DTN Management Architecture
draft-ietf-dtn-dtnma-01
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| Last updated | 2022-07-10 | ||
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draft-ietf-dtn-dtnma-01
Delay-Tolerant Networking E.J. Birrane
Internet-Draft E. Annis
Intended status: Informational S.E. Heiner
Expires: 11 January 2023 Johns Hopkins Applied Physics Laboratory
10 July 2022
DTN Management Architecture
draft-ietf-dtn-dtnma-01
Abstract
This document describes the motivation for, and services required of,
the management of devices deployed in a Delay-Tolerant Networking
(DTN) environment. Together, this set of information outlines a
conceptual DTN Management Architecture (DTNMA) suitable for
deployment in any of the challenged and constrained DTN operational
environments.
The DTNMA is supported by two types of asynchronous behavior. First,
the DTNMA does not presuppose any synchronized transport behavior
between managed and managing devices. Second, the DTNMA does not
support any query-response semantics. In this way, the DTNMA allows
for operation in extremely challenging conditions, to include over
uni-directional links and cases where delays/disruptions prevent
operation over traditional transport layers.
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
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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 11 January 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 5
1.3. Organization . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Constrained and Challenged Networks . . . . . . . . . . . 8
3.2. Management of Challenged Networks . . . . . . . . . . . . 10
3.3. Current Network Management Approaches and Limitations . . 11
3.3.1. Simple Network Management Protocol (SNMP) . . . . . . 12
3.3.2. YANG Data Model and NETCONF, RESTCONF, and
CORECONF . . . . . . . . . . . . . . . . . . . . . . 13
3.3.3. The Future of Autonomous and Autonomic Network
Management Solutions . . . . . . . . . . . . . . . . 15
3.3.4. Takeaways from Existing Network Management
Protocols . . . . . . . . . . . . . . . . . . . . . . 15
3.4. A Network Management Approach for DTNs . . . . . . . . . 16
4. Desirable Properties of an DTNMA . . . . . . . . . . . . . . 16
4.1. Asynchronous, Dynamic, and Highly Logical Architecture . 17
4.2. Model-derived and Hierarchically Organized Definition of
Information . . . . . . . . . . . . . . . . . . . . . . . 17
4.3. Intelligent Push of Information . . . . . . . . . . . . . 17
4.4. Minimize Message Size Not Node Processing . . . . . . . . 18
4.5. Absolute Data Identification . . . . . . . . . . . . . . 18
4.6. Custom Data Definition . . . . . . . . . . . . . . . . . 19
4.7. Autonomous Operation . . . . . . . . . . . . . . . . . . 19
5. Services Provided by an DTNMA . . . . . . . . . . . . . . . . 20
5.1. Configuration . . . . . . . . . . . . . . . . . . . . . . 21
5.2. Reporting . . . . . . . . . . . . . . . . . . . . . . . . 21
5.3. Autonomous Parameterized Procedure Calls . . . . . . . . 22
5.4. Authorized Administration, accounting, and error
control . . . . . . . . . . . . . . . . . . . . . . . . . 23
6. DTNMA Roles and Responsibilities . . . . . . . . . . . . . . 23
6.1. Agent Responsibilities . . . . . . . . . . . . . . . . . 23
6.2. Manager Responsibilities . . . . . . . . . . . . . . . . 25
7. Logical Data Model . . . . . . . . . . . . . . . . . . . . . 26
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7.1. Data Representations: Constants, Externally Defined Data,
and Variables . . . . . . . . . . . . . . . . . . . . . . 27
7.2. Data Collections: Reports and Tables . . . . . . . . . . 27
7.2.1. Report Templates and Reports . . . . . . . . . . . . 28
7.2.2. Table Templates and Tables . . . . . . . . . . . . . 28
7.3. Command Execution: Controls and Macros . . . . . . . . . 29
7.4. Autonomy: Time and State-Based Rules . . . . . . . . . . 30
7.4.1. State-Based Rule (SBR) . . . . . . . . . . . . . . . 30
7.4.2. Time-Based Rule (TBR) . . . . . . . . . . . . . . . . 30
7.5. Calculations: Expressions, Literals, and Operators . . . 31
8. System Model . . . . . . . . . . . . . . . . . . . . . . . . 31
8.1. Control and Data Flows . . . . . . . . . . . . . . . . . 31
8.2. Control Flow by Role . . . . . . . . . . . . . . . . . . 32
8.2.1. Notation . . . . . . . . . . . . . . . . . . . . . . 32
8.2.2. Serialized Management . . . . . . . . . . . . . . . . 33
8.2.3. Challenged, DTN Management . . . . . . . . . . . . . 34
8.2.4. Consolidated Message Management . . . . . . . . . . . 35
8.2.5. Multiplexed Management . . . . . . . . . . . . . . . 36
8.2.6. Data Fusion . . . . . . . . . . . . . . . . . . . . . 38
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
10. Security Considerations . . . . . . . . . . . . . . . . . . . 39
11. Informative References . . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
1. Introduction
The Delay-Tolerant Networking (DTN) architecture (as described in
[RFC4838]) has been designed to cope with data exchange in challenged
networks. Just as the DTN architecture requires new capabilities for
transport and transport security, special consideration must be given
for the management of DTN devices.
This document describes the DTN Management Architecture (DTNMA)
designed to provide configuration, monitoring, and local control of
both application and network services on a managed device operating
either within or across a challenged network.
The structure of the DTNMA is derived from the unique properties of
challenged networks are defined in [RFC7228]. These properties
include cases where an end-to-end transport path may not exist at any
moment in time and when delivery delays may prevent timely
communications between a network operator and a managed device.
These challenges may be caused by physical impairments such as long
signal propagations and frequent link disruptions or by other factors
such as quality-of-service prioritizations, service-level agreements,
and other consequences of traffic management and scheduling.
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Device management in these environments must occur without human
interactivity, without system-in-the-loop synchronous function, and
without requiring a synchronous underlying transport layer. This
means that managed devices need to determine their own schedules for
data reporting, their own operational configuration, and perform
their own error discovery and mitigation. Importantly, these
capabilities must be designed and implemented in a way that results
in outcomes that are determinable by an outside observer as such
observers may need to connect with a managed device after significant
periods of disconnectivity.
The desire to define asynchronous and autonomous device management is
not new. However, challenged networks (in general) and the DTN
environment (in particular) represent unique deployment scenarios and
impose unique design constraints. To the extent that these
environments differ from more traditional, enterprise networks their
management may also differ from the management of enterprise
networks. Therefore, existing techniques may need to be adapted to
operate in the DTN environment or new techniques may need to be
created.
Ultimately, the DTNMA is designed to leverage any transport, network,
and security solutions designed for challenged networks. However the
DTNMA is designed to be usable in any environment in which the Bundle
Protocol (BPv7) [RFC9171] may be deployed.
1.1. Scope
This document describes the motivation, services, desirable
properties, roles/responsibilities, logical data model, and system
model that form the DTNMA. These descriptions comprise a concept of
operations for management in challenged networks
This document is not a normative standardization of a physical data
model or any individual protocol. Instead, it serves as informative
guidance to authors and users of such models and protocols.
The DTNMA is independent of transport and network layers. It does
not, for example, require the use of BP, TCP, or UDP. Similarly, it
does not pre-suppose the use of IPv4 or IPv6.
The DTNMA is not bound to a particular security solution and does not
presume that transport layers can exchange messages in a timely
manner. It is assumed that any network using this architecture
supports services such as naming, addressing, routing, and security
that are required to communicate DTNMA messages as would be the case
with any other messages in the network.
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While possible that a challenged network may interface with an
unchallenged network, this document does not specifically address
compatibility with other management approaches.
1.2. 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 [RFC2119].
1.3. Organization
The remainder of this document is organized into the following seven
sections, described as follows.
* Terminology - This section identifies those terms critical to
understanding DTNMA concepts. Whenever possible, these terms
align in both word selection and meaning with their analogs from
other management protocols.
* Motivation - This section provides an overall motivation for this
work, to include explaining why this approach is a useful
alternative to existing network management approaches.
* Desirable Properties - This section identifies the properties that
guide the definition of the system and logical models that
comprise the DTNMA.
* Services Provided - This section identifies and defines the DTNMA
services provided to network and mission operators.
* Roles and Responsibilities - This section identifies roles in the
DTNMA and their associated responsibilities. It provides the
context for discussing how services are provided for both managed
and managing devices.
* Logical Data Model - This section describes the kinds of data,
procedures, autonomy, and associated hierarchical structure
inherent to the DTNMA.
* System Model - This section describes data flows amongst various
defined DTNMA roles. These flows capture how the DTNMA system
works to manage devices across a challenged network.
