draft-unyte-netconf-distributed-notif-00.xml

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<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
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<rfc category="std" docName="draft-unyte-netconf-distributed-notif-00"
     ipr="trust200902">
  <front>
    <title abbrev="Distributed Notifications">Subscription to Distributed
    Notifications</title>

    <author fullname="Tianran Zhou" initials="T." surname="Zhou">
      <organization>Huawei</organization>

      <address>
        <postal>
          <street>156 Beiqing Rd., Haidian District</street>

          <city>Beijing</city>

          <region/>

          <code/>

          <country>China</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>zhoutianran@huawei.com</email>

        <uri/>
      </address>
    </author>

    <author fullname="Guangying Zheng" initials="G." surname="Zheng">
      <organization>Huawei</organization>

      <address>
        <postal>
          <street>101 Yu-Hua-Tai Software Road</street>

          <city>Nanjing</city>

          <code/>

          <region>Jiangsu</region>

          <country>China</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>zhengguangying@huawei.com</email>
      </address>
    </author>

    <author fullname="Eric Voit" initials="E." surname="Voit">
      <organization>Cisco Systems</organization>

      <address>
        <postal>
          <street/>

          <city/>

          <code/>

          <region/>

          <country>United States of America</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>evoit@cisco.com</email>
      </address>
    </author>

    <author fullname="Thomas Graf" initials="T." surname="Graf">
      <organization>Swisscom</organization>

      <address>
        <postal>
          <street>Binzring 17</street>

          <city>Zuerich 8045</city>

          <region/>

          <code/>

          <country>Switzerland</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>thomas.graf@swisscom.com</email>

        <uri/>
      </address>
    </author>

    <author fullname="Pierre Francois" initials="P." surname="Francois">
      <organization>INSA-Lyon</organization>

      <address>
        <postal>
          <street/>

          <city>Lyon</city>

          <region/>

          <code/>

          <country>France</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>pierre.francois@insa-lyon.fr</email>

        <uri/>
      </address>
    </author>

    <date day="10" month="July" year="2020"/>

    <workgroup>NETCONF</workgroup>

    <abstract>
      <t>This documents describes extensions to the YANG notifications
      subscription to allow metrics being published directly from processors
      on line cards to target receivers, while subscription is still
      maintained at the route processor in a distributed forwarding
      system.</t>
    </abstract>

    <note title="Requirements Language">
      <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
      "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
      document are to be interpreted as described in <xref
      target="RFC2119">RFC 2119</xref>.</t>
    </note>
  </front>

  <middle>
    <section title="Introduction">
      <t>The mechanism to support a subscription to a continuous and
      customized stream of updates from a YANG datastore is defined in <xref
      target="RFC8639"/> and <xref target="RFC8641"/>. Requirements for
      Subscription to YANG Datastores are defined in <xref
      target="RFC7923"/></t>

      <t>By streaming data from publishers to receivers, much better
      performance and fine-grained sampling can be achieved than with polling.
      In a distributed forwarding system, the packet forwarding is delegated
      to multiple processors on line cards. To not to overhelm the route
      processor resources, it is not uncomon that data records are published
      directly from processors on line cards to target Receivers to further
      increase efficency on the routing system.</t>

      <t>This documents complement the general subscription requirements
      defined in section 4.2.1 of <xref target="RFC7923"/> by the paragraph: A
      Subscription Service MAY support the ability to export from multiple
      software processes on a single routing system and expose the information
      which software process produced which message to maintain data
      integrity.</t>
    </section>

    <section title="Terminologies">
      <t>The following terms are defined in <xref target="RFC8639"/> and are
      not redefined here:</t>

      <t>Subscriber</t>

      <t>Publisher</t>

      <t>Receiver</t>

      <t>Subscription</t>

      <t>In addition, this document defines the following terms:</t>

      <t>Global Subscription: the Subscription requested by the subscriber. It
      may be decomposed into multiple Component Subscriptions.</t>

      <t>Component Subscription: is the Subscription that defines a data
      source which is managed and controlled by a single Publisher.</t>

