Management of Networks with Constrained Devices: Problem Statement and Requirements
RFC 7547
| Document | Type | RFC - Informational (May 2015; No errata) | |
|---|---|---|---|
| Authors | Mehmet Ersue , Dan Romascanu , Jürgen Schönwälder , Ulrich Herberg | ||
| Last updated | 2015-10-14 | ||
| Replaces | draft-ersue-opsawg-coman-probstate-reqs | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Warren Kumari | ||
| Shepherd write-up | Show (last changed 2014-10-30) | ||
| IESG | IESG state | RFC 7547 (Informational) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Joel Jaeggli | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | No IANA Actions | ||
Internet Engineering Task Force (IETF) M. Ersue, Ed.
Request for Comments: 7547 Nokia Networks
Category: Informational D. Romascanu
ISSN: 2070-1721 Avaya
J. Schoenwaelder
Jacobs University Bremen
U. Herberg
May 2015
Management of Networks with Constrained Devices:
Problem Statement and Requirements
Abstract
This document provides a problem statement, deployment and management
topology options, as well as requirements addressing the different
use cases of the management of networks where constrained devices are
involved.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7547.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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 ....................................................3
1.1. Overview ...................................................3
1.2. Terminology ................................................4
1.3. Network Types and Characteristics in Focus .................5
1.4. Constrained Device Deployment Options ......................9
1.5. Management Topology Options ...............................10
1.6. Managing the Constrainedness of a Device or Network .......10
1.7. Configuration and Monitoring Functionality Levels .........13
2. Problem Statement ..............................................14
3. Requirements on the Management of Networks with
Constrained Devices ............................................16
3.1. Management Architecture/System ............................18
3.2. Management Protocols and Data Models ......................22
3.3. Configuration Management ..................................25
3.4. Monitoring Functionality ..................................27
3.5. Self-Management ...........................................32
3.6. Security and Access Control ...............................33
3.7. Energy Management .........................................35
3.8. Software Distribution .....................................37
3.9. Traffic Management ........................................37
3.10. Transport Layer ..........................................39
3.11. Implementation Requirements ..............................40
4. Security Considerations ........................................41
5. Informative References .........................................42
Acknowledgments ...................................................44
Authors' Addresses ................................................44
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1. Introduction
1.1. Overview
Constrained devices (also known as sensors, smart objects, or smart
devices) with limited CPU, memory, and power resources can be
connected to a network. It might be based on unreliable or lossy
channels, it may use wireless technologies with limited bandwidth and
a dynamic topology, or it may need the service of a gateway or proxy
to connect to the Internet. In other scenarios, the constrained
devices can be connected to a unconstrained network using off-the-
shelf protocol stacks.
Constrained devices might be in charge of gathering information in
diverse settings including natural ecosystems, buildings, and
factories and sending the information to one or more server stations.
Constrained devices may also work under severe resource constraints
such as limited battery and computing power, little memory and
insufficient wireless bandwidth, and communication capabilities. A
central entity, e.g., a base station or controlling server, might
have more computational and communication resources and can act as a
gateway between the constrained devices and the application logic in
the core network.
Today, constrained devices of diverse size and with different
resources and capabilities are being connected. Mobile personal
gadgets, building-automation devices, cellular phones, machine-to-
machine (M2M) devices, etc., benefit from interacting with other
"things" in the near or somewhere in the Internet. With this the
Internet of Things (IoT) becomes a reality, built up of uniquely
identifiable objects (things). And over the next decade, this could
grow to trillions of constrained devices and will greatly increase
the Internet's size and scope.
Network management is characterized by monitoring network status,
detecting faults (and inferring their causes), setting network
parameters, and carrying out actions to remove faults, maintain
normal operation, and improve network efficiency and application
performance. The traditional network monitoring application
periodically collects information from a set of managed network
elements, it processes the data, and it presents the results to the
network management users. Constrained devices, however, often have
limited power, have low transmission range, and might be unreliable.
They might also need to work in hostile environments with advanced
security requirements or need to be used in harsh environments for a
long time without supervision. Due to such constraints, the
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management of a network with constrained devices faces a different
type of challenges compared to the management of a traditional IP
network.
The IETF has already done substantial standardization work to enable
communication in IP networks and to manage such networks as well as
the manifold types of nodes in these networks [RFC6632]. However,
the IETF so far has not developed any specific technologies for the
management of constrained devices and the networks comprised by
constrained devices. IP-based sensors or constrained devices in such
an environment (i.e., devices with very limited memory, CPU, and
energy resources) nowadays use application-layer protocols in an ad
hoc manner to do simple resource management and monitoring.
This document provides a problem statement and lists requirements for
the different use cases of management of a network with constrained
devices. Sections 1.3 and 1.5 describe different topology options
for the networking and management of constrained devices. Section 2
provides a problem statement on the issue of the management of
networked constrained devices. Section 3 lists requirements on the
management of applications and networks with constrained devices.
Note that the requirements listed in Section 3 have been separated
from the context in which they may appear. Depending on the concrete
circumstances, an implementer may decide to address a certain
relevant subset of the requirements.
The use cases in the context of networks with constrained devices can
be found in [RFC7548]. This document provides a list of objectives
for discussions and does not aim to be a strict requirements document
for all use cases. In fact, there likely is not a single solution
that works equally well for all the use cases.
1.2. Terminology
Concerning constrained devices and networks, this document generally
builds on the terminology defined in [RFC7228], where the terms
"constrained device", "constrained network", and others are defined.
Additionally, the following terms are used throughout:
AMI: (Advanced Metering Infrastructure) A system including
hardware, software, and networking technologies that measures,
collects, and analyzes energy use and that communicates with a
hierarchically deployed network of metering devices, either on
request or on a schedule.
C0: Class 0 constrained device as defined in Section 3 of
[RFC7228].
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C1: Class 1 constrained device as defined in Section 3 of
[RFC7228].
C2: Class 2 constrained device as defined in Section 3 of
[RFC7228].
Network of Constrained Devices: A network to which constrained
devices are connected that may or may not be a constrained
network (see [RFC7228] for the definition of the term
constrained network).
M2M: (Machine to Machine) The automatic data transfer between
devices of different kinds. In M2M scenarios, a device (such
as a sensor or meter) captures an event, which is relayed
through a network (wireless, wired, or hybrid) to an
application.
MANET: (Mobile Ad Hoc Network [RFC2501]) A self-configuring and
infrastructureless network of mobile devices connected by
wireless technologies.
Smart Grid: An electrical grid that uses communication technologies
to gather and act on information in an automated fashion to
improve the efficiency, reliability, and sustainability of the
production and distribution of electricity.
Smart Meter: An electrical meter in the context of a smart grid.
For a detailed discussion on the constrained networks as well as
classes of constrained devices and their capabilities, please see
[RFC7228].
