Internet-Draft Adaptive Subscription October 2021
Wu, et al. Expires 25 April 2022 [Page]
Workgroup:
NETCONF Working Group
Internet-Draft:
draft-wang-netconf-adaptive-subscription-07
Published:
Intended Status:
Standards Track
Expires:
Authors:
Q. Wu
Huawei
W. Song
Huawei
P. Liu
China Mobile
Q. Ma
Huawei
W. Wang
China Telecom

Adaptive Subscription to YANG Notification

Abstract

This document defines a YANG data model and associated mechanism enabling 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 volume of telemetry traffic and rate of traffic sent from publisher to the 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 25 April 2022.

1. Introduction

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

  • Periodic subscription allows subscribed data to be streamed to the destination at a configured fixed periodic interval
  • On-change subscription allows update to be triggered whenever a change in the subscribed information is detected. The periodic interval is set to zero value in the on-change subscription case.

However in some large scale deployments (e.g., wireless network performance monitoring) where an increased data collection rate is being used, it becomes more likely that a burst of streamed data may temporarily overwhelm a receiver and consume expensive network resource (e.g., radio resource). If the rate at which we can collect a stream of data is set too low or getting low priority telemetry data dropped, these telemetry data are not sufficient to detect and diagnose problems and verify correct network behavior.

There is a need for a service to configure both clients and servers with multiple different period intervals and corresponding subscription update policy which allows servers/publishers automatically switch to different period intervals according to resource usage change without the interaction with the client for policy update instruction, e.g., when the wireless signal strength falls below a configured low watermark, the subscribed data can be streamed at a higher rate while when the wireless signal strength crosses a configured high watermark, the subscribed data can be streamed at lower rate.

This document defines a YANG data model and associated mechanism enabling subscriber's adaptive subscriptions to a publisher's event streams. Applying these elements allows servers to automatically adjust the volume of telemetry traffic and rate of traffic sent from publisher to the 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 automatically switch to different period intervals according to the resource usage change without the interaction with the client for update policy instruction.

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 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 update interval change.

The following tree diagrams [RFC8340] provide an overview of the data model for "ietf-adaptive-subscription.yang" 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 watermark?              uint32
                +--rw period                  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 watermark?              uint32
                +--rw period                  centiseconds
                +--rw anchor-time?            yang:date-and-time
  notifications:
    +---n adaptive-period-update
       +--ro id?                                     sn:subscription-id
       +--ro period                                  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}?

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 adaptive periodic parameters:

  • a "period" that defines the new duration between push updates, the period can be changed based on trigger condition.
  • 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 "watermark" that defines the threshold value of the targeted data object, e.g., it can be lower boundary or upper boundary of targeted data object.
  • a "xpath-external-eval" represents a stanard XPath Evaluation criteria (See section 6.4 of [RFC7950]) that is applied against the targeted data object, which is used to trigger update interval switch in the server. It follows the rules defined in section 3.4 of [XPATH1.0] and contains comparisons of datastore node with its value to the specific threshold (i.e., watermark) and associated logical operation in the XPath format. Different from stream-xpath-filter defined in [RFC8639], it doesn't influence the event records output generation from a publisher.

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 adaptive subscriptions. These parameters are same as one defined in Section 2.1.

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 'adpative-update' notification include:

  • a "period" that defines the duration between push updates, the period can be changed based on trigger condition.
  • 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 identifying 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 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 and "watermark" parameter defined by update trigger.

3. Arbitrary XPath Complexity Evaluation

YANG-Push subscriptions [RFC8641] specifies 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 that contain conditions that trigger the generation and pushing of new update records. To support adaptive subscription defined in this document, the trigger condition can also use similar selection filter to express a standard XPath Evaluation criteria (section 6.4 of [RFC7950]) against targeted data object.

Similar to on change subscription, the adaptive subscription 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 objects;
  • Support any type of node set in the XPath Evaluation criteria, e.g., string,int64, uint64, and decimal64 types;
  • Both objects in the XPath Evaluation criteria to be compared are node-sets;
  • Two objects to be compared are in different data type, e.g., one is integer, the other is 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 type, conversion function is needed to convert different data type into numbers.

In both objects in the 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 minimal set of data objects in the data model, these minimal set of data objects can be advertised using Notification capabilities model defined in [I-D.netconf-notification-capabilities].
  • XPath Evaluation criteria only support condition expression that filter updates based on numbers.
  • One object to be compared in the XPath Evaluation criteria MUST be nodeset.
  • The other object to be compared in the XPath Evaluation criteria MUST be numbers data type.

