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NETCONF                                                          T. Zhou
Internet-Draft                                                  G. Zheng
Intended status: Standards Track                                  Huawei
Expires: January 11, 2021                                        E. Voit
                                                           Cisco Systems
                                                                 T. Graf
                                                                Swisscom
                                                             P. Francois
                                                               INSA-Lyon
                                                           July 10, 2020


               Subscription to Distributed Notifications
                draft-unyte-netconf-distributed-notif-00

Abstract

   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.

Requirements Language

   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 RFC 2119 [RFC2119].

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 January 11, 2021.






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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Subscription Decomposition  . . . . . . . . . . . . . . . . .   6
   5.  Publication Composition . . . . . . . . . . . . . . . . . . .   6
   6.  Subscription State Change Notifications . . . . . . . . . . .   7
   7.  Publisher Configurations  . . . . . . . . . . . . . . . . . .   7
   8.  YANG Tree . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .   7
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  10
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  11
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     14.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  12
     A.1.  Dynamic Subscription  . . . . . . . . . . . . . . . . . .  12
     A.2.  Configured Subscription . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   The mechanism to support a subscription to a continuous and
   customized stream of updates from a YANG datastore is defined in
   [RFC8639] and [RFC8641].  Requirements for Subscription to YANG
   Datastores are defined in [RFC7923]

   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



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   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.

   This documents complement the general subscription requirements
   defined in section 4.2.1 of [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.

2.  Terminologies

   The following terms are defined in [RFC8639] and are not redefined
   here:

   Subscriber

   Publisher

   Receiver

   Subscription

   In addition, this document defines the following terms:

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

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

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

   Component Capability: is the subscription capability that each
   Publisher can expose to the Subscriber.

   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.

   Agent: is the Publisher that interacts with the Master to deal with
   the Component Subscription and pushing the data to the collector.






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3.  Solution Overview

   Figure 2 below shows the distributed data export framework.

   A collector usually includes two components,

   o  the Subscriber generates the subscription instructions to express
      what and how the collector want to receive the data;

   o  the Receiver is the target for the data publication.

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

   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.

   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.























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                +-----------------------------------------+
                |        Collector        |-------------+ |
                |                        +------------+ | |
                |      +------------+    || Receiver  | | |
                |      | Subscriber |    |--------------+ |
                |      +-----^-+----+    +------------^   |
                |            | |                      |   |
                +-----------------------------------------+
                   Global    | | Global               |
                   Capability| | Subscription         |
                +-----------------------------------------+
                |            | |                      |   |
                |   +--------+-v-------------------+  |   |
                |   |       Publisher(Master)      |  |   |
                |   +--------^-+-------------------+  |   |
                |            | |                      |   |
                |            | |                      |   |
                |  Component | | Component       Push |   |
                |  Capability| | Subscription         |   |
                |   +--------+-v-------------------+  |   |
                |   |       Publisher(Agent)       +--+   |
                |   +------------------------------+      |
                |                                         |
                |                Device                   |
                +-----------------------------------------+


               Fig. 2 The Distributed Data Export Framework

   Master and Agents interact with each other in several ways:

   o  Agents need to register at the Master at the beginning of their
      process life-cycle

   o  Contracts are created between the Master and each Agent on the
      Component Capability, and the format for streaming data structure.

   o  The Master relays the component subscriptions to the Agents.

   o  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.

   The technical mechanisms or protocols used for the coordination of
   operational information between Master and Agent is out-of-scope of
   this document.




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4.  Subscription Decomposition

   The Collector can only subscribe to the Master.  This requires the
   Master to:

   1.  expose the Global Capability that can be served by multiple
       Publisher Agents;

   2.  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;

   3.  notify on changes when portions of a subscription moving between
       different Publisher Agents over time.

   And the Agent to:

   o  Inherit the Global Subscription properties from Publisher Master
      for its Component Subscription;

   o  share the same life-cycle as the Global Subscription;

   o  share the same Subscription ID as the Global Subscription.

5.  Publication Composition

   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.

   The Receiver is able to associate the YANG data records with
   Subscription ID [RFC8639] to the subscribed subscription and with
   Message Generator ID [I-D.ietf-netconf-notification-messages] to one
   of the Publisher Agents software processes to enable message
   integrity.

   For the dynamic subscription, the output of the "establish-
   subscription" RPC defined in [RFC8639] MUST include a list of Message
   Generator IDs to indicate how the Global Subscription is decomposed
   into several Component Subscriptions.

   The "subscription-started" and "subscription-modified" notification
   defined in [RFC8639] MUST also include a list of Message Generator
   IDs to notify the current Publishers for the corresponding Global
   Subscription.




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6.  Subscription State Change Notifications

   In addition to sending event records to Receivers, the Master MUST
   also send subscription state change notifications [RFC8639] when
   events related to subscription management have occurred.  All the
   subscription state change notifications MUST be delivered by the
   Master.

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

7.  Publisher Configurations

   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.