2. Terminology
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* Actor - A software service running on either managed or managing
devices for the purpose of implementing management protocols
between such devices. Actors may implement the "Manager" role,
"Agent" role, or both.
* Agent Role (or Agent) - A role associated with a managed device,
responsible for reporting performance data, accepting/performing
controls, error handling and validation, and executing any
autonomous behaviors. DTNMA Agents exchange information with
DTNMA Managers operating either on the same device or on a remote
managing device.
* DTN Management - Management that does not depend on stateful
connections or real time delivery of management messages. Such
management allows for asynchronous commanding to autonomous
managers running on managed devices. This management is designed
to run in any environment conformant to the DTN architecture and/
or in any environment deploying a BPv7 network.
* Externally Defined Data (EDD) - Information made available to a
DTNMA Agent by a managed device, but not computed directly by the
DTNMA Agent itself.
* Variables (VARs) - Typed information that is computed by a DTNMA
Agent, typically as a function of EDD values and/or other
Variables.
* Constants (CONST) - A Constant represents a typed, immutable value
that is referred to by a semantic name. Constants are used in
situations where substituting a name for a fixed value provides
useful semantic information. For example, using the named
constant PI rather than the literal value 3.14159.
* Controls (CTRLs) - Procedures run by a DTNMA Actor to change the
behavior, configuration, or state of an application or protocol
being managed within a DTN. Controls may also be used to request
data from an Agent and define the rules associated with generation
and delivery.
* Literals (LITs) - A Literal represents a typed value without a
semantic name. Literals are used in cases where adding a semantic
name to a fixed value provides no useful semantic information.
For example, the number 4 is a Literal value.
* Macros (MACROs) - A named, ordered collection of Controls and/or
other Macros.
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* Manager Role (or Manager) - A role associated with a managing
device responsible for configuring the behavior of, and eventually
receiving information from, DTNMA Agents. DTNMA Managers interact
with one or more DTNMA Agents located on the same device and/or on
remote devices in the network.
* Operator (OP) - The enumeration and specification of a
mathematical function used to calculate variable values and
construct expressions to evaluate DTNMA Agent state.
* Report (RPT) - A typed, ordered collection of data values gathered
by one or more DTNMA Agents and provided to one or more DTNMA
Managers. Reports only contain typed data values and the identity
of the Report Template (RPTT) to which they conform.
* Report Template (RPTT) - A named, typed, ordered collection of
data types that represent the schema of a Report. This template
is generated by a DTNMA Manager and communicated to one or more
other DTNMA Managers and DTNMA Agents.
* Rule - A unit of autonomous specification that provides a
stimulus-response relationship between time or state on an DTNMA
Agent and the actions or operations to be run as a result of that
time or state. A Rule might trigger actions such as updating a
Variable, producing a Report or a Table, and running a Control.
* State-Based Rule (SBR) - Any Rule triggered by the calculable
internal state of the DTNMA Agent.
* Synchronous Management - Management that assumes messages will be
delivered and acted upon in real or near-real-time. Synchronous
management often involves immediate replies of acknowledgment or
error status. Synchronous management is often bound to underlying
transport protocols and network protocols to ensure reliability or
source and sender identification.
* Table (TBL) - A typed collection of data values organized in a
tabular way in which columns represent homogeneous types of data
and rows represent unique sets of data values conforming to column
types. Tables only contain typed data values and the identity of
the Table Template (TBLT) to which they conform.
* Table Template (TBLT) - A named, typed, ordered collection of
columns that comprise the structure for representing tabular data
values. This template forms the structure of a table (TBL).
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* Time-Based Rule (TBR) - A time-based rule is a specialization, and
simplification, of a state-based rule in which the rule stimulus
is triggered by relative or absolute time on an Agent.
3. Motivation
Early work on the rationale and motivation for specialized management
for the DTN architecture was captured in [BIRRANE1], [BIRRANE2], and
[BIRRANE3]. Prototyping work done in accordance with the DTN
Research Group within the IRTF as documented in
[I-D.irtf-dtnrg-dtnmp] provides some of the desirable properties and
necessary adaptations for this proposed management system for
challenged networks.
The unique nature and constraints that characterize challenged
networks require the development of new network capabilities to
deliver expected network functions. For example, the distinctive
constraints of the DTN architecture required the development of BPv7
[RFC9171] for transport functions and the Bundle Protocol Security
Extensions (BPSec) [RFC9172] to provide end-to-end security.
Similarly, a new approach to network management and the associated
capabilities is necessary for operation in these challenged
environments and when using these new transport and security
mechanisms.
This section discusses the characteristics of challenged networks and
how they may violate the assumptions made by non-DTNMA approaches
about the operating environment.
3.1. Constrained and Challenged Networks
Constrained networks are defined as networks where "some of the
characteristics pretty much taken for granted with link layers in
common use in the Internet at the time of writing are not
attainable." ([RFC7228]). This broad definition captures a variety
of potential issues relating to physical, technical, or regulatory
constraints on message transmission. Constrained networks typically
include nodes that regularly reboot or are otherwise turned off for
long periods of time, transmit at low or asynchronous bitrates, or
have very limited computational resources.
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Separately, a challenged network is defined as one that "has serious
trouble maintaining what an application would today expect of the
end-to-end IP model" ([RFC7228]). This definition includes networks
where there is never simultaneous end-to-end connectivity, when such
connectivity is interrupted at planned or unplanned intervals, or
when delays exceed those that could be accommodated by IP-based
transport. Links in such networks are often unavailable due to
attenuations, propagation delays, mobility, occultation, and other
limitations imposed by energy and mass considerations.
These networks exhibit the following properties that impact the way
in which the function of network management is considered.
* No end-to-end path is guaranteed to exist at any given time
between any two nodes.
* Round-trip communications between any two nodes within any given
time window may be impossible.
* Latencies on the order of seconds, hours, or days must be
tolerated.
* Links may be uni-directional.
* Bi-directional links may have asymmetric data rates.
* Dependence on external infrastructure, software, systems, or
processes such as Domain Name Service (DNS) or Certificate
authorities (CAs) cannot be guaranteed.
Finally, it is noted that "all challenged networks are constrained
networks ... but not all constrained networks are challenged networks
... Delay-Tolerant Networking (DTN) has been designed to cope with
challenged networks" ([RFC7228]).
Challenged networks differ from other kinds of constrained networks,
in part, in the way that the topology and roles and responsibilities
of the network may evolve over time. From the time at which data is
generated to the time at which that data is delivered, the topology
of the network and the roles assigned to various nodes, devices, and
other actors may have changed several times. In certain
circumstances, the physical node receiving messages for a given
logical destination may have also changed.
Challenged networks cannot guarantee that a timely data exchange can
be maintained between managing and managed devices. The topological
changes characteristic of these networks can impact the path of
messages, requiring the transport to wait to establish the
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incremental connectivity necessary to advance messages along their
expected route. The BPv7 transport protocol implements this store-
and-forward operation for DTNs.
3.2. Management of Challenged Networks
When topological change impacts the semantic roles and
responsibilities of nodes in the network then local configuration and
autonomy must be present at the node to determine and execute time-
variant changes. For example, the BPSec protocol does not encode
security destinations and, instead, requires nodes in a network to
identify themselves as security verifiers or acceptors when receiving
secured messages.
When applied to network management, the semantic roles of Agent and
Manager may also change with the evolving topology of the network.
Individual nodes must implement desirable behavior without relying on
a single configuration oracle or other coordinating function such as
an operator-in-the-loop and/or supporting infrastructure. These
mechanisms cannot be supported by an asynchronous, challenged
network.
The support for changing roles implies that there MUST NOT be a
defined relationship between a particular manager and agent in a
network. A network management architecture for challenged networks
must support the association of multiple managers with a single
agent, allow "control from" and "reporting to" managers to function
independent of one another, and allow the logical role of a manager
to be physically shared among assets and change over time.
Together, this means that a network management architecture suitable
for challenged environments must account for certain operational
situations.
* Managed devices that are only accessible via a uni-directional
link, or via a link whose duration is shorter than a single round-
trip propagation time.
* Links that may be significantly constrained by capacity or
reliability, but at (predictable or unpredictable) times may offer
significant throughput.
* Multi-hop challenged networks that interconnect two or more
unchallenged networks such that managed and managing devices exist
in different networks.
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* Networks unable to support session-based transport. For example,
when propagation delays exceed the Maximum Segment Lifetime (MSL)
of the Transmission Control Protocol (TCP).