      <t>Global Capability: is the overall subscription capability that the
      group of Publishers can expose to the Subscriber.</t>

      <t>Component Capability: is the subscription capability that each
      Publisher can expose to the Subscriber.</t>

      <t>Master: is the Publisher that interacts with the Subscriber to deal
      with the Global Subscription. It decomposes the Global Subscription to
      multiple Component Subscriptions and interacts with the Agents.</t>

      <t>Agent: is the Publisher that interacts with the Master to deal with
      the Component Subscription and pushing the data to the collector.</t>
    </section>

    <section title="Solution Overview">
      <t>Figure 2 below shows the distributed data export framework.</t>

      <t>A collector usually includes two components,</t>

      <t><list style="symbols">
          <t>the Subscriber generates the subscription instructions to express
          what and how the collector want to receive the data;</t>

          <t>the Receiver is the target for the data publication.</t>
        </list></t>

      <t>For one subscription, there are one or more Receivers. And the
      Subscriber does not necessarily share the same IP address as the
      Receivers.</t>

      <t>In this framework, the Publisher pushes data to the Receiver
      according to the subscription. The Publisher is either in the Master or
      Agent role. The Master knows all the capabilities that his Agents are
      able to provide and exposes the Global Capability to the collector. The
      Subscriber maintains the Global Subscription at the Master and
      disassembles the Global Subscription to multiple Component
      Subscriptions, depending from which source data is needed. The Component
      Subscriptions are then distributed to the corresponding Publisher Agents
      on route and processors on line cards.</t>

      <t>Publisher Agents collects metrics according to the Component
      Subscription, add its metadata, encapsulate and pushes data to the
      Receiver where packets are reassembled and decapsulated.</t>

      <t><figure title="Fig. 2 The Distributed Data Export Framework">
          <artwork align="center"><![CDATA[
+-----------------------------------------+
|        Collector        |-------------+ |
|                        +------------+ | |
|      +------------+    || Receiver  | | |
|      | Subscriber |    |--------------+ |
|      +-----^-+----+    +------------^   |
|            | |                      |   |
+-----------------------------------------+
   Global    | | Global               |
   Capability| | Subscription         |
+-----------------------------------------+
|            | |                      |   |
|   +--------+-v-------------------+  |   |
|   |       Publisher(Master)      |  |   |
|   +--------^-+-------------------+  |   |
|            | |                      |   |
|            | |                      |   |
|  Component | | Component       Push |   |
|  Capability| | Subscription         |   |
|   +--------+-v-------------------+  |   |
|   |       Publisher(Agent)       +--+   |
|   +------------------------------+      |
|                                         |
|                Device                   |
+-----------------------------------------+

]]></artwork>
        </figure></t>

      <t>Master and Agents interact with each other in several ways: <list
          style="symbols">
          <t>Agents need to register at the Master at the beginning of their
          process life-cycle</t>

          <t>Contracts are created between the Master and each Agent on the
          Component Capability, and the format for streaming data
          structure.</t>

          <t>The Master relays the component subscriptions to the Agents.</t>

          <t>The Agents announce the status of their Component Subscriptions
          to the Master. The status of the overall subscription is maintained
          by the Master. The Master is responsible for notifying the
          subscriber in case of problems with the Component Subscriptions.</t>
        </list>The technical mechanisms or protocols used for the coordination
      of operational information between Master and Agent is out-of-scope of
      this document.</t>
    </section>

    <section title="Subscription Decomposition">
      <t>The Collector can only subscribe to the Master. This requires the
      Master to:</t>

      <t><list style="numbers">
          <t>expose the Global Capability that can be served by multiple
          Publisher Agents;</t>

          <t>disassemble the Global Subscription to multiple Component
          Subscriptions, and distribute them to the Publisher Agents of the
          corresponding metric sources so that they not overlap;</t>

          <t>notify on changes when portions of a subscription moving between
          different Publisher Agents over time.</t>
        </list></t>

      <t>And the Agent to:</t>

      <t><list style="symbols">
          <t>Inherit the Global Subscription properties from Publisher Master
          for its Component Subscription;</t>

