NETCONF Working Group                                              Q. Wu
Internet-Draft                                                   W. Song
Intended status: Experimental                                     Huawei
Expires: 24 December 2022                                         P. Liu
                                                            China Mobile
                                                                   Q. Ma
                                                                  Huawei
                                                                 W. Wang
                                                           China Telecom
                                                                  Z. Niu
                                                               Microsoft
                                                            22 June 2022


               Adaptive Subscription to YANG Notification
              draft-ietf-netconf-adaptive-subscription-00

Abstract

   This document defines a YANG data model and associated mechanism
   enabling the subscriber's adaptive subscriptions to a publisher's
   event streams with various different period intervals to report
   updates.  Applying these elements allows servers automatically adjust
   the rate and volume of telemetry traffic sent from a publisher to
   receivers.

Status of This Memo

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

   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 24 December 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Model Overview  . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Subscription Configuration  . . . . . . . . . . . . . . .   6
     2.2.  YANG RPC  . . . . . . . . . . . . . . . . . . . . . . . .   7
       2.2.1.  "establish-subscription" RPC  . . . . . . . . . . . .   7
     2.3.  Notifications for Adaptive Subscribed Content . . . . . .   8
   3.  XPath Complexity Evaluation . . . . . . . . . . . . . . . . .   9
   4.  Adaptive Subscription YANG Module . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  Updates to the IETF XML Registry  . . . . . . . . . . . .  14
     5.2.  Updates to the YANG Module Names Registry . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  16
   8.  Acknowledges  . . . . . . . . . . . . . . . . . . . . . . . .  16
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Appendix A.  Example YANG Module  . . . . . . . . . . . . . . . .  18
     A.1.  "example-wifi-mac" YANG Module  . . . . . . . . . . . . .  18
   Appendix B.  Adaptive Subscription and Notification Example . . .  23
     B.1.  "edit-config" Example . . . . . . . . . . . . . . . . . .  23
     B.2.  Create Adaptive Subscription Example  . . . . . . . . . .  24
     B.3.  "xpath-evaluation-unsupported" error response example . .  25
     B.4.  "adaptive-period-update" notification example . . . . . .  26
     B.5.  Changes between Revisions . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

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 subscriptions are introduced in [RFC8641],
   distinguished by how updates are triggered: periodic and on-change.




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

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

   However in some large scale deployments (e.g., massive data
   collection for wireless network performance monitoring) where an
   increased data collection rate is used, it becomes more likely that
   both clients and servers are temporarily overwhelmed with a burst of
   streamed data and consumes expensive network resource (e.g.,
   bandwidth resource, radio resource) and computation resource,
   therefore hard to continuously monitor operational data, especially
   values that fall outside normal operational ranges.  If the rate at
   which we can collect a stream of data is set too low or chosen to get
   low priority telemetry data dropped, these telemetry data are not
   sufficient to detect and diagnose problems and verify correct network
   behavior.

   A client might choose to monitor the operational state and send a
   request to modify the data collection rate on the server.  But how
   often the client evaluates if the modification of the data 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, which may
   result in service discontinuity.  In addition, when tens of thousands
   of network devices need to be managed, frequent follow-up
   modification requests are prone to errors.

   There is a need for a service to balance between data management cost
   and real time streaming telemetry.  To achieve this, servers can be
   configured with multiple different period intervals and corresponding
   subscription update policy which allows servers/publishers
   automatically switch to different period intervals according to the
   network condition change without the interaction with the client for
   policy update instruction, e.g., 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 (e.g., continuous service degeneration); while when the
   wireless signal strength crosses a configured threshold, the
   subscribed data can be streamed at a lower rate.

   This document defines a YANG data model and associated mechanism
   enabling the subscriber's adaptive subscriptions to a publisher's
   event streams.  Applying these elements allows servers to
   automatically adjust the rate and volume of telemetry traffic sent
   from a publisher to receivers.




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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] [RFC3198]
   [RFC8342] [RFC8639] [RFC8641] and are not redefined here:

   *  Event

   *  Client

   *  Configuration

   *  Configured subscription

   *  Configuration datastore

   *  Notification message

   *  Publisher

   *  Receiver

   *  Subscriber

   *  Subscription

   *  On-change subscription

   *  Periodic subscription

   *  Selection filter

   This document defines the following term:

   Adaptive Subscription:  Apply subscription update policy on the
      servers and allow servers/publishers automatically switch to
      different period intervals according to the network condition
      change without the interaction with the client for update policy
      instruction.







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2.  Model Overview

   This document defines a YANG module "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" YANG module also defines "adaptive-period-
   update" notification to report the update interval change.