In these and related scenarios, managed devices need to operate with
local autonomy because managing devices may not be available within
operationally-relevant timeframes. Managing devices deliver
instruction sets that govern the local, autonomous behavior of the
managed device. These behaviors include (but are not limited to)
collecting performance data, state, and error conditions, and
applying pre-determined responses to pre-determined events. The goal
is asynchronous and autonomous communication between the device being
managed and the manager, at times never expecting a reply, and with
knowledge that commands and queries may be delivered much later than
the initial request.
3.3. Current Network Management Approaches and Limitations
Several network management solutions have been developed for both
local-area and wide-area networks. Their capabilities range from
simple configuration and report generation to complex modeling of
device settings, state, and behavior. Each of these approaches are
successful in the domains for which they have been built, but are not
all equally functional when deployed in a challenged network.
Generally, network management solutions that require managers and
agents to push and pull large sets of data may fail to operate in a
challenged (and thus, constrained) environment as a function of
transmit power, bitrates, and the ability of the network to store and
forward large data volumes over long periods of time.
Newer network management approaches are exploring the application of
moe efficient message-based management, less reliance on end-to-end
transport sessions, and increased levels of autonomy on managed
devices. These approaches focus on problems different from those
described above for challenged networks. For example, much of the
autonomous network management work currently undertaken focuses more
on well-resourced, unchallenged networks where devices self-
configure, self-heal, and self-optimize with other nodes in their
vicinity. While an important and transformational capability, such
solutions will not be deployable in a challenged network environment.
This section describes some of the well-known, standardized protocols
for network management and contrasts their purposes with the needs of
challenged network management solutions.
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3.3.1. Simple Network Management Protocol (SNMP)
Early network management tools designed for unchallenged networks
provide synchronous mechanisms for communicating locally-collected
data from devices to operators. Applications are managed using a
"pull" mechanism, requiring a manager to explicitly request the data
to be produced and transmitted by an agent.
The de facto example of this architecture is the Simple Network
Management Protocol (SNMP) [RFC3416]. SNMP utilizes a request/
response model to set and retrieve data values such as host
identifiers, link utilizations, error rates, and counters between
application software on agents and managers. Data may be directly
sampled or consolidated into representative statistics.
Additionally, SNMP supports a model for unidirectional push
notification messages, called traps, based on predefined triggering
events.
SNMP managers can query agents for status information, send new
configurations, and request to be informed when specific events have
occurred. Traps and queryable data are defined in a data model known
as Managed Information Bases (MIBs) which define the information for
a particular data standard, protocol, device, or application.
While there is a large installation base for SNMP, there are several
aspects of the protocol that make it inappropriate for use in a
challenged network. SNMP relies on sessions with low round-trip
latency to support its "pull" model that challenged networks cannot
maintain. Complex management can be achieved, but only through
craftful orchestration using a series of real-time, end-to-end,
manager-generated query-and-response logic that is not possible in
challenged networks.
The SNMP trap model provides some low-fidelity Agent-side processing.
Traps are typically used for alerting purposes, as they do not
support an agent response to the event occurrence. In a challenged
network where the delay between a manager receiving an alert and
sending a response can be significant, the SNMP trap model is
insufficient for event handling.
Adaptive modifications to SNMP to support challenged networks and
more complex application-level management would alter the basic
function of the protocol (data models, control flows, and syntax) so
as to be functionally incompatible with existing SNMP installations.
This approach is therefore not suitable for use in challenged
networks.
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3.3.2. YANG Data Model and NETCONF, RESTCONF, and CORECONF
3.3.2.1. The YANG Data Model
Yet Another Next Generation (YANG) [RFC6020] is a data modeling
language used to model configuration and state data of managed
devices and applications. The YANG model defines a schema for
organizing and accessing a device's configuration or operational
information. Once a model is developed, it is loaded to both the
client and server, and serves as a contract between the two. A YANG
model can be complex, describing many containers of managed elements,
each providing methods for device configuration or reporting of
operational state.
YANG supports the definition of parameterized Remote Procedure Calls
(RPCs) to be executed on managed nodes as well as the definition of
push notifications within the model. The RPCs are used to execute
commands on a device, generating an expected, structured response.
However, RPC execution is strictly limited to those issued by the
client. Commands are executed immediately and sequentially as they
are received by the server, and there is no method to autonomously
execute RPCs triggered by specific events or conditions.
YANG defines the schema for data used by network management protocols
such as NETCONF [RFC6241], RESTCONF [RFC8040], and CORECONF
[I-D.ietf-core-comi]. These protocols provide the mechanisms to
install, manipulate, and delete the configuration of network devices.
3.3.2.2. YANG-Based Management Protocols
NETCONF is a stateful, XML-based protocol that provides a RPC syntax
to retrieve, edit, copy, or delete any data nodes or exposed
functionality on the server. It requires that underlying transport
protocols support long-lived, reliable, low-latency, sequenced data
delivery sessions. NETCONF connections are required to provide
authentication, data integrity, confidentiality, and replay
protection through secure transport protocols such as SSH or TLS. A
bi-directional NETCONF session must be established before any data
transfer can occur.
NETCONF uses verbose XML files to provide the ability to update and
fetch multiple data elements simultaneously. These XML files are not
easily or efficiently compressed, which is an important consideration
for challenged networks.
RESTCONF is a stateless RESTful protocol based on HTTP. RESTCONF
configures or retrieves individual data elements or containers within
YANG data models by passing JSON over REST. This JSON encoding is
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used to GET, POST, PUT, PATCH, or DELETE data nodes within YANG
modules. RESTCONF requires the use of a secure transport such as
TLS.
Unlike NETCONF, RESTCONF is stateless. However, the transfer of
large data sets, such as configuration changes of many data elements,
or the collection of information, depends greatly on the support of
synchronous communication.
CORECONF is stateless, as RESTCONF is, and is built atop the
Constrained Application Protocol (CoAP) [RFC7252] which defines a
messaging construct developed to operate specifically on constrained
devices and networks by limiting message size and fragmentation.
CORECONF requires the use of DTLS or Object Security for Constrained
RESTful Environments (OSCORE) [RFC8613] to fulfil its security
requirements. COAP supports a store and forward operation similar to
DTN; however, it operates strictly at the application layer and
requires specification of pre-determined proxies and moments of bi-
directional communication.
CORECONF leverages the Concise Binary Object Representation (CBOR)
[RFC8949] of YANG modules [I-D.ietf-core-yang-cbor] and provides
further compressibility through the use of YANG Schema Item
iDentifiers (SIDs) [I-D.ietf-core-sid]. While these design choices
offer reductions in encoded data size, data compressibility is still
dependent on underlying transport protocols and limited by the
organization of the YANG schema.
3.3.2.3. Limitations of YANG-Based Approaches
YANG notifications are promising for challenged network management,
defined as subscriptions to both YANG notifications [RFC8639]] and
YANG PUSH notifications [RFC8641]. In this model, a client may
subscribe to the delivery of specific containers or data nodes
defined in the model, either on a periodic or "on change" basis. The
notification events can be filtered according to XPath ([xpath]) or
subtree ([RFC6241]) filtering as described in [RFC8639] Section 2.2.
While the YANG model provides great flexibility for configuring a
homogeneous network of devices, it becomes a burden in challenged
networks where concise encoding is necessary. The YANG schema
provides flexibility in the organization of data to the model
developer. The YANG schema supports a broad range of data types
noted in [RFC6991]. All the data nodes within a YANG model are
referenced by a verbose, string-based path of the module, sub-module,
container, and any data nodes such as lists, leaf-lists, or leaves,
without any explicit hierarchical organization based on data or
object type.
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Recent efforts for compression of the YANG model have used CBOR and
SIDs to address YANG data nodes through integer identifiers.
However, these compression strategies lack a formal hierarchical
structure. The manual mapping of SIDs to YANG modules and data nodes
limits the portability of these models and further increases the size
of any encoding scheme.
3.3.3. The Future of Autonomous and Autonomic Network Management
Solutions
The future of network operations requires more autonomous behavior
including self-configuration, self-management, self-healing, and
self-optimization. One approach to support this is termed Autonomic
Networking [RFC7575] and includes many recent efforts describe
Autonomic architecture and protocols [RFC8993] as well as cite the
gaps that exist between traditional and Autonomic Networking
approaches [RFC7576]. Challenged networks require similar degrees of
autonomy, however they lack the ability to depend on the complex
coordination between nodes and the centralized and distributed
supporting infrastructure that Autonomic networking proposes.
Policy-based management is a well-established approach that uses
business and operations support systems to monitor and manage devices
and networks in real-time. These systems leverage various, existing
network management protocols and their supporting features, such as
the use of YANG module classification types [RFC8199], to describe
abstract services and support configuration of service level
agreements. These services can then enact additional control over
devices using network element modules. This approach is quite
comprehensive but requires sufficient, supporting infrastructure and
synchronous access, which cannot be provided by challenged networks.
