Subscribing to YANG datastore push updates
draft-clemm-netconf-yang-push-02.txt

Abstract

This document defines a subscription and push mechanism for YANG datastores. This mechanism allows client applications to request updates from a YANG datastore, which are then pushed by the server to the client per a subscription policy, without requiring additional client requests.

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Table of Contents

• 1. Introduction
• 2. Definitions and Acronyms
• 3. Solution Overview
• 3.1. Subscription Model
• 3.2. Negotiation of Subscription Policies
• 3.3. On-Change Considerations
• 3.4. Data Encodings
• 3.4.1. Periodic Subscriptions
• 3.4.2. On-Change Subscriptions
• 3.5. Subscription Filters
• 3.6. Push Data Stream and Transport Mapping
• 3.7. Subscription management
• 3.7.1. Subscription management by RPC
• 3.7.2. Subscription management by configuration
• 3.8. Other considerations
• 3.8.1. Authorization
• 3.8.2. Additional subscription primitives
• 3.8.3. Robustness and reliability considerations
• 3.8.4. Update size and fragmentation considerations
• 3.8.5. Additional data streams
• 3.8.6. Implementation considerations
• 4. A YANG data model for management of datastore push subscriptions
• 4.1. Overview
• 4.2. System streams
• 4.3. Filters
• 4.4. Subscription configuration
• 4.5. Subscription monitoring
• 4.6. Notifications
• 4.7. RPCs
• 4.7.1. Create-subscription RPC
• 4.7.2. Modify-subscription RPC
• 4.7.3. Delete-subscription RPC
• 5. YANG module
• 6. Security Considerations
• 7. Acknowledgments
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

1. Introduction

YANG [RFC6020] was originally designed for the Netconf protocol [RFC6241], which originally put most emphasis on configuration. However, YANG is not restricted to configuration data. YANG datastores, i.e. datastores that contain data modeled according using YANG, can contain configuration as well as operational data. It is therefore reasonable to expect that data in YANG datastores will increasingly be used to support applications that are not focused on managing configurations but that are, for example, related to service assurance.

Service assurance applications typically involve monitoring operational state of networks and devices; of particular interest are changes that this data undergoes over time. Likewise, there are applications in which data and objects from one datastore need to be made available both to applications in other systems and to remote datastores [I-D.voit-netmod-peer-mount-requirements] [I-D.clemm-netmod-mount]. This requires mechanisms that allow remote systems to become quickly aware of any updates to allow to validate and maintain cross-network integrity and consistency.

Traditional approaches to remote network state visibility rely heavily on polling. With polling, data is periodically explicitly retrieved by a client from a server to stay up-to-date.

There are various issues associated with polling-based management:

• It introduces additional load on network, devices, and applications. Each polling cycle requires a separate yet arguably redundant request that results in an interrupt, requires parsing, consumes bandwidth.
• It lacks robustness. Polling cycles may be missed, requests may be delayed or get lost, often particularly in cases when the network is under stress and hence exactly when the need for the data is the greatest.
• Data may be difficult to calibrate and compare. Polling requests may undergo slight fluctuations, resulting in intervals of different lengths which makes data hard to compare. Likewise, pollers may have difficulty issuing requests that reach all devices at the same time, resulting in offset polling intervals which again make data hard to compare.

A more effective alternative is when an application can request to be automatically updated as necessary of current content of the datastore (such as a subtree, or data in a subtree that meets a certain filter condition), and in which the server that maintains the datastore subsequently pushes those updates. However, such a solution does not currently exist.

The need to perform polling-based management is typically considered an important shortcoming of management applications that rely on MIBs polled using SNMP [RFC1157]. However, without a provision to support a push-based alternative, there is no reason to believe that management applications that operate on YANG datastores using protocols such as NETCONF or Restconf [I-D.ietf-netconf-restconf] will be any more effective, as they would follow the same request/response pattern.

While YANG allows the definition of notifications, such notifications are generally intended to indicate the occurrence of certain well-specified event conditions, such as a the onset of an alarm condition or the occurrence of an error. A capability to subscribe to and deliver event notifications has been defined in [RFC5277]. In addition, configuration change notifications have been defined in [RFC6470]. These change notifications pertain only to configuration information, not to operational state, and convey the root of the subtree to which changes were applied along with the edits, but not the modified data nodes and their values.

Accordingly, there is a need for a service that allows client applications to subscribe to updates of a YANG datastore and that allows the server to push those updates. The requirements for such a service are documented in [I-D.i2rs-pub-sub-requirements]. This document proposes a solution that features the following capabilities: [RFC5277] that allow to extend notification subscriptions to subscriptions for datastore updates. It also defines a notification that can be used to carry data updates and thus serve as push mechanism.

• A mechanism that allows clients to subscribe to automatic datastore updates, and the means to manage those subscription. The subscription allows clients to specify which data they are interested in, and to provide optional filters with criteria that data must meet for updates to be sent. Furthermore, subscription can specify a policy that directs when updates are provided. For example, a client may request to be updated periodically in certain intervals, or whenever data changes occur.
• The ability for a server to push back on requested subscription parameters. Because not every server may support every requested interval for every piece of data, it is necessary for a server to be able to indicate whether or not it is capable of supporting a requested subscription, and possibly allow to negotiate subscription parameters.
• A mechanism to communicate the updates themselves. For this, the proposal leverages and extends existing YANG/Netconf/Restconf mechanisms, defining special notifications that carry updates.

This document specifies a YANG data model to manage subscriptions to data in YANG datastores, and to configure associated filters and data streams. It defines extensions to RPCs defined in

2. Definitions and Acronyms

Data node: An instance of management information in a YANG datastore.

Data record: A record containing a set of one or more data node instances and their associated values.

Datastore: A conceptual store of instantiated management information, with individual data items represented by data nodes which are arranged in hierarchical manner.

Datastream: A continuous stream of data records, each including a set of updates, i.e. data node instances and their associated values.