   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:
    +--rw (adaptive-subscription)?
       +--:(adaptive-subscriptions)
          +--rw adaptive-subscriptions
              +--rw adaptive-period* [name]
                +--rw name                    string
                +--rw xpath-external-eval     string
                +--rw period                  yp:centiseconds
                +--rw anchor-time?            yang:date-and-time
  augment /sn:establish-subscription/sn:input/yp:update-trigger:
    +-- (adaptive-subscription)?
       +--:(adaptive-subscriptions)
          +--rw adaptive-subscriptions
             +--rw adaptive-period* [name]
                +--rw name                    string
                +--rw xpath-external-eval     string
                +--rw period                  yp:centiseconds
                +--rw anchor-time?            yang:date-and-time
  notifications:
    +---n adaptive-period-update
       +--ro id?                                     sn:subscription-id
       +--ro period                                  yp:centiseconds
       +--ro anchor-time?                            yang:date-and-time
       +--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}?



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2.1.  Subscription Configuration

   For adaptive subscriptions, triggered updates will occur at the
   boundaries of specified time intervals when a trigger condition is
   satisfied.  These boundaries can be calculated from the following
   adaptive periodic parameters:

   *  a "name" represents the name of each adaptive period;

   *  a "period" that defines the new duration between push updates.
      The period can be switched based on trigger conditions;

   *  an "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.

   *  an "xpath-external-eval" represents a standard XPath evaluation
      expression (See section 6.4 of [RFC7950]) that is applied against
      the targeted data object, 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 comparisons of
      the targeted datastore node with its value to the specific
      threshold in the XPath format.  Different from selection filter
      defined in [RFC8641],

      -  it is applied against a single targeted object rather than a
         set of target objects.

      -  it monitors a specific data object change and evaluates the
         trigger condition associated with the targeted object to be
         true or false using XPATH rules and does not influence the
         event records output generation from a publisher.

      How often the XPath expression criterion is evaluated is up to the
      publisher's implementation.  With minimal delay, the expression
      can be evaluated whenever changes to targeted object occur, or at
      the end of each high-frequency streaming update period.  To reduce
      the frequency of evaluation, the server can choose to check
      targeted object change at every multiple (e.g.,2 or 3) high-
      frequency streaming update periods.

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







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      -  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 "xpath-external-eval" 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 in RFC 7950.

      -  The context node is the root node.

      For the cases where multiple list instances are needed to handle
      in "xpath-external-eval", 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 expression defined in "xpath-
      external-eval" 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.

   Note that the adaptive subscription may not be supported by every
   YANG datastore nodes.  A publisher MAY decide to simply reject an
   adaptive subscription with "adaptive-unsupported" (defined in
   Section 2.2.1.1) if the scope of the subscription contains selected
   data nodes for which adaptive subscription is not supported.

2.2.  YANG RPC

2.2.1.  "establish-subscription" RPC

   The augmentation of YANG module "ietf-yang-push" made to RPCs
   specified in YANG module "ietf-subscribed-notifications" [RFC8639] is
   introduced.  This augmentation concerns the "establish-subscription"
   RPC, which is augmented with parameters that are needed to specify a
   subscriber's adaptive subscriptions.  These parameters are the same
   as ones defined in Section 2.1.





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2.2.1.1.  RPC Failures

   As specified in [RFC8639] and [RFC8641], RPC error responses from the
   publisher are used to indicate a rejection of an RPC for any reason.
   This document introduces three new RPC errors for "establish-
   subscription" RPC.

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

   Adaptive-unsupported is used to indicate that the adaptive
   subscription is not supported for any objects that are selectable by
   the filter.

   Xpath-evaluation-unsupported is used to indicate that a server fails
   to parse syntax defined in "xpath-external-eval".  The failure can be
   caused by either a syntax error or some XPath 1.0 syntax not
   supported against the specific object.

   Multi-xpath-criteria-conflict is used to indicate that the multiple
   Xpath evaluation criteria represented by "xpath-external-eval" is
   evaluated as conflict, i.e., more than one condition expressions are
   evaluated to "true".  Such a conflict may also cause an ongoing
   adaptive-subscription terminated.

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

2.3.  Notifications for Adaptive Subscribed Content

   The adaptive update notification is similar to subscription state
   change notifications defined in [RFC8639].  It is inserted into the
   sequence of notification messages sent to a particular receiver.  The
   adaptive 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 adaptive
   update notification is easy to separate from other notification
   messages through the use of the YANG extension "subscription-state-
   notif".  This extension tags a notification as a subscription state
   change notification.

   The objects in the 'adaptive-period-update' notification include:





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

   *  an "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.