3.3.4. Takeaways from Existing Network Management Protocols
While the protocols described above are useful and well-realized for
different applications and networking environments, they simply do
not meet the requirements for the management of challenged networks.
However, that does not exclude features from each from contributing
to the design of DTNMA.
The concept of a data model for describing network configuration
elements has been used by many protocols to ensure compliance between
managing and managed devices. A data model provides error checking
and bounds operations, which is necessary when controlling mission
critical devices.
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The SNMP MIBs provide well-organized, hierarchical OIDs which support
the compressibility necessary for challenged DTNs. YANG, NETCONF,
and RESTCONF support notification abilities needed for DTN network
management, but have limited features for describing autonomous
execution and behavior.
CORECONF provides CBOR encoding and concise reference abilities using
SIDs, but lack a hierarchical structure or authoritative planning to
allocation. While this approach will become too verbose and prove
limiting in the future, the encoding considerations from CORECONF can
be used to inform the design of the DTNMA.
3.4. A Network Management Approach for DTNs
The DTNMA is designed with consideration for the constraints
discussed in section Section 3.1. The DTNMA seeks to incorporate
existing network management protocols and feature. However, there
are core capabilities the DTNMA must provide in order to serve a
challenged network that are not supported by these approaches.
The DTNMA proposes a data model that is that is designed for the
compression required for a challenged network. The efficiency of
data encoding is limited by the efficiency of the underlying data
model. For this reason, naming schemes for the DTNMA must be
hierarchical and patternable, supporting the level of compressibility
needed by the resource-constrained devices that form a challenged
network.
Autonomous behavior is required for the management of a DTN, which is
characterized by link delays and disruptions. The constrained
autonomy model of the DTNMA provides the deterministic management
necessary for managed devices to detect and respond to events without
intervention from an in-the-loop manager. The separation of remote
and local, autonomous managing devices supports autonomous behavior
even when synchronization is not feasible.
The sections below describe the desirable features of the DTNMA and
build from e xisting protocols and mechanisms where possible, with
adaptations made for the challenged networking environment.
4. Desirable Properties of an DTNMA
This section describes those design properties that are desirable
when defining an architecture that must operate across challenged
links in a network. These properties ensure that network management
capabilities are retained even as delays and disruptions in the
network scale. Ultimately, these properties are the driving design
principles for the DTNMA.
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4.1. Asynchronous, Dynamic, and Highly Logical Architecture
An DTNMA built to support DTN must be agnostic of the underlying
physical topology, transport protocols, security solutions, and
supporting infrastructure. The DTNMA shall be limited to only the
network management protocols, message structure, and information
content, including but not limited to the type of objects to manage
and the expected behavior and interaction upon access or execution of
those objects. There shall be no prescribed association between
between a manager and an agent other than those defined in the
responsibilities associated with each in this document. There should
be no limitation to the number of managers that can control an agent,
the number of managers that an agent should report to, or any
requirement that a manager and agent relationship implies a pair.
4.2. Model-derived and Hierarchically Organized Definition of
Information
A means to define a shared contract between agent and manager has
long been an approach to network management solutions. A model is a
schema that defines this contract and defines all sources of
information that can be retrieved, configured, or executed, as well
as the various functions for parameterization, filtering, or event
driven behavior. A model gives way to concise representation of
information, intelligent suffixing, and patterning. The DTNMA model
shall be designed with a limited set of object and data types to
allow and be organized hierarchally to provide for highly
compressible and concise encoding. This allows the agents and
managers to infer context with limited link utilization necessary in
DTN.
4.3. Intelligent Push of Information
Pull management mechanisms require that a Manager send a query to an
Agent and then wait for the response to that query. This practice
implies a control-session between entities and increases the overall
message traffic in the network. Challenged networks cannot guarantee
that the round-trip data-exchange will occur in a timely fashion. In
extreme cases, networks may be comprised of solely uni-directional
links which drastically increases the amount of time needed for a
round-trip data exchange. Therefore, pull mechanisms must be avoided
in favor of push mechanisms.
Push mechanisms, in this context, refer to the ability of Agents to
leverage rule-based criteria to determine when and what information
should be sent to managers. This could be based solely off logic
applied to existing VARs or EDDs, based off operations applied to
data elements, or triggered as a function of relative time. Such
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mechanisms do not require round-trip communications as Managers do
not request each reporting instance; Managers need only request once,
in advance, that information be produced in accordance with a
predetermined schedule or in response to a predefined state on the
Agent. In this way information is "pushed" from Agents to Managers
and the push is "intelligent" because it is based on some internal
evaluation performed by the Agent.
4.4. Minimize Message Size Not Node Processing
Protocol designers must balance message size versus message
processing time at sending and receiving nodes. Verbose
representations of data simplify node processing whereas compact
representations require additional activities to generate/parse the
compacted message. There is no asynchronous management advantage to
minimizing node processing time in a challenged network. However,
there is a significant advantage to smaller message sizes in such
networks. Compact messages require smaller periods of viable
transmission for communication, incur less re-transmission cost, and
consume less resources when persistently stored en-route in the
network. A DTN Management Protocol (DTNMP) should minimize PDUs
whenever practical, to include packing and unpacking binary data,
variable-length fields, and pre-configured data definitions.
4.5. Absolute Data Identification
Elements within the management system must be uniquely identifiable
so that they can be individually manipulated. Identification schemes
that are relative to system configuration make data exchange between
Agents and Managers difficult as system configurations may change
faster than nodes can communicate.
Consider the following common technique for approximating an
associative array lookup. A manager wishing to do an associative
lookup for some key K1 will (1) query a list of array keys from the
agent, (2) find the key that matches K1 and infer the index of K1
from the returned key list, and (3) query the discovered index on the
agent to retrieve the desired data.
Ignoring the inefficiency of two pull requests, this mechanism fails
when the Agent changes its key-index mapping between the first and
second query. Rather than constructing an artificial mapping from K1
to an index, an AMP must provide an absolute mechanism to lookup the
value K1 without an abstraction between the Agent and Manager.
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4.6. Custom Data Definition
Custom definition of new data from existing data (such as through
data fusion, averaging, sampling, or other mechanisms) provides the
ability to communicate desired information in as compact a form as
possible. Specifically, an Agent should not be required to transmit
a large data set for a Manager that only wishes to calculate a
smaller, inferred data set. These new defined data elements could be
calculated and used both as parameters for local stimulus-response
rules-based criteria or simply serve to populate custom reports and
tables. Since the identification of custom data sets is likely to
occur in the context of a specific network deployment, AMPs must
provide a mechanism for their definition.
Aggregation of controls and custom formatting of reports and tables
are equally important. Custom reporting provides the flexibility
allowing the manager to define the desired format of all information
to be sent over the challenged network from the agents, serving to
both save link capacity and increase the value of returned
information. Aggregation of controls allows a manager to specify a
set of controls to execute, specifying both the order and criteria of
execution. This aggregate set of controls can be sent as a single
command rather than a series of sequential operands. In this case it
is additionally possible to use outputs of one command to serve as an
input to the next at the agent.
4.7. Autonomous Operation
DTNMA network functions must be achievable using only knowledge local
to the Agent. Rather than directly controlling an Agent, a Manager
configures an engine of the Agent to take its own action under the
appropriate conditions in accordance with the Agent's notion of local
state and time.
Such an engine may be used for simple automation of predefined tasks
or to support semi-autonomous behavior in determining when to run
tasks and how to configure or parameterize tasks when they are run.
Wholly autonomous operations MAY be supported where required.
Generally, autonomous operations should provide the following
benefits.
* Distributed Operation - The concept of pre-configuration allows
the Agent to operate without regular contact with Managers in the
system. The initial configuration (and periodic update) of the
system remains difficult in a challenged network, but an initial
synchronization on stimuli and responses drastically reduces needs
for centralized operations.
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* Deterministic Behavior - Such behavior is necessary in critical
operational systems where the actions of a platform must be well
understood even in the absence of an operator in the loop.
Depending on the types of stimuli and responses, these systems may
be considered to be maintaining simple automation or semi-
autonomous behavior. In either case, this preserves the ability
of a frequently-out-of-contact Manager to predict the state of an
Agent with more reliability than cases where Agents implement
independent and fully autonomous systems.
* Engine-Based Behavior - Several operational systems are unable to
deploy "mobile code" based solutions due to network bandwidth,
memory or processor loading, or security concerns. Engine-based
approaches provide configurable behavior without incurring these
types of concerns associated with mobile code.
* Intelligent authentication, authorization, accounting (AAA), and
error checking - A means of autonomous AAA, error checking, and
validation of data and controls will be be required in all cases
where agents or managers are disconnected from the rest of the
network. In addition, there is a need to handle conflicts
including messages that arrive out of order, or at the same time
from different managers whose controls would otherwise conflict.