          <t>share the same life-cycle as the Global Subscription;</t>

          <t>share the same Subscription ID as the Global Subscription.</t>
        </list></t>
    </section>

    <section title="Publication Composition">
      <t>The Publisher Agent collects data and encapsulates the packets per
      Component Subscription. The format and structure of the data records are
      defined by the YANG schema, so that the decomposition at the Receiver
      can benefit from the structured and hierarchical data records.</t>

      <t>The Receiver is able to associate the YANG data records with <xref
      target="RFC8639">Subscription ID</xref> to the subscribed subscription
      and with <xref target="I-D.ietf-netconf-notification-messages">Message
      Generator ID</xref> to one of the Publisher Agents software processes to
      enable message integrity.</t>

      <t>For the dynamic subscription, the output of the
      "establish-subscription" RPC defined in <xref target="RFC8639"/> MUST
      include a list of Message Generator IDs to indicate how the Global
      Subscription is decomposed into several Component Subscriptions.</t>

      <t>The "subscription-started" and "subscription-modified" notification
      defined in <xref target="RFC8639"/> MUST also include a list of Message
      Generator IDs to notify the current Publishers for the corresponding
      Global Subscription.</t>
    </section>

    <section title="Subscription State Change Notifications">
      <t>In addition to sending event records to Receivers, the Master MUST
      also send <xref target="RFC8639">subscription state change
      notifications</xref> when events related to subscription management have
      occurred. All the subscription state change notifications MUST be
      delivered by the Master.</t>

      <t>When the subscription decomposition result changed, the
      "subscription-modified" notification MUST be sent to indicate the new
      list of Publishers.</t>
    </section>

    <section title="Publisher Configurations">
      <t>This document assumes that all Publisher Agents are preconfigured to
      push data. The actual working Publisher Agents are selected based on the
      subscription decomposition result.</t>

      <t>All Publisher Agents share the same source IP address for data
      export. For connectionless data transport such as <xref
      target="I-D.unyte-netconf-udp-notif">UDP based transport</xref> the same
      Layer 4 source port for data export can be used. For connection based
      data transport such as <xref target="I-D.ietf-netconf-https-notif">
      HTTPS based transport</xref>, each Publisher Agent MUST be able to
      acknowledge packet retrieval from Receivers, and therefore requires a
      dedicated Layer 4 source port per software process.</t>

      <t>The specific configuration on transports is described in the
      resposible documents.</t>
    </section>

    <section title="YANG Tree">
      <t/>

      <t><figure>
          <artwork><![CDATA[
module: ietf-distributed-notifications
  augment /sn:subscriptions/sn:subscription:
    +--ro message-generator-id*   string
  augment /sn:subscription-started:
    +--ro message-generator-id*   string
  augment /sn:subscription-modified:
    +--ro message-generator-id*   string
  augment /sn:establish-subscription/sn:output:
    +--ro message-generator-id*   string
]]></artwork>
        </figure></t>
    </section>

    <section title="YANG Module">
      <t/>

      <t><figure>
          <artwork><![CDATA[
<CODE BEGINS> file "ietf-distributed-notifications@2020-05-09.yang"
module ietf-distributed-notif {
  yang-version 1.1;
  namespace 
    "urn:ietf:params:xml:ns:yang:ietf-distributed-notifications";
  prefix mso;
  import ietf-subscribed-notifications {
    prefix sn;
  }

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

     Editor:   Tianran Zhou
               <mailto:zhoutianran@huawei.com>
     
     Editor:   Guangying Zheng
               <mailto:zhengguangying@huawei.com>";


  description
    "Defines augmentation for ietf-subscribed-notifications to 
    enable the distributed publication with single subscription.

