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Versions: (draft-voit-netconf-restconf-notif) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

NETCONF                                                          E. Voit
Internet-Draft                                        A. Gonzalez Prieto
Intended status: Standards Track                             A. Tripathy
Expires: September 14, 2017                            E. Nilsen-Nygaard
                                                           Cisco Systems
                                                                A. Clemm
                                                                  Huawei
                                                              A. Bierman
                                                               YumaWorks
                                                          March 13, 2017


          Restconf and HTTP Transport for Event Notifications
                  draft-ietf-netconf-restconf-notif-02

Abstract

   This document defines Restconf, HTTP2, and HTTP1.1 bindings for the
   transport of Subscription requests and corresponding push updates.
   Being subscribed may be either Event Notifications or objects or
   subtress of YANG Datastores.

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 http://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 September 14, 2017.

Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Dynamic YANG Subscription with RESTCONF control . . . . .   3
     3.2.  Subscription Multiplexing . . . . . . . . . . . . . . . .   6
   4.  Encoded Subscription and Event Notification Examples  . . . .   7
     4.1.  Restconf Subscription and Events over HTTP1.1 . . . . . .   7
     4.2.  Event Notification over HTTP2 . . . . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  End-to-End Deployment Guidance . . . . . . . . . . .  14
     A.1.  Call Home . . . . . . . . . . . . . . . . . . . . . . . .  14
     A.2.  TLS Heartbeat . . . . . . . . . . . . . . . . . . . . . .  15
   Appendix B.  Issues being worked and resolved . . . . . . . . . .  15
     B.1.  Unresolved Issues . . . . . . . . . . . . . . . . . . . .  15
   Appendix C.  Changes between revisions  . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   Mechanisms to support Event subscription and push are defined in
   [sn].  Enhancements to [sn] which enable YANG Datastore subscription
   and push are defined in [yang-push].  This document provides a
   transport specification for these protocols over Restconf and HTTP.
   Driving these requirements is [RFC7923].

   The streaming of Subscription Event Notifications has synergies with
   HTTP2 streams.  Benefits which can be realized when transporting
   events directly HTTP2 [RFC7540] include:

   o  Elimination of head-of-line blocking

   o  Weighting and proportional dequeuing of Events from different
      subscriptions

   o  Explicit precedence in subscriptions so that events from one
      subscription must be sent before another dequeues



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2.  Terminology

   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].

   The following terms use the defintions from [sn]: Configured
   Subscription, Dynamic Subscription, Event Notification, Publisher,
   Receiver, Subscriber, Subscription.

3.  Solution

   Event subscription is defined in [sn], YANG Datastore subscription is
   defined in [yang-push].  This section specifies transport mechanisms
   applicable to both.

3.1.  Dynamic YANG Subscription with RESTCONF control

   Dynamic Subscriptions for both [sn] and its [yang-push] augmentations
   are configured and managed via signaling messages transported over
   [RFC8040].  These interactions will be accomplished via a Restconf
   POST into RPCs located on the Publisher.  HTTP responses codes will
   indicate the results of the interaction with the Publisher.  An HTTP
   status code of 200 is the proper response to a successful <establish-
   subscription> RPC call.  The successful <establish-subscription> will
   result in a HTTP message with returned subscription URI on a
   logically separate mechanism than was used for the original Restconf
   POST.  This mechanism is via a parallel TCP connection in the case of
   HTTP 1.x, or in the case of HTTP2 via a separate HTTP stream within
   the HTTP connection.  When a being returned by the Publisher, failure
   will be indicated by error codes transported in payload.

   Once established, the resulting stream of Event Notifications are
   then delivered via SSE for HTTP1.1 and via HTTP Data for HTTP2.

3.1.1.  Call Flow for HTTP2

   Requests to [yang-push] augmented RPCs are sent on one or more HTTP2
   streams indicated by (a) in Figure 2.  Event Notifications related to
   a single subscription are pushed on a unique logical channel (b).  In
   the case below, a newly established subscription has its events
   pushed over HTTP2 stream (7).









