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draft-ietf-netconf-distributed-notif-01.txt
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NETCONF T. Zhou
Internet-Draft G. Zheng
Intended status: Standards Track Huawei
Expires: May 6, 2021 E. Voit
Cisco Systems
T. Graf
Swisscom
P. Francois
INSA-Lyon
November 02, 2020
Subscription to Distributed Notifications
draft-ietf-netconf-distributed-notif-01
Abstract
This documents describes extensions to the YANG notifications
subscription to allow metrics being published directly from
processors on line cards to target receivers, while subscription is
still maintained at the route processor in a distributed forwarding
system.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 6, 2021.
Zhou, et al. Expires May 6, 2021 [Page 1]
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4
5. Subscription Decomposition . . . . . . . . . . . . . . . . . 6
6. Publication Composition . . . . . . . . . . . . . . . . . . . 6
7. Subscription State Change Notifications . . . . . . . . . . . 7
8. Publisher Configurations . . . . . . . . . . . . . . . . . . 7
9. YANG Tree . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 8
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
12. Security Considerations . . . . . . . . . . . . . . . . . . . 10
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
15.1. Normative References . . . . . . . . . . . . . . . . . . 11
15.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 13
A.1. Dynamic Subscription . . . . . . . . . . . . . . . . . . 13
A.2. Configured Subscription . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The mechanism to support a subscription to a continuous and
customized stream of updates from a YANG datastore is defined in
[RFC8639] and [RFC8641]. Requirements for Subscription to YANG
Datastores are defined in [RFC7923]
By streaming data from publishers to receivers, much better
performance and fine-grained sampling can be achieved than with
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polling. In a distributed forwarding system, the packet forwarding
is delegated to multiple processors on line cards. To not to
overhelm the route processor resources, it is not uncomon that data
records are published directly from processors on line cards to
target Receivers to further increase efficency on the routing system.
This documents complement the general subscription requirements
defined in section 4.2.1 of [RFC7923] by the paragraph: A
Subscription Service MAY support the ability to export from multiple
software processes on a single routing system and expose the
information which software process produced which message to maintain
data integrity.
2. Terminologies
The following terms are defined in [RFC8639] and are not redefined
here:
Subscriber
Publisher
Receiver
Subscription
In addition, this document defines the following terms:
Global Subscription: the Subscription requested by the subscriber.
It may be decomposed into multiple Component Subscriptions.
Component Subscription: is the Subscription that defines a data
source which is managed and controlled by a single Publisher.
Global Capability: is the overall subscription capability that the
group of Publishers can expose to the Subscriber.
Component Capability: is the subscription capability that each
Publisher can expose to the Subscriber.
Master: is the Publisher that interacts with the Subscriber to deal
with the Global Subscription. It decomposes the Global Subscription
to multiple Component Subscriptions and interacts with the Agents.
Agent: is the Publisher that interacts with the Master to deal with
the Component Subscription and pushing the data to the collector.
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Observation Domain: An Observation Domain is the largest set of
Observation Points for which metrics can be collected by a metering
process. For example, a router line card may be an Observation
Domain if it is composed of several interfaces, each of which is an
Observation Point. In the YANG notification messages it generates,
the Observation Domain includes its Observation Domain ID, which is
unique per publisher process. That way, the collecting process can
identify the specific Observation Domain from the publisher that
sends the YANG notification messages. Every Observation Point is
associated with an Observation Domain.
Observation Domain ID: A 32-bit identifier of the Observation Domain
that is locally unique to the publisher process. The publisher
process uses the Observation Domain ID to uniquely identify to the
collecting process the Observation Domain that meters the metrics.
Receivers SHOULD use the transport session and the Observation Domain
ID field to separate different publisher streams originating from the
same publisher.
3. Motivation
Lost and corrupt YANG notification messages need to be recognized at
the receiver to ensure data integrity even when multiple publisher
processes publishing from the same transport session.
To preserve data integrity down to the publisher process, the
Observation Domain ID in the transport message header of the YANG
notification message is introduced. In case of UDP transport, this
is described in Section 3.2 of UDP based transport
[I-D.ietf-netconf-udp-notif].
4. Solution Overview
Figure 2 below shows the distributed data export framework.
A collector usually includes two components,
o the Subscriber generates the subscription instructions to express
what and how the collector want to receive the data;
o the Receiver is the target for the data publication.
For one subscription, there are one or more Receivers. And the
Subscriber does not necessarily share the same IP address as the
Receivers.
In this framework, the Publisher pushes data to the Receiver
according to the subscription. The Publisher is either in the Master
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or Agent role. The Master knows all the capabilities that his Agents
are able to provide and exposes the Global Capability to the
collector. The Subscriber maintains the Global Subscription at the
Master and disassembles the Global Subscription to multiple Component
Subscriptions, depending from which source data is needed. The
Component Subscriptions are then distributed to the corresponding
Publisher Agents on route and processors on line cards.