    Copyright (c) 2018 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 Simplified 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; see the 
    RFC itself for full legal notices.";

  revision 2020-05-09 {
    description
      "Initial version";
    reference
      "RFC XXXX: Subscription to Distributed Notifications";
  }

  grouping message-generator-ids {
    description
      "Provides a reusable list of message-generator-ids.";
    
    leaf-list message-generator-id {
      type string;
      config false;
      ordered-by user;
      description
        "Software process which created the message (e.g.,
         processor 1 on linecard 1). This field is
         used to  notify the collector the working originator.";
    }
  }

  augment "/sn:subscriptions/sn:subscription" {
    description
      "This augmentation allows the message generators to be 
      exposed for a subscription.";

    uses message-generator-ids;
  }
 
  augment "/sn:subscription-started" {
    description
      "This augmentation allows MSO specific parameters to be
       exposed for a subscription.";

    uses message-generator-ids;
  }

  augment "/sn:subscription-modified" {
    description
      "This augmentation allows MSO specific parameters to be
       exposed for a subscription.";

    uses message-generator-ids;
  }

  augment "/sn:establish-subscription/sn:output" {
    description
      "This augmentation allows MSO specific parameters to be
       exposed for a subscription.";
    
    uses message-generator-ids;
  }
}
<CODE ENDS>
]]></artwork>
        </figure></t>
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <t>This document registers the following namespace URI in the <xref
      target="RFC3688">IETF XML Registry</xref>:</t>

      <t><list style="empty">
          <t>URI:
          urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications</t>

          <t>Registrant Contact: The IESG.</t>

          <t>XML: N/A; the requested URI is an XML namespace.</t>
        </list>This document registers the following YANG module in the <xref
      target="RFC3688">YANG Module Names registry</xref>:</t>

      <t><list style="empty">
          <t>Name: ietf-subscribed-notifications</t>

          <t>Namespace:
          urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications</t>

          <t>Prefix: mso</t>

          <t>Reference: RFC XXXX</t>
        </list></t>
    </section>

    <section anchor="Security" title="Security Considerations">
      <t>The YANG module specified in this document defines a schema for data
      that is designed to be accessed via network management protocols such as
      <xref target="RFC6241">NETCONF</xref> or <xref
      target="RFC8040">RESTCONF</xref>. The lowest NETCONF layer is the secure
      transport layer, and the mandatory-to-implement secure transport is
      <xref target="RFC6242">Secure Shell (SSH)</xref>. The lowest RESTCONF
      layer is HTTPS, and the mandatory-to-implement secure transport is <xref
      target="RFC5246">TLS</xref>.</t>

      <t>The NETCONF <xref target="RFC6536">Access Control Model (NACM)</xref>
      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.</t>

      <t>The new data nodes introduced in this YANG module may be considered
      sensitive or vulnerable in some network environments. It is thus
      important to control read access (e.g., via get-config or notification)
      to this data nodes. These are the subtrees and data nodes and their
      sensitivity/vulnerability:</t>

      <t><list style="symbols">
          <t>/subscriptions/subscription/message-generator-ids</t>
        </list>The entries in the two lists above will show where subscribed
      resources might be located on the publishers. Access control MUST be set
      so that only someone with proper access permissions has the ability to
      access this resource.</t>

      <t>Other Security Considerations is the same as those discussed in <xref
      target="RFC8641">YANG-Push</xref>.</t>
    </section>

    <section title="Contributors">
      <figure>
        <artwork><![CDATA[   Alexander Clemm
   Futurewai
   2330 Central Expressway
   Santa Clara
   California
   United States of America
   Email: ludwig@clemm.org]]></artwork>
      </figure>
    </section>

    <section anchor="Acknowledgements" title="Acknowledgements">
      <t>We thank Kent Watsen, Mahesh Jethanandani, Martin Bjorklund, Tim
      Carey and Qin Wu for their constructive suggestions for improving this
      document.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include="reference.RFC.2119"?>

      <?rfc include='reference.RFC.5246'?>

      <?rfc include='reference.RFC.3688'?>

      <?rfc include='reference.RFC.6241'?>

      <?rfc include='reference.RFC.8040'?>

      <?rfc include='reference.RFC.8639'?>

      <?rfc include='reference.RFC.8641'?>

      <?rfc include='reference.RFC.6536'?>

      <?rfc include='reference.RFC.6242'?>

      <?rfc include='reference.RFC.7923'?>
    </references>

    <references title="Informative References">
      <?rfc include="reference.I-D.ietf-netconf-notification-messages"?>