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   +------------+                                 +------------+
   | Subscriber |                                 | Publisher  |
   |HTTP2 Stream|                                 |HTTP2 Stream|
   |  (a)  (b)  |                                 |  (a)  (b)  |
   +------------+                                 +------------+
       | Restconf POST (RPC:establish-subscription)   |
       |--------------------------------------------->|
       |                             HTTP 200 OK (URI)|
       |<---------------------------------------------|
       |   (7)HTTP POST (URI)                             (7)
       |    |--------------------------------------------->|
       |    |                                   HTTP 200 OK|
       |    |<---------------------------------------------|
       |    |                       HTTP Data (event-notif)|
       |    |<---------------------------------------------|
       | Restconf POST (RPC:modify-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |             HTTP Data (subscription-modified)|
       |    |<---------------------------------------------|
       |    |                       HTTP Data (event-notif)|
       |    |<---------------------------------------------|
       | Restconf POST (RPC:delete-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                  HTTP Headers (end of stream)|
       |   (/7)<-----------------------------------------(/7)
       |

                       Figure 1: Dynamic with HTTP2

3.1.2.  Call flow for HTTP1.1

   Requests to [yang-push] RPCs are sent on the TCP connection indicated
   by (a).  Event Notifications are pushed on a separate connection (b).
   This connection (b) will be used for all Event Notifications across
   all subscriptions.












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   +--------------+                             +--------------+
   |  Subscriber  |                             |   Publisher  |
   |TCP connection|                             |TCP connection|
   |  (a)  (b)    |                             |    (a)  (b)  |
   +--------------+                             +--------------+
       | Restconf POST (RPC:establish-subscription)   |
       |--------------------------------------------->|
       |                             HTTP 200 OK (URI)|
       |<---------------------------------------------|
       |    |HTTP GET (URI)                                |
       |    |--------------------------------------------->|
       |    |                                   HTTP 200 OK|
       |    |<---------------------------------------------|
       |    |                             SSE (event-notif)|
       |    |<---------------------------------------------|
       | Restconf POST (RPC:modify-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                   SSE (subscription-modified)|
       |    |<---------------------------------------------|
       |    |                             SSE (event-notif)|
       |    |<---------------------------------------------|
       | Restconf POST (RPC:delete-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                                              |
       |    |

                      Figure 2: Dynamic with HTTP1.1

3.1.3.  Configured Subscription over HTTP2

   With a Configured Subscription, all information needed to establish a
   secure relationship with that Receiver is available on the Publisher.
   With this information, the Publisher will establish a secure
   transport connection with the Receiver and then begin pushing the
   Event Notifications to the Receiver.  Since Restconf might not exist
   on the Receiver, it is not desirable to require that such Event
   Notifications be pushed with any dependency on Restconf.  Nor is
   there value which Restconf provides on top of HTTP.  Therefore in
   place of Restconf, a TLS secured HTTP2 Client connection must be
   established with an HTTP2 Server located on the Receiver.  Event
   Notifications will then be sent as part of an extended HTTP POST to
   the Receiver.





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   POST messages will be addressed to HTTP augmentation code on the
   Receiver capable of accepting and responding to Event Notifications.
   The first POST message must be a subscription-started notification.
   Push update notifications must not be sent until the receipt of an
   HTTP 200 OK for this initial notification.  The 200 OK will indicate
   that the Receiver is ready for Event Notifications.  At this point a
   Subscription must be allocated its own HTTP2 stream.  Figure 4
   depicts this message flow.

   +------------+                                 +------------+
   |  Receiver  |                                 | Publisher  |
   |HTTP2 Stream|                                 |HTTP2 Stream|
   |  (a)  (b)  |                                 |  (a)  (b)  |
   +------------+                                 +------------+
       |    HTTP Post Headers, Data (sub-start, SubID)|
       |<---------------------------------------------|
       | HTTP 200 OK                                  |
       |--------------------------------------------->|
       |    |         HTTP Post Headers, Data (event-notif)|
       |    |<---------------------------------------------|
       |    |                       HTTP Data (event-notif)|
       |    |<---------------------------------------------|
       |    |                     HTTP Data (sub-terminate)|
       |    |<---------------------------------------------|
       |    |HTTP 200 OK                                   |
       |    |--------------------------------------------->|

                      Figure 3: Configured over HTTP2

   As the HTTP2 transport is available to the Receiver, the Publisher
   should:

   o  take any subscription-priority and copy it into the HTTP2 stream
      priority, and

   o  take a subscription-dependency if it has been provided and map the
      HTTP2 stream for the parent subscription into the HTTP2 stream
      dependency.

