Internet-Draft Adaptive Subscription May 2023
Wu, et al. Expires 1 December 2023 [Page]
Workgroup:
NETCONF Working Group
Internet-Draft:
draft-ietf-netconf-adaptive-subscription-03
Published:
Intended Status:
Experimental
Expires:
Authors:
Q. Wu
Huawei
W. Song
Huawei
P. Liu
China Mobile
Q. Ma
Huawei
W. Wang
China Telecom
Z. Niu
Microsoft

Adaptive Subscription to YANG Notification

Abstract

This document defines a YANG data model and associated mechanism that enable adaptive subscription to a publisher's event streams. The periodic update interval for the event streams can be set adaptively. Applying these elements allows servers to 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 1 December 2023.

Table of Contents

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.

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 could be temporarily overwhelmed with a burst of streamed data, and that network resources (e.g., bandwidth resource, radio resource) and computation resource could be excessively consumed. Therefore, it may be hard to continuously monitor operational data, especially values that fall outside normal operational ranges. Conversely, if the rate at which we collect a stream of data is set too low or chosen so that low priority telemetry data are dropped, these telemetry data will not be sufficient to detect and diagnose problems and to 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 policies 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. 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 that enable adaptive subscription to a publisher's event streams. The periodic update interval for the event streams can be set adaptively. Applying these elements allows servers to automatically adjust the rate and volume of telemetry traffic sent from a publisher 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], [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 to automatically switch to different period intervals according to network condition changes without interacting with the client for update policy instructions.

2. Model Overview

This document defines a YANG module "ietf-adapt-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-adapt-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-adapt-subscription" module.

module: ietf-adapt-subscription
  augment /sn:subscriptions/sn:subscription/yp:update-trigger:
    +--:(adaptive-periodic)
       +--rw adaptive-periods
          +--rw adaptive-period* [name]
             +--rw name                   yang:yang-identifier
             +--rw xpath-external-eval    yang:xpath1.0
             +--rw period                 yp:centiseconds
             +--rw anchor-time?           yang:date-and-time
  augment /sn:establish-subscription/sn:input/yp:update-trigger:
    +--:(adaptive-periodic)
       +-- adaptive-periods
          +-- adaptive-period* [name]
             +-- name                   yang:yang-identifier
             +-- xpath-external-eval    yang:xpath1.0
             +-- period                 yp:centiseconds
             +-- anchor-time?           yang:date-and-time
  augment /sn:modify-subscription/sn:input/yp:update-trigger:
    +--:(adaptive-periodic)
       +-- adaptive-periods
          +-- adaptive-period* [name]
             +-- name                   yang:yang-identifier
             +-- xpath-external-eval    yang:xpath1.0
             +-- period                 yp:centiseconds
             +-- anchor-time?           yang:date-and-time
  augment /sn:subscription-started/yp:update-trigger:
    +--:(adaptive-periodic)
       +-- adaptive-periods
          +-- adaptive-period* [name]
             +-- name                   yang:yang-identifier
             +-- xpath-external-eval    yang:xpath1.0
             +-- period                 yp:centiseconds
             +-- anchor-time?           yang:date-and-time
  augment /sn:subscription-modified/yp:update-trigger:
    +--:(adaptive-periodic)
       +-- adaptive-periods
          +-- adaptive-period* [name]
             +-- name                   yang:yang-identifier
             +-- xpath-external-eval    yang:xpath1.0
             +-- period                 yp:centiseconds
             +-- anchor-time?           yang:date-and-time

  notifications:
    +---n adaptive-period-update
       +--ro id?                                     sn:subscription-id
       +--ro period                                  yp:centiseconds
       +--ro period-update-time?                     yang:date-and-time
       +--ro datastore                               identityref
       +--ro (selection-filter)?
          +--:(by-reference)
          |  +--ro selection-filter-ref              selection-filter-ref
          +--:(within-subscription)
             +--ro (filter-spec)?
                +--:(datastore-subtree-filter)
                |  +--ro datastore-subtree-filter?
                           <anydata> {sn:subtree}?
                +--:(datastore-xpath-filter)
                   +--ro datastore-xpath-filter?
                           yang:xpath1.0 {sn:xpath}?

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" 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 co-exist with an "xpath-external-eval" parameter and can be switched based on trigger conditions indicated by the "xpath-external-eval" parameter;
  • 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.

    It is not always trivial for a subscriber to determine the threshold used in an XPath expression criterion. Sometimes the threshold needs to be adjusted during the lifecycle of an adaptive subscription, depending on historical fluctuation range and how fast the targeted data object changes, distribution characteristics of the targeted data object or even the generated volume of telemetry traffic.

    How often the XPath expression criterion is evaluated to decide whether to switch to another period interval is up to the publisher's implementation. With minimal delay, the expression can be evaluated whenever changes to targeted data object occur, or at the end of each shortest 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:

    • 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 the "xpath-external-eval" parameter refers to multiple 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 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 value. Only if the Xpath expression is evaluated as "true", does the publisher switch to the corresponding period with which push updates are reported.