Data subtree: An instantiated data node and the data nodes that are hierarchically contained within it.

NACM: NETCONF Access Control Model

NETCONF: Network Configuration Protocol

Push-update stream: A conceptual data stream of a datastore that streams the entire datastore contents continuously and perpetually.

RPC: Remote Procedure Call

SNMP: Simple Network Management Protocol

Subscription: A contract between a client ("subscriber") and a server ("publisher"), stipulating which information the client wishes to receive from the server (and which information the server has to provide to the client) without the need for further solicitation.

Subscription filter: A filter that contains evaluation criteria which are evaluated against YANG objects of a subscription. An update is only published if the object meets the specified filter criteria.

Subscription policy: A policy that specifies under what circumstances to push an update, e.g. whether updates are to be provided periodically or only whenever changes occur.

Update: A data item containing the current value of a data node.

Update trigger: A trigger, as specified by a subscription policy, that causes an update to be sent, respectively a data record to be generated. An example of a trigger is a change trigger, invoked when the value of a data node changes or a data node is created or deleted, or a time trigger, invoked after the laps of a periodic time interval.

URI: Uniform Resource Identifier

YANG: A data definition language for NETCONF

Yang-push: The subscription and push mechanism for YANG datastores that is specified in this document.

3. Solution Overview

This document specifies a solution that allows clients to subscribe to information updates in a YANG datastore, which are subsequently pushed from the server to the client.

Subscriptions are initiated by clients. Servers respond to a subscription request explicitly positively or negatively. Negative responses include information about why the subscription was not accepted, in order to facilitate converging on an acceptable set of subscription parameters. Once a subscription has been established, datastore push updates are pushed from the server to the subscribing client until the subscription ends.

Accordingly, the solution encompasses several components:

• The subscription model for configuration and management of the subscriptions, with a set of associated services.
• The ability to provide hints for acceptable subscription parameters, in cases where a subscription desired by a client cannot currently be served.
• The stream of datastore push updates.

In addition, there are a number of additional considerations, such as the tie-in of the mechanisms with security mechanisms. Each of those aspects will be discussed in the following subsections.

3.1. Subscription Model

Yang-push subscriptions are defined using a data model that is itself defined in YANG. This model is based on the subscriptions defined in [RFC5277], which are also reused in Restconf. The model is extended with several parameters, including a subscription type and a subscription ID.

The subscription model assumes the presence of a conceptual perpetual datastream "push-update" of continuous datastore updates that can be subscribed to, although other datastreams may be supported as well. A subscription refers to a datastream and specifies filters that are to be applied to, it for example, to provide only those subsets of the information that match a filter criteria. In addition, a subscription specifies a set of subscription parameters that define the trigger when data records should be sent, for example at periodic intervals or whenever underlying data items change.

The complete set of subscription parameters is as follows:

• The stream being subscribed to. The subscription model assumes the presence of perpetual and continuous streams of updates. The stream "push-update" is always available and covers the entire set of YANG data in the server, but a system may provide other streams to choose from.
• The datastore to target. By default, the datastore will always be "running". However, it is conceivable that implementations want to also support subscriptions to updates to other datastores.
• An encoding for the data updates. By default, updates are encoded using XML, but JSON can be requested as an option and other encodings may be supported in the future.
• An optional start time for the subscription. If the specified start time is in the past, the subscription goes into effect immediately. The start time also serves as anchor time for periodic subscriptions, from which intervals at which to send updates are calculated (see also below).
• An optional stop time for the subscription. Once the stop time is reached, the subscription is automatically terminated.
• A subscription policy definition regarding the update trigger when to send new updates. The trigger can be periodic or based on change.
  • For periodic subscriptions, the trigger is defined by a parameter that defines the interval with which updates are to be pushed. The start time of the subscription serves as anchor time, defining one specific point in time at which an update needs to be sent. Update intervals always fall on the points in time that are a multiple of a period after the start time.
  • For on-change subscriptions, the trigger occurs whenever a change in the subscribed information is detected. On-change subscriptions have more complex semantics that can be guided by additional parameters. Please refer also to Section 3.3.
    • One parameter is needed to specify the dampening period, i.e. the interval that must pass before a successive update for the same data node is sent. The first time a change is detected, the update is sent immediately. If a subsequent change is detected, another update is only sent once the dampening period has passed, containing the value of the data node that is then valid.
    • Another parameter allows to restrict the types of changes for which updates are sent (changes to object values, object creation or deletion events). It is conceivable to augment the data model with additional parameters in the future to specify even more refined policies, such as parameters that specify the magnitude of a change that must occur before an update is triggered.
    • A third parameter specifies whether or not a complete update with all the subscribed data should be sent at the beginning of a subscription.

• Optionally, a filter, or set of filters, describing the subset of data items in the stream's data records that are of interest to the subscriber. The server should only send to the subscriber the data items that match the filter(s), when present. The absence of a filter indicates that all data items from the stream are of interest to the subscriber and all data records must be sent in their entirety to the subscriber. Two types of filters are support: subtree filter, with the same semantics as defined in [RFC 6241], and XPath filters. Additional filter types can be added through augmentations. Filters can be specified "inline" as part of the subscription, or can be configured separately and referenced by a subscription, in order to facilitate reuse of complex filters.

The subscription data model is specified as part of the YANG data model described later in this specification. Specifically, the subscription parameters are defined in the "subscription-info" grouping. It is conceivable that additional subscription parameters might be added in the future. This can be accomplished through augmentation of the subscription data model.

3.2. Negotiation of Subscription Policies

A subscription rejection can be caused by the inability of the server to provide a stream with the requested semantics. For example, a server may not be able to support "on-change" updates for operational data, or only support them for a limited set of data nodes. Likewise, a server may not be able to support a requested updated frequency, or a requested encoding.