The need to perform these operations still exists however they
will need to be performed with context provided with controls sent
or in accordance with pre-defined behavior and policy.
5. Services Provided by an DTNMA
The DTNMA provides a method of configuring DTNMA Agents with local,
autonomous management functions, such as rule-based execution of
procedures and generation of reports, to achieve expected behavior
when managed devices exist over a challenged network. It further
allows for dynamic instantiation and population of Variables and
reports through local operations defined by the manager, as well as
custom formatting of tables and reports to be sent back. This gives
the DTNMA significant flexibility to operate over challenged
networks, both providing new degrees of freedom over existing
configuration based data models used in synchronous networks and
allowing for more concise formatting over constrained networks. This
architecture makes very few assumptions on the nature of the network
and allow for continuous operation through periods of connectivity
and lack of connectivity. The DTNMA deviates from synchronous
management approaches because it never requires periods of bi-
directional connectivity, and provides the manager flexibility to
describe agent behavior that was unpredicted at the time of the data
model creation.
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This section identifies the services that a DTNMA would provide for
management of challenged network resources. These services include
configuration, reporting, autonomous parameterized control, and
administration.
5.1. Configuration
Configuration services update Agent data associated with managed
applications and protocols. Some configuration data might be defined
in the context of an application or protocol, such that any network
using that application or protocol would understand that data. Other
configuration data may be defined tactically for use in a specific
network deployment and not available to other networks even if they
use the same applications or protocols.
With no guarantee of round-trip data exchange, Agents cannot rely on
remote Managers to correct erroneous or stale configurations from
harming the flow of data through a challenged network.
Examples of configuration service behavior include the following.
* Creating a new datum as a function of other well-known data:
C = A + B.
* Creating a new report as a unique, ordered collection of known
data:
RPT = {A, B, C}.
* Storing predefined, parameterized responses to potential future
conditions:
IF (X > 3) THEN RUN CMD(PARM).
5.2. Reporting
Reporting services populate report templates with values collected or
computed by an Agent. The resultant reports are sent to one or more
Managers by the Agent. The term "reporting" is used in place of the
term "monitoring", as monitoring implies a timeliness and regularity
that cannot be guaranteed by a challenged network. Reports sent by
an Agent provide best-effort information to receiving Managers.
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Since a Manager is not actively "monitoring" an Agent, the Agent must
make its own determination on when to send what Reports based on its
own local time and state information. Agents should produce Reports
of varying fidelity and with varying frequency based on thresholds
and other information set as part of configuration services.
Examples of reporting service behavior include the following.
* Generate Report R1 every hour (time-based production).
* Generate Report R2 when X > 3 (state-based production).
5.3. Autonomous Parameterized Procedure Calls
Similar to an RPC call, some mechanism MUST exist which allows a
procedure to be run on an Agent in order to affect its behavior or
otherwise change its internal state. Since there is no guarantee
that a Manager will be in contact with an Agent at any given time,
the decisions of whether and when a procedure should be run MUST be
made locally and autonomously by the Agent. Two types of automation
triggers are identified in the DTNMA: triggers based on the internal
state of the Agent and triggers based on an Agent's notion of time.
As such, the autonomous execution of procedures can be viewed as a
stimulus-response system, where the stimulus is the positive
evaluation of a state or time based predicate and the response is the
function to be executed.
The autonomous nature of procedure execution by an Agent implies that
the full suite of information necessary to run a procedure may not be
known by a Manager in advance. To address this situation, a
parameterization mechanism MUST be available so that required data
can be provided at the time of execution on the Agent rather than at
the time of definition/configuration by the Manager.
Autonomous, parameterized procedure calls provide a powerful
mechanism for Managers to "manage" an Agent asynchronously during
periods of no communication by pre-configuring responses to events
that may be encountered by the Agent at a future time.
Examples of potential behavior include the following.
* Updating local routing information based on instantaneous link
analysis.
* Managing storage on the device to enforce quotas.
* Applying or modifying local security policy.
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5.4. Authorized Administration, accounting, and error control
Administration services enforce the potentially complex mapping of
auhorization to configuration, reporting, and control services
amongst Agents and Managers in the network. Fine-grained access
control can specify which Managers may apply which services to which
Agents. This is particularly beneficial in networks that either deal
with multiple administrative entities or overlay networks that cross
administrative boundaries. Whitelists, blacklists, key-based
infrastructures, or other schemes may be used for this purpose.
Other administrative services may place practical restrictions on the
overall number of items that can be kept in a system. This includes
items such as the number of rows kept by an Agent for a given table
template or number of entries for a given report template.
Examples of administration service behavior include the following.
* Agent A1 only Sends reports for Protocol P1 to Manager M1.
* Agent A2 only accepts a configurations for Application Y from
Managers M2 and M3.
* Agent A3 accepts services from any Manager providing the proper
authentication token.
Note that the administrative enforcement of access control is
different from security services provided by the networking stack
carrying such messages.
6. DTNMA Roles and Responsibilities
By definition, Agents reside on managed devices and Managers reside
on managing devices. There is however no pre-supposed architecture
that connects managers and agents and therefore a single device could
assume both roles. This section describes the responsibilities
associated with each role and how these roles participate in network
management.
6.1. Agent Responsibilities
Manager Mapping
Agents must receive messages from managers that govern
application control, reporting, and autonomous behavior.
Agents must maintain a list of managers which have delivered
control messages along with a list of "report to" managers.
The list of requested reports must be mapped to one or more
managers.
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Application Support
Agents MUST collect all data, execute all controls, populate
all reports and run operations required by each application
which the Agent manages. Agents MUST report supported
applications by their data model so that Managers in a
network understands what information is understood by what
Agent.
Local Data Collection
Agents MUST collect from local firmware (or other on-board
mechanisms) and report all data defined for the management of
applications for which they have been configured. Agents
must further use this information in the computation of
variable expressions and rules-based autonomy.
Autonomous Control
Agents MUST determine, as previously prescribed by a manager,
whether a procedure should be invoked.
Autonomous Reporting
Agents MUST determine, without real-time Manager
intervention, whether and when to populate and transmit a
given report or table targeted to one or more Managers in the
network.
Custom Data Definition
Agents MUST provide mechanisms for operators in the network
to use configuration services to create customized data
definitions in the context of a specific network or network
use-case. Agents MUST allow for the creation, listing, and
removal of such definitions in accordance with whatever
security models are deployed within the particular network.
Where applicable, Agents MUST verify the validity of these
definitions when they are configured and respond in a way
consistent with the logging/error-handling policies of the
Agent and the network.
Consolidate Messages
Agents SHOULD produce as few messages as possible when
sending information. For example, rather than sending
multiple messages, each with one report to a Manager, an
Agent SHOULD prefer to send a single message containing
multiple reports.
Error Checking and State Control
Agents should perform error checking and validation of
incoming manager messages as well as internally computed
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values. This includes but is not limited to validating the
syntax of messages and controls according to the data model,
preventing circular references in custom defined data, and
verifying maximum nesting levels or table lengths have not
been exceeded. This also includes control of internal agent
operations and state. Finally there must be a means to
handle conflicts such as messages that arrive out of order or
messages from more than one authorized manager.
Authorized Administration and Accounting
The Agent shall provide authorized administration and
accounting to restrict execution of controls, custom data
definition, and reporting to only those authorized nodes.
Both nominal and exception events shall be logged where
applicable.
6.2. Manager Responsibilities
Agent Capabilities Mapping
Managers must maintain a list of supported models and managed
applications. Managers MUST understand what applications are
managed by the various Agents with which they communicate and
maintain a list of those managed agents. Managers should not
attempt to request, invoke, or refer to application
information for applications not managed by an Agent. Agents
must further maintain a list of all agents that are reporting
to this manager.
Agent Messaging
Managers must generate and transmit control messages destined
for agents. This includes all the control types,
configuration, and parameterization described in the logical
data model.
Data Collection
Managers MUST receive information from Agents asynchronously
upon the configuration and production of reports by the local
and other external managers, collecting responses from Agents
over time. Managers MAY try to detect conditions where Agent
information has not been received within operationally
relevant time spans and react in accordance with network
policy.
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Custom Data Definitions
Managers should provide the ability to define custom data
definitions. Any custom definitions MUST be transmitted to
appropriate Agents and these definitions MUST be remembered
to interpret the reporting of these custom values from Agents
in the future.
Data Fusion
Managers MAY support the fusion of data from multiple Agents
with the purpose of transmitting fused data results to other
Managers within the network. Managers MAY receive fused
reports from other Managers pursuant to appropriate security
and administrative configurations.