      <reference anchor="I-D.unyte-netconf-udp-notif" target="">
        <front>
          <title>UDP-based Transport for Configured Subscriptions</title>

          <author fullname="Tianran Zhou" initials="T." surname="Zhou">
            <organization>Huawei</organization>
          </author>

          <author fullname="Guangying Zheng" initials="G." surname="Zheng">
            <organization>Huawei</organization>
          </author>

          <author fullname="Paolo Lucente" initials="P." surname="Lucente">
            <organization>NTT</organization>
          </author>

          <author fullname="Thomas Graf" initials="T." surname="Graf">
            <organization>Swisscom</organization>
          </author>

          <author fullname="Pierre Francois" initials="P." surname="Francois">
            <organization>INSA-Lyon</organization>
          </author>

          <date month="July" year="2020"/>
        </front>

        <seriesInfo name="Internet-Draft"
                    value="draft-unyte-netconf-udp-notif-00"/>
      </reference>

      <?rfc include='reference.I-D.ietf-netconf-https-notif'?>
    </references>

    <section title="Examples">
      <t>This appendix is non-normative.</t>

      <section title="Dynamic Subscription">
        <t>Figure 3 shows a typical dynamic subscription to the device with
        distributed data export capability.</t>

        <t><figure title="Fig. 3 Call Flow for Dynamic Subscription">
            <artwork><![CDATA[
+-------------+                 +-------------+ +-------------+
| Subscriber/ |                 |  Publisher  | |  Publisher  |
| Receiver    |                 |  (Master)   | |  (Agent)    |
+-------------+                 +------+------+ +------+------+
       |                               |               |
       | establish-subscription        |               |
       +------------------------------>+ component     |
       |                               | subscription  |
       | RPC Reply: OK, id #22         +-------------->+
       | message generator ID [#1, #2] |               |
       +<------------------------------+               |
       |                               |               |
       | notif-mesg, id #22            |               |
       | message generator ID #1       |               |
       +<------------------------------+               |
       |                               |               |
       | notif-mesg, id#22             |               |
       | message generator ID #2       |               |
       +<----------------------------------------------+
       |                               |               |
       | modify-subscription (id#22)   |               |
       +------------------------------>+ component     |
       |                               | subscription  |
       | RPC Reply: OK, id #22         +-------------->+
       +<------------------------------+               |
       |                               |               |
       | subscription-modified, id#22  |               |
       | message generator ID [#1]     |               |
       +<------------------------------+               |
       |                               |               |
       | notif-mesg, id #22            |               |
       | message generator ID #1       |               |
       +<------------------------------+               |
       |                               |               |
       |                               |               |
       +                               +               +
]]></artwork>
          </figure></t>

        <t>A "establish-subscription" RPC request as per <xref
        target="RFC8641"/> is sent to the Master with a successful response.
        An example of using NETCONF:</t>

        <t><figure title="Fig. 4 &quot;establish-subscription&quot; Request">
            <artwork><![CDATA[
<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:ex="https://example.com/sample-data/1.0">
       /ex:foo
     </yp:datastore-xpath-filter>
     <yp:periodic>
       <yp:period>500</yp:period>
     </yp:periodic>
   </establish-subscription>
 </netconf:rpc>]]></artwork>
          </figure>As the device is able to fully satisfy the request, the
        request is given a subscription ID of 22. The response as in Figure 5
        indicates that the subscription is decomposed into two component
        subscriptions which will be published by two message generators: #1
        and #2.</t>

        <t><figure
            title="Fig. 5 &quot;establish-subscription&quot; Positive RPC Response">
            <artwork><![CDATA[<rpc-reply message-id="101"
   xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <id
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
      22
   </id>
   <message-generator-id
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications>
      1
   </message-generator-id>
   <message-generator-id
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications>
      2
   </message-generator-id>
</rpc-reply>]]></artwork>
          </figure>Then, both Publishers send notifications with the
        corresponding piece of data to the Receiver.</t>