Note that the adaptive subscription need not be supported by every YANG datastore node. 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 the ones defined in Section 2.1.

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 failed 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" are evaluated as conflicting, i.e., more than one condition expressions are evaluated to "true". However, the publisher should still push updates at the shortest streaming period among multiple corresponding period intervals if multiple Xpath evaluations conflict with each other during the lifecycle of an adaptive subscription.

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

Note that existing RPC errors defined in RFC 8639 and RFC 8641 are still supported by this document. For example, if any configured period for adaptive subscription is not supported by the publisher, a "period-unsupported" error response could be used.

2.3. 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. As stated in RFC 8639, section 2.7, 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 the 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:

  • 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 "xpath-external-eval" expression result changed.
  • 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 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 the "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]:

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, 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 design principles are recommended:

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

4. Adaptive Subscription YANG Module

This YANG module makes imports from [RFC8639], [RFC8641] and [I-D.ietf-netmod-rfc6991-bis].

<CODE BEGINS> file "ietf-adapt-subscription@2023-05-30.yang"

   module ietf-adapt-subscription {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-adapt-subscription";
     prefix as;

     import ietf-subscribed-notifications {
       prefix sn;
       reference
         "RFC 8639: Subscription to YANG Notifications";
     }
     import ietf-yang-push {
       prefix yp;
       reference
         "RFC 8641: Subscription to YANG Notifications for Datastore
          Updates";
     }
     import ietf-yang-types {
       prefix yang;
       reference
         "RFC YYYY: Common YANG Data Types";
     }

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

        Editor: Qin Wu
              <mailto:bill.wu@huawei.com>

        Editor: Wei Song
              <mailto: songwei80@huawei.com>

        Editor: Peng Liu
              <mailto: liupengyjy@chinamobile.com>

        Editor: Qiufang Ma
              <mailto: maqiufang1@huawei.com>

        Editor: Wei Wang
             <mailto: wangw36@chinatelecom.cn>

        Editor: 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) 2023 IETF Trust and the persons identified
        as authors of the code. All rights reserved.

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

        This version of this YANG module is part of RFC xxxx
        (https://www.rfc-editor.org/info/rfcxxxx); see the RFC
        itself for full legal notices.

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
        'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
        'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
        are to be interpreted as described in BCP 14 (RFC 2119)
        (RFC 8174) when, and only when, they appear in all
        capitals, as shown here.";

     revision 2023-05-30 {
       description
         "Initial revision";
       reference
         "RFC xxxx: 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
         "Multiple Xpath evaluation criteria represented by
          'xpath-external-eval' are evaluated as a conflict. I.e.,
          more than one condition expression is evaluated to
          'true'.";
     }

     grouping adaptive-subscription-modifiable {
       description
         "This grouping describes the datastore-specific adaptive
          subscription conditions that can be changed during the
          lifetime of the subscription.";
       container adaptive-periods {
         list adaptive-period {
           key "name";
           description
             "An entry in this list represents an 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 yang:yang-identifier;
             description
               "The name of adaptive period.";
           }
           leaf xpath-external-eval {
             type yang:xpath1.0;
             mandatory true;
             description
               "An 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
               "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.";
           }
         }
         description
           "Container for adaptively periodic subscription.";
       }
     }

     augment "/sn:subscriptions/sn:subscription/yp:update-trigger" {
       description
         "This augmentation adds additional subscription parameters
          that apply specifically to adaptive subscription.";
       case adaptive-periodic {
         description
           "Defines adaptively periodic case for sending an event
            record to the subscriber.";
         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 {
         description
           "Defines adaptively periodic case for sending an event
            record to the subscriber.";
         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 {
         description
           "Defines adaptively periodic case for sending an event
            record to the subscriber.";
         uses adaptive-subscription-modifiable;
       }
     }

     augment "/sn:subscription-started/yp:update-trigger" {
       description
         "This augmentation adds additional adaptive subscription
          parameters to the notification that a subscription has
          started.";
       case adaptive-periodic {
         description
           "Defines adaptively periodic case for sending an event
            record to the subscriber.";
         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 {
         description
           "Defines adaptively periodic case for sending an event
            record to the subscriber.";
         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;
         mandatory true;
         description
           "New duration of time that should occur between periodic
            push updates, in units of 0.01 seconds.";
       }
       leaf period-update-time {
         type yang:date-and-time;
         description
           "Designates a timestamp when the server starts to switch
            to another period interval because the evaluated 'xpath-
            external-eval' expression result changed.";
       }
       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-adapt-subscription
      Registrant Contact: The IESG.
      XML: N/A, the requested URI is an XML namespace.
   ---------------------------------------------------------------------

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-adapt-subscription
      Namespace:    urn:ietf:params:xml:ns:yang:ietf-adapt-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:

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, Chong Feng, Adrian Farrel 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

[I-D.ietf-netmod-rfc6991-bis]
Schönwälder, J., "Common YANG Data Types", Work in Progress, Internet-Draft, draft-ietf-netmod-rfc6991-bis-15, , <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-rfc6991-bis-15>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC3198]
Westerinen, A., Schnizlein, J., Strassner, J., Scherling, M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry, J., and S. Waldbusser, "Terminology for Policy-Based Management", RFC 3198, DOI 10.17487/RFC3198, , <https://www.rfc-editor.org/info/rfc3198>.
[RFC5277]
Chisholm, S. and H. Trevino, "NETCONF Event Notifications", RFC 5277, DOI 10.17487/RFC5277, , <https://www.rfc-editor.org/info/rfc5277>.
[RFC6241]
Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://www.rfc-editor.org/info/rfc6241>.
[RFC6242]
Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, , <https://www.rfc-editor.org/info/rfc6242>.
[RFC7950]
Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, , <https://www.rfc-editor.org/info/rfc7950>.
[RFC8040]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://www.rfc-editor.org/info/rfc8040>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8342>.
[RFC8446]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://www.rfc-editor.org/info/rfc8446>.
[RFC8639]
Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard, E., and A. Tripathy, "Subscription to YANG Notifications", RFC 8639, DOI 10.17487/RFC8639, , <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, , <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, , <https://www.rfc-editor.org/info/rfc9196>.

9.2. Informative References

[CHIP]
CSA, "Connected Home over IP Specification", .
[IEEE754-2008]
IEEE, "IEEE Standard for Floating-Point Arithmetic", DOI 10.1109/IEEESTD.2008.4610935, , <http://standards.ieee.org/findstds/standard/754-2008.html>.
[RFC3688]
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://www.rfc-editor.org/info/rfc3688>.
[RFC6020]
Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, , <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, , <https://www.rfc-editor.org/info/rfc8340>.
[XPATH1.0]
W3C, "https://www.w3.org/TR/1999/REC-xpath-19991116/", .

Appendix A. Example YANG Module

This section presents an example YANG module so that Appendix B can give examples of how the YANG module defined in Section 4 is used to perform adaptive subscription. The example YANG module used in this section represents a Wi-Fi Network Diagnostics data specified in [CHIP] which can be used by a Node to assist a user or Administrative Node in diagnosing potential problems.

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

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

A.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 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;
        }
        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;
      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 {
    config false;
    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;
        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
          "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-adapt-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.

<rpc message-id="101"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <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>
     <as:adaptive-periods
      xmlns:as="urn:ietf:params:xml:ns:yang:ietf-adapt-subscription">
      <as:adaptive-period>
       <as:name>adaptive-period-1</as:name>
       <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:name>adaptive-period-2</as:name>
       <as:xpath-external-eval>
        /wnd:server/wnd:rssi&gt;=-65
       </as:xpath-external-eval>
       <as:period>60</as:period>
     </as:adaptive-period>
     </as:adaptive-periods>
     <receivers>
       <receiver>
        <name>host.example.com</name>
       </receiver>
     </receivers>
     </subscription>
    </subscriptions>
   </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)

 <netconf:rpc message-id="101"
  xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription
   xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
   xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
   <yp:datastore
    xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
           ds:operational
   </yp:datastore>
   <yp:datastore-xpath-filter
    xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
        /wnd:server
   </yp:datastore-xpath-filter>
   <as:adaptive-periods
    xmlns:as="urn:ietf:params:xml:ns:yang:ietf-adapt-subscription">
    <as:adaptive-period>
     <as:name>adaptive-period-1</as:name>
     <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:name>adaptive-period-2</as:name>
     <as:xpath-external-eval>
      /wnd:server/wnd:rssi&gt;=-65
     </as:xpath-external-eval>
     <as:period>60</as:period>
    </as:adaptive-period>
   </as:adaptive-periods>
  </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:

<?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-adapt-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>

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.

<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="urn:ietf:params:xml:ns:yang:ietf-adapt-subscription">
  <id>1011</id>
  <period>60</period>
  <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>

Appendix C. Changes between Revisions

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

v02 -v03

v01 -v02

v00 -v01

v09 -v10

v08 -v09

v07 -v08

v06 -v07

v05 -v06

v04 -v05

v03 - v04

v02 - v03

Authors' Addresses

Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing
Jiangsu, 210012
China
Wei Song
Huawei
101 Software Avenue, Yuhua District
Nanjing
Jiangsu, 210012
China
Peng Liu
China Mobile
32 Xuanwumen West St, Xicheng District
Beijing
Qiufang Ma
Huawei
101 Software Avenue, Yuhua District
Nanjing
Jiangsu, 210012
China
Wei Wang
China Telecom
32 Xuanwumen West St, Xicheng District
Beijing
Zhixiong Niu
Microsoft