Publisher Agents collects metrics according to the Component
Subscription, add its metadata, encapsulate and pushes data to the
Receiver where packets are reassembled and decapsulated.
+-----------------------------------------+
| Collector |-------------+ |
| +------------+ | |
| +------------+ || Receiver | | |
| | Subscriber | |--------------+ |
| +-----^-+----+ +------------^ |
| | | | |
+-----------------------------------------+
Global | | Global |
Capability| | Subscription |
+-----------------------------------------+
| | | | |
| +--------+-v-------------------+ | |
| | Publisher(Master) | | |
| +--------^-+-------------------+ | |
| | | | |
| | | | |
| Component | | Component Push | |
| Capability| | Subscription | |
| +--------+-v-------------------+ | |
| | Publisher(Agent) +--+ |
| +------------------------------+ |
| |
| Device |
+-----------------------------------------+
Fig. 2 The Distributed Data Export Framework
Master and Agents interact with each other in several ways:
o Agents need to register at the Master at the beginning of their
process life-cycle
o Contracts are created between the Master and each Agent on the
Component Capability, and the format for streaming data structure.
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o The Master relays the component subscriptions to the Agents.
o The Agents announce the status of their Component Subscriptions to
the Master. The status of the overall subscription is maintained
by the Master. The Master is responsible for notifying the
subscriber in case of problems with the Component Subscriptions.
The technical mechanisms or protocols used for the coordination of
operational information between Master and Agent is out-of-scope of
this document.
5. Subscription Decomposition
The Collector can only subscribe to the Master. This requires the
Master to:
1. expose the Global Capability that can be served by multiple
Publisher Agents;
2. disassemble the Global Subscription to multiple Component
Subscriptions, and distribute them to the Publisher Agents of the
corresponding metric sources so that they not overlap;
3. notify on changes when portions of a subscription moving between
different Publisher Agents over time.
And the Agent to:
o Inherit the Global Subscription properties from Publisher Master
for its Component Subscription;
o share the same life-cycle as the Global Subscription;
o share the same Subscription ID as the Global Subscription.
6. Publication Composition
The Publisher Agent collects data and encapsulates the packets per
Component Subscription. The format and structure of the data records
are defined by the YANG schema, so that the decomposition at the
Receiver can benefit from the structured and hierarchical data
records.
The Receiver is able to associate the YANG data records with
Subscription ID [RFC8639] to the subscribed subscription and with
Message Observation Domain ID
[I-D.ietf-netconf-notification-messages] to one of the Publisher
Agents software processes to enable message integrity.
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For the dynamic subscription, the output of the "establish-
subscription" RPC defined in [RFC8639] MUST include a list of Message
Observation Domain IDs to indicate how the Global Subscription is
decomposed into several Component Subscriptions.
The "subscription-started" and "subscription-modified" notification
defined in [RFC8639] MUST also include a list of Message Observation
Domain IDs to notify the current Publishers for the corresponding
Global Subscription.
7. Subscription State Change Notifications
In addition to sending event records to Receivers, the Master MUST
also send subscription state change notifications [RFC8639] when
events related to subscription management have occurred. All the
subscription state change notifications MUST be delivered by the
Master.
When the subscription decomposition result changed, the
"subscription-modified" notification MUST be sent to indicate the new
list of Publishers.
8. Publisher Configurations
This document assumes that all Publisher Agents are preconfigured to
push data. The actual working Publisher Agents are selected based on
the subscription decomposition result.
All Publisher Agents share the same source IP address for data
export. For connectionless data transport such as UDP based
transport [I-D.ietf-netconf-udp-notif] the same Layer 4 source port
for data export can be used. For connection based data transport
such as HTTPS based transport [I-D.ietf-netconf-https-notif], each
Publisher Agent MUST be able to acknowledge packet retrieval from
Receivers, and therefore requires a dedicated Layer 4 source port per
software process.
The specific configuration on transports is described in the
resposible documents.
9. YANG Tree
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module: ietf-distributed-notifications
augment /sn:subscriptions/sn:subscription:
+--ro message-observation-domain-id* string
augment /sn:subscription-started:
+--ro message-observation-domain-id* string
augment /sn:subscription-modified:
+--ro message-observation-domain-id* string
augment /sn:establish-subscription/sn:output:
+--ro message-observation-domain-id* string
10. YANG Module
<CODE BEGINS> file "[email protected]"
module ietf-distributed-notif {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-distributed-notifications";
prefix mso;
import ietf-subscribed-notifications {
prefix sn;
}
organization "IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http:/tools.ietf.org/wg/netconf/>
WG List: <mailto:[email protected]>
Editor: Tianran Zhou
<mailto:[email protected]>
Editor: Guangying Zheng
<mailto:[email protected]>";
description
"Defines augmentation for ietf-subscribed-notifications to
enable the distributed publication with single subscription.
