



Internet Engineering Task Force (IETF)                         Y-G. Hong
Request for Comments: 9453                            Daejeon University
Category: Informational                                         C. Gomez
ISSN: 2070-1721                                                      UPC
                                                                 Y. Choi
                                                                    ETRI
                                                                A. Sangi
                                                 Wenzhou-Kean University
                                                          S. Chakrabarti
                                                                 Verizon
                                                          September 2023


    Applicability and Use Cases for IPv6 over Networks of Resource-
                        constrained Nodes (6lo)

Abstract

   This document describes the applicability of IPv6 over constrained-
   node networks (6lo) and provides practical deployment examples.  In
   addition to IEEE Std 802.15.4, various link-layer technologies are
   used as examples, such as ITU-T G.9959 (Z-Wave), Bluetooth Low Energy
   (Bluetooth LE), Digital Enhanced Cordless Telecommunications - Ultra
   Low Energy (DECT-ULE), Master-Slave/Token Passing (MS/TP), Near Field
   Communication (NFC), and Power Line Communication (PLC).  This
   document targets an audience who would like to understand and
   evaluate running end-to-end IPv6 over the constrained-node networks
   for local or Internet connectivity.

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 candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9453.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  6lo Link-Layer Technologies
     2.1.  ITU-T G.9959
     2.2.  Bluetooth LE
     2.3.  DECT-ULE
     2.4.  MS/TP
     2.5.  NFC
     2.6.  PLC
     2.7.  Comparison between 6lo Link-Layer Technologies
   3.  Guidelines for Adopting an IPv6 Stack (6lo)
   4.  6lo Deployment Examples
     4.1.  Wi-SUN Usage of 6lo in Network Layer
     4.2.  Thread Usage of 6lo in the Network Layer
     4.3.  G3-PLC Usage of 6lo in Network Layer
     4.4.  Netricity Usage of 6lo in the Network Layer
   5.  6lo Use-Case Examples
     5.1.  Use Case of ITU-T G.9959: Smart Home
     5.2.  Use Case of Bluetooth LE: Smartphone-Based Interaction
     5.3.  Use Case of DECT-ULE: Smart Home
     5.4.  Use Case of MS/TP: Building Automation Networks
     5.5.  Use Case of NFC: Alternative Secure Transfer
     5.6.  Use Case of PLC: Smart Grid
   6.  IANA Considerations
   7.  Security Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Appendix A.  Design Space Dimensions for 6lo Deployment
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Running IPv6 on constrained-node networks presents challenges due to
   the characteristics of these networks, such as small packet size, low
   power, low bandwidth, and large number of devices, among others
   [RFC4919] [RFC7228].  For example, many IEEE Std 802.15.4 variants
   [IEEE-802.15.4] exhibit a frame size of 127 octets, whereas IPv6
   requires its underlying layer to support an MTU of 1280 bytes.
   Furthermore, those IEEE Std 802.15.4 variants do not offer
   fragmentation and reassembly functionality.  (It is noted that IEEE
   Std 802.15.9-2021 provides a multiplexing and fragmentation layer for
   the IEEE Std 802.15.4 [IEEE-802.15.9].)  Therefore, an appropriate
   adaptation layer supporting fragmentation and reassembly must be
   provided below IPv6.  Also, the limited IEEE Std 802.15.4 frame size
   and low energy consumption requirements motivate the need for packet
   header compression.  The IETF IPv6 over Low-Power Wireless Personal
   Area Network (6LoWPAN) Working Group published a suite of
   specifications that provides an adaptation layer to support IPv6 over
   IEEE Std 802.15.4 comprising the following functionalities:

   *  fragmentation and reassembly, address autoconfiguration, and a
      frame format [RFC4944]

   *  IPv6 (and UDP) header compression [RFC6282]

   *  Neighbor Discovery Optimization for 6LoWPAN [RFC6775] [RFC8505]

   As Internet of Things (IoT) services become more popular, the IETF
   has defined adaptation layer functionality to support IPv6 over
   various link-layer technologies other than IEEE Std 802.15.4, such as
   Bluetooth Low Energy (Bluetooth LE), ITU-T G.9959 (Z-Wave), Digital
   Enhanced Cordless Telecommunications - Ultra Low Energy (DECT-ULE),
   Master-Slave/Token Passing (MS/TP), Near Field Communication (NFC),
   and Power Line Communication (PLC).  The 6lo adaptation layers use a
   variation of the 6LoWPAN stack applied to each particular link-layer
   technology.

   The 6LoWPAN Working Group produced the document entitled "Design and
   Application Spaces for IPv6 over Low-Power Wireless Personal Area
   Networks (6LoWPANs)" [RFC6568], which describes potential application
   scenarios and use cases for LoWPANs.  The present document aims to
   provide guidance to an audience that is new to the IPv6 over
   constrained-node networks (6lo) concept and want to assess its
   application to the constrained-node network of their interest.  This
   6lo applicability document describes a few sets of practical 6lo
   deployment scenarios and use-case examples.  In addition, it
   considers various network design space dimensions, such as
   Deployment, Network Size, Power Source, Connectivity, Multi-Hop
   Communication, Traffic pattern, Mobility, and QoS requirements (see
   Appendix A).

   This document provides the applicability and use cases of 6lo,
   considering the following aspects:

   *  Various IoT-related wired or wireless link-layer technologies
      providing practical information about such technologies.

   *  General guidelines on how the 6LoWPAN stack can be modified for a
      given L2 technology.

   *  Various 6lo use cases and practical deployment examples.

   Note that the use of "master" and "slave" have been retained in this
   document to align with use within the industry (e.g., [TIA-485-A] and
   [BACnet]).

2.  6lo Link-Layer Technologies

2.1.  ITU-T G.9959

   The ITU-T G.9959 Recommendation [G.9959] targets LoWPANs and defines
   physical-layer and link-layer functionality.  Physical layers of 9.6
   kbit/s, 40 kbit/s, and 100 kbit/s are supported.
   [G.9959] defines how a unique 32-bit HomeID network identifier is
   assigned by a network controller and how an 8-bit NodeID host
   identifier is allocated to each node.  NodeIDs are unique within the
   network identified by the HomeID.  The G.9959 HomeID represents an
   IPv6 subnet that is identified by one or more IPv6 prefixes
   [RFC7428].  ITU-T G.9959 can be used for smart home applications, and
   the transmission range is 100 meters per hop.

2.2.  Bluetooth LE

   Bluetooth LE was introduced in Bluetooth 4.0, enhanced in Bluetooth
   4.1, and developed further in successive versions.  The data rate of
   Bluetooth LE is 125 kb/s, 500 kb/s, 1 Mb/s, 2 Mb/s; and max
   transmission range is around 100 meters (outdoors).  The Bluetooth
   Special Interest Group (Bluetooth SIG) has also published the
   Internet Protocol Support Profile (IPSP).  The IPSP enables discovery
   of IP-enabled devices and establishment of link-layer connections for
   transporting IPv6 packets.  IPv6 over Bluetooth LE is dependent on
   both Bluetooth 4.1 [BTCorev5.4] and IPSP 1.0 [IPSP] or newer.

   Many devices such as mobile phones, notebooks, tablets, and other
   handheld computing devices that support Bluetooth 4.0 or subsequent
   versions also support the low-energy variant of Bluetooth.  Bluetooth
   LE is also being included in many different types of accessories that
   collaborate with mobile devices.  An example of a use case for a
   Bluetooth LE accessory is a heart rate monitor that sends data via
   the mobile phone to a server on the Internet [RFC7668].  A typical
   usage of Bluetooth LE is smartphone-based interaction with
   constrained devices.  Bluetooth LE was originally designed to enable
   star topology networks.  However, recent Bluetooth versions support
   the formation of extended topologies, and IPv6 support for mesh
   networks of Bluetooth LE devices has been developed [RFC9159].

2.3.  DECT-ULE

   DECT-ULE is a low-power air interface technology that is designed to
   support both circuit-switched services, such as voice communication,
   and packet-mode data services at modest data rate [TS102.939-1]
   [TS102.939-2].

   The DECT-ULE protocol stack consists of the physical layer operating
   at frequencies in the dedicated 1880 - 1920 MHz frequency band
   depending on the region and uses a symbol rate of 1.152 Mbps.  Radio
   bearers are allocated by use of Frequency-Division Multiplex (FDMA),
   Time-Division Multiple Access (TDMA), and Time-Division Duplex (TDD)
   techniques.  The coverage distance is from 70 meters (indoors) to 600
   meters (outdoors).

   In its generic network topology, DECT is defined as a cellular
   network technology.  However, the most common configuration is a star
   network with a single Fixed Part (FP) defining the network with a
   number of Portable Parts (PPs) attached.  The Medium Access Control
   (MAC) layer supports classical DECT as this is used for services like
   discovery, pairing, and security features.  All these features have
   been reused from DECT.

   The DECT-ULE device can switch to the ULE mode of operation,
   utilizing the new Ultra Low Energy (ULE) MAC layer features.  The
   DECT-ULE Data Link Control (DLC) provides multiplexing as well as
   segmentation and re-assembly for larger packets from layers above.
   The DECT-ULE layer also implements per-message authentication and
   encryption.  The DLC layer ensures packet integrity and preserves
   packet order, but delivery is based on best effort.

   The current DECT-ULE MAC layer standard supports low bandwidth data
   broadcast.