1.3. Network Types and Characteristics in Focus
In this document, we differentiate the following types of networks
concerning their transport and communication technologies:
(Note that a network in general can involve constrained and
unconstrained devices.)
1. Wireline unconstrained networks, e.g., an Ethernet LAN with
constrained and unconstrained devices involved.
2. A combination of wireline and wireless networks, possibly with a
multi-hop connectivity between constrained devices, utilizing
dynamic routing in both the wireless and wireline portions of the
network. Such networks usually support highly distributed
applications with many nodes (e.g., environmental monitoring) and
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tend to deal with large-scale multipoint-to-point (MP2P) systems.
Wireless Mesh Networks (WMNs), as a specific variant, use off-
the-shelf radio technology such as Wi-Fi, WiMAX, and cellular
3G/4G. WMNs are reliable based on the redundancy they offer and
have often a more planned deployment to provide dynamic and cost
effective connectivity over a certain geographic area.
3. A combination of wireline and wireless networks with point-to-
point (P2P) or point-to-multipoint (P2MP) communication generally
with single-hop connectivity to constrained devices, utilizing
static routing over the wireless network. Such networks support
short-range, P2P, low-data-rate, source-to-sink types of
applications, such as RFID systems, light switches, fire/smoke
detectors, and home appliances. This type of network also
supports confined short-range spaces such as a home, a factory, a
building, or the human body. [IEEE802.15.1] (Bluetooth) and
[IEEE802.15.4] are well-known examples of applicable standards
for such networks. By using 6LoWPANs (IPv6 over Low-Power
Wireless Personal Area Networks) [RFC4919] and RPL (Routing
Protocol for Low-Power and Lossy Networks) [RFC6550] on top of
IEEE 802.15.4, multi-hop connectivity and dynamic routing can be
achieved. With RPL, the IETF has specified a proactive "route-
over" architecture where routing and forwarding is implemented at
the network layer. The protocol provides a mechanism whereby
MP2P, P2MP, and P2P traffic are supported.
4. Self-configuring infrastructureless networks of mobile devices
(e.g., MANET) are a particular type of network connected by
wireless technologies. Infrastructureless networks are mostly
based on P2P communications of devices moving independently in
any direction and changing the links to other devices frequently.
Such devices do act as a router to forward traffic unrelated to
their own use.
Wireline unconstrained networks with constrained and unconstrained
devices are mainly used for specific applications like Building
Automation or Infrastructure Monitoring. Wireline and wireless
networks with multi-hop or P2MP connectivity are used, e.g., for
environmental monitoring as well as transport and mobile
applications.
Furthermore, different network characteristics are determined by
multiple dimensions: dynamicity of the topology, bandwidth, and loss
rate. In the following, each dimension is explained, and networks in
scope for this document are outlined:
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Network Topology:
The topology of a network can be represented as a graph, with edges
(i.e., links) and vertices (routers and hosts). Examples of
different topologies include "star" topologies (with one central node
and multiple nodes in one-hop distance), tree structures (with each
node having exactly one parent), directed acyclic graphs (with each
node having one or more parents), clustered topologies (where one or
more "cluster heads" are responsible for a certain area of the
network), mesh topologies (fully distributed), etc.
Management protocols may take advantage of specific network
topologies, for example, by distributing large-scale management tasks
amongst multiple distributed network management stations (e.g., in
case of a mesh topology), or by using a hierarchical management
approach (e.g., in case of a tree or clustered topology). These
different management topology options are described in Section 1.6.
Note that in certain network deployments, such as community ad hoc
networks (see the use case "Community Network Applications" in
[RFC7548]), the topology is not preplanned; thus, it may be unknown
for management purposes. In other use cases, such as industrial
applications (see the use case "Industrial Applications" in
[RFC7548]), the topology may be designed in advance and therefore
taken advantage of when managing the network.
Dynamicity of the network topology:
The dynamicity of the network topology determines the rate of change
of the graph as a function of time. Such changes can occur due to
different factors, such as mobility of nodes (e.g., in MANETs or
cellular networks), duty cycles (for low-power devices enabling their
network interface only periodically to transmit or receive packets),
or unstable links (in particular wireless links with strongly
fluctuating link quality).
Examples of different levels of dynamicity of the topology are
Ethernets (with typically a very static topology) on the one side,
and Low-power and Lossy Networks (LLNs) on the other side. LLNs
nodes are often duty-cycled and operate on unreliable wireless links
and are potentially mobile (e.g., for sensor networks).
The more dynamic the topology is, the more have routing, transport
and application-layer protocols to cope with interrupted connectivity
and/or longer delays. For example, management protocols (with a
given underlying transport protocol) that expect continuous session
flows without changes of routes during a communication flow, may fail
to operate.
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Networks with a very low dynamicity (e.g., Ethernet) with no or
infrequent topology changes (e.g., less than once every 30 minutes),
are in the scope of this document if they are used with constrained
devices (see, e.g., the use case "Building Automation" in [RFC7548]).
Traffic flows:
The traffic flow in a network determines from which sources data
traffic is sent to which destinations in the network. Several
different traffic flows are defined in [RFC7102], including P2P,
MP2P, and P2MP flows as:
o P2P: Point-to-point refers to traffic exchanged between two nodes
(regardless of the number of hops between the two nodes).
o P2MP: Point-to-multipoint traffic refers to traffic between one
node and a set of nodes. This is similar to the P2MP concept in
Multicast or MPLS Traffic Engineering.
o MP2P: Multipoint-to-point is used to describe a particular traffic
pattern (e.g., MP2P flows collecting information from many nodes
flowing inwards towards a collecting sink).
If one of these traffic patterns is predominant in a network,
protocols (routing, transport, application) may be optimized for the
specific traffic flow. For example, in a network with a tree
topology and MP2P traffic, collection tree protocols are efficient to
send data from the leaves of the tree to the root of the tree, via
each node's parent.
Bandwidth:
The bandwidth of the network is the amount of data that can be sent
per unit of time between two communication endpoints. It is usually
determined by the link with the minimum bandwidth on the path from
the source to the destination of data packets. The bandwidth in
networks can range from a few kilobytes per second (such as on some
IEEE 802.15.4 link layers) to many gigabytes per second (e.g., on
fiber optics).
For management purposes, the management protocol typically requires
the sending of information between the network management station and
the clients, for monitoring or control purposes. If the available
bandwidth is insufficient for the management protocol, packets will
be buffered and eventually dropped; thus, management is not possible
with such a protocol.
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Networks without bandwidth limitation (e.g., Ethernet) are in the
scope of this document if they are used with constrained devices (see
the use case "Building Automation" in [RFC7548]).