Error Checking and State Control
Managers should perform error checking and validation of
incoming agent messages as well as internally configured
controls for agents. This includes but is not limited to
validating the syntax of messages and controls according to
the data model, preventing circular references in custom
defined data, and verifying maximum nesting levels or table
lengths have not been exceeded. This also includes control
of internal manager operations and state.
Authorized Administration and Accounting
The Manager shall provide authorized administration and
accounting and send controls to only those agents for which
it is authorized. It shall additionally validate incoming
agent reports according to any defined restrictions. Both
nominal and exception events shall be logged where
applicable.
7. Logical Data Model
The DTNMA logical data model captures the types of information that
should be collected and exchanged to implement necessary roles and
responsibilities. The data model presented in this section does not
presuppose a specific mapping to a physical data model or encoding
technique; it is included to provide a way to logically reason about
the types of data that should be exchanged in a DTN managed network.
The elements of the DTNMA logical data model are described as
follows.
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7.1. Data Representations: Constants, Externally Defined Data, and
Variables
There are three fundamental representations of data in the DTNMA: (1)
data whose values do not change as a function of time or state, (2)
data whose values change as determined by sampling/calculation
external to the network management system, and (3) data whose values
are calculated internal to the network management system.
Data whose values do not change as a function of time or state are
defined as Constants (CONST). CONST values are strongly typed, named
values that cannot be modified once they have been defined.
Data sampled/calculated external to the network management system are
defined as Externally Defined Data" (EDD). EDD values represent the
most useful information in the management system as they are provided
by the applications or protocols being managed on the Agent. It is
RECOMMENDED that EDD values be strongly typed to avoid issues with
interpreting the data value. It is also RECOMMENDED that the
timeliness/staleness of the data value be considered when using the
data in the context of autonomous action on the Agent.
Data that is calculated internal to the network management system is
defined as a Variable (VAR). VARs allow the creation of new data
values for use in the network management system. New value
definitions are useful for storing user-defined information, storing
the results of complex calculations for easier re-use, and providing
a mechanism for combining information from multiple external sources.
It is RECOMMENDED that VARs be strongly typed to avoid issues with
interpreting the data value. In cases where a VAR definition relies
on other VAR definitions, mechanisms to prevent circular references
MUST be included in any actual data model or implementation.
7.2. Data Collections: Reports and Tables
Individual data values may be exchanged amongst Agents and Managers
in the DTNMA. However, data are typically most useful to a Manager
when received as part of a set of information. Ordered collections
of data values can be produced by Agents and sent to Managers as a
way of efficiently communicating Agent status. Within the DTNMA, the
structure of the ordered collection is treated separately from the
values that populate such a structure.
The DTNMA provides two ways of defining collections of data: reports
and tables. Reports are ordered sets of data values, whereas Tables
are special types of reports whose entries have a regular, tabular
structure.
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7.2.1. Report Templates and Reports
The typed, ordered structure of a data collection is defined as a
Report Template (RPTT). A particular set of data values provided in
compliance with such a template is called a Report (RPT).
Separating the structure and content of a report reduces the overall
size of RPTs in cases where reporting structures are well known and
unchanging. RPTTs can be synchronized between an Agent and a Manager
so that RPTs themselves do not incur the overhead of carrying self-
describing data. RPTTs may include EDD values, VARs, and also other
RPTTs. In cases where a RPTT includes another RPTTs, mechanisms to
prevent circular references MUST be included in any actual data model
or implementation.
Protocols and applications managed in the DTNMA may define common
RPTTs. Additionally, users within a network may define their own
RPTTs that are useful in the context of a particular deployment.
Unlike tables, reports do not exploit assumptions on the underlying
structure of their data. Therefore, unlike tables, operators can
define new reports at any time as part of the runtime configuration
of the network.
7.2.2. Table Templates and Tables
Tables optimize the communication of multiple sets of data in
situations where each data set has the same syntactic structure and
with the same semantic meaning. Unlike reports, the regularity of
tabular data representations allow for the addition of new rows
without changing the structure of the table. Attempting to add a new
data set at the end of a report would require alterations to the
report template.
The typed, ordered structure of a table is defined as a
Table Template (TBLT). A particular instance of values populating
the table template is called a Table (TBL).
TBLTs describes the "columns" that define the table schema. A TBL
represents the instance of a specific TBLT that holds actual data
values. These data values represent the "rows" of the table.
The prescriptive nature of the TBLT allows for the possibility of
advanced filtering which may reduce traffic between Agents and
Managers. However, the unique structure of each TBLT along may make
them difficult or impossible to change dynamically in a network.
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7.3. Command Execution: Controls and Macros
Low-latency, high-availability approaches to network management use
mechanisms such as (or similar to) RPCs to cause some action to be
performed on an Agent. The DTNMA enables similar capabilities
without requiring that the Manager be in the processing loop of the
Agent. Command execution in the DTNMA happens through the use of
controls and macros.
A Control (CTRL) represents a parameterized, predefined procedure
that can be run on an Agent. While conceptually similar to a "remote
procedure call", CTRLs differ in that they do not provide numeric
return codes. The concept of a return code when running a procedure
implies a synchronous relationship between the caller of the
procedure and the procedure being called, which is disallowed in an
DTN management system. Instead, CTRLs may create reports which
describe the status and other summarizations of their operation, and
these reports may be sent to the Manager(s) calling the CTRL.
Parameters can be provided when running a command from a Manager,
pre-configured as part of a response to a time-based or state-based
rule on the Agent, or auto-generated as needed on the Agent. The
success or failure of a control MAY be inferred by reports generated
for that purpose.
NOTE: The DTNMA term control is derived in part from the concept of
Command and Control (C2) where control implies the operational
instructions that must be undertaken to implement (or maintain) a
commanded objective. A DTN management function controls an Agent to
allow it to fulfill its commanded purpose in a variety of operational
scenarios. For example, attempting to maintain a safe internal
thermal environment for a spacecraft is considered "thermal control"
(not "thermal commanding") even though thermal control involves
"commanding" heaters, louvers, radiators, and other temperature-
affecting components. That said, CTRLs should be developed for
specific autonomous and deterministic behavior where possible. Some
controls may be designed to set configuration parameters or load
complex policies, but there should be no assumption that it will be
executed in real time.
Often, a series of controls must be executed in sequence to achieve a
particular outcome. A Macro (MACRO) represents an ordered collection
of controls (or other macros). In cases where a MACRO includes
another MACRO, mechanisms to prevent circular references and maximum
nesting levels MUST be included in any actual data model or
implementation.
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7.4. Autonomy: Time and State-Based Rules
The DTNMA data model contains EDDs and VARs that capture the state of
applications on an Agent. The model also contains controls and
macros to perform actions on an Agent. A mechanism is needed to
relate these two capabilities: to perform an action on the Agent
autonomously in response to the state of the Agent. This mechanism
in the DTNMA is the "rule" and can be activated based on Agent
internal state (state-based rule) or based on the Agent's notion of
relative time (time-based rule).
7.4.1. State-Based Rule (SBR)
State-Based Rules (SBRs) perform actions based on the Agent's
internal state, as identified by EDD and VAR values. An SBR
represents a stimulus-response pairing in the following form: IF
predicate THEN response The predicate is a logical expression that
evaluates to true if the rule stimulus is present and evaluates to
false otherwise. The response may be any control or macro known to
the Agent.
An example of an SBR could be to initiate a thermal control self
check if some internal temperature is greater than a threshold: IF
(current_temp > maximum_temp) THEN thermal_control_self_check
Rules may construct their stimuli from the full set of values known
to the network management system. Similarly, responses may be
constructed from the full set of controls and macros that can be run
on the Agent. By allowing rules to evaluate the variety of all known
data and run the variety of all known controls, multiple applications
can be monitored and managed by one Agent instance.
7.4.2. Time-Based Rule (TBR)
Time-Based Rules (TBR) perform actions based on the Agent's notion of
the passage of time. A possible TBR construct would be to perform
some action at 1Hz on the Agent.
A TBR is a specialization of an SBR as the Agent's notion of time is
a type of Agent state. For example, a TBR to perform an action every
24 hours could be expressed using some type of predicate of the form:
IF (((current_time - base_time) % 24_hours) == 0) THEN ... However,
time-based events are popular enough that special semantics for
expressing them would likely significantly reduce the computations
necessary to represent time functions in a SBR.
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7.5. Calculations: Expressions, Literals, and Operators
Actions such as computing a VAR value or describing a rule predicate
require some mechanism for calculating the value of mathematical
expressions. In addition to the aforementioned DTNMA logical data
objects, Literals, Operators, and Expressions are used to perform
these calculations.