Copyright (c) 2018 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Simplified BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
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This version of this YANG module is part of RFC XXXX; see the
RFC itself for full legal notices.";
revision 2020-05-09 {
description
"Initial version";
reference
"RFC XXXX: Subscription to Distributed Notifications";
}
grouping message-observation-domain-ids {
description
"Provides a reusable list of message-observation-domain-ids.";
leaf-list message-observation-domain-id {
type string;
config false;
ordered-by user;
description
"Software process which created the message (e.g.,
processor 1 on linecard 1). This field is
used to notify the collector the working originator.";
}
}
augment "/sn:subscriptions/sn:subscription" {
description
"This augmentation allows the message
Observation Domain ID to be exposed for a subscription.";
uses message-observation-domain-ids;
}
augment "/sn:subscription-started" {
description
"This augmentation allows MSO specific parameters to be
exposed for a subscription.";
uses message-observation-domain-ids;
}
augment "/sn:subscription-modified" {
description
"This augmentation allows MSO specific parameters to be
exposed for a subscription.";
uses message-observation-domain-ids;
}
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augment "/sn:establish-subscription/sn:output" {
description
"This augmentation allows MSO specific parameters to be
exposed for a subscription.";
uses message-observation-domain-ids;
}
}
<CODE ENDS>
11. IANA Considerations
This document registers the following namespace URI in the IETF XML
Registry [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
This document registers the following YANG module in the YANG Module
Names registry [RFC3688]:
Name: ietf-subscribed-notifications
Namespace: urn:ietf:params:xml:ns:yang:ietf-subscribed-
notifications
Prefix: mso
Reference: RFC XXXX
12. Security Considerations
The YANG module specified in this document defines a schema for data
that is designed to be accessed via network management protocols such
as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer
is the secure transport layer, and the mandatory-to-implement secure
transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer
is HTTPS, and the mandatory-to-implement secure transport is TLS
[RFC5246].
The NETCONF Access Control Model (NACM) [RFC6536] provides the means
to restrict access for particular NETCONF or RESTCONF users to a
preconfigured subset of all available NETCONF or RESTCONF protocol
operations and content.
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The new data nodes introduced in this YANG module may be considered
sensitive or vulnerable in some network environments. It is thus
important to control read access (e.g., via get-config or
notification) to this data nodes. These are the subtrees and data
nodes and their sensitivity/vulnerability:
o /subscriptions/subscription/message-observation-domain-ids
The entries in the two lists above will show where subscribed
resources might be located on the publishers. Access control MUST be
set so that only someone with proper access permissions has the
ability to access this resource.
Other Security Considerations is the same as those discussed in YANG-
Push [RFC8641].
13. Contributors
Alexander Clemm
Futurewai
2330 Central Expressway
Santa Clara
California
United States of America
Email: [email protected]
14. Acknowledgements
We thank Kent Watsen, Mahesh Jethanandani, Martin Bjorklund, Tim
Carey and Qin Wu for their constructive suggestions for improving
this document.
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
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[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536,
DOI 10.17487/RFC6536, March 2012,
<https://www.rfc-editor.org/info/rfc6536>.
[RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
for Subscription to YANG Datastores", RFC 7923,
DOI 10.17487/RFC7923, June 2016,
<https://www.rfc-editor.org/info/rfc7923>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8639] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "Subscription to YANG Notifications",
RFC 8639, DOI 10.17487/RFC8639, September 2019,
<https://www.rfc-editor.org/info/rfc8639>.
[RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
September 2019, <https://www.rfc-editor.org/info/rfc8641>.
15.2. Informative References
[I-D.ietf-netconf-https-notif]
Jethanandani, M. and K. Watsen, "An HTTPS-based Transport
for YANG Notifications", draft-ietf-netconf-https-notif-08
(work in progress), February 2021.
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[I-D.ietf-netconf-notification-messages]
Voit, E., Jenkins, T., Birkholz, H., Bierman, A., and A.
Clemm, "Notification Message Headers and Bundles", draft-
ietf-netconf-notification-messages-08 (work in progress),
November 2019.
[I-D.ietf-netconf-udp-notif]
Zhou, T., Zheng, G., Lucente, P., Graf, T., and P.
Francois, "UDP-based Transport for Configured
Subscriptions", draft-ietf-netconf-udp-notif-01 (work in
progress), July 2020.
Appendix A. Examples
This appendix is non-normative.
A.1. Dynamic Subscription
Figure 3 shows a typical dynamic subscription to the device with
distributed data export capability.