3.2.  Subscription Multiplexing

   It is possible that updates might be delivered in a different
   sequence than generated.  Reasons for this might include (but are not
   limited to):

   o  replay of pushed updates





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   o  temporary loss of transport connectivity, with update buffering
      and different dequeuing priorities per Subscription

   o  population, marshalling and bundling of independent Subscription
      Updates, and

   Therefore each Event Notification will include a timestamp to ensure
   that a Receiver understands the time when a that update was
   generated.  Use of this timestamp can give an indication of the state
   of objects at a Publisher when state-entangled information is
   received across different subscriptions.  The use of the latest Event
   Notification timestamp for a particular object update can introduce
   errors.  So when state-entangled updates have inconsistent object
   values and temporally close timestamps, a Receiver might consider
   performing a GET to validate the current state of a Publisher.

4.  Encoded Subscription and Event Notification Examples

   Transported updates will contain context data for one or more Event
   Notifications.  Each transported Event Notification will contain
   several parameters:

4.1.  Restconf Subscription and Events over HTTP1.1

   Subscribers can dynamically learn whether a RESTCONF server supports
   various types of Event or Yang datastore subscription capabilities.
   This is done by issuing an HTTP request OPTIONS, HEAD, or GET on the
   stream.  Some examples building upon the Call flow for HTTP1.1 from
   Section 3.2.2 are:

   GET /restconf/data/ietf-restconf-monitoring:restconf-state/
            streams/stream=yang-push HTTP/1.1
   Host: example.com
   Accept: application/yang.data+xml

   If the server supports it, it may respond















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   HTTP/1.1 200 OK
   Content-Type: application/yang.api+xml
   <stream xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
               <name>yang-push</name>
               <description>Yang push stream</description>
               <access>
                  <encoding>xml</encoding>
                  <location>https://example.com/streams/yang-push-xml
                  </location>
               </access>
               <access>
                  <encoding>json</encoding>
                  <location>https://example.com/streams/yang-push-json
                  </location>
               </access>
            </stream>

   If the server does not support any form of subscription, it may
   respond

   HTTP/1.1 404 Not Found
   Date: Mon, 25 Apr 2012 11:10:30 GMT
   Server: example-server

   Subscribers can determine the URL to receive updates by sending an
   HTTP GET as a request for the "location" leaf with the stream list
   entry.  The stream to use for may be selected from the Event Stream
   list provided in the capabilities exchange.  Note that different
   encodings are supporting using different Event Stream locations.  For
   example, the Subscriber might send the following request:

   GET /restconf/data/ietf-restconf-monitoring:restconf-state/
            streams/stream=yang-push/access=xml/location HTTP/1.1
   Host: example.com
   Accept: application/yang.data+xml

   The Publisher might send the following response:

   HTTP/1.1 200 OK
   Content-Type: application/yang.api+xml
      <location
           xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
           https://example.com/streams/yang-push-xml
      </location>

   To subscribe and start receiving updates, the subscriber can then
   send an HTTP GET request for the URL returned by the Publisher in the
   request above.  The accept header must be "text/event-stream".  The



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   Publisher uses the Server Sent Events [W3C-20150203] transport
   strategy to push filtered Event Notifications from the Event stream.

   The Publisher MUST support individual parameters within the POST
   request body for all the parameters of a subscription.  The only
   exception is the encoding, which is embedded in the URI.  An example
   of this is:

   // subtree filter = /foo
   // periodic updates, every 5 seconds
   POST /restconf/operations/ietf-event-notifications:
        establish-subscription HTTP/1.1
         Host: example.com
         Content-Type: application/yang-data+json

         {
           "ietf-event-notifications:input" : {
             ?stream?: ?push-data"
             ?period" : 5,
             "xpath-filter" : ?/ex:foo[starts-with(?bar?.?some']"
           }
         }

   Should the publisher not support the requested subscription, it may
   reply:


























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   HTTP/1.1 501 Not Implemented
   Date: Mon, 23 Apr 2012 17:11:00 GMT
   Server: example-server
   Content-Type: application/yang.errors+xml
       <errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
          <error>
              <error-type>application</error-type>
              <error-tag>operation-not-supported</error-tag>
              <error-severity>error</error-severity>
              <error-message>Xpath filters not supported</error-message>
              <error-info>
                  <supported-subscription xmlns="urn:ietf:params:xml:ns:
                      netconf:datastore-push:1.0">
                      <subtree-filter/>
                  </supported-subscription>
              </error-info>
          </error>
        </errors>

   with an equivalent JSON encoding representation of:

   HTTP/1.1 501 Not Implemented
   Date: Mon, 23 Apr 2012 17:11:00 GMT
   Server: example-server
   Content-Type: application/yang.errors+json
         {
           "ietf-restconf:errors": {
             "error": {
               "error-type": "protocol",
               "error-tag": "operation-not-supported",
               "error-message": "Xpath filters not supported."
               "error-info": {
                  "datastore-push:supported-subscription": {
                        "subtree-filter": [null]
                    }
               }
             }
           }
         }

