Adaptive Subscription to YANG Notification
draft-ietf-netconf-adaptive-subscription-13

NETCONF Working Group Q. Wu
Internet-Draft Huawei
Intended status: Experimental P. Liu
Expires: 6 June 2026 China Mobile
 Q. Ma
 Huawei
 W. Wang
 China Telecom
 Z. Niu
 Microsoft
 3 December 2025
 Adaptive Subscription to YANG Notification
 draft-ietf-netconf-adaptive-subscription-13
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年12月04日 --> 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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 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 6 June 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 . . . . . . . . . . . . . . . . . . . 24
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 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 . . . . . . . . . 28
 A.2. Reducing Impact on High CPU Utilization . . . . . . . . . 29
 Appendix B. Example YANG Module . . . . . . . . . . . . . . . . 29
 B.1. "example-wifi-network-diagnostic" YANG Module . . . . . . 30
 Appendix C. Adaptive Subscription and Notification Example . . . 34
 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 . . . . . . . . . . . . . . . . . . . . . . . 39
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.
 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.
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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
 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.
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 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.
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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.
 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.
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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.
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.
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 * 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]
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 +-- 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 identityref
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 +--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 [RFC6991],[RFC8639], [RFC8641],
 and [RFC9196].
 <CODE BEGINS> file "ietf-adaptive-subscription@2025年12月04日.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 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;
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 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.";
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 revision 2025年12月04日 {
 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'.";
 }
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 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.
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 - 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 parameters
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 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 has
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 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.";
 }
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 leaf period-update-time {
 type yang:date-and-time;
 description
 "The timestamp when the server started to switch
 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, or
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 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 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].
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 ---------------------------------------------------------------------
 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 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).
 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;
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 * 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;
 * Comparing a numerical (e.g., signed/unsigned integer) leaf or
 leaf-list node directly against a constant numeric value in the
 XPath evaluation criterion.
 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
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 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.com
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 * 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].
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 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.com
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9. 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. References
10.1. 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>.
 [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>.
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 [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>.
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>.
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 [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
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.
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 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.
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:
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 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? enumeration
B.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.";
 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 {
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 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;
 }
 enum 80211ax {
 value 5;
 }
 }
 description
 "The highest 802.11 standard version usable
 by the Node.";
 }
 leaf channel-num {
 type int8;
 description
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 "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;
 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 {
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 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;
 }
 }
 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;
 }
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 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.";
 }
 }
 }
 }
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.
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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>
 <adaps:eval-interval>200</adaps:eval-interval>
 <adaps:period>500</adaps:period>
 <adaps:anchor-time>2025年04月11日T08:00:00Z</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>
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 <adaps:period>2000</adaps:period>
 <adaps:anchor-time>2025年04月11日T08:00:00Z</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 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>
 <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年04月11日T08:00:00Z</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年04月11日T08:00:00Z</adaps:anchor-time>
 </adaps:periodic>
 </adaps: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年04月11日T08:00:00Z and
 continuing through 2025年04月11日T08:02:05Z. The server evaluates the
 RSSI value against -65 dB every 2 seconds and from
 2025年04月11日T08:02:06Z it detects that the RSSI value exceeds -65 dB
 continuously. As the "anchor-time" is set to 2025年04月11日T08:00:00Z
 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年04月11日T08:02:20Z 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年04月11日T08:02:19.33Z</eventTime>
 <adaptive-period-update
 xmlns="urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription">
 <id>1011</id>
 <period>2000</period>
 <period-update-time>2025年04月11日T08:02:20Z</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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