NETCONF Working Group                                              Q. WuInternet-Draft                                                    HuaweiIntended status: Experimental                                     P. LiuExpires: 2 July 2026                                        China Mobile                                                                   Q. Ma                                                                  Huawei                                                                 W. Wang                                                           China Telecom                                                                  Z. Niu                                                               Microsoft                                                        29 December 2025               Adaptive Subscription to YANG Notification              draft-ietf-netconf-adaptive-subscription-14Abstract   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   *  2025-12-29 --> the actual date of the publication of this documentStatus of This Memo   This Internet-Draft is submitted in full conformance with the   provisions of BCP 78 and BCP 79.Wu, et al.                 Expires 2 July 2026                  [Page 1]Internet-Draft            Adaptive Subscription            December 2025   Internet-Drafts are working documents of the Internet Engineering   Task Force (IETF).  Note that other groups may also distribute   working documents as Internet-Drafts.  The list of current Internet-   Drafts is at https://datatracker.ietf.org/drafts/current/.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   time.  It is inappropriate to use Internet-Drafts as reference   material or to cite them other than as "work in progress."   This Internet-Draft will expire on 2 July 2026.Copyright Notice   Copyright (c) 2025 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject to BCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents (https://trustee.ietf.org/   license-info) in effect on the date of publication of this document.   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.  Code Components   extracted from this document must include Revised BSD License text as   described in Section 4.e of the Trust Legal Provisions and are   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 . . . . . . . . . . . . . . . . . . . . . .   6     2.1.  Adaptive Subscription Parameters  . . . . . . . . . . . .   6     2.2.  RPC Failures  . . . . . . . . . . . . . . . . . . . . . .   8     2.3.  Subscription State Change Notifications . . . . . . . . .   9     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  . . . . . . . . . . . . . . . . . . . . . . . . .  21   5.  Operational Considerations  . . . . . . . . . . . . . . . . .  21     5.1.  XPath Complexity Evaluation . . . . . . . . . . . . . . .  21     5.2.  Threshold Selection for XPath Evaluation  . . . . . . . .  22   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  23   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  24Wu, et al.                 Expires 2 July 2026                  [Page 2]Internet-Draft            Adaptive Subscription            December 2025   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  25   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  26   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26     10.1.  Normative References . . . . . . . . . . . . . . . . . .  26     10.2.  Informative References . . . . . . . . . . . . . . . . .  27   Appendix A.  Use Cases  . . . . . . . . . . . . . . . . . . . . .  28     A.1.  Wireless Network Performance Monitoring . . . . . . . . .  29     A.2.  Reducing Impact on High CPU Utilization . . . . . . . . .  29   Appendix B.  Example YANG Module  . . . . . . . . . . . . . . . .  30     B.1.  "example-wifi-network-diagnostic" YANG Module . . . . . .  30   Appendix C.  Adaptive Subscription and Notification Example . . .  35     C.1.  Configured Subscription Example . . . . . . . . . . . . .  35     C.2.  Dynamic Subscription Example  . . . . . . . . . . . . . .  36     C.3.  "xpath-evaluation-unsupported" error response example . .  37     C.4.  "adaptive-period-update" notification example . . . . . .  38   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  391.  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 dataWu, et al.                 Expires 2 July 2026                  [Page 3]Internet-Draft            Adaptive Subscription            December 2025   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   *  SubscriptionWu, et al.                 Expires 2 July 2026                  [Page 4]Internet-Draft            Adaptive Subscription            December 2025   *  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.   As of the time of writing, the end date of the experiment has not   been determined, it may remain open-ended to gather long-term   operational experience and feedback.  Success criteria for the   experiment include:   *  Demonstrated stability under high-frequency state change scenarios      (e.g., interface flapping).   *  Scalability across diverse network scales.   *  Reasonable impact on system resources.   *  Positive feedback from at least three independent implementations      indicating that the proposed mechanism reduces the telemetry data      volume by at least 20% compared with periodic subscription but      still ensures network events can be capture at the same time.   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.Wu, et al.                 Expires 2 July 2026                  [Page 5]Internet-Draft            Adaptive Subscription            December 20252.  Solution Overview2.1.  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      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.Wu, et al.                 