Yang-push supports a simple negotiation between clients and servers for subscription parameters. The negotiation is limited to a single pair of subscription request and response. For negative responses, the server SHOULD include in the returned error what subscription parameters would have been accepted for the request. The returned acceptable parameters constitute suggestions that, when followed, increase the likelihood of success for subsequent requests. However, they are no guarantee that subsequent requests for this client or others will in fact be accepted.

In case a subscriber requests an encoding other than XML, and this encoding is not supported by the server, the server simply indicates in the response that the encoding is not supported.

3.3. On-Change Considerations

On-change subscriptions allow clients to subscribe to updates whenever changes to objects occur. As such, on-change subscriptions are of particular interest for data that changes relatively infrequently, yet that require applications to be notified with minimal delay when changes do occur.

On-change subscriptions tend to be more difficult to implement than periodic subscriptions. Specifically, on-change subscriptions may involve a notion of state to see if a change occurred between past and current state, or the ability to tap into changes as they occur in the underlying system. Accordingly, on-change subscriptions may not be supported by all implementations or for every object.

When an on-change subscription is requested for a datastream with a given subtree filter, where not all objects support on-change update triggers, the subscription request MUST be rejected. As a result, on-change subscription requests will tend to be directed at very specific, targeted subtrees with only few objects.

Any updates for an on-change subscription will include only objects for which a change was detected. To avoid flooding clients with repeated updates for fast-changing objects, or objects with oscillating values, an on-change subscription allows for the definition of a dampening period. Once an update for a given object is sent, no other updates for this particular object are sent until the end of the dampening period. In addition, updates include information about objects that were deleted and ones that were newly created.

On-change subscriptions can be refined to let users subscribe only to certain types of changes, for example, only to object creations and deletions, but not to modifications of object values.

Additional refinements are conceivable. For example, in order to avoid sending updates on objects whose values undergo only a negligible change, additional parameters might be added to an on-change subscription specifying a policy that states how large or "significant" a change has to be before an update is sent. A simple policy is a "delta-policy" that states, for integer-valued data nodes, the minimum difference between the current value and the value that was last reported that triggers an update. Also more sophisticated policies are conceivable, such as policies specified in percentage terms or policies that take into account the rate of change. While not specified as part of this draft, such policies can be accommodated by augmenting the subscription data model accordingly.

3.4. Data Encodings

Subscribed data is encoded in either XML or JSON format. A server MUST support XML encoding and MAY support JSON encoding.

It is conceivable that additional encodings may be supported as options in the future. This can be accomplished by augmenting the subscription data model with additional identity statements used to refer to requested encodings.

3.4.1. Periodic Subscriptions

In a periodic subscription, the data included as part of an update corresponds to data that could have been simply retrieved using a get operation and is encoded in the same way. XML encoding rules for data nodes are defined in [RFC6020]. JSON encoding rules are defined in [I-D.ietf-netmod-yang-json]. This encoding is valid JSON, but also has special encoding rules to identify module namespaces and provide consistent type processing of YANG data.

3.4.2. On-Change Subscriptions

In an on-change subscription, updates need to allow to differentiate between data nodes that were newly created since the last update, data nodes that were deleted, and data nodes whose value changed.

XML encoding rules correspond to how data would be encoded in input to Netconf edit-config operations as specified in [RFC6241] section 7.2, adding "operation" attributes to elements in the data subtree. Specifically, the following values will be utilized:

• create: The data identified by the element has been added since the last update.
• delete: The data identified by the element has been deleted since the last update.
• merge: The data identified by the element has been changed since the last update.
• replace: The data identified by the element has been replaced with the update contents since the last update.

The remove value will not be utilized.

Contrary to edit-config operations, the data is sent from the server to the client, not from the client to the server, and will not be restricted to configuration data.

JSON encoding rules are roughly analogous to how data would be encoded in input to a YANG-patch operation, as specified in [I-D.ietf-netconf-yang-patch] section 2.2. However, no edit-ids will be needed. Specifically, changes will be grouped under respective "operation" containers for creations, deletions, and modifications.

3.5. Subscription Filters

Subscriptions can specify filters for subscribed data. The following filters are supported:

• subtree-filter: A subtree filter specifies a subtree that the subscription refers to. When specified, updates will only concern data nodes from this subtree. Syntax and semantics correspond to that specified for [RFC6241] section 6.
• xpath-filter: An XPath filter specifies an XPath expression applied to the data in an update, assuming XML-encoded data.

If multiple subscription filters are specified, all of them are applied. In other words, it is possible to (for example) apply an XPath filter on top of a subtree filter.

It is conceivable for implementations to support other filters. For example, an on-change filter might specify that changes in values should be sent only when the magnitude of the change since previous updates exceeds a certain threshold. It is possible to augment the subscription data model with additional filter types.

3.6. Push Data Stream and Transport Mapping

Pushing data based on a subscription could be considered analogous to a response to a data retrieval request, e.g. a "get" request. However, contrary to such a request, multiple responses to the same request may get sent over a longer period of time.

A more suitable mechanism is therefore that of a notification. Contrary to notifications associated with alarms and unexpected event occurrences, push updates are solicited, i.e. tied to a particular subscription which triggered the notification. (An alternative conceptual model would consider a subscription an "opt-in" filter on a continuous stream of updates.)

The notification contains several parameters: [RFC5277]. Alternative transports are conceivable but outside the scope of this specification.

• A subscription correlator, referencing the name of the subscription on whose behalf the notification is sent.
• A data node that contains a representation of the datastore subtree containing the updates. The subtree is filtered per access control rules to contain only data that the subscriber is authorized to see. Also, depending on the subscription type, i.e., specifically for on-change subscriptions, the subtree contains only the data nodes that contain actual changes. (This can be simply a node of type string or, for XML-based encoding, anyxml.)

Notifications are sent using <notification> elements as defined in

The solution specified in this document uses notifications to communicate datastore updates. The contents of the notification includes a set of explicitly defined data nodes. For this purpose, two new generic notifications are introduced, "push-update" and "push-change-update". Both notifications are used to define how to carry data records with updates of datastore contents as specified by a subscription.