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 {
    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 2019-12-15 {
    description
      "Initial revision";
    reference
      "RFCxxx Adaptive subscription to YANG notification.";
  }

  typedef centiseconds {
    type uint32;
    description
      "A period of time, measured in units of 0.01 seconds.";
  }

  typedef seconds {
    type uint32;
    description
      "A period of time, measured in units of 1 seconds.";
  }

  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 influeced 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 watermark {
            type uint32;
            description
              "The watermark for targeted data object. The high
               watermark, lowe watermark can be specified for the
               targeted data object.";
          }
          leaf period {
            type 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 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 centiseconds;
      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 two URIs in the IETF XML registry [RFC3688]. Following the format in [RFC3688], the following registrations are 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.
   ---------------------------------------------------------------------

5.2. Updates to the YANG Module Names Registry

This document registers two YANG modules in the YANG Module Names registry [RFC7950]. . Following the format in [RFC6020], the following registration has been 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:watermark
  • /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:watermark
  • /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

7. Contributors

Michale Wang, Liang Geng for his major contributions to the initial modeling and use cases.

   Michale 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 thanks Rob Wilton, Thomas Graf, Andy Bierman, Michael Richardson, Henk Birkholz for valuable review on this document, special thanks to Thmas and Michael to organize 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, , <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, , <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>.
[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, , <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, , <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>.
[RFC8407]
Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8641>.

9.2. Informative References

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

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 

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;
        }
        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 {
    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-adaptive-subscription" as defined in Section 4 and the non-normative example YANG module "example-wifi-network-diagnostic" as 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 scan all clients every 60 seconds in the sampling window if the rssi value of client is greater than or equal to -65dB in the sampling window; If the rssi value of client is less than -65dB, switch to 5 seconds period value, and then scan all clients every 60 seconds.

 <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[rssi &lt; -65]
      </as:xpath-external-eval>
      <as:watermark>-65</as:watermark>
       <as:period>5</as:period>
      </as:adaptive-period>
      <as:adaptive-period>
       <as:xpath-external-eval>
             /wnd:server[rssi &ge; -65]
          </as:xpath-external-eval>
       <as:watermark>-65</as:watermark>
       <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 a adaptive subscription. The adaptive subscription configuration parameters require the server to scan all clients every 5 seconds if the rssi value of client is less than -65dB; If the rssi value of client is great than or equal to -65dB, switch to 60 seconds period value, and then report all clients every 60 seconds or scan every 5 seconds, collect 12 measurement values but report the last measurement value or average value of 12 measurement values. (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: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[rssi &lt; -65]
         </as:xpath-external-eval>
    <as:watermark>-65</as:watermark>
    <as:period>5</as:period>
   </as:adaptive-period>
   <as:adaptive-period>
    <as:xpath-external-eval>wnd:server[rssi &ge; -65]
    </as:xpath-external-eval>
    <as:watermark>-65</as:watermark>
    <as:period>60</as:period>
   </as:adaptive-period>
  </as:adaptive-subscriptions>
 </establish-subscription>
</netconf:rpc>

In another example, the adaptive subscription configuration parameters could also require the server to scan all clients every 5 seconds and report if the difference between maximum value of client rssi and minimum value of client rssi is greater than 0.20 dB in the sampling window; If the difference between maximum value of client rssi and minimum value of client rssi is less than 0.20 dB, switch to 60 seconds period value and then scan all clients every 60 seconds and report the last measurement value. If the difference between maximum value of client rssi and minimum value of client rssi is greater than or equal to 0.20 dB in two consecutive sampling windows, then in the second sampling window, only report the measurement value not reported by the previous sampling window.

<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-dianostic
  </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[max(rssi)-min(rssi) &ge; 20]
         </as:xpath-external-eval>
    <as:watermark>20</as:watermark>
    <as:period>5</as:period>
   </as:adaptive-period>
   <as:adaptive-period>
    <as:xpath-external-eval>
        wnd:server[max(rssi)-min(rssi) &lt; 20]
    </as:xpath-external-eval>
    <as:watermark>20</as:watermark>
    <as:period>60</as:period>
   </as:adaptive-period>
  </as:adaptive-subscriptions>
 </establish-subscription>
</netconf:rpc>

B.3. "adaptive-period-update" notification example

Upon the server switches to from the update interval 5 seconds to the new update interval 60 seconds, Before sending event records to receivers, the "adaptive-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="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.4. Changes between Revisions

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

  • 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
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