Expires 2 July 2026                  [Page 6]Internet-Draft            Adaptive Subscription            December 2025      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 evaluate 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.   *  "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.Wu, et al.                 Expires 2 July 2026                  [Page 7]Internet-Draft            Adaptive Subscription            December 20252.2.  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.   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.Wu, et al.                 Expires 2 July 2026                  [Page 8]Internet-Draft            Adaptive Subscription            December 20252.3.  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.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 refers to the timestamp when the      server switched 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.Wu, et al.                 Expires 2 July 2026                  [Page 9]Internet-Draft            Adaptive Subscription            December 2025   *  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.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]Wu, et al.                 Expires 2 July 2026                 [Page 10]Internet-Draft            Adaptive Subscription            December 2025                +-- 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                +-- 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                               identityrefWu, et al.                 Expires 2 July 2026                 [Page 11]Internet-Draft            Adaptive Subscription            December 2025          +--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)                      +--ro datastore-xpath-filter?     yang:xpath1.0                              {sn:xpath}?3.2.  The "ietf-adaptive-subscription" Module   This YANG module imports modules from [RFC9911],[RFC8639], [RFC8641],   and [RFC9196].   <CODE BEGINS> file "ietf-adaptive-subscription@2025-12-29.yang"   module ietf-adaptive-subscription {     yang-version 1.1;     namespace "urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription";     prefix adaps;     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 9911: 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;Wu, et al.                 Expires 2 July 2026                 [Page 12]Internet-Draft            Adaptive Subscription            December 2025       reference         "RFC 9196: YANG Modules Describing Capabilities for          Systems and Datastore Update Notifications";     }     organization       "IETF NETCONF (Network Configuration) Working Group";     contact       "WG Web:   <https://datatracker.ietf.org/wg/netconf/>        WG List:  <netconf@ietf.org>        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.";Wu, et al.                 Expires 2 July 2026                 [Page 13]Internet-Draft            Adaptive Subscription            December 2025     revision 2025-12-29 {       description         "Initial revision";       reference         "RFC XXXX: Adaptive Subscription to YANG Notification.";     }     feature adaptive-subscription {       description         "This feature indicates that adaptive-subscriptions are          supported.";     }     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'.";     }Wu, et al.                 Expires 2 July 2026                 [Page 14]Internet-Draft            Adaptive Subscription            December 2025     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            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;             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.Wu, et al.                 Expires 2 July 2026                 [Page 15]Internet-Draft            Adaptive Subscription            December 2025                -  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                   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 parametersWu, et al.                 Expires 2 July 2026                 [Page 16]Internet-Draft            Adaptive Subscription            December 2025          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.";         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 hasWu, et al.                 Expires 2 July 2026                 [Page 17]Internet-Draft            Adaptive Subscription            December 2025          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.";         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.";       }Wu, et al.                 Expires 2 July 2026                 [Page 18]Internet-Draft            Adaptive Subscription            December 2025       leaf period-update-time {         type yang:date-and-time;         description           "The timestamp when the server switched to another period            interval because the evaluated 'eval-expression' expression            result changed.";       }       anydata satisfied-criteria-data {         description           "The corresponding instance nodes and values specified in            'eval-expression' that satisfied the condition and thus            triggered 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, orWu, et al.                 Expires 2 July 2026                 [Page 19]Internet-Draft            Adaptive Subscription            December 2025            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            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 Considerations4.1.  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].Wu, et al.                 Expires 2 July 2026                 [Page 20]Internet-Draft            Adaptive Subscription            December 2025   ---------------------------------------------------------------------      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.   ---------------------------------------------------------------------      Name:       ietf-adaptive-subscription      Maintained by IANA? N      Namespace:  urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription      Prefix:     adaps      Reference:  RFC XXXX   ---------------------------------------------------------------------5.  Operational Considerations5.1.  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).   Care must be taken when using an arbitrary complex XPath evaluation   criteria.  While well-supported by Section 3.4 of [XPATH1.0], it   could be error-prone, exhaust computational resources, or not fully   implemented by XPath interpreter in real deployments.  Some examples   are given below for illustration:   *  Applying XPath evaluation criteria on any arbitrary "config true"      and "config false" data nodes;   *  Including more than one target data node selection and operation      (e.g., addition, subtraction, division and multiplication) within      a single XPath evaluation criterion;   *  Targeting any type of node value in the XPath evaluation      criterion, e.g., string, int64, uint64, and decimal64 types;Wu, et al.                 Expires 2 July 2026                 [Page 21]Internet-Draft            Adaptive Subscription            December 2025   *  Comparing two node-sets within the XPath evaluation criterion;   *  Comparing targeted data of 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.   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;   *  When comparing a numerical leaf or leaf-list node (e.g., signed/      unsigned integer) against a threshold value, use a constant      numeric value in the XPath evaluation criteria.   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 generatedWu, et al.                 Expires 2 July 2026                 [Page 22]Internet-Draft            Adaptive Subscription            December 2025   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   [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.comWu, et al.                 Expires 2 July 2026                 [Page 23]Internet-Draft            Adaptive Subscription            December 2025   *  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:      -  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].Wu, et al.                 Expires 2 July 2026                 [Page 24]Internet-Draft            Adaptive Subscription            December 2025   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.   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.   There are no particular sensitive RPC or action operations.8.  Contributors      Wei Song      Email: songwei80@huawei.com      Michael Wang      Email: wangzitao@huawei.comWu, et al.                 Expires 2 July 2026                 [Page 25]Internet-Draft            Adaptive Subscription            December 20259.  Acknowledgments   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.   The authors would also like to thank Michael for providing CHIP/   Matter WI-FI statistics reference.   Thanks to Dhruv Dhody for the OPSDIR Early review, and thanks to Joe   Clarke for the YANGDOCTORS Early review.   Thanks to Mahesh Jethanandani for the careful AD review.10.  References10.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels", BCP 14, RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [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>.   [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>.Wu, et al.                 Expires 2 July 2026                 [Page 26]Internet-Draft            Adaptive Subscription            December 2025   [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>.   [RFC9911]  Schönwälder, J., Ed., "Common YANG Data Types", RFC 9911,              DOI 10.17487/RFC9911, December 2025,              <https://www.rfc-editor.org/info/rfc9911>.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>.Wu, et al.                 Expires 2 July 2026                 [Page 27]Internet-Draft            Adaptive Subscription            December 2025   [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>.   [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   The use cases presented in this section are for illustrative   purposes; they do not prescribe or imply any normative behavior for   deployments.Wu, et al.                 Expires 2 July 2026                 [Page 28]Internet-Draft            Adaptive Subscription            December 2025A.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.   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.Wu, et al.                 Expires 2 July 2026                 [Page 29]Internet-Draft            Adaptive Subscription            December 2025Appendix 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?           yang:zero-based-counter32     |  +--ro beacon-rx-count?             yang:zero-based-counter32     |  +--ro packet-multicast-rx-count?   yang:zero-based-counter32     |  +--ro packet-multicast-tx-count?   yang:zero-based-counter32     |  +--ro packet-unicast-rx-count?     yang:zero-based-counter32     |  +--ro packet-unicast-tx-count?     yang:zero-based-counter32     |  +--ro current-max-rate?            uint32     |  +--ro overrun-count?               yang:zero-based-counter32     +--ro events        +--ro event* [name]           +--ro name                   string           +--ro disconnection?         enumeration           +--ro association-failure?   enumeration           +--ro connection-status?     enumerationB.1.  "example-wifi-network-diagnostic" YANG Module   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.";Wu, et al.                 