Loss rate:
The loss rate (or bit error rate) is the number of bit errors divided
by the total number of bits transmitted. For wired networks, loss
rates are typically extremely low, e.g., around 10^-12 or 10^-13 for
the latest 10 Gbit Ethernet. For wireless networks, such as IEEE
802.15.4, the bit error rate can be as high as 10^-1 to 1 in case of
interferences. Even when using a reliable transport protocol,
management operations can fail if the loss rate is too high, unless
they are specifically designed to cope with these situations.
1.4. Constrained Device Deployment Options
We differentiate the following deployment options for the constrained
devices:
o A network of constrained devices that communicate with each other,
o Constrained devices that are connected directly to an IP network,
o A network of constrained devices that communicate with a gateway
or proxy with more communication capabilities possibly acting as a
representative of the device to entities in the unconstrained
network,
o Constrained devices that are connected to the Internet or an IP
network via a gateway/proxy,
o A hierarchy of constrained devices, e.g., a network of C0 devices
connected to one or more C1 devices -- connected to one or more C2
devices -- connected to one or more gateways -- connected to some
application servers or NMS, and
o The possibility of device grouping (possibly in a dynamic manner)
such as that the grouped devices can act as one logical device at
the edge of the network and one device in this group can act as
the managing entity.
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1.5. Management Topology Options
We differentiate the following options for the management of networks
of constrained devices:
o A network of constrained devices managed by one central manager.
A logically centralized management might be implemented in a
hierarchical fashion for scalability and robustness reasons. The
manager and the management application logic might have a gateway/
proxy in between or might be on different nodes in different
networks, e.g., management application running on a cloud server.
o Distributed management, where a network of constrained devices is
managed by more than one manager. Each manager controls a
subnetwork and may communicate directly with other manager
stations in a cooperative fashion. The distributed management may
be weakly distributed, where functions are broken down and
assigned to many managers dynamically, or strongly distributed,
where almost all managed things have embedded management
functionality and explicit management disappears, which usually
comes with the price that the strongly distributed management
logic now needs to be managed.
o Hierarchical management, where a hierarchy of networks with
constrained devices are managed by the managers at their
corresponding hierarchy level. That is, each manager is
responsible for managing the nodes in its subnetwork. It passes
information from its subnetwork to its higher-level manager and
disseminates management functions received from the higher-level
manager to its subnetwork. Hierarchical management is essentially
a scalability mechanism, logically the decision-making may be
still centralized.
1.6. Managing the Constrainedness of a Device or Network
The capabilities of a constrained device or network and the
constrainedness thereof influence and have an impact on the
requirements for the management of such a network or devices.
Note that the list below gives examples and does not claim
completeness.
A constrained device:
o might only support an unreliable (e.g., lossy) radio link, i.e.,
the client and server of a management protocol need to gracefully
handle incomplete command exchanges or missing commands.
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o might only be able to go online from time to time, where it is
reachable, i.e., a command might be necessary to repeat after a
longer timeout or the timeout value with which one endpoint waits
on a response needs to be sufficiently high.
o might only be able to support a limited operating time (e.g.,
based on the available battery) or may behave as 'sleepy
endpoints', setting their network links to a disconnected state
during long periods of time, i.e., the devices need to economize
their energy usage with suitable mechanisms and the managing
entity needs to monitor and control the energy status of the
constrained devices it manages.
o might only be able to support one simple communication protocol,
i.e., the management protocol needs to be possible to downscale
from constrained (C2) to very constrained (C0) devices with
modular implementation and a very basic version with just a few
simple commands.
o might only be able to support a communication protocol, which is
not IP based.
o might only be able to support limited or no user and/or transport
security, i.e., the management system needs to support a less-
costly and simple but sufficiently secure authentication
mechanism.
o might not be able to support compression and decompression of
exchanged data based on limited CPU power, i.e., an intermediary
entity which is capable of data compression should be able to
communicate with both, devices that support data compression
(e.g., C2) and devices that do not support data compression (e.g.,
C1 and C0).
o might only be able to support a simple encryption, i.e., it would
be beneficial if the devices use cryptographic algorithms that are
supported in hardware and the encryption used is efficient in
terms of memory and CPU usage.
o might only be able to communicate with one single managing entity
and cannot support the parallel access of many managing entities.
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o might depend on a self-configuration feature, i.e., the managing
entity might not know all devices in a network and the device
needs to be able to initiate connection setup for the device
configuration.
o might depend on self- or neighbor-monitoring features, i.e., the
managing entity might not be able to monitor all devices in a
network continuously.
o might only be able to communicate with its neighbors, i.e., the
device should be able to get its configuration from a neighbor.
o might only be able to support parsing of data models with limited
size, i.e., the device data models need to be compact containing
the most necessary data and if possible parsable as a stream.
o might only be able to support a limited or no-failure detection,
i.e., the managing entity needs to handle the situation, where a
failure does not get detected or gets detected late gracefully,
e.g., with asking repeatedly.
o might only be able to support the reporting of just one or a
limited set failure types.
o might only be able to support a limited set of notifications,
possible only an "I am alive." message.
o might only be able to support a soft-reset from failure recovery.
o might possibly generate a large amount of redundant reporting
data, i.e., the intermediary management entity (see [RFC7252])
should be able to filter and aggregate redundant data.
A network of constrained devices:
o might only support an unreliable (e.g., lossy) radio link, i.e.,
the client and server of a management protocol need to repeat
commands as necessary or gracefully ignore incomplete commands.
o might be necessary to manage based on multicast communication,
i.e., the managing entity needs to be prepared to configure many
devices at once based on the same data model.
o might have a very large topology supporting 10,000 or more nodes
for some applications and as such node naming is a specific issue
for constrained networks.
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o needs to support self-organization, i.e., given the large number
of nodes and their potential placement in hostile locations and
frequently changing topology, manual configuration of nodes is
typically not feasible. As such, the network would benefit from
the ability to reconfigure itself so that it can continue to
operate properly and support reliable connectivity.
o might need a management solution that is energy efficient, using
as little wireless bandwidth as possible since communication is
highly energy demanding.
o needs to support localization schemes to determine the location of
devices since the devices might be moving and location information
is important for some applications.
o needs a management solution that is scalable as the network may
consist of thousands of nodes and may need to be extended
continuously.
o needs to provide fault tolerance. Faults in network operation
including hardware and software errors or failures detected by the
transport protocol should be handled smoothly. In such a case, it
should be possible to run the protocol at a reduced level but
avoid failing completely. For example, self-monitoring mechanisms
or graceful degradation of features can be used to provide fault
tolerance.
o might require new management capabilities, for example, network
coverage information and a constrained device power distribution
map.
o might require a new management function for data management, since
the type and amount of data collected in constrained networks is
different from those of the traditional networks.
o might also need energy-efficient key management.
1.7. Configuration and Monitoring Functionality Levels
Devices often differ significantly on the level of configuration
management support they provide. This document classifies the
configuration management functionality as follows:
CL0: Devices are preconfigured and allow no runtime configuration
changes. Configuration parameters are often hard coded and
compiled directly into the firmware image.