   *  A selection filter is 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 Evaluation criteria defined in section
      6.4 of [RFC7950].  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 "xpath-
      external-eval" parameter defined by the update trigger.

3.  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 can also
   use similar selection filters to express a standard XPath Evaluation
   criterion (section 6.4 of [RFC7950]) against targeted data objects.

   Similar to on-change subscriptions, adaptive subscriptions are
   particularly effective for data that changes infrequently, the
   following complex design choices need to be cautious, although these
   designs have already been well supported by the section 3.4 of
   [XPATH1.0]:

   *  Support XPath Evaluation criteria against every data object;

   *  Support more than one target object selection and operation(e.g.,
      addition, subtraction, division and multiplication) in the XPath
      evaluation criterion;

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

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





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

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

   If two objects to be compared are in different data types, 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 design principles are
   recommended:

   *  XPath Evaluation criteria against a minimal set of data objects in
      the data model, the minimal set of data objects can be advertised
      using Notification capabilities model defined in [RFC9196].

   *  XPath Evaluation criteria only support condition expressions that
      filter updates based on numbers.

   *  One object to be compared in the XPath Evaluation criteria MUST be
      a leaf data node.

   *  The other object to be compared in the XPath Evaluation criteria
      MUST be a number data type.

   If a server receives an XPath Evaluation criterion with some XPath
   syntax unsupported against the specific object, an RPC error with
   "xpath-evaluation-unsupported" should be returned.

4.  Adaptive Subscription YANG Module

   <CODE BEGINS> file "ietf-adaptive-subscription@2020-02-14.yang"
   module ietf-adaptive-subscription {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription";
     prefix as;
     import ietf-subscribed-notifications {
       prefix sn;
     }
     import ietf-yang-push {
       prefix yp;
     }
     import ietf-yang-types {



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       prefix yang;
     }

     organization
       "IETF NETCONF (Network Configuration) Working Group";
     contact
       "";
     description
       "NETCONF Protocol Data Types and Protocol Operations.
        Copyright (c) 2020 IETF Trust and the persons identified as
        the document authors.  All rights reserved.

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

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

     revision 2020-02-14 {
       description
         "Initial revision";
       reference
         "RFCxxx Adaptive subscription to YANG notification.";
     }

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

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

     identity multi-xpath-criteria-conflict {
       base sn:establish-subscription-error;
       base sn:subscription-terminated-reason;
       description



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         "Multiple Xpath evaluation criteria represented by
          'xpath-external-eval' is evaluated as conflict, i.e.,
          more than one condition expressions are evaluated to
         'true'.";
   }

     grouping adaptive-subscription-modifiable {
       description
         "This grouping describes the datastore-specific adaptive subscription
          conditions that can be changed during the lifetime of the
          subscription.";
       choice adaptive-subscription {
         description
           "Defines necessary conditions for sending an event record to
                  the subscriber.";
         container adaptive-subscriptions {
           list adaptive-period {
             key "name";
             description
               "Defines necessary conditions to switch update interval for
               sending an event record to the subscriber. The event record output
               generation will not be influenced these conditions.";
             leaf name {
               type string {
             length "1..64";
              }
           description
             "The name of the condition to be matched.  A device MAY further
              restrict the length of this name; space and special
              characters are not allowed.";
            }
             leaf xpath-external-eval {
               type string;
               description
                 "A XPath string, representing a logical expression,
                  which can contain comparisons of datastore values
                  and logical operations in the XPath format.";
             }
             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



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                 "Designates a timestamp before or after which a series
                  of periodic push updates are 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.";
             }
           }
           description
             "Container for adaptive subscription.";
         }
       }
     }

     augment "/sn:subscriptions/sn:subscription/yp:update-trigger" {
       description
         "This augmentation adds additional subscription parameters
          that apply specifically to adaptive subscription.";
       uses adaptive-subscription-modifiable;
     }
     augment "/sn:establish-subscription/sn:input/yp:update-trigger" {
       description
         "This augmentation adds additional subscription parameters
            that apply specifically to datastore updates to RPC input.";
       uses adaptive-subscription-modifiable;
     }

     notification adaptive-period-update {
       sn:subscription-state-notification;
       description
         "This notification contains a push update that in turn contains
          data subscribed to via a subscription.  In the case of a
          periodic subscription, this notification is sent for periodic
          updates.  It can also be used for synchronization updates of
          an on-change subscription.  This notification shall only be
          sent to receivers of a subscription.  It does not constitute
          a general-purpose notification that would be subscribable as
          part of the NETCONF event stream by any receiver.";
       leaf id {
         type sn:subscription-id;
         description
           "This references the subscription that drove the
            notification to be sent.";
       }
       leaf period {
         type yp:centiseconds;



