-interval>200</as:eval-interval>
       <as:period>500</as:period>
       <as:anchor-time>2025-04-11T08:00:00Z</as:anchor-time>
      </as:periodic>
      <as:periodic>
       <as:name>adaptive-period-2</as:name>
       <as:eval-expression>
        /wnd:server/wnd:rssi&gt;=-65
       </as:eval-expression>
       <as:eval-interval>200</as:eval-interval>
       <as:period>2000</as:period>
       <as:anchor-time>2025-04-11T08:00:00Z</as:anchor-time>
      </as:periodic>
     </as:adaptive-periodic>
    </establish-subscription>
   </netconf:rpc>

                Figure 2: An Example of Dynamic Subscription

C.3.  "xpath-evaluation-unsupported" error response example

   If the subscriber has authorization to establish the subscription
   with a server, but the server had not been able to fully satisfy the
   request from the subscriber, the server should send an RPC error
   response.






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   For instance, if the XPATH 1.0 syntax against the targeted data node
   defined in "eval-expression" is not supported by the server' s
   implementation, the server returns a reply indicating a failure.
   Figure 3 illustrates an example of RPC error response with this.

   <?xml version="1.0" encoding="utf-8"?>
   <rpc-reply message-id="101"
    xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <rpc-error>
       <error-type>application</error-type>
       <error-tag>invalid-value</error-tag>
       <error-severity>error</error-severity>
       <error-app-tag>
         ietf-adaptive-subscription:xpath-evaluation-unsupported
       </error-app-tag>
       <error-path
         xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
         /wnd:server/wnd:rssi
       </error-path>
     </rpc-error>
   </rpc-reply>

                 Figure 3: An Example of RPC Error Response

   Since adaptive subscription allows a server to be configured with
   multiple different period intervals and corresponding XPath
   evaluation criteria to trigger update interval switch in the server,
   it may be possible for the server to return multiple <rpc-error>
   elements with "xpath-evaluation-unsupported" failure specified by
   different error paths.  The subscriber can use this information in
   future attempts to establish a subscription.

C.4.  "adaptive-period-update" notification example

   Suppose initially the RSSI value is below -65dB, the server pushes
   updates every 5 seconds starting at 2025-04-11T08:00:00Z and
   continuing through 2025-04-11T08:02:05Z.  The server evaluates the
   RSSI value against -65 dB every 2 seconds and from
   2025-04-11T08:02:06Z it detects that the RSSI value exceeds -65 dB
   continuously.  As the "anchor-time" is set to 2025-04-11T08:00:00Z
   for adaptive-period-2, which means updates can only be sent at the
   top of every 00, 20, 40 second, the server sends the next update
   record at 2025-04-11T08:02:20Z and adjust the update interval to 20
   seconds.  Before this, the server generates and sends an "adaptive-
   period-update" notification to inform receivers of the new period
   interval value.  An example of "adaptive-period-update" notification
   is indicated in Figure 4.




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   <notification
    xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0"
    xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
    <eventTime>2025-04-11T08:02:19.33Z</eventTime>
    <adaptive-period-update
     xmlns="urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription">
     <id>1011</id>
     <period>2000</period>
     <period-update-time>2025-04-11T08:02:20Z</period-update-time>
     <satisfied-criteria-data>
      <path>/wnd:server/wnd:rssi</path>
      <value>-40</value>
     </satisfied-criteria-data>
     <yp:datastore
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
          ds:operational
     </yp:datastore>
     <yp:datastore-xpath-filter
      xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
          /wnd:server
     </yp:datastore-xpath-filter>
    </adaptive-period-update>
   </notification>

       Figure 4: An Example of "adaptive-period-update" Notification

Authors' Addresses

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


   Peng Liu
   China Mobile
   32 Xuanwumen West St, Xicheng District
   Beijing
   Email: liupengyjy@chinamobile.com









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   Qiufang Ma
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: maqiufang1@huawei.com


   Wei Wang
   China Telecom
   32 Xuanwumen West St, Xicheng District
   Beijing
   Email: wangw36@chinatelecom.cn


   Zhixiong Niu
   Microsoft
   Email: Zhixiong.Niu@microsoft.com
































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