A Literal (LIT) represents a strongly typed datum whose identity is
equivalent to its value. An example of a LIT value is "4" - its
identifier (4) is the same as its value (4). Literals differ from
constants in that constants have an identifier separate from their
value. For example, the constant PI may refer to a value of 3.14.
However, the literal 3.14159 always refers to the value 3.14159.
An Operator (OP) represents a mathematical operation in an
expression. OPs should support multiple operands based on the
operation supported. A common set of OPs SHOULD be defined for any
Agent and systems MAY choose to allow individual applications to
define new OPs to assist in the generation of new VAR values and
predicates for managing that application. OPs may be simple binary
operations such as "A + B" or more complex functions such as sin(A)
or avg(A,B,C,D). Additionally, OPs may be typed. For example,
addition of integers may be defined separately from addition of real
numbers.
An Expression (EXPR) is a combination of operators and operands used
to construct a numerical value from a series of other elements of the
DTNMA logical model. Operands include any DTNMA logical data model
object that can be interpreted as a value, such as EDD, VAR, CONST,
and LIT values. Operators perform some function on operands to
generate new values.
8. System Model
This section describes the notional data flows and control flows that
illustrate how Managers and Agents within an DTNMA cooperate to
perform network management services.
8.1. Control and Data Flows
The DTNMA identifies three significant data flows: control flows from
Managers to Agents, reports flows from Agents to Managers, and fusion
reports from Managers to other Managers. These data flows are
illustrated in Figure 1.
DTNMA Control and Data Flows
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+---------+ +------------------------+ +---------+
| Node A | | Node B | | Node C |
| | | | | |
|+-------+| |+-------+ +-------+| |+-------+|
|| ||=====>>||Manager|====>>| ||====>>|| ||
|| ||<<=====|| B |<<====|Agent B||<<====|| ||
|| || |+--++---+ +-------+| ||Manager||
|| Agent || +---||-------------------+ || C ||
|| A || || || ||
|| ||<<=========||==========================|| ||
|| ||===========++========================>>|| ||
|+-------+| |+-------+|
+---------+ +---------+
Figure 1
In this data flow, the Agent on node A receives Controls from
Managers on nodes B and C, and replies with Report Entries back to
these Managers. Similarly, the Agent on node B interacts with the
local Manager on node B and the remote Manager on node C. Finally,
the Manager on node B may fuse Report Entries received from Agents at
nodes A and B and send these fused Report Entries back to the Manager
on node C. From this figure it is clear that there exist many-to-
many relationships amongst Managers, amongst Agents, and between
Agents and Managers. Note that Agents and Managers are roles, not
necessarily different software applications. Node A may represent a
single software application fulfilling only the Agent role, whereas
node B may have a single software application fulfilling both the
Agent and Manager roles. The specifics of how these roles are
realized is an implementation matter.
8.2. Control Flow by Role
This section describes three common configurations of Agents and
Managers and the flow of messages between them. These configurations
involve local and remote management and data fusion.
8.2.1. Notation
The notation outlined in Table 1 describes the types of control
messages exchanged between Agents and Managers.
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+============+===================================+===========+
| Term | Definition | Example |
+============+===================================+===========+
| EDD# | EDD definition. | EDD1 |
+------------+-----------------------------------+-----------+
| V# | Variable definition. | V1 = EDD1 |
| | | + V0. |
+------------+-----------------------------------+-----------+
| DEF([ACL], | Define ID from expression. Allow | DEF([*], |
| ID,EXPR) | managers in access control list | V1, EDD1 |
| | (ACL) to request this ID. | + EDD2) |
+------------+-----------------------------------+-----------+
| PROD(P,ID) | Produce ID according to predicate | PROD(1s, |
| | P. P may be a time period (1s) | EDD1) |
| | or an expression (EDD1 > 10). | |
+------------+-----------------------------------+-----------+
| RPT(ID) | A report identified by ID. | RPT(EDD1) |
+------------+-----------------------------------+-----------+
Table 1: Terminology
8.2.2. Serialized Management
This is a nominal configuration of network management where a Manager
interacts with a set of Agents. The control flows for this are
outlined in Figure 2.
Serialized Management Control Flow
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+----------+ +---------+ +---------+
| Manager | | Agent A | | Agent B |
+----+-----+ +----+----+ +----+----+
| | |
|-----PROD(1s, EDD1)--->| | (1)
|----------------------------PROD(1s, EDD1)-->|
| | |
| | |
|<-------RPT(EDD1)------| | (2)
|<----------------------------RPT(EDD1)-------|
| | |
| | |
|<-------RPT(EDD1)------| |
|<----------------------------RPT(EDD1)-------|
| | |
| | |
|<-------RPT(EDD1)------| |
|<----------------------------RPT(EDD1)-------|
| | |
Figure 2
In a simple network, a Manager interacts with multiple Agents.
In this figure, the Manager configures Agents A and B to produce EDD1
every second in (1). Upon receiving and configuring this message,
Agents A and B then build a Report Entry containing EDD1 and send
those reports back to the Manager in (2). This behavior then repeats
this action every 1s without requiring other inputs from the Manager.
8.2.3. Challenged, DTN Management
This is a challenged configuration of network management where Agent
B temporarily looses connectivity between the agent and the Manager.
Flows in this case are outlined in Figure 3.
Challenged Management Control Flow
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+----------+ +---------+ +---------+
| Manager | | Agent A | | Agent B |
+----+-----+ +----+----+ +----+----+
| | |
|-----PROD(1s, EDD1)--->| | (1)
|----------------------------PROD(1s, EDD1)-->|
| | |
| | |
|<-------RPT(EDD1)------| | (2)
|<----------------------------RPT(EDD1)-------|
| | |
| | |
|<-------RPT(EDD1)------| |
|<----------------------------RPT(EDD1)-------|
| | |
| | |
|<-------RPT(EDD1)------| |
|< RPT(EDD1)| (3)
| | |
| | |
|<-------RPT(EDD1)------| |
|< RPT(EDD1)|
| | |
| | |
|<-------RPT(EDD1)------| |
|<----------------RPT(EDD1, EDD1, EDD1)-------| (4)
| | |
Figure 3
In a challenged network, an agent must store and forward reports
until links are available.
In this figure, the Manager configures Agents A and B to produce EDD1
every second in (1). Upon receiving and configuring this message,
Agents A and B then build a Report Entry containing EDD1 and send
those reports back to the Manager in (2). At step (3) the connection
between Agent B and Manager is not available. The agent still
generates the reports and stores locally using DTN protocols. At
step (4) the link has been restored and all stored reports are
successfully delivered to the manager.
8.2.4. Consolidated Message Management
This is a configuration of network management where Agent B has been
configured to deliver two sets of data and demonstrates the Agent's
responsibility to consolidate messages for transport. Flows in this
case are outlined in Figure 4.
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Consolidated Management Control Flow
+----------+ +---------+ +---------+
| Manager | | Agent A | | Agent B |
+----+-----+ +----+----+ +----+----+
| | |
|-----PROD(1s, EDD1)--->| | (1)
|----------------------------PROD(1s, EDD1)-->|
| | |
| | |
|<-------RPT(EDD1)------| | (2)
|<----------------------------RPT(EDD1)-------|
| | |
| | |
|----------------------------PROD(1s, EDD2)-->| (3)
| | |
| | |
|<-------RPT(EDD1)------| | (4)
|<--------------------------RPT(EDD1,EDD2)----|
| | |
| | |
|<-------RPT(EDD1)------| |
|<--------------------------RPT(EDD1,EDD2)----|
| | |
Figure 4
In a challenged network, Agents shall consolidate messages where
possible.
In this figure, the Manager configures Agents A and B to produce EDD1
every second in (1). Upon receiving and configuring this message,
Agents A and B then build a Report Entry containing EDD1 and send
those reports back to the Manager in (2). At step (3), the manager
configures Agent B to additionally report EDD2 every second. At step
(4) Agent B proceeds to deliver EDD1 and EDD2 in the same report.
8.2.5. Multiplexed Management
Networks spanning multiple administrative domains may require
multiple Managers (for example, one per domain). When a Manager
defines custom Reports/Variables to an Agent, that definition may be
tagged with an Access Control List (ACL) to limit what other Managers
will be privy to this information. Managers in such networks should
synchronize with those other Managers granted access to their custom
data definitions. When Agents generate messages, they MUST only send
messages to Managers according to these ACLs, if present. The
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control flows in this scenario are outlined in Figure 5.