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         mandatory true;
         description
           "New 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 are 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.";
       }
       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.";
         }
       }
     }
   }
   <CODE ENDS>

5.  IANA Considerations

5.1.  Updates to the IETF XML Registry

   This document registers one URI in the IETF XML registry [RFC3688].
   Following the format in [RFC3688], the following registration is
   requested to be made:

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







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5.2.  Updates to the YANG Module Names Registry

   This document registers one YANG module in the YANG Module Names
   registry [RFC7950].  Following the format in [RFC6020], the following
   registration is requested to be made:

   ---------------------------------------------------------------------
      Name:         ietf-adaptive-subscription
      Namespace:    urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription
      Prefix:       as
      Reference:    RFC xxxx
   ---------------------------------------------------------------------

6.  Security Considerations

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

   The NETCONF 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).  These data nodes may be considered sensitive in some
   network environments.  Write operations (e.g., edit-config) to these
   data nodes without proper protection can have a negative effect on
   network operations.  These are the subtrees and data nodes and their
   sensitivity/vulnerability:

   *  /sn:subscriptions/sn:subscription/yp:update-trigger/as:adaptive-
      subscriptions/as:adaptive-period/as:period

   *  /sn:subscriptions/sn:subscription/yp:update-trigger/as:adaptive-
      subscriptions/as:adaptive-period/as:anchor-time

   *  /sn:establish-subscription/sn:input/yp:update-trigger/as:adaptive-
      subscriptions/as:adaptive-period/as:period

   *  /sn:establish-subscription/sn:input/yp:update-trigger/as:adaptive-
      subscriptions/as:adaptive-period/as:anchor-time




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7.  Contributors

   Thanks Michael Wang, Liang Geng for their major contributions to the
   initial modeling and use cases.

      Michael Wang
      Email: wangzitao@huawei.com

      Liang Geng
      China Mobile
      32 Xuanwumen West St, Xicheng District
      Beijing  10053

      Email: gengliang@chinamobile.com

8.  Acknowledges

   We would like to thank Rob Wilton, Thomas Graf, Andy Bierman, Michael
   Richardson, Henk Birkholz for valuable review on this document,
   special thanks to Thomas and Michael for organizing the discussion on
   several relevant drafts and reach the common understanding on the
   concept and ideas.  Thanks Michael for providing CHIP/Matter WIFI
   statistics reference.

9.  References

9.1.  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>.

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

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

   [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>.






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   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

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

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

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

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,
              <https://www.rfc-editor.org/info/rfc8407>.

   [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>.

   [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>.

9.2.  Informative References

   [CHIP]     CSA, "Connected Home over IP Specification", April 2021.

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



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   [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>.

   [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>.

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

Appendix A.  Example YANG Module

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

A.1.  "example-wifi-mac" YANG Module







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

     import ietf-yang-types {
       prefix yang;
     }

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



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



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



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



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

Appendix B.  Adaptive Subscription and Notification Example

   The examples within this document use the normative YANG module
   "ietf-adaptive-subscription" defined in Section 4 and the non-
   normative example YANG module "example-wifi-network-diagnostic"
   defined in Appendix A.1.

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

B.1.  "edit-config" 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, 60
   seconds) and report updates every 60 seconds if the rssi value is
   greater than or equal to -65dB; If the rssi value is less than -65dB,
   switch to 5 seconds period value to report updates.
























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 <rpc message-id="101"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <edit-config>
   <target>
    <running/>
   </target>
   <config
    xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
    <top
     xmlns="http://example.com/schema/1.2/config"
     xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
     <yp:datastore
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
              ds:running
     </yp:datastore>
     <yp:datastore-xpath-filter
      xmlns:wnd="https://example.com/sample-data/1.0">
             /wnd:example-wifi-network-diagnostic
     </yp:datastore-xpath-filter>
     <as:adaptive-subscriptions
      xmlns:as="urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription">
      <as:adaptive-period>
       <as:xpath-external-eval>
        /wnd:server/wnd:rssi&lt;-65
       </as:xpath-external-eval>
       <as:period>5</as:period>
      </as:adaptive-period>
      <as:adaptive-period>
       <as:xpath-external-eval>
        /wnd:server/wnd:rssi&gt;=-65
       </as:xpath-external-eval>
       <as:period>60</as:period>
     </as:adaptive-period>
     </as:adaptive-subscriptions>
    </top>
   </config>
  </edit-config>
 </rpc>