        <t>The subscriber may invoke the "modify-subscription" RPC for a
        subscription it previously established. The RPC has no difference to
        the single publisher case as in [RFC8641]. Figure 6 provides an
        example where a subscriber attempts to modify the period and datastore
        XPath filter of a subscription using NETCONF.</t>

        <t><figure title="Fig. 6 &quot;modify-subscription&quot; Request">
            <artwork><![CDATA[     <rpc message-id="102"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <modify-subscription
           xmlns=
             "urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
           xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
         <id>22</id>
         <yp:datastore
             xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
           ds:operational
         </yp:datastore>
         <yp:datastore-xpath-filter
             xmlns:ex="https://example.com/sample-data/1.0">
           /ex:bar
         </yp:datastore-xpath-filter>
         <yp:periodic>
           <yp:period>250</yp:period>
         </yp:periodic>
        </modify-subscription>
     </rpc>]]></artwork>
          </figure></t>

        <t>If the modification is successfully accepted, the
        "subscription-modified" subscription state notification is sent to the
        subscriber by the Master. The notification, Figure 7 for example,
        indicates the modified subscription is decomposed into one component
        subscription which will be published by message generator #1.</t>

        <t><figure
            title="Fig. 7 &quot;subscription-modified&quot; Subscription State Notification">
            <artwork><![CDATA[<notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2007-09-01T10:00:00Z</eventTime>
  <subscription-modified
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
      xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
    <id>22</id>
    <yp:datastore
        xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
      ds:operational
    </yp:datastore>
    <yp:datastore-xpath-filter
        xmlns:ex="https://example.com/sample-data/1.0">
      /ex:bar
    </yp:datastore-xpath-filter>
    <yp:periodic>
        <yp:period>250</yp:period>
    </yp:periodic>
    <message-generator-id
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notificationss>
       1
    </message-generator-id>    
  </subscription-modified>
</notification>]]></artwork>
          </figure></t>

        <t/>
      </section>

      <section title="Configured Subscription">
        <t>Figure 8 shows a typical configured subscription to the device with
        distributed data export capability.</t>

        <t/>

        <t><figure title="Fig. 8 Call Flow for Configured Subscription">
            <artwork><![CDATA[
+-------------+                 +-------------+ +-------------+
| Receiver    |                 |  Publisher  | |  Publisher  |
|             |                 |  (Master)   | |  (Agent)    |
+------+------+                 +------+------+ +------+------+
       |                               |               |
       | subscription-started, id#39   |               |
       | message generator ID [#1, #2] |               |
       +<------------------------------+               |
       |                               |               |
       | notif-mesg, id#39             |               |
       | message generator ID #1       |               |
       +<------------------------------+               |
       |                               |               |
       | notif-mesg, id#39             |               |
       | message generator ID #2       |               |
       +<----------------------------------------------+
       |                               |               |
       |                               |               |
       |                               |               |
]]></artwork>
          </figure></t>

        <t>Before starting to push data, the "subscription-started"
        subscription state notification is sent to the Receiver. The following
        example assumes the NETCONF transport has already established. The
        notification indicates that the configured subscription is decomposed
        into two component subscriptions which will be published by two
        message generators: #1 and #2.</t>

        <t><figure
            title="Fig. 9 &quot;subscription-started&quot; Subscription State Notification">
            <artwork><![CDATA[
<notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2007-09-01T10:00:00Z</eventTime>
  <subscription-started
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
      xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
    <identifier>39</identifier>
    <yp:datastore
        xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
      ds:operational
    </yp:datastore>
    <yp:datastore-xpath-filter
        xmlns:ex="https://example.com/sample-data/1.0">
      /ex:foo
    </yp:datastore-xpath-filter>
    <yp:periodic>
        <yp:period>250</yp:period>
    </yp:periodic>
    <message-generator-id
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications>
       1
    </message-generator-id>
    <message-generator-id
    xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications>
       2
    </message-generator-id>
  </subscription-started>
</notification>]]></artwork>
          </figure></t>

        <t>Then, both Publishers send notifications with the corresponding
        data record to the Receiver.</t>
      </section>
    </section>
  </back>
</rfc>