   The following is an example of a pushed Event Notification data for
   the Subscription above.  It contains a subtree with root foo that
   contains a leaf called bar:








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   XML encoding representation:
     <?xml version="1.0" encoding="UTF-8"?>
     <notification xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
        <subscription-id xmlns="urn:ietf:params:xml:ns:restconf:
            datastore-push:1.0">
              my-sub
        </subscription-id>
        <eventTime>2015-03-09T19:14:56.233Z</eventTime>
        <datastore-contents xmlns="urn:ietf:params:xml:ns:restconf:
           datastore-push:1.0">
           <foo xmlns="http://example.com/yang-push/1.0">
             <bar>some_string</bar>
           </foo>
        </datastore-contents>
     </notification>

   Or with the equivalent YANG over JSON encoding representation as
   defined in [RFC7951]:

   {
     "ietf-restconf:notification": {
       "datastore-push:subscription-id": "my-sub",
       "eventTime": "2015-03-09T19:14:56.233Z",
       "datastore-push:datastore-contents": {
         "example-mod:foo": { "bar": "some_string" }
       }
     }
   }

   To modify a Subscription, the subscriber issues another POST request
   on the provided URI using the same subscription-id as in the original
   request.  For example, to modify the update period to 10 seconds, the
   subscriber may send:

   POST /restconf/operations/ietf-event-notifications:
         modify-subscription HTTP/1.1
         Host: example.com
         Content-Type: application/yang-data+json

         {
           "ietf-event-notifications:input" : {
             ?subscription-id?: 100,
             ?period" : 10
           }
         }






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   To delete a Subscription, the Subscriber issues a DELETE request on
   the provided URI using the same subscription-id as in the original
   request

4.2.  Event Notification over HTTP2

   The basic encoding will look as below.  It will consists of a JSON
   representation wrapped in an HTTP2 header.

   HyperText Transfer Protocol 2
         Stream: HEADERS, Stream ID: 5
         Header: :method: POST
         Stream: HEADERS, Stream ID: 5

   {
     "ietf-yangpush:notification": {
       "datastore-push:subscription-id": "my-sub",
       "eventTime": "2015-03-09T19:14:56.233Z",
       "datastore-push:datastore-contents": {
         "foo": { "bar": "some_string" }
       }
     }
   }

5.  Security Considerations

   Subscriptions could be used to intentionally or accidentally overload
   the resources of a Publisher.  For this reason, it is important that
   the Publisher has the ability to prioritize the establishment and
   push of Event Notifications where there might be resource exhaust
   potential.  In addition, a server needs to be able to suspend
   existing Subscriptions when needed.  When this occurs, the
   subscription status must be updated accordingly and the Receivers
   notified.

   A Subscription could be used to attempt retrieve information for
   which a Receiver has no authorized access.  Therefore it is important
   that data pushed via a Subscription is authorized equivalently with
   regular data retrieval operations.  Data being pushed to a Receiver
   needs therefore to be filtered accordingly, just like if the data
   were being retrieved on-demand.  The Netconf Authorization Control
   Model [RFC6536] applies even though the transport is not NETCONF.

   One or more Publishers of Configured Subscriptions could be used to
   overwhelm a Receiver which doesn't even support Subscriptions.  There
   are two protections here.  First Event Notifications for Configured
   Subscriptions MUST only be transmittable over Encrypted transports.
   Clients which do not want pushed Event Notifications need only



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   terminate or refuse any transport sessions from the Publisher.
   Second, the HTTP transport augmentation on the Receiver must send an
   HTTP 200 OK to a subscription started notification before the
   Publisher starts streaming any events.

   One or more Publishers could overwhelm a Receiver which is unable to
   control or handle the volume of Event Notifications received.  In
   deployments where this might be a concern, HTTP2 transport such as
   HTTP2) should be selected.

6.  Acknowledgments

   We wish to acknowledge the helpful contributions, comments, and
   suggestions that were received from: Susan Hares, Tim Jenkins, Balazs
   Lengyel, Kent Watsen, Michael Scharf, and Guangying Zheng.

7.  References

7.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC6520]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
              Layer Security (TLS) and Datagram Transport Layer Security
              (DTLS) Heartbeat Extension", RFC 6520,
              DOI 10.17487/RFC6520, February 2012,
              <http://www.rfc-editor.org/info/rfc6520>.