B.2.  Create Adaptive Subscription Example

   The subscriber sends an "establish-subscription" RPC with the
   parameters listed in 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 -65dB; If the rssi value is greater than or equal
   to -65dB, switch to 60 seconds period value.  (Section 2)




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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:running
     </yp:datastore>
     <yp:datastore-xpath-filter
      xmlns:wnd="https://example.com/sample-data/1.0">
          /wnd:example-wifi-network-diagnostic
     </yp:datastore-xpath-filter>
     <as:adaptive-subscriptions
      xmlns:as="urn:ietf:params:xml:ns:yang:ietf-adaptive-subscription">
      <as:adaptive-period>
       <as:xpath-external-eval>
        wnd:server/wnd:rssi&lt;-65
       </as:xpath-external-eval>
       <as:period>5</as:period>
      </as:adaptive-period>
      <as:adaptive-period>
       <as:xpath-external-eval>
        wnd:server/wnd:rssi&gt;=-65
       </as:xpath-external-eval>
       <as:period>60</as:period>
      </as:adaptive-period>
     </as:adaptive-subscriptions>
    </establish-subscription>
   </netconf:rpc>

B.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.

   For instance, if the XPATH 1.0 syntax against the targeted data
   object defined in "xpath-external-eval" is not supported by the
   server' s implementation, the server returns a reply indicating a
   failure.  The following <rpc-reply> illustrates an example:









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<?xml version="1.0" encoding="utf-8"?>
<rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" message-id="101">
  <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="https://example.com/sample-data/1.0">
      /wnd:server/wnd:rssi
    </error-path>
  </rpc-error>
</rpc-reply>

   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.

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

   Upon the server switches from the update interval 5 seconds to the
   new update interval 60 seconds, before sending event records to
   receivers, the "adaptive-period-update" notification should be
   generated and sent to the receivers to inform the receivers that the
   update interval value is switched to the new value.





















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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>2016-11-21T13:51:00Z</eventTime>
    <adaptive-period-update
     xmlns="http://example.com/ietf-adaptive-subscription">
     <id>0</id>
     <period>60</period>
     <yp:datastore
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
          ds:running
     </yp:datastore>
     <yp:datastore-xpath-filter
      xmlns:ex="https://example.com/sample-data/1.0">
          /ex:example-wifi-network-diagnostic
     </yp:datastore-xpath-filter>
    </adaptive-period-update>
   </notification>

B.5.  Changes between Revisions

   v09 -v10

   *  Change the draft intended status to "experimental"

   *  Problem statement refinement

   v08 -v09

   *  Define two new RPC errors to report when adaptive subscription
      unsupported or multiple XPath criteria conflict.

   *  Remove the "watermark" parameter.

   *  Add clarification about how to evaluate the XPath expression
      defined in "xpath-external-eval".

   *  Add clarification about how to compare a targeted data object in a
      specific list entry.

   v07 -v08

   *  Define a new RPC error to report when an XPath syntax defined in
      "xpath-external-eval" is unsupported by a server.

   *  Add a new example showing how the RPC error being returned by a
      publisher.




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   *  The usage examples fixed in the Appendix.

   *  Grammatical errors correction(missing articles, plurality
      mismatches, etc).

   v06 -v07

   *  The usage examples typo fixed in the Appendix.

   *  Add reference to RFC7950 XPATH Evaluation section and XPATH 1.0

   *  Clarify the definitions of 'xpath-external-eval' and 'selection-
      filter' by reusing XPATH Evaluation rules in RFC7950.

   *  Add a new terminology "adaptive subscription".

   *  Add one section to discuss Arbitrary XPath Complexity.

   v05 -v06

   *  Replace example-wifi-mac module with example-wifi-network-
      diagnostic using WIFI statistics specified in CHIP specification.

   *  Update adaptive subscription Example to align with WIFI example
      module change.

   *  Add one more reference to CHIP Specification.

   v04 -v05

   *  Remove "modify-subscption" RPC usage.

   *  Module update to fix the nits.

   *  Update adaptive subscription Example.

   *  Other Editorial changes.

   v03 - v04

   *  Add missing subtrees and data nodes in the security section;

   *  Change "adaptive-update" notification into "adaptive-period-
      update" notification;

   *  Other Editorial changes.

   v02 - v03



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   *  Clarify the difference between low priority telemetry data
      dropping and collection rate switching in the introduction
      section;

   *  Update the abstract and introduction section to focus on
      collection rate switching in the server without interaction with
      the remote client;

   *  Format usage example and change ssid into rssi in the appendix;

   *  Use boilerplate and reuse the terms in the terminology section.

Authors' Addresses

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


   Wei Song
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: songwei80@huawei.com


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


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





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   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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