Push-update notification defines updates for a periodic subscription, as well as for the initial update of an on-change subscription used to synchronize the receiver at the start of a new subscription. The update record contains a data snippet that contains an instantiated subtree with the subscribed contents. The content of the update record is equivalent to the contents that would be obtained had the same data been explicitly retrieved using e.g. a Netconf "get"-operation, with the same filters applied.

The contents of the notification conceptually represents the union of all data nodes in the yang modules supported by the server. However, in a YANG data model, it is not practical to model the precise data contained in the updates as part of the notification. This is because the specific data nodes supported depend on the implementing system and may even vary dynamically. Therefore, to capture this data, a single parameter that can represent any datastore contents is used, not parameters that represent data nodes one at a time.

Push-change-update notification defines updates for on-change subscriptions. The update record here contains a data snippet that indicates the changes that data nodes have undergone, i.e. that indicates which data nodes have been created, deleted, or had changes to their values. The format follows the same format that operations that apply changes to a data tree would apply, indicating the creates, deletes, and modifications of data nodes.

The following is an example of push notification. It contains an update for subscription my-sub, including a subtree with root foo that contains a leaf, bar:

 
<?xml version="1.0" encoding="UTF-8"?>
   <notification 
         xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
      <subscription-id 
            xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         my-sub
      </subscription-id>
      <eventTime>2015-03-09T19:14:56Z</eventTime> 
      <datastore-contents xmlns="urn:ietf:params:xml:ns:netconf:
            datastore-push:1.0">
         <foo>
            <bar>some_string</bar>
         </foo>
      </datastore-contents>
   </notification>
          

 
<?xml version="1.0" encoding="UTF-8"?>
  <notification 
        xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
     <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
           datastore-push:1.0">
        my-on-change-sub
     </subscription-id>
     <eventTime>2015-10-13T12:13:02Z</eventTime>
     <datastore-changes-xml xmlns="urn:ietf:params:xml:ns:netconf:
           datastore-push:1.0">
       <alpha xmlns="http://example.com/yang-push/1.0" >
         <beta>1500</beta>
       </alpha>       
    </datastore-changes-xml>
</notification>
          

 
<?xml version="1.0" encoding="UTF-8"?>
  <notification 
        xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
     <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
           datastore-push:1.0">
        my-on-change-sub
     </subscription-id>
     <eventTime>2015-10-13T12:13:02Z</eventTime>
     <datastore-changes-json 
           xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
    {
    "ietf-yang-patch:yang-patch": {
        "patch-id": [
            null
        ],
        "edit": [
            {
                "edit-id": "edit1",
                "operation": "merge",
                "target": "/alpha/beta",
                "value": {
                    "beta": 1500
                }
            }
        ]
      }
   }
  </datastore-changes-json>
</notification>
          

 
<?xml version="1.0" encoding="UTF-8"?>
  <notification 
        xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
     <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
           datastore-push:1.0">
        my-on-change-sub
     </subscription-id>
     <eventTime>2015-10-13T12:13:02Z</eventTime>
     <datastore-changes-xml xmlns="urn:ietf:params:xml:ns:netconf:
           datastore-push:1.0">
       <alpha xmlns="http://example.com/yang-push/1.0" >
         <beta xc:operation="delete"/>
       </alpha>
    </datastore-changes-xml>
</notification>

          

 
<netconf:rpc message-id="101"
   xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
   <create-subscription
         xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
      <stream>push-update</stream>
      <filter netconf:type="xpath"
            xmlns:ex="http://example.com/foo/1.0"
            select="/ex:foo"/>
      <period xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         500
      </period>
      <encoding 
            xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         encode-xml
      </encoding>
   </create-subscription>
</netconf:rpc>

 
<rpc-reply message-id="101" 
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <rpc-error>
      <error-type>application</error-type>
      <error-tag>access-denied</error-tag>
      <error-severity>error</error-severity>
      <error-info>
         <access-denied xmlns="urn:ietf:params:xml:ns:
               netconf:datastore-push:1.0">
            <data-node>/ex:foo</data-node>
         </ access-denied >
      </error-info>
   </rpc-error>
</rpc-reply>

          
                 +-------------+                 +-------------+
    subscription |  protocol   |                 |   target    |
    request -->  |  operation  | ------------->  |  data node  |
                 |  allowed?   |   datastore     |   access    |
                 +-------------+   or state      |  allowed?   |
                                   data access   +-------------+
 
        

          
                   +-------------+      +-------------------+
    subscription   |  data node  |  yes |                   |  
    update  -->    |   access    | ---> | add data node     |
                   |  allowed?   |      | to update message |
                   +-------------+      +-------------------+
          