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+-------------+ +-------------+ +-------------+
| Subscriber/ | | Publisher | | Publisher |
| Receiver | | (Master) | | (Agent) |
+-------------+ +------+------+ +------+------+
| | |
| establish-subscription | |
+------------------------------>+ component |
| | subscription |
| RPC Reply: OK, id #22 +-------------->+
| Observation Domain ID [#1,#2] | |
+<------------------------------+ |
| | |
| notif-mesg, id #22 | |
| Observation Domain ID #1 | |
+<------------------------------+ |
| | |
| notif-mesg, id#22 | |
| Observation Domain ID #2 | |
+<----------------------------------------------+
| | |
| modify-subscription (id#22) | |
+------------------------------>+ component |
| | subscription |
| RPC Reply: OK, id #22 +-------------->+
+<------------------------------+ |
| | |
| subscription-modified, id#22 | |
| Observation Domain ID [#1] | |
+<------------------------------+ |
| | |
| notif-mesg, id #22 | |
| Observation Domain ID #1 | |
+<------------------------------+ |
| | |
| | |
+ + +
Fig. 3 Call Flow for Dynamic Subscription
A "establish-subscription" RPC request as per [RFC8641] is sent to
the Master with a successful response. An example of using NETCONF:
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<netconf:rpc message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
<yp:datastore
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
ds:operational
</yp:datastore>
<yp:datastore-xpath-filter
xmlns:ex="https://example.com/sample-data/1.0">
/ex:foo
</yp:datastore-xpath-filter>
<yp:periodic>
<yp:period>500</yp:period>
</yp:periodic>
</establish-subscription>
</netconf:rpc>
Fig. 4 "establish-subscription" Request
As the device is able to fully satisfy the request, the request is
given a subscription ID of 22. The response as in Figure 5 indicates
that the subscription is decomposed into two component subscriptions
which will be published by two message Observation Domain ID: #1 and
#2.
<rpc-reply message-id="101"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<id
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
22
</id>
<message-observation-domain-id
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications>
1
</message-observation-domain-id>
<message-observation-domain-id
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications>
2
</message-observation-domain-id>
</rpc-reply>
Fig. 5 "establish-subscription" Positive RPC Response
Then, both Publishers send notifications with the corresponding piece
of data to the Receiver.
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The subscriber may invoke the "modify-subscription" RPC for a
subscription it previously established. The RPC has no difference to
the single publisher case as in [RFC8641]. Figure 6 provides an
example where a subscriber attempts to modify the period and
datastore XPath filter of a subscription using NETCONF.
<rpc message-id="102"
xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<modify-subscription
xmlns=
"urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
<id>22</id>
<yp:datastore
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
ds:operational
</yp:datastore>
<yp:datastore-xpath-filter
xmlns:ex="https://example.com/sample-data/1.0">
/ex:bar
</yp:datastore-xpath-filter>
<yp:periodic>
<yp:period>250</yp:period>
</yp:periodic>
</modify-subscription>
</rpc>
Fig. 6 "modify-subscription" Request
If the modification is successfully accepted, the "subscription-
modified" subscription state notification is sent to the subscriber
by the Master. The notification, Figure 7 for example, indicates the
modified subscription is decomposed into one component subscription
which will be published by message Observation Domain #1.
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<notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2007-09-01T10:00:00Z</eventTime>
<subscription-modified
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
<id>22</id>
<yp:datastore
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
ds:operational
</yp:datastore>
<yp:datastore-xpath-filter
xmlns:ex="https://example.com/sample-data/1.0">
/ex:bar
</yp:datastore-xpath-filter>
<yp:periodic>
<yp:period>250</yp:period>
</yp:periodic>
<message-observation-domain-id
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notificationss>
1
</message-observation-domain-id>
</subscription-modified>
</notification>
Fig. 7 "subscription-modified" Subscription State Notification
A.2. Configured Subscription
Figure 8 shows a typical configured subscription to the device with
distributed data export capability.
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+-------------+ +-------------+ +-------------+
| Receiver | | Publisher | | Publisher |
| | | (Master) | | (Agent) |
+------+------+ +------+------+ +------+------+
| | |
| subscription-started, id#39 | |
| Observation Domain ID [#1,#2] | |
+<------------------------------+ |
| | |
| notif-mesg, id#39 | |
| Observation Domain ID #1 | |
+<------------------------------+ |
| | |
| notif-mesg, id#39 | |
| Observation Domain ID #2 | |
+<----------------------------------------------+
| | |
| | |
| | |
Fig. 8 Call Flow for Configured Subscription
Before starting to push data, the "subscription-started" subscription
state notification is sent to the Receiver. The following example
assumes the NETCONF transport has already established. The
notification indicates that the configured subscription is decomposed
into two component subscriptions which will be published by two
message Observation Domain: #1 and #2.