Multiplexed Management Control Flow
+-----------+ +-------+ +-----------+
| Manager A | | Agent | | Manager B |
+-----+-----+ +---+---+ +-----+-----+
| | |
|---DEF(A,V1,EDD1*2)-->|<-DEF(B, V2, EDD2*2)--| (1)
| | |
|---PROD(1s, V1)------>|<---PROD(1s, V2)------| (2)
| | |
|<--------RPT(V1)------| | (3)
| |--------RPT(V2)------>|
|<--------RPT(V1)------| |
| |--------RPT(V2)------>|
| | |
| |<---PROD(1s, V1)------| (4)
| | |
| |---ERR(V1 no perm.)-->|
| | |
|--DEF(*,V3,EDD3*3)--->| | (5)
| | |
|---PROD(1s, V3)------>| | (6)
| | |
| |<----PROD(1s, V3)-----|
| | |
|<--------RPT(V3)------|--------RPT(V3)------>| (7)
|<--------RPT(V1)------| |
| |--------RPT(V2)------>|
|<-------RPT(V3)-------|--------RPT(V3)------>|
|<-------RPT(V1)-------| |
| |--------RPT(V2)------>|
Figure 5
Complex networks require multiple Managers interfacing with Agents.
In more complex networks, any Manager may choose to define custom
Reports and Variables, and Agents may need to accept such definitions
from multiple Managers. Variable definitions may include an ACL that
describes who may query and otherwise understand these definitions.
In (1), Manager A defines V1 only for A while Manager B defines V2
only for B. Managers may, then, request the production of Report
Entries containing these definitions, as shown in (2). Agents
produce different data for different Managers in accordance with
configured production rules, as shown in (3). If a Manager requests
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the production of a custom definition for which the Manager has no
permissions, a response consistent with the configured logging policy
on the Agent should be implemented, as shown in (4). Alternatively,
as shown in (5), a Manager may define custom data with no access
restrictions, allowing all other Managers to request and use this
definition. This allows all Managers to request the production of
Report Entries containing this definition, shown in (6) and have all
Managers receive this and other data going forward, as shown in (7).
8.2.6. Data Fusion
Data fusion reduces the number and size of messages in the network
which can lead to more efficient utilization of networking resources.
The DTNMA supports fusion of NM reports by co-locating Agents and
Managers on nodes and offloading fusion activities to the Manager.
This process is illustrated in Figure 6.
Data Fusion Control Flow
---------------------------------------
| Actor B |
| |
+-----------+ | +-----------+ +---------+ | +---------+
| Manager A | | | Manager B | | Agent B | | | Agent C |
+---+-------+ | +-----+-----+ +----+----+ | +----+----+
| | | | | |
|------------------DEF(A,V0,EDD1+EDD2)->| | | (1)
|------------------PROD(EDD1&EDD2,V0)-->| | |
| | | | | |
| | |--PROD(1s,EDD1)->| | | (2)
| | |--------------------PROD(1s, EDD2)->|
| | | | | |
| | |<---RPT(EDD1)----| | | (3)
| | |<--------------------RPT(EDD2)------|
| | | | | |
|<------------------RPT(A,V0)-----------| | | (4)
| | | | | |
| | | | | |
| |
| |
---------------------------------------
Figure 6
Data fusion occurs amongst Managers in the network.
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In this example, Manager A requires the production of a Variable V0,
from node B, as shown in (1). The Manager role understands what data
is available from what agents in the subnetwork local to B,
understanding that EDD1 is available locally and EDD2 is available
remotely. Production messages are produced in (2) and data collected
in (3). This allows the Manager at node B to fuse the collected
Report Entries into V0 and return it in (4). While a trivial
example, the mechanism of associating fusion with the Manager
function rather than the Agent function scales with fusion
complexity, though it is important to reiterate that Agent and
Manager designations are roles, not individual software components.
There may be a single software application running on node B
implementing both Manager B and Agent B roles.
9. IANA Considerations
This protocol has no fields registered by IANA.
10. Security Considerations
Security within an DTNMA MUST exist in two layers: transport layer
security and access control.
Transport-layer security addresses the questions of authentication,
integrity, and confidentiality associated with the transport of
messages between and amongst Managers and Agents in the DTNMA. This
security is applied before any particular Actor in the system
receives data and, therefore, is outside of the scope of this
document.
Finer grain application security is done via ACLs which are defined
via configuration messages and implementation specific.
11. Informative References
[BIRRANE1] Birrane, E.B. and R.C. Cole, "Management of Disruption-
Tolerant Networks: A Systems Engineering Approach", 2010.
[BIRRANE2] Birrane, E.B., Burleigh, S.B., and V.C. Cerf, "Defining
Tolerance: Impacts of Delay and Disruption when Managing
Challenged Networks", 2011.
[BIRRANE3] Birrane, E.B. and H.K. Kruse, "Delay-Tolerant Network
Management: The Definition and Exchange of Infrastructure
Information in High Delay Environments", 2011.
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[I-D.ietf-core-comi]
Veillette, M., Van der Stok, P., Pelov, A., Bierman, A.,
and I. Petrov, "CoAP Management Interface (CORECONF)",
Work in Progress, Internet-Draft, draft-ietf-core-comi-11,
17 January 2021, <https://www.ietf.org/archive/id/draft-
ietf-core-comi-11.txt>.
[I-D.ietf-core-sid]
Veillette, M., Pelov, A., Petrov, I., and C. Bormann,
"YANG Schema Item iDentifier (YANG SID)", Work in
Progress, Internet-Draft, draft-ietf-core-sid-16, 24 June
2021, <https://www.ietf.org/archive/id/draft-ietf-core-
sid-16.txt>.
[I-D.ietf-core-yang-cbor]
Veillette, M., Petrov, I., Pelov, A., and C. Bormann,
"CBOR Encoding of Data Modeled with YANG", Work in
Progress, Internet-Draft, draft-ietf-core-yang-cbor-16, 24
June 2021, <https://www.ietf.org/archive/id/draft-ietf-
core-yang-cbor-16.txt>.
[I-D.irtf-dtnrg-dtnmp]
Birrane, E. and V. Ramachandran, "Delay Tolerant Network
Management Protocol", Work in Progress, Internet-Draft,
draft-irtf-dtnrg-dtnmp-01, 31 December 2014,
<http://www.ietf.org/internet-drafts/draft-irtf-dtnrg-
dtnmp-01.txt>.
[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>.
[RFC3416] Presuhn, R., Ed., "Version 2 of the Protocol Operations
for the Simple Network Management Protocol (SNMP)",
STD 62, RFC 3416, DOI 10.17487/RFC3416, December 2002,
<https://www.rfc-editor.org/info/rfc3416>.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838, DOI 10.17487/RFC4838,
April 2007, <https://www.rfc-editor.org/info/rfc4838>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
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[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>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", DOI 10.17487/RFC7228,
RFC 7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking: Definitions and Design Goals", RFC 7575,
DOI 10.17487/RFC7575, June 2015,
<https://www.rfc-editor.org/info/rfc7575>.
[RFC7576] Jiang, S., Carpenter, B., and M. Behringer, "General Gap
Analysis for Autonomic Networking", RFC 7576,
DOI 10.17487/RFC7576, June 2015,
<https://www.rfc-editor.org/info/rfc7576>.
[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>.
[RFC8199] Bogdanovic, D., Claise, B., and C. Moberg, "YANG Module
Classification", RFC 8199, DOI 10.17487/RFC8199, July
2017, <https://www.rfc-editor.org/info/rfc8199>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
[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>.
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[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>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", DOI 10.17487/RFC8949, STD 94,
RFC 8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
[RFC8993] Behringer, M., Ed., Carpenter, B., Eckert, T., Ciavaglia,
L., and J. Nobre, "A Reference Model for Autonomic
Networking", RFC 8993, DOI 10.17487/RFC8993, May 2021,
<https://www.rfc-editor.org/info/rfc8993>.
[RFC9171] Burleigh, S., Fall, K., Birrane, E., and III., "Bundle
Protocol Version 7", RFC 9171, DOI 10.17487/RFC9171,
January 2022, <https://www.rfc-editor.org/info/rfc9171>.
[RFC9172] Birrane, E., III., and K. McKeever, "Bundle Protocol
Security (BPSec)", RFC 9172, DOI 10.17487/RFC9172, January
2022, <https://www.rfc-editor.org/info/rfc9172>.
[xpath] Clark, J.C. and R.D. DeRose, "XML Path Language (XPath)
Version 1.0", 1999.
Authors' Addresses
Edward J. Birrane
Johns Hopkins Applied Physics Laboratory
Email: Edward.Birrane@jhuapl.edu
Emery Annis
Johns Hopkins Applied Physics Laboratory
Email: Emery.Annis@jhuapl.edu
Sarah E. Heiner
Johns Hopkins Applied Physics Laboratory
Email: Sarah.Heiner@jhuapl.edu
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