module: ietf-datastore-push
   +--ro system-streams
   |  +--ro system-stream*   system-stream
   +--rw filters
   |  +--rw filter* [filter-id]
   |     +--rw filter-id         filter-id
   |     +--rw (filter-type)?
   |        +--:(subtree)
   |        |  +--rw subtree-filter?   subtree-filter
   |        +--:(xpath)
   |           +--rw xpath-filter?     yang:xpath1.0
   +--rw subscription-config
   |  +--rw datastore-push-subscription* [subscription-id]
   |     +--rw subscription-id      subscription-id
   |     +--rw target-datastore?    datastore
   |     +--rw stream?              system-stream
   |     +--rw encoding?            encoding
   |     +--rw start-time?          yang:date-and-time
   |     +--rw stop-time?           yang:date-and-time
   |     +--rw (update-trigger)?
   |     |  +--:(periodic)
   |     |  |  +--rw period?              yang:timeticks
   |     |  +--:(on-change)
   |     |     +--rw no-synch-on-start?   empty
   |     |     +--rw dampening-period     yang:timeticks
   |     |     +--rw excluded-change*     change-type
   |     +--rw (filterspec)?
   |     |  +--:(inline)
   |     |  |  +--rw (filter-type)?
   |     |  |     +--:(subtree)
   |     |  |     |  +--rw subtree-filter?      subtree-filter
   |     |  |     +--:(xpath)
   |     |  |        +--rw xpath-filter?        yang:xpath1.0
   |     |  +--:(by-reference)
   |     |     +--rw filter-ref?          filter-ref
   |     +--rw receiver-address
   |        +--rw (push-base-transport)?
   |           +--:(tcpudp)
   |              +--rw tcpudp
   |                 +--rw address?   inet:host
   |                 +--rw port?      inet:port-number
   +--ro subscriptions
      +--ro datastore-push-subscription* [subscription-id]
         +--ro subscription-id            subscription-id
         +--ro configured-subscription?   empty
         +--ro subscription-status?       identityref
         +--ro target-datastore?          datastore
         +--ro stream?                    system-stream
         +--ro encoding?                  encoding
         +--ro start-time?                yang:date-and-time
         +--ro stop-time?                 yang:date-and-time
         +--ro (update-trigger)?
         |  +--:(periodic)
         |  |  +--ro period?                    yang:timeticks
         |  +--:(on-change)
         |     +--ro no-synch-on-start?         empty
         |     +--ro dampening-period           yang:timeticks
         |     +--ro excluded-change*           change-type
         +--ro (filterspec)?
         |  +--:(inline)
         |  |  +--ro (filter-type)?
         |  |     +--:(subtree)
         |  |     |  +--ro subtree-filter?            subtree-filter
         |  |     +--:(xpath)
         |  |        +--ro xpath-filter?              yang:xpath1.0
         |  +--:(by-reference)
         |     +--ro filter-ref?                filter-ref
         +--ro receiver-address
            +--ro (push-base-transport)?
               +--:(tcpudp)
                  +--ro tcpudp
                     +--ro address?   inet:host
                     +--ro port?      inet:port-number
		    

   <netconf:rpc message-id="101"
         xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
      <create-subscription
            xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
         <stream>push-update</stream>
         <filter netconf:type="xpath"
               xmlns:ex="http://example.com/foo/1.0"
               select="/ex:foo"/>
         <period xmlns="urn:ietf:params:xml:ns:netconf:
               datastore-push:1.0">
            500
         </period>
         <encoding xmlns="urn:ietf:params:xml:ns:netconf:
               datastore-push:1.0">
            encode-xml
         </encoding>
      </create-subscription>
   </netconf:rpc>
    

<rpc-reply message-id="101"
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <data>
      <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
            datastore-push:1.0">
         my-sub
      </subscription-id>
   </data>
</rpc-reply>
     
    

          
<rpc-reply message-id="101" 
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <rpc-error>
      <error-type>application</error-type>
      <error-tag>access-denied</error-tag>
      <error-severity>error</error-severity>
      <error-info>
         <access-denied xmlns="urn:ietf:params:xml:ns:
               netconf:datastore-push:1.0">
            <data-node>/ex:foo</ data-node >
         </ access-denied >
      </error-info>
   </rpc-error>
</rpc-reply>

       

          
<netconf:rpc message-id="101"
      xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
   <create-subscription
         xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
      <stream>push-update</stream>
      <filter netconf:type="xpath"
            xmlns:ex="http://example.com/foo/1.0"
            select="/ex:foo"/>
      <dampening-period 
            xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         10
      </dampening-period>
      <encoding 
            xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         encode-xml
      </encoding>
   </create-subscription>
</netconf:rpc>
          

<rpc-reply message-id="101" 
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <rpc-error>
      <error-type>application</error-type>
      <error-tag>operation-not-supported</error-tag>
      <error-severity>error</error-severity>
      <error-info>
         <unsupported-parameters xmlns="urn:ietf:params:xml:ns:
               netconf:datastore-push:1.0">
            <dampening-period 
                  xmlns="urn:ietf:params:xml:ns:netconf:
                  datastore-push:1.0">
               10
            </dampening-period>
         </unsupported-parameters >
         <supported-subscription xmlns="urn:ietf:params:xml:ns:
               netconf:datastore-push:1.0">
            <period>3000</period>
         </supported-subscription>
      </error-info>
   </rpc-error>
</rpc-reply>
             

      
<netconf:rpc message-id="101"
   xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
   <modify-subscription
         xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
      <stream>push-update</stream>
      <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
            datastore-push:1.0">
         my-sub
      </subscription-id>
      <filter netconf:type="xpath"
            xmlns:ex="http://example.com/foo/1.0"
            select="/ex:foo"/>
      <period 
            xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         500
      </period>
      <encoding 
            xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         encode-xml
      </encoding>
   </create-subscription>
</netconf:rpc>

    

<rpc-reply message-id="101"
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <data>
      <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
            datastore-push:1.0">
         my-sub
      </subscription-id>
   </data>
</rpc-reply>


<netconf:rpc message-id="102"
      xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
   <modify-subscription
         xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
      <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
            datastore-push:1.0">
         my-sub
      </subscription-id>
      <period xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         100
      </period>
      <encoding 
            xmlns="urn:ietf:params:xml:ns:netconf:datastore-push:1.0">
         encode-xml
      </encoding>
   </modify-subscription>
</netconf:rpc>

<rpc-reply message-id="102"
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
         datastore-push:1.0">
      my-sub
   </subscription-id>
</rpc-reply>
    

<netconf:rpc message-id="103"
      xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
   <delete-subscription
         xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
      <subscription-id xmlns="urn:ietf:params:xml:ns:netconf:
            datastore-push:1.0">
         my-sub
      </subscription-id>
   </delete-subscription>
</netconf:rpc>

<rpc-reply message-id="103"
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <ok/>       
</rpc-reply>

    