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CL1: Devices have explicit configuration objects. However, changes
require a restart of the device to take effect.
CL2: Devices allow management systems to replace the entire
configuration (or predetermined subsets) in bulk.
Configuration changes take effect by soft-restarts of the
system (or subsystems).
CL3: Devices allow management systems to modify configuration
objects without bulk replacements and changes take effect
immediately.
CL4: Devices support multiple configuration datastores and they
might distinguish between the currently running and the next
startup configuration.
CL5: Devices support configuration datastore locking and device-
local configuration change transactions, i.e., either all
configuration changes are applied or none of them are.
CL6: Devices support configuration change transactions across
devices.
This document defines a classification of devices with regard to
different levels of monitoring support. In general, a device may be
in several of the levels listed below:
ML0: Devices push predefined monitoring data.
ML1: Devices allow management systems to pull predefined monitoring
data.
ML2: Devices allow management systems to pull user-defined filtered
subsets of monitoring data.
ML3: Devices are able to locally process monitoring data in order to
detect threshold crossings or to aggregate data.
At the time of this writing, constrained devices often implement a
combination of one of CL0-CL2 with one of ML0-ML1.
2. Problem Statement
The terminology for the "Internet of Things" is still nascent, and
depending on the network type or layer in focus, diverse technologies
and terms are in use. Common to all these considerations is the
"Things" or "Objects" are supposed to have physical or virtual
identities using interfaces to communicate. In this context, we need
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to differentiate between the constrained and smart devices identified
by an IP address compared to virtual entities such as Smart Objects,
which can be identified as a resource or a virtual object by using a
unique identifier. Furthermore, the smart devices usually have
limited memory and CPU power as well as aim to be self-configuring
and easy to deploy.
However, the constraints of the network nodes require a rethinking of
the protocol characteristics concerning power consumption,
performance, bandwidth consumption, memory, and CPU usage. As such,
there is a demand for protocol simplification, energy-efficient
communication, less CPU usage, and a smaller memory footprint.
On the application layer, the IETF is already developing protocols
like the Constrained Application Protocol (CoAP) [RFC7252] enabling
the communication of constrained devices and networks, e.g., for
smart energy applications or home automation environments. In fact,
the deployment of such an environment involves many, in some
scenarios up to million, constrained devices (e.g., smart meters),
which produce a large amount of data. This data needs to be
collected, filtered, and preprocessed for further use in diverse
services.
Considering the high number of nodes to deploy, one has to think
about the manageability aspects of the smart devices and plan for
easy deployment, configuration, and management of the networks of
constrained devices as well as the devices themselves. Consequently,
seamless monitoring and self-configuration of such network nodes
becomes more and more imperative. Self-configuration and self-
management are already a reality in the standards of some
organizations such as 3GPP. To introduce self-configuration of smart
devices successfully, a device-initiated connection establishment is
often required.
A simple and efficient application-layer protocol, such as CoAP, is
essential to address the issue of efficient object-to-object
communication and information exchange. Such an information exchange
should be done based on interoperable data models to enable the
exchange and interpretation of diverse application- and management-
related data.
In an ideal world, we would have only one network management protocol
for monitoring, configuration, and exchanging management data,
independently of the type of the network (e.g., smart grid, wireless
access, or core network). Furthermore, it would be desirable to
derive the basic data models for constrained devices from the core
models used today to enable reuse of functionality and end-to-end
information exchange. However, the current management protocols seem
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to be too heavyweight compared to the capabilities the constrained
devices have and are not applicable directly for use in a network of
constrained devices. Furthermore, the data models addressing the
requirements of such smart devices need yet to be designed.
So far, the IETF has not developed any specific technologies for the
management of constrained devices and the networks comprised by
constrained devices. IP-based sensors or constrained devices in such
an environment, i.e., today, devices with very limited memory and CPU
resources use, e.g., application-layer protocols to do simple
resource management and monitoring. This might be sufficient for
some basic cases; however, there is a need to reconsider the network
management mechanisms based on the new, changed, and reduced
requirements coming from smart devices and the network of such
constrained devices. Although it is questionable whether we can take
the same comprehensive approach we use in an IP network and use it
for the management of constrained devices. Hence, the management of
a network with constrained devices is necessarily designed in a
simplified and less complex manner.
As Section 1.6 highlights, there are diverse characteristics of
constrained devices or networks, which stem from their
constrainedness and therefore have an impact on the requirements for
the management of such a network with constrained devices. The use
cases discussed in [RFC7548] show that the requirements on
constrained networks are manifold and need to be analyzed from
different angles, e.g., concerning the design of the management
architecture, the selection of the appropriate protocol features, as
well as the specific issues that are new in the context of
constrained devices. Examples of such issues are careful management
of scarce energy resources, the necessity for self-organization and
self-management of such devices but also the implementation
considerations to enable the use of common communication technologies
on a constrained hardware in an efficient manner. For an exhaustive
list of issues and requirements that need to be addressed for the
management of a network with constrained devices, please see Sections
1.6 and 3.
3. Requirements on the Management of Networks with Constrained Devices
This section describes the requirements categorized by management
areas listed in subsections.
Note that the requirements listed in this section have been separated
from the context in which they may appear. In general, this document
does not recommend the realization of any subset of the described
requirements. As such, this document avoids selecting any of the
requirements as mandatory to implement. A device might be able to
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provide only a particular selected set of requirements and might not
be capable to provide all requirements in this document. On the
other hand, a device vendor might select a specific relevant subset
of the requirements to implement.
The following template is used for the definition of the
requirements.
Req-ID: An ID composed of two numbers: a section number indicating
the topic area and a unique three-digit number per section.
Title: The title of the requirement.
Description: The rationale and description of the requirement.
Source: The origin of the requirement and the matching use case or
application. For the discussion of referred use cases for
constrained management, please see [RFC7548].
Requirement Type: Functional Requirement, Non-functional
Requirement. A functional requirement is related to a function or
component. As such, functional requirements may be technical
details or specific functionality that define what a system is
supposed to accomplish. Non-functional requirements (also known
as design constraints or quality requirements) impose
implementation-related considerations such as performance
requirements, security, or reliability.
Device type: The device types by which this requirement can be
supported: C0, C1, and/or C2.
Priority: The priority of the requirement showing its importance for
a particular type of device: High, Medium, and Low. The priority
of a requirement can be High, e.g., for a C2 device, but Low for a
C1 or C0 device, as the realization of complex features in a C1
device is in many cases not possible.
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3.1. Management Architecture/System
Req-ID: 1.001
Title: Support multiple device classes within a single network
Description: Larger networks usually consist of devices belonging to
different device classes (e.g., constrained mesh endpoints and
less constrained routers) communicating with each other. Hence,
the management architecture must be applicable to networks that
have a mix of different device classes. See Section 3 of
[RFC7228] for the definition of Constrained Device Classes.
Source: All use cases
Requirement Type: Non-functional Requirement
Device type: C1 and/or C2
Priority: High
---
Req-ID: 1.002
Title: Management scalability
Description: The management architecture must be able to scale with
the number of devices involved and operate efficiently in any
network size and topology. This implies that, e.g., the managing
entity is able to handle large amounts of device monitoring data
and the management protocol is not sensitive to the decrease of
the time between two client requests. To achieve good
scalability, caching techniques, in-network data aggregation
techniques, and hierarchical management models may be used.
Source: General requirement for all use cases to enable large-scale
networks
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: High
---
Req-ID: 1.003
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Title: Hierarchical management
Description: Provide a means of hierarchical management, i.e.,
provide intermediary management entities on different levels,
which can take over the responsibility for the management of a
subhierarchy of the network of constraint devices. The
intermediary management entity can, e.g., support management data
aggregation to handle, e.g., high-frequent monitoring data or
provide a caching mechanism for the uplink and downlink
communication. Hierarchical management contributes to management
scalability.
Source: Use cases where a large amount of devices are deployed with
a hierarchical topology
Requirement Type: Non-functional Requirement
Device type: Managing and intermediary entities
Priority: Medium
---
Req-ID: 1.004
Title: Minimize state maintained on constrained devices
Description: The amount of state that needs to be maintained on
constrained devices should be minimized. This is important in
order to save memory (especially relevant for C0 and C1 devices)
and in order to allow devices to restart, for example, to apply
configuration changes or to recover from extended periods of
inactivity.
Note: One way to achieve this is to adopt a RESTful architecture
that minimizes the amount of state maintained by managed
constrained devices and that makes resources of a device
addressable via URIs.
Source: Basic requirement that concerns all use cases
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High
---
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Req-ID: 1.005
Title: Automatic resynchronization with eventual consistency
Description: To support large scale networks, where some constrained
devices may be offline at any point in time, it is necessary to
distribute configuration parameters in a way that allows temporary
inconsistencies but eventually converges, after a sufficiently
long period of time without further changes, towards global
consistency.
Source: Use cases with large-scale networks with many devices
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High
---
Req-ID: 1.006
Title: Support for lossy links and unreachable devices
Description: Some constrained devices will only be able to support
lossy and unreliable links characterized by a limited data rate, a
high latency, and a high transmission error rate. Furthermore,
constrained devices often duty cycle their radio or the whole
device in order to save energy. Some classes of devices labeled
as 'sleepy endpoints' set their network links to a disconnected
state during long periods of time. In all cases, the management
system must not assume that constrained devices are always
reachable.
Source: Basic requirement for networks of constrained devices with
unreliable links and constrained devices that sleep to save energy
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: High
---
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Req-ID: 1.007
Title: Network-wide configuration
Description: Provide means by which the behavior of the network can
be specified at a level of abstraction (network-wide
configuration) higher than a set of configuration information
specific to individual devices. It is useful to derive the
device-specific configuration from the network-wide configuration.
Such a repository can be used to configure predefined device or
protocol parameters for the whole network. Furthermore, such a
network-wide view can be used to monitor and manage a group of
routers or a whole network. For example, monitoring the
performance of a network requires information additional to what
can be acquired from a single router using a management protocol.
Note: The identification of the relevant subset of the policies to
be provisioned is according to the capabilities of each device and
can be obtained from a preconfigured data-repository.
Source: In general, all use cases of network and device
configuration based on a network view in a top-down manner
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: Medium
---
Req-ID: 1.008
Title: Distributed management
Description: Provide a means of simple distributed management, where
a network of constrained devices can be managed or monitored by
more than one manager. Since the connectivity to a server cannot
be guaranteed at all times, a distributed approach may provide
higher reliability, at the cost of increased complexity. This
requirement implies the handling of data consistency in case of
concurrent read and write access to the device datastore. It
might also happen that no management (configuration) server is
accessible and the only reachable node is a peer device. In this
case, the device should be able to obtain its configuration from
peer devices.
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Source: Use cases where the count of devices to manage is high
Requirement Type: Non-functional Requirement
Device type: C1 and C2
Priority: Medium
3.2. Management Protocols and Data Models
Req-ID: 2.001
Title: Modular implementation of management protocols
Description: Management protocols should be specified to allow for
modular implementations, i.e., it should be possible to implement
only a basic set of protocol primitives on highly constrained
devices, while devices with additional resources may provide more
support for additional protocol primitives. See Section 1.7 for a
discussion on the level of configuration management and monitoring
support constrained devices may provide.
Source: Basic requirement interesting for all use cases
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: High
---
Req-ID: 2.002
Title: Compact encoding of management data
Description: The encoding of management data should be compact and
space efficient, enabling small message sizes.
Source: General requirement to save memory for the receiver buffer
and on-air bandwidth
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High
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---
Req-ID: 2.003
Title: Compression of management data or complete messages
Description: Management data exchanges can be further optimized by
applying data compression techniques or delta encoding techniques.
Compression typically requires additional code size and some
additional buffers and/or the maintenance of some additional state
information. For C0 devices, compression may not be feasible.
Source: Use cases where it is beneficial to reduce transmission time
and bandwidth, e.g., mobile applications that require saving on-
air bandwidth
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: Medium
---
Req-ID: 2.004
Title: Mapping of management protocol interactions
Description: It is desirable to have a lossless automated mapping
between the management protocol used to manage constrained devices
and the management protocols used to manage regular devices. In
the ideal case, the same core management protocol can be used with
certain restrictions taking into account the resource limitations
of constrained devices. However, for very resource-constrained
devices, this goal might not be achievable.
Source: Use cases where high-frequency interaction with the
management system of a unconstrained network is required
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: Medium
---
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Req-ID: 2.005
Title: Consistency of data models with the underlying information
model
Description: The data models used by the management protocol must be
consistent with the information model used to define data models
for unconstrained networks. This is essential to facilitate the
integration of the management of constrained networks with the
management of unconstrained networks. Using an underlying
information model for future data model design enables further
top-down model design and model reuse as well as data
interoperability (i.e., exchange of management information between
the constrained and unconstrained networks). This is a strong
requirement, despite the fact that the underlying information
models are often not explicitly documented in the IETF.
Source: General requirement to support data interoperability,
consistency, and model reuse
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: High
---
Req-ID: 2.006
Title: Lossless mapping of management data models
Description: It is desirable to have a lossless automated mapping
between the management data models used to manage regular devices
and the management data models used for managing constrained
devices. In the ideal case, the same core data models can be used
with certain restrictions taking into account the resource
limitations of constrained devices. However, for very resource-
constrained devices, this goal might not be achievable.
Source: Use cases where consistent data exchange with the management
system of a unconstrained network is required
Requirement Type: Functional Requirement
Device type: C2
Priority: Medium
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---
Req-ID: 2.007
Title: Protocol extensibility
Description: Provide means of extensibility for the management
protocol, i.e., by adding new protocol messages or mechanisms that
can deal with changing requirements on a supported message and
data types effectively, without causing interoperability problems
or having to replace/update large amount of deployed devices.
Source: Basic requirement useful for all use cases
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High
3.3. Configuration Management
Req-ID: 3.001
Title: Self-configuration capability
Description: Automatic configuration and reconfiguration of devices
without manual intervention. Compared to the traditional
management of devices where the management application is the
central entity configuring the devices, in the autoconfiguration
scenario the device is the active part and initiates the
configuration process. Self-configuration can be initiated during
the initial configuration or for subsequent configurations, where
the configuration data needs to be refreshed. Self-configuration
should be also supported during the initialization phase or in the
event of failures, where prior knowledge of the network topology
is not available or the topology of the network is uncertain.
Source: In general, all use cases requiring easy deployment and
plug&play behavior as well as easy maintenance of many constrained
devices
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High for device categories C0 and C1; Medium for C2
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---
Req-ID: 3.002
Title: Capability discovery
Description: Enable the discovery of supported optional management
capabilities of a device and their exposure via at least one
protocol and/or data model.
Source: Use cases where the device interaction with other devices or
applications is a function of the level of support for its
capabilities
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: Medium
---
Req-ID: 3.003
Title: Asynchronous transaction support
Description: Provide configuration management with asynchronous
(event-driven) transaction support. Configuration operations must
support a transactional model, with asynchronous indications that
the transaction was completed.
Source: Use cases that require transaction-oriented processing
because of reliability or distributed architecture functional
requirements
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: Medium
---
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Req-ID: 3.004
Title: Network reconfiguration
Description: Provide a means of iterative network reconfiguration in
order to recover the network from node and communication failures.
The network reconfiguration can be failure-driven and self-
initiated (automatic reconfiguration). The network
reconfiguration can be also performed on the whole hierarchical
structure of a network (network topology).
Source: Practically all use cases, as network connectivity is a
basic requirement
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: Medium
3.4. Monitoring Functionality
Req-ID: 4.001
Title: Device status monitoring
Description: Provide a monitoring function to collect and expose
information about device status and expose it via at least one
management interface. The device monitoring might make use of the
hierarchical management through the intermediary entities and the
caching mechanism. The device monitoring might also make use of
neighbor-monitoring (fault detection in the local network) to
support fast fault detection and recovery, e.g., in a scenario
where a managing entity is unreachable and a neighbor can take
over the monitoring responsibility.
Source: All use cases
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High; Medium for neighbor-monitoring
---
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Req-ID: 4.002
Title: Energy status monitoring
Description: Provide a monitoring function to collect and expose
information about device energy parameters and usage (e.g.,
battery level and average power consumption).
Source: Use case "Energy Management"
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High for energy reporting devices; Low for others
---
Req-ID: 4.003
Title: Monitoring of current and estimated device availability
Description: Provide a monitoring function to collect and expose
information about current device availability (energy, memory,
computing power, forwarding-plane utilization, queue buffers,
etc.) and estimation of remaining available resources.
Source: All use cases. Note that monitoring energy resources (like
battery status) may be required on all kinds of devices.
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: Medium
---
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Req-ID: 4.004
Title: Network status monitoring
Description: Provide a monitoring function to collect, analyze, and
expose information related to the status of a network or network
segments connected to the interface of the device.
Source: All use cases
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: Low, based on the realization complexity
---
Req-ID: 4.005
Title: Self-monitoring
Description: Provide self-monitoring (local fault detection) feature
for fast fault detection and recovery.
Source: Use cases where the devices cannot be monitored centrally in
an appropriate manner, e.g., self-healing is required
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: High for C2; Medium for C1
---
Req-ID: 4.006
Title: Performance monitoring
Description: The device will provide a monitoring function to
collect and expose information about the basic performance
parameter of the device. The performance management functionality
might make use of the hierarchical management through the
intermediary devices.
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Source: Use cases "Building Automation" and "Transport Applications"
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: Low
---
Req-ID: 4.007
Title: Fault detection monitoring
Description: The device will provide fault detection monitoring.
The system collects information about network states in order to
identify whether faults have occurred. In some cases, the
detection of the faults might be based on the processing and
analysis of the parameters retrieved from the network or other
devices. In case of C0 devices, the monitoring might be limited
to the check whether or not the device is alive.
Source: Use cases "Environmental Monitoring", "Building Automation",
"Energy Management", "Infrastructure Monitoring"
Requirement Type: Functional Requirement
Device type: C0, C1 and C2
Priority: Medium
---
Req-ID: 4.008
Title: Passive and reactive monitoring
Description: The device will provide passive and reactive monitoring
capabilities. The system or manager collects information about
device components and network states (passive monitoring) and may
perform postmortem analysis of collected data. In case events of
interest have occurred, the system or the manager can adaptively
react (reactive monitoring), e.g., reconfigure the network.
Typically, actions (reactions) will be executed or sent as
commands by the management applications.
Source: Diverse use cases relevant for device status and network
state monitoring
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Requirement Type: Functional Requirement
Device type: C2
Priority: Medium
---
Req-ID: 4.009
Title: Recovery
Description: Provide local, central and hierarchical recovery
mechanisms (recovery is in some cases achieved by recovering the
whole network of constrained devices).
Source: Use cases "Industrial Applications", "Home Automation", and
"Building Automation", as well as mobile applications that involve
different forms of clustering or area managers
Requirement Type: Functional Requirement
Device type: C2
Priority: Medium
---
Req-ID: 4.010
Title: Network topology discovery
Description: Provide a network topology discovery capability (e.g.,
use of topology extraction algorithms to retrieve the network
state) and a monitoring function to collect and expose information
about the network topology.
Source: Use cases "Community Network Applications" and mobile
applications
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: Low, based on the realization complexity
---
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Req-ID: 4.011
Title: Notifications
Description: The device will provide the capability of sending
notifications on critical events and faults.
Source: All use cases
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: Medium for C2; Low for C0 and C1
---
Req-ID: 4.012
Title: Logging
Description: The device will provide the capability of building,
keeping, and allowing retrieval of logs of events (including but
not limited to critical faults and alarms).
Source: Use cases "Industrial Applications", "Building Automation",
and "Infrastructure Monitoring"
Requirement Type: Functional Requirement
Device type: C2
Priority: High for some medical or industrial applications; Medium
otherwise
3.5. Self-Management
Req-ID: 5.001
Title: Self-management -- Self-healing
Description: Enable event-driven and/or periodic self-management
functionality in a device. The device should be able to react in
case of a failure, e.g., by initiating a fully or partly reset and
initiate a self-configuration or management data update as
necessary. A device might be further able to check for failures
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cyclically or on a schedule in order to trigger self-management as
necessary. It is a matter of device design and subject for
discussion how much self-management a C1 device can support.
Failure detection and self-management logic are assumed to be
generally useful for the self-healing of a device.
Source: The requirement generally relates to all use cases in this
document.
Requirement Type: Functional Requirement
Device type: C1 and C2
Priority: High for C2; Medium for C1
3.6. Security and Access Control
Req-ID: 6.001
Title: Authentication of management system and devices
Description: Systems having a management role must be properly
authenticated to the device such that the device can exercise
proper access control and in particular distinguish rightful
management systems from rogue systems. On the other hand, managed
devices must authenticate themselves to systems having a
management role such that management systems can protect
themselves from rogue devices. In certain application scenarios,
it is possible that a large number of devices need to be
(re-)started at about the same time. Protocols and authentication
systems should be designed such that a large number of devices
(re-)starting simultaneously does not negatively impact the device
authentication process.
Source: Basic security requirement for all use cases
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High; Medium for the (re-)start of a large number of
devices
---
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Req-ID: 6.002
Title: Support suitable security bootstrapping mechanisms
Description: Mechanisms should be supported that simplify the
bootstrapping of device that is the discovery of newly deployed
devices in order to provide them with appropriate access control
permissions.
Source: Basic security requirement for all use cases
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High
---
Req-ID: 6.003
Title: Access control on management system and devices
Description: Systems acting in a management role must provide an
access control mechanism that allows the security administrator to
restrict which devices can access the managing system (e.g., using
an access control white list of known devices). On the other
hand, managed constrained devices must provide an access control
mechanism that allows the security administrator to restrict how
systems in a management role can access the device (e.g., no-
access, read-only access, and read-write access).
Source: Basic security requirement for use cases where access
control is essential
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High
---
Req-ID: 6.004
Title: Select cryptographic algorithms that are efficient in both
code space and execution time
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Description: Cryptographic algorithms have a major impact in terms
of both code size and overall execution time. Therefore, it is
necessary to select mandatory to implement cryptographic
algorithms that are reasonable to implement with the available
code space and that have a small impact at runtime. Furthermore,
some wireless technologies (e.g., IEEE 802.15.4) require the
support of certain cryptographic algorithms. It might be useful
to choose algorithms that are likely to be supported in wireless
chipsets for certain wireless technologies.
Source: Generic requirement to reduce the footprint and CPU usage of
a constrained device
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: High; Medium for hardware-supported algorithms
3.7. Energy Management
Req-ID: 7.001
Title: Management of energy resources
Description: Enable managing power resources in the network, e.g.,
reduce the sampling rate of nodes with critical battery and reduce
node transmission power, put nodes to sleep, put single interfaces
to sleep, reject a management job based on available energy or
criteria predefined by the management application (such as
importance levels forcing execution even if the energy level is
low), etc. The device may further implement standard data models
for energy management and expose it through a management protocol
interface, e.g., EMAN MIB modules [RFC7460] and [RFC7461] as well
as other EMAN extensions. It might be necessary to use a subset
of EMAN MIBs for C1 and C2 devices.
Source: Use case "Energy Management"
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: Medium for the use case "Energy Management"; Low otherwise
---
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Req-ID: 7.002
Title: Support of energy-optimized communication protocols
Description: Use an optimized communication protocol to minimize
energy usage for the device (radio) receiver/transmitter, on-air
bandwidth usage (i.e., maximize protocol efficiency), and the
amount of data communication between nodes. Minimizing data
communication implies data aggregation and filtering but also a
compact format for the transferred data.
Source: Use cases "Energy Management" and mobile applications
Requirement Type: Non-functional Requirement
Device type: C2
Priority: Medium
---
Req-ID: 7.003
Title: Support for Layer 2 (L2) energy-aware protocols
Description: The device will support L2 energy-management protocols
(e.g., energy-efficient Ethernet [IEEE802.3az]) and be able to
report on these.
Source: Use case "Energy Management"
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: Medium
---
Req-ID: 7.004
Title: Dying gasp
Description: When energy resources draw below the red-line level,
the device will send a "dying gasp" notification and perform, if
still possible, a graceful shutdown including conservation of
critical device configuration and status information.
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Source: Use case "Energy Management"
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: Medium
3.8. Software Distribution
Req-ID: 8.001
Title: Group-based provisioning
Description: Support group-based provisioning, i.e., firmware update
and configuration management of a large set of constrained devices
with eventual consistency and coordinated reload times. The
device should accept group-based configuration management based on
bulk commands, which aim similar configurations of a large set of
constrained devices of the same type in a given group and which
may share a common data model. Activation of configuration may be
based on preloaded sets of default values.
Source: All use cases
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: Medium
3.9. Traffic Management
Req-ID: 9.001
Title: Congestion avoidance
Description: Support congestion control principles as defined in
[RFC2914], e.g., the ability to avoid congestion by modifying the
device's reporting rate for periodical data (which is usually
redundant) based on the importance and reliability level of the
management data. This functionality is usually controlled by the
managing entity, where the managing entity marks the data as
important or relevant for reliability. However, reducing a
device's reporting rate can also be initiated by a device if it is
able to detect congestion or has insufficient buffer memory.
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Source: Use cases with high reporting rate and traffic, e.g., AMI or
M2M
Requirement Type: Non-functional Requirement
Device type: C1 and C2
Priority: Medium
---
Req-ID: 9.002
Title: Reroute traffic
Description: Provide the ability for network nodes to redirect
traffic from overloaded intermediary nodes in a network to another
path in order to prevent congestion on a central server and in the
primary network.
Source: Use cases with high reporting rate and traffic, e.g., AMI or
M2M
Requirement Type: Non-functional Requirement
Device type: Intermediary entity in the network
Priority: Medium
---
Req-ID: 9.003
Title: Traffic Shaping
Description: Provide the ability to apply traffic-shaping policies
to incoming and outgoing links on an overloaded intermediary node
(as necessary) in order to reduce the amount of traffic in the
network.
Source: Use cases with high reporting rate and traffic, e.g., AMI or
M2M
Requirement Type: Non-functional Requirement
Device type: Intermediary entity in the network
Priority: Medium
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3.10. Transport Layer
Req-ID: 10.001
Title: Scalable transport layer
Description: Enable the use of a scalable transport layer, i.e., not
sensitive to a high rate of incoming client requests, which is
useful for applications requiring frequent access to device data.
Source: Applications with frequent access to the device data
Requirement Type: Non-functional Requirement
Device type: C0, C1 and C2
Priority: Medium
---
Req-ID: 10.002
Title: Reliable unicast transport of messages
Description: Diverse applications need a reliable transport of
messages. The reliability might be achieved based on a transport
protocol such as TCP or can be supported based on message
repetition if an acknowledgment is missing.
Source: Generally, applications benefit from the reliability of the
message transport
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: High
---
Req-ID: 10.003
Title: Best-effort multicast
Description: Provide best-effort multicast of messages, which is
generally useful when devices need to discover a service provided
by a server or many devices need to be configured by a managing
entity at once based on the same data model.
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Source: Use cases where a device needs to discover services as well
as use cases with high amount of devices to manage, which are
hierarchically deployed, e.g., AMI or M2M
Requirement Type: Functional Requirement
Device type: C0, C1, and C2
Priority: Medium
---
Req-ID: 10.004
Title: Secure message transport
Description: Enable secure message transport providing
authentication, data integrity, and confidentiality by using
existing transport-layer technologies with a small footprint such
as TLS/DTLS.
Source: All use cases
Requirement Type: Non-functional Requirements
Device type: C1 and C2
Priority: High
3.11. Implementation Requirements
Req-ID: 11.001
Title: Avoid complex application-layer transactions requiring large
application-layer messages
Description: Complex application-layer transactions tend to require
large memory buffers that are typically not available on C0 or C1
devices and only by limiting functionality on C2 devices.
Furthermore, the failure of a single large transaction requires
repeating the whole transaction. On constrained devices, it is
often more desirable to split a large transaction into a sequence
of smaller transactions that require less resources and allow
making progress using a sequence of smaller steps.
Source: Basic requirement that concerns all use cases with memory
constrained devices
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Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: High
---
Req-ID: 11.002
Title: Avoid reassembly of messages at multiple layers in the
protocol stack
Description: Reassembly of messages at multiple layers in the
protocol stack requires buffers at multiple layers, which leads to
inefficient use of memory resources. This can be avoided by
making sure the application layer, the security layer, the
transport layer, the IPv6 layer, and any adaptation layers are
aware of the limitations of each other such that unnecessary
fragmentation and reassembly can be avoided. In addition, message
size constraints must be announced to protocol peers such that
they can adapt and avoid sending messages that can't be processed
due to resource constraints on the receiving device.
Source: Basic requirement that concerns all use cases with memory
constrained devices
Requirement Type: Non-functional Requirement
Device type: C0, C1, and C2
Priority: High
4. Security Considerations
This document discusses the problem statement and requirements on
networks of constrained devices. Section 1.6 mentions a number of
limitations that could prevent the implementation of strong
cryptographic algorithms. Requirements for security and access
control are listed in Section 3.6.
Often, constrained devices might be deployed in unsafe environments
where attackers can gain physical access to the devices. As a
consequence, it is crucial that devices are robust and tamper
resistant, have no backdoors, do not provide services that are not
essential for the primary function, and properly protect any security
credentials that may be stored on the device (e.g., by using hardware
protection mechanisms). Furthermore, it is important that any
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credentials leaking from a single device do not simplify the attack
on other (similar) devices. In particular, security credentials
should never be shared.
Since constrained devices often have limited computational resources,
care should be taken in choosing efficient but cryptographically
strong cryptographic algorithms. Designers of constrained devices
that have a long expected lifetime need to ensure that cryptographic
algorithms can be updated once devices have been deployed. The
ability to perform secure firmware and software updates is an
important management requirement.
Constrained devices might also generate sensitive data or require the
processing of sensitive data. Therefore, it is an important
requirement to properly protect access to the data in order to
protect the privacy of humans using Internet-enabled devices. For
certain types of data, protection during the transmission over the
network may not be sufficient, and methods should be investigated
that provide protection of data while it is cached or stored (e.g.,
when using a store-and-forward transport mechanism).
5. Informative References
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000,
<http://www.rfc-editor.org/info/rfc2914>.
[RFC2501] Corson, S. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501,
DOI 10.17487/RFC2501, January 1999,
<http://www.rfc-editor.org/info/rfc2501>.
[RFC6632] Ersue, M., Ed. and B. Claise, "An Overview of the IETF
Network Management Standards", RFC 6632,
DOI 10.17487/RFC6632, June 2012,
<http://www.rfc-editor.org/info/rfc6632>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <http://www.rfc-editor.org/info/rfc7102>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
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RFC 7547 Constrained Mgmt. Problem Statement & Reqs. May 2015
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
<http://www.rfc-editor.org/info/rfc4919>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<http://www.rfc-editor.org/info/rfc6550>.
[RFC7460] Chandramouli, M., Claise, B., Schoening, B., Quittek, J.,
and T. Dietz, "Monitoring and Control MIB for Power and
Energy", RFC 7460, DOI 10.17487/RFC7460, March 2015,
<http://www.rfc-editor.org/info/rfc7460>.
[RFC7461] Parello, J., Claise, B., and M. Chandramouli, "Energy
Object Context MIB", RFC 7461, DOI 10.17487/RFC7461, March
2015, <http://www.rfc-editor.org/info/rfc7461>.
[RFC7548] Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A.
Sehgal, "Management of Networks with Constrained Devices:
Use Cases", RFC 7548, DOI 10.17487/RFC7548, May 2015,
<http://www.rfc-editor.org/info/rfc7548>.
[IEEE802.15.4]
IEEE, "Part 15.4: Low-Rate Wireless Personal Area Networks
(LR-WPANs)", IEEE Standard 802.15.4, September 2011,
<https://standards.ieee.org/about/get/802/802.15.html>.
[IEEE802.15.1]
IEEE, "Part 15.1: Wireless medium access control (MAC) and
physical layer (PHY) specifications for wireless personal
area networks (WPANs)", IEEE Standard 802.15.1, June 2005,
<https://standards.ieee.org/about/get/802/802.15.html>.
[IEEE802.3az]
IEEE, "ETHERNET", IEEE Standard 802.3az, 2012-2014,
<https://standards.ieee.org/about/get/802/802.3.html>.
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Acknowledgments
The following reviewed and provided valuable comments during the
creation of this document:
Dominique Barthel, Andy Bierman, Carsten Bormann, Zhen Cao, Benoit
Claise, Hui Deng, Bert Greevenbosch, Joel M. Halpern, Ulrich Herberg,
James Nguyen, Anuj Sehgal, Zach Shelby, Peter van der Stok, Thomas
Watteyne, and Bert Wijnen.
The authors would like to thank the reviewers and the participants on
the Coman and OPSAWG mailing lists for their valuable contributions
and comments.
Juergen Schoenwaelder was partly funded by Flamingo, a Network of
Excellence project (ICT-318488) supported by the European Commission
under its Seventh Framework Programme.
Authors' Addresses
Mehmet Ersue (editor)
Nokia Networks
EMail: mehmet.ersue@nokia.com
Dan Romascanu
Avaya
EMail: dromasca@avaya.com
Juergen Schoenwaelder
Jacobs University Bremen
EMail: j.schoenwaelder@jacobs-university.de
Ulrich Herberg
EMail: ulrich@herberg.name
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