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

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <http://www.rfc-editor.org/info/rfc7540>.

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







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   [sn]       Voit, E., Clemm, A., Gonzalez Prieto, A., Prasad Tripathy,
              A., and E. Nilsen-Nygaard, "Subscribing to Event
              Notifications", February 2017,
              <https://datatracker.ietf.org/doc/draft-ietf-netconf-
              subscribed-notifications/>.

7.2.  Informative References

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

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <http://www.rfc-editor.org/info/rfc7951>.

   [RFC8071]  Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
              RFC 8071, DOI 10.17487/RFC8071, February 2017,
              <http://www.rfc-editor.org/info/rfc8071>.

   [W3C-20150203]
              "Server-Sent Events, World Wide Web Consortium CR CR-
              eventsource-20121211", February 2015,
              <https://www.w3.org/TR/2015/REC-eventsource-20150203/>.

   [yang-push]
              Clemm, A., Voit, E., Gonzalez Prieto, A., Prasad Tripathy,
              A., Nilsen-Nygaard, E., Bierman, A., and B. Lengyel,
              "Subscribing to YANG datastore push updates", March 2017,
              <https://datatracker.ietf.org/doc/draft-ietf-netconf-yang-
              push/>.

Appendix A.  End-to-End Deployment Guidance

   Several technologies are expected to be seen within a deployment to
   achieve security and ease-of-use requirements.  These are not
   necessary for an implementation of this specification, but will be
   useful to consider when considering the operational context.

A.1.  Call Home

   Pub/Sub implementations should have the ability to transparently
   incorporate 'call home' [RFC8071] so that secure TLS connections can
   originate from the desired device.






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A.2.  TLS Heartbeat

   HTTP sessions might not quickly allow a Subscriber to recognize when
   the communication path has been lost from the Publisher.  To
   recognize this, it is possible for a Receiver to establish a TLS
   heartbeat [RFC6520].  In the case where a TLS heartbeat is included,
   it should be sent just from Receiver to Publisher.  Loss of the
   heartbeat should result in any Subscription related TCP sessions
   between those endpoints being torn down.  The subscription can then
   attempt to re-establish.

Appendix B.  Issues being worked and resolved

   (To be removed by RFC editor prior to publication)

B.1.  Unresolved Issues

   GRPC compatibility 1: Mechanisms for HTTP2 to GRPC mapping need to be
   considered.  There is a good start there as this draft only uses
   POST, not GET.  As GET is used in RESTCONF for capabilities
   discovery, we have some backwards compatibility issues with existing
   IETF drafts.  Possible options to address are (1) provide a POST
   method for anything done by GET in RESTCONF, (2) await support of GET
   by GRPC, or (3) tunnel RESTCONF's GET messages within a GRPC POST.

   GRPC compatibility 2: We need to expose a method against which POST
   is done as events begin on a stream.  See Stream 7 in figure 2.  Can
   only send traffic to a method, not a URI.  URI points to a method,
   not a resource.

   Need to add into document examples of Event streams.  Document only
   includes yang-push examples at this point.

   We need to reference the viable encodings of notifications.

Appendix C.  Changes between revisions

   (To be removed by RFC editor prior to publication)

   v01 - v02

   o  Removed sections now redundant with [sn] and [yang-push] such as:
      mechanisms for subscription maintenance, terminology definitions,
      stream discovery.

   o  3rd party subscriptions are out-of-scope.

   o  SSE only used with Restconf and HTTP1.1 Dynamic Subscriptions



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   o  Timeframes for event tagging are self-defined.

   o  Clean-up of wording, references to terminology, section numbers.

   v00 - v01

   o  Removed the ability for more than one subscription to go to a
      single HTTP2 stream.

   o  Updated call flows.  Extensively.

   o  SSE only used with Restconf and HTTP1.1 Dynamic Subscriptions

   o  HTTP is not used to determine that a Receiver has gone silent and
      is not Receiving Event Notifications

   o  Many clean-ups of wording and terminology

Authors' Addresses

   Eric Voit
   Cisco Systems

   Email: evoit@cisco.com


   Alberto Gonzalez Prieto
   Cisco Systems

   Email: albertgo@cisco.com


   Ambika Prasad Tripathy
   Cisco Systems

   Email: ambtripa@cisco.com


   Einar Nilsen-Nygaard
   Cisco Systems

   Email: einarnn@cisco.com


   Alexander Clemm
   Huawei

   Email: ludwig@clemm.org



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   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com















































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