<CODE BEGINS>
file "ietf-datastore-push@2015-10-09.yang"

module ietf-datastore-push {
  namespace "urn:ietf:params:xml:ns:yang:ietf-datastore-push";
  prefix yp;

  import ietf-inet-types {
    prefix inet;
  }
  import ietf-yang-types {
    prefix yang;
  }

  organization "IETF";
  contact
    "WG Web:   <http://tools.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>
     
     WG Chair: Mahesh Jethanandani
               <mailto:mjethanandani@gmail.com>
     
     WG Chair: Mehmet Ersue 
               <mailto:mehmet.ersue@nokia.com>
               
     Editor:   Alexander Clemm
               <mailto:alex@cisco.com>
     
     Editor:   Alberto Gonzalez Prieto
               <mailto:albertgo@cisco.com>
     
     Editor:   Eric Voit
               <mailto:evoit@cisco.com>";
  description
    "This module contains conceptual YANG specifications
    for datastore push.";

  revision 2015-10-13 {
    description
      "Initial revision.";
    reference 
      "YANG Datastore Push, draft-clemm-netconf-yang-push-02";
  }

  feature on-change {
    description
      "This feature indicates that on-change updates are supported.";
  }

  feature json {
    description
      "This feature indicates that JSON encoding of push updates is 
      supported.";
  }

  identity subscription-stream-status {
    description
      "Base identity for the status of subscriptions and 
      datastreams.";
  }

  identity active {
    base subscription-stream-status;
    description
      "Status is active and healthy.";
  }

  identity inactive {
    base subscription-stream-status;
    description
      "Status is inactive, for example outside the 
      interval between start time and stop time.";
  }

  identity in-error {
    base subscription-stream-status;
    description
      "The status is in error or degraded, meaning that 
      stream and/or subscription are currently unable to provide 
      the negotiated updates.";
  }

  identity subscription-errors {
    description
      "Base identity for subscription errors.";
  }

  identity internal-error {
    base subscription-errors;
    description
      "Subscription failures caused by server internal error.";
  }

  identity no-resources {
    base subscription-errors;
    description
      "Lack of resources, e.g. CPU, memory, bandwidth";
  }

  identity subscription-deleted {
    base subscription-errors;
    description
      "The subscription was terminated because the subscription 
      was deleted.";
  }

  identity other {
    base subscription-errors;
    description
      "Fallback reason - any other reason";
  }

  identity encodings {
    description
      "Base identity to represent data encodings";
  }

  identity encode-xml {
    base encodings;
    description
      "Encode data using XML";
  }

  identity encode-json {
    base encodings;
    description
      "Encode data using JSON";
  }

  identity system-streams {
    description
      "Base identity to represent a conceptual system-provided 
      datastream of datastore updates with predefined semantics.";
  }

  identity datastore-push {
    base system-streams;
    description
      "A conceptual datastream consisting of all datastore 
      updates, including operational and configuration data.";
  }

  identity operational-push {
    base system-streams;
    description
      "A conceptual datastream consisting of updates of all 
      operational data.";
  }

  identity config-push {
    base system-streams;
    description
      "A conceptual datastream consisting of updates of all
      configuration data.";
  }

  identity datastore {
    description
      "An identity that represents a datastore.";
  }

  identity running {
    base datastore;
    description
      "Designates the running datastore";
  }

  identity startup {
    base datastore;
    description
      "Designates the startup datastore";
  }

  typedef datastore-contents-xml {
    type string;
    description
      "This type is be used to represent datastore contents,      
      i.e. a set of data nodes with their values, in XML. 
      The syntax corresponds to the syntax of the data payload 
      returned in a corresponding Netconf get operation with the 
      same filter parameters applied.";
    reference "RFC 6241 section 7.7";
  }

  typedef datastore-changes-xml {
    type string;
    description
      "This type is used to represent a set of changes in a
      datastore encoded in XML, indicating for datanodes whether 
      they have been created, deleted, or updated.  The syntax 
      corresponds to the syntax used to when editing a 
      datastore using the edit-config operation in Netconf.";
    reference "RFC 6241 section 7.2";
  }

  typedef datastore-contents-json {
    type string;
    description
      "This type is be used to represent datastore contents, 
      i.e. a set of data nodes with their values, in JSON.  
      The syntax corresponds to the syntax of the data 
      payload returned in a corresponding RESTCONF get 
      operation with the same filter parameters applied.";
    reference "RESTCONF Protocol";
  }

  typedef datastore-changes-json {
    type string;
    description
      "This type is used to represent a set of changes in a
      datastore encoded in JSON, indicating for datanodes whether 
      they have been created, deleted, or updated.  The syntax 
      corresponds to the syntax used to patch a datastore 
      using the yang-patch operation with Restconf.";
    reference "draft-ietf-netconf-yang-patch";
  }

  typedef filter-id {
    type string;
    description
      "This type defines an identifier for a filter.";
  }

  typedef subtree-filter {
    type string;
    description
      "This type is used to specify the subtree that the 
      subscription refers to. Its syntax follows the subtree 
      filter syntax specified for Netconf in RFC 6241, 
      section 6.";
    reference "RFC 6241 section 6";
  }

  typedef datastore {
    type identityref {
      base datastore;
    }
    description
      "Used to refer to a datastore, for example, to running";
  }

  typedef subscription-id {
    type string {
      length "1 .. max";
    }
    description
      "A client-provided identifier for the subscription.";
  }

  typedef subscription-term-reason {
    type identityref {
      base subscription-errors;
    }
    description
      "Reason for a server to terminate a subscription.";
  }

  typedef subscription-susp-reason {
    type identityref {
      base subscription-errors;
    }
    description
      "Reason for a server to suspend a subscription.";
  }

  typedef encoding {
    type identityref {
      base encodings;
    }
    description
      "Specifies a data encoding, e.g. for a data subscription.";
  }

  typedef change-type {
    type enumeration {
      enum "create" {
        description
          "A new data node was created";
      }
      enum "delete" {
        description
          "A data node was deleted";
      }
      enum "modify" {
        description
          "The value of a data node has changed";
      }
    }
    description
      "Specifies different types of changes that may occur 
      to a datastore.";
  }

  typedef system-stream {
    type identityref {
      base system-streams;
    }
    description
      "Specifies a system-provided datastream.";
  }

  typedef filter-ref {
    type leafref {
      path "/yp:filters/yp:filter/yp:filter-id";
    }
    description
      "This type is used to reference a yang push filter.";
  }

  grouping datatree-filter {
    description
      "This grouping defines filters for a datastore tree.";
    choice filter-type {
      description
        "A filter needs to be a single filter of a given type.  
        Mixing and matching of multiple filters does not occur 
        at the level of this grouping.";
      case subtree {
        description
          "Subtree filter";
        leaf subtree-filter {
          type subtree-filter;
          description
            "Datastore subtree of interest.";
        }
      }
      case xpath {
        description
          "XPath filter";
        leaf xpath-filter {
          type yang:xpath1.0;
          description
            "Xpath defining the data items of interest.";
        }
      }
    }
  }

  grouping subscription-info {
    description
      "This grouping describes basic information concerning a 
       subscription.";
    leaf target-datastore {
      type datastore;
      default "running";
      description
        "The datastore that is the target of the subscription.  
        If not specified, running applies.";
    }
    leaf stream {
      type system-stream;
      default "datastore-push";
      description
        "The name of the stream subscribed to.";
    }
    leaf encoding {
      type encoding;
      default "encode-xml";
      description
        "The type of encoding for the subscribed data.  
        Default is XML";
    }
    leaf start-time {
      type yang:date-and-time;
      description
        "Designates the time at which a subscription is supposed 
        to start, or immediately, in case the start-time is in 
        the past. For periodic subscription, the start time also  
        serves as anchor time from which the time of the next
        update is computed. The next update will take place at the
        next period interval from the anchor time.  
        For example, for an anchor time at the top of a minute 
        and a period interval of a minute, the next update will 
        be sent at the top of the next minute.";
    }
    leaf stop-time {
      type yang:date-and-time;
      description
        "Designates the time at which a subscription will end.
        When a subscription reaches its stop time, it will be 
        automatically deleted.";
    }
    choice update-trigger {
      description
        "Defines necessary conditions for sending an event  to 
         the subscriber.";
      case periodic {
        description
          "The agent is requested to notify periodically the 
          current values of the datastore or the subset 
          defined by the filter.";
        leaf period {
          type yang:timeticks;
          description
            "Elapsed time between notifications.";
        }
      }
      case on-change {
        description
          "The agent is requested to notify changes in 
           values in the datastore or a subset of it defined 
           by a filter.";
        leaf no-synch-on-start {
          type empty;
          description
            "This leaf acts as a flag that determines behavior at the
            start of the subscription.  When present, 
            synchronization of state at the beginning of the 
            subscription is outside the scope of the subscription.  
            Only updates about changes that are observed from the 
            start time, i.e. only push-change-update notifications 
            are sent.  
            When absent (default behavior), in order to facilitate 
            a receiver's synchronization, a full update is sent 
            when the subscription starts using a push-update 
            notification, just like in the case of a periodic 
            subscription.  After that, push-change-update 
            notifications are sent.";
        }
        leaf dampening-period {
          type yang:timeticks;
          mandatory true;
          description
            "Minimum amount of time that needs to have 
            passed since the last time an update was 
            provided.";
        }
        leaf-list excluded-change {
          type change-type;
          description
            "Use to restrict which changes trigger an update.
            For example, if modify is excluded, only creation and 
            deletion of objects is reported.";
        }
      }
    }
    choice filterspec {
      description
        "Filter can be specified in-line, as part of the 
        subscription, or configured separately and referenced
        here.  If no filter is specified, the entire datatree
        is of interest.";
      case inline {
        description
          "Filter is defined as part of the subscription.";
        uses datatree-filter;
      }
      case by-reference {
        description
          "Incorporate a filter that has been configured 
          separately.";
        leaf filter-ref {
          type filter-ref;
          description
            "References the filter to incorporate for the 
            subscription.";
        }
      }
    }
  }

  grouping receiver-info {
    description
      "Defines a reusable snippet that defines the address of the 
      intended receiver of push updates for a subscription.";
    container receiver-address {
      description
        "This container contains the address information of the
         receiver.";
      choice push-base-transport {
        description
          "This choice can be augmented with different options, 
           depending on the transport underlying the push 
           transport.";
        case tcpudp {
          description
            "For Netconf and Restconf, TCP is the base transport.";
          container tcpudp {
            description
              "Contains TCP / UDP addressing information";
            leaf address {
              type inet:host;
              description
                "The leaf uniquely specifies the address of the
                 remote host. One of the following must be
                 specified: an ipv4 address, an ipv6 address,
                 or a host name.";
            }
            leaf port {
              type inet:port-number;
              description
                "This leaf specifies the port number used to
                 deliver messages to the remote server.";
            }
          }
        }
      }
    }
  }

  rpc create-subscription {
    description
      "This RPC allows a subscriber to create a subscription 
      on its own behalf.  If successful, the subscription 
      remains in effect for the duration of the subscriber's 
      association with the publisher, or until the subscription 
      is terminated by virtue of a delete-subscription request.";
    input {
      uses subscription-info;
    }
    output {
      leaf subscription-id {
        type subscription-id;
        description
          "Identifier used for this subscription.";
      }
    }
  }
  rpc modify-subscription {
    description
      "This RPC allows a subscriber to modify a subscription 
      that was previously created using create-subscription.  
      If successful, the subscription 
      remains in effect for the duration of the subscriber's 
      association with the publisher, or until the subscription 
      is terminated by virtue of a delete-subscription request.";
    input {
      leaf subscription-id {
        type subscription-id;
        description
          "Identifier to use for this subscription.";
      }
    }
  }
  rpc delete-subscription {
    description
      "This RPC allows a subscriber to delete a subscription that
      was previously created using create-subscription.";
    input {
      leaf subscription-id {
        type subscription-id;
        description
          "Identifier of the subscription that is to be deleted.
          Only subscriptions that were created using 
          create-subscription can be deleted via this RPC.";
      }
    }
  }
  notification push-update {
    description
      "This notification contains a periodic push update.
      This notification shall only be sent to receivers 
      of a subscription; it does not constitute a general-purpose 
      notification.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the subscription because of which the 
        notification is sent.";
    }
    leaf time-of-update {
      type yang:date-and-time;
      description
        "This leaf contains the time of the update.";
    }
    choice encoding {
      description
        "Distinguish between the proper encoding that was specified 
        for the subscription";
      case encode-xml {
        description
          "XML encoding";
        leaf datastore-contents-xml {
          type datastore-contents-xml;
          description
            "This contains data encoded in XML,  
            per the subscription.";
        }
      }
      case encode-json {
        if-feature json;
        description
          "JSON encoding";
        leaf datastore-contents-json {
          type datastore-contents-json;
          description
            "This leaf contains data encoded in JSON, 
            per the subscription.";
        }
      }
    }
  }
  notification push-change-update {
    description
      "This notification contains an on-change push update.
      This notification shall only be sent to the receivers 
      of a subscription; it does not constitute a general-purpose 
      notification.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the subscription because of which the 
        notification is sent.";
    }
    leaf time-of-update {
      type yang:date-and-time;
      description
        "This leaf contains the time of the update, i.e. the
        time at which the change was observed.";
    }
    choice encoding {
      description
        "Distinguish between the proper encoding that was specified 
        for the subscription";
      case encode-xml {
        description
          "XML encoding";
        leaf datastore-changes-xml {
          type datastore-changes-xml;
          description
            "This contains datastore contents that has changed 
            since the previous update, per the terms of the 
            subscription.  Changes are encoded analogous to 
            the syntax of a corresponding Netconf edit-config
            operation.";
        }
      }
      case encode-json {
        if-feature json;
        description
          "JSON encoding";
        leaf datastore-changes-yang {
          type datastore-changes-json;
          description
            "This contains datastore contents that has changed
            since the previous update, per the terms of the 
            subscription.  Changes are encoded analogous 
            to the syntax of a corresponding RESTCONF yang-patch
            operation.";
        }
      }
    }
  }
  notification subscription-started {
    description
      "This notification indicates that a subscription has 
      started and data updates are beginning to be sent.
      This notification shall only be sent to receivers 
      of a subscription; it does not constitute a general-purpose 
      notification.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses subscription-info;
  }
  notification subscription-suspended {
    description
      "This notification indicates that a suspension of the 
      subscription by the server has occurred.  No further 
      datastore updates will be sent until subscription 
      resumes.
      This notification shall only be sent to receivers 
      of a subscription; it does not constitute a general-purpose 
      notification.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    leaf reason {
      type subscription-susp-reason;
      description
        "Provides a reason for why the subscription was 
        suspended.";
    }
  }
  notification subscription-resumed {
    description
      "This notification indicates that a subscription that had 
      previously been suspended has resumed. Datastore updates 
      will once again be sent.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
  }
  notification subscription-modified {
    description
      "This notification indicates that a subscription has 
      been modified.  Datastore updates sent from this point 
      on will conform to the modified terms of the 
      subscription.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses subscription-info;
  }
  notification subscription-terminated {
    description
      "This notification indicates that a subscription has been 
      terminated.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    leaf reason {
      type subscription-term-reason;
      description
        "Provides a reason for why the subscription was 
        terminated.";
    }
  }
  container system-streams {
    config false;
    description
      "This container contains a leaf list of built-in 
       streams that are provided by the system.";
    leaf-list system-stream {
      type system-stream;
      description
        "Identifies a built-in stream that is supported by the
        system.  Streams are associated with their own identities, 
        each of which carries a special semantics.";
    }
  }
  container filters {
    description
      "This container contains a list of configurable filters 
      that can be applied to subscriptions.  This facilitates 
      the reuse of complex filters once defined.";
    list filter {
      key "filter-id";
      description
        "A list of configurable filters that can be applied to 
        subscriptions.";
      leaf filter-id {
        type filter-id;
        description
          "An identifier to differentiate between filters.";
      }
      uses datatree-filter;
    }
  }
  container subscription-config {
    description
      "Contains the list of subscriptions that are configured, 
       as opposed to established via RPC or other means.";
    list datastore-push-subscription {
      key "subscription-id";
      description
        "Content of a yang-push subscription.";
      leaf subscription-id {
        type subscription-id;
        description
          "Identifier to use for this subscription.";
      }
      uses subscription-info;
      uses receiver-info;
    }
  }
  container subscriptions {
    config false;
    description
      "Contains the list of currently active subscriptions, 
      i.e. subscriptions that are currently in effect, 
      used for subscription management and monitoring purposes.
      This includes subscriptions that have been setup via RPC 
      primitives, e.g. create-subscription, delete-subscription,
      and modify-subscription, as well as subscriptions that 
      have been established via configuration.";
    list datastore-push-subscription {
      key "subscription-id";
      config false;
      description
        "Content of a yang-push subscription.  
        Subscriptions can be created using a control channel 
        or RPC, or be established through configuration.";
      leaf subscription-id {
        type subscription-id;
        description
          "Identifier of this subscription.";
      }
      leaf configured-subscription {
        type empty;
        description
          "The presence of this leaf indicates that the 
          subscription originated from configuration, not through
          a control channel or RPC.";
      }
      leaf subscription-status {
        type identityref {
          base subscription-stream-status;
        }
        description
          "The status of the subscription.";
      }
      uses subscription-info;
      uses receiver-info;
    }
  }
}
<CODE ENDS>