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

   The specific configuration on transports is described in the
   resposible documents.

8.  YANG Tree

   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

9.  YANG Module

   <CODE BEGINS> file "ietf-distributed-notifications@2020-05-09.yang"
   module ietf-distributed-notif {
     yang-version 1.1;
     namespace



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       "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;



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         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>

10.  IANA Considerations

   This document registers the following namespace URI in the IETF XML
   Registry [RFC3688]:




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      URI: urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications

      Registrant Contact: The IESG.

      XML: N/A; the requested URI is an XML namespace.

   This document registers the following YANG module in the YANG Module
   Names registry [RFC3688]:

      Name: ietf-subscribed-notifications

      Namespace: urn:ietf:params:xml:ns:yang:ietf-subscribed-
      notifications

      Prefix: mso

      Reference: RFC XXXX

11.  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
   [RFC5246].

   The NETCONF Access Control Model (NACM) [RFC6536] 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.

   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:

   o  /subscriptions/subscription/message-generator-ids

   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.

   Other Security Considerations is the same as those discussed in YANG-
   Push [RFC8641].



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12.  Contributors

      Alexander Clemm
      Futurewai
      2330 Central Expressway
      Santa Clara
      California
      United States of America
      Email: ludwig@clemm.org

13.  Acknowledgements

   We thank Kent Watsen, Mahesh Jethanandani, Martin Bjorklund, Tim
   Carey and Qin Wu for their constructive suggestions for improving
   this document.

14.  References

14.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

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

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

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <https://www.rfc-editor.org/info/rfc6536>.




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   [RFC7923]  Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
              for Subscription to YANG Datastores", RFC 7923,
              DOI 10.17487/RFC7923, June 2016,
              <https://www.rfc-editor.org/info/rfc7923>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

14.2.  Informative References

   [I-D.ietf-netconf-https-notif]
              Jethanandani, M. and K. Watsen, "An HTTPS-based Transport
              for Configured Subscriptions", draft-ietf-netconf-https-
              notif-02 (work in progress), March 2020.

   [I-D.ietf-netconf-notification-messages]
              Voit, E., Jenkins, T., Birkholz, H., Bierman, A., and A.
              Clemm, "Notification Message Headers and Bundles", draft-
              ietf-netconf-notification-messages-08 (work in progress),
              November 2019.

   [I-D.unyte-netconf-udp-notif]
              Zhou, T., Zheng, G., Lucente, P., Graf, T., and P.
              Francois, "UDP-based Transport for Configured
              Subscriptions", draft-unyte-netconf-udp-notif-00 (work in
              progress), July 2020.

Appendix A.  Examples

   This appendix is non-normative.

A.1.  Dynamic Subscription

   Figure 3 shows a typical dynamic subscription to the device with
   distributed data export capability.






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   +-------------+                 +-------------+ +-------------+
   | 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       |               |
          +<------------------------------+               |
          |                               |               |
          |                               |               |
          +                               +               +

                 Fig. 3 Call Flow for Dynamic Subscription

   A "establish-subscription" RPC request as per [RFC8641] is sent to
   the Master with a successful response.  An example of using NETCONF:










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<netconf:rpc message-id="101"
     xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
   <establish-subscription
       xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
       xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
     <yp:datastore
          xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
       ds:operational
     </yp:datastore>
     <yp:datastore-xpath-filter
         xmlns: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>

                  Fig. 4 "establish-subscription" Request

   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.

  <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>

           Fig. 5 "establish-subscription" Positive RPC Response

   Then, both Publishers send notifications with the corresponding piece
   of data to the Receiver.





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   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.

     <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>

                   Fig. 6 "modify-subscription" Request

   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.

















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 <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>

      Fig. 7 "subscription-modified" Subscription State Notification

A.2.  Configured Subscription

   Figure 8 shows a typical configured subscription to the device with
   distributed data export capability.





















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   +-------------+                 +-------------+ +-------------+
   | 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       |               |
          +<----------------------------------------------+
          |                               |               |
          |                               |               |
          |                               |               |

               Fig. 8 Call Flow for Configured Subscription

   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.























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 <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>

       Fig. 9 "subscription-started" Subscription State Notification

   Then, both Publishers send notifications with the corresponding data
   record to the Receiver.

Authors' Addresses

   Tianran Zhou
   Huawei
   156 Beiqing Rd., Haidian District
   Beijing
   China

   Email: zhoutianran@huawei.com









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   Guangying Zheng
   Huawei
   101 Yu-Hua-Tai Software Road
   Nanjing, Jiangsu
   China

   Email: zhengguangying@huawei.com


   Eric Voit
   Cisco Systems
   United States of America

   Email: evoit@cisco.com


   Thomas Graf
   Swisscom
   Binzring 17
   Zuerich 8045
   Switzerland

   Email: thomas.graf@swisscom.com


   Pierre Francois
   INSA-Lyon
   Lyon
   France

   Email: pierre.francois@insa-lyon.fr




















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