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INFORMATIONAL

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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   [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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