Expires 2 July 2026                 [Page 30]Internet-Draft            Adaptive Subscription            December 2025       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;           }           enum 80211b {             value 1;           }           enum 80211g {             value 2;           }           enum 80211n {             value 3;           }           enum 80211ac {             value 4;           }Wu, et al.                 Expires 2 July 2026                 [Page 31]Internet-Draft            Adaptive Subscription            December 2025           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 yang:zero-based-counter32;         description           "The count of the number of missed beacons the            Node has detected.";       }       leaf beacon-rx-count {         type yang:zero-based-counter32;         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 {         type yang:zero-based-counter32;         description           "The number of multicast packets received by            the Node.";       }       leaf packet-multicast-tx-count {         type yang:zero-based-counter32;         description           "The number of multicast packets transmitted by            the Node.";       }       leaf packet-unicast-rx-count {         type yang:zero-based-counter32;Wu, et al.                 Expires 2 July 2026                 [Page 32]Internet-Draft            Adaptive Subscription            December 2025         description           "The number of multicast packets received by            the Node.";       }       leaf packet-unicast-tx-count {         type yang:zero-based-counter32;         description           "The number of multicast packets transmitted by            the Node.";       }       leaf current-max-rate {         type uint32;         description           "The current maximum PHY rate of transfer of            data in bytes-per-second.";       }       leaf overrun-count {         type yang:zero-based-counter32;         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.";         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;             }Wu, et al.                 Expires 2 July 2026                 [Page 33]Internet-Draft            Adaptive Subscription            December 2025           }           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;             }           }           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.";         }       }     }   }Wu, et al.                 Expires 2 July 2026                 [Page 34]Internet-Draft            Adaptive Subscription            December 2025Appendix 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>     <yp:datastore-xpath-filter      xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">      /wnd:server     </yp:datastore-xpath-filter>     <adaps:adaptive-periodic     xmlns:adaps="urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription">      <adaps:periodic>       <adaps:name>adaptive-period-1</adaps:name>       <adaps:eval-expression>        /wnd:server/wnd:rssi&lt;-65       </adaps:eval-expression>Wu, et al.                 Expires 2 July 2026                 [Page 35]Internet-Draft            Adaptive Subscription            December 2025       <adaps:eval-interval>200</adaps:eval-interval>       <adaps:period>500</adaps:period>       <adaps:anchor-time>2025-04-11T08:00:00Z</adaps:anchor-time>      </adaps:periodic>      <adaps:periodic>       <adaps:name>adaptive-period-2</adaps:name>       <adaps:eval-expression>        /wnd:server/wnd:rssi&gt;-65       </adaps:eval-expression>       <adaps:eval-interval>200</adaps:eval-interval>       <adaps:period>2000</adaps:period>       <adaps:anchor-time>2025-04-11T08:00:00Z</adaps:anchor-time>      </adaps:periodic>     </adaps:adaptive-periodic>     <receivers>      <receiver>       <name>host.example.com</name>      </receiver>     </receivers>    </subscription>   </subscriptions>  </config> </edit-config></rpc>           Figure 1: An Example of Configured SubscriptionC.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.Wu, et al.                 Expires 2 July 2026                 [Page 36]Internet-Draft            Adaptive Subscription            December 2025<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>  <adaps:adaptive-periodic   xmlns:adaps="urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription">   <adaps:periodic>    <adaps:name>adaptive-period-1</adaps:name>    <adaps:eval-expression>     /wnd:server/wnd:rssi&lt;-65    </adaps:eval-expression>    <adaps:eval-interval>200</adaps:eval-interval>    <adaps:period>500</adaps:period>    <adaps:anchor-time>2025-04-11T08:00:00Z</adaps:anchor-time>   </adaps:periodic>   <adaps:periodic>    <adaps:name>adaptive-period-2</adaps:name>    <adaps:eval-expression>     /wnd:server/wnd:rssi&gt;-65    </adaps:eval-expression>    <adaps:eval-interval>200</adaps:eval-interval>    <adaps:period>2000</adaps:period>    <adaps:anchor-time>2025-04-11T08:00:00Z</adaps:anchor-time>   </adaps:periodic>  </adaps:adaptive-periodic> </establish-subscription></netconf:rpc>             Figure 2: An Example of Dynamic SubscriptionC.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.Wu, et al.                 Expires 2 July 2026                 [Page 37]Internet-Draft            Adaptive Subscription            December 2025   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.Wu, et al.                 Expires 2 July 2026                 [Page 38]Internet-Draft            Adaptive Subscription            December 2025   <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" NotificationAuthors' 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.comWu, et al.                 Expires 2 July 2026                 [Page 39]Internet-Draft            Adaptive Subscription            December 2025   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.comWu, et al.                 Expires 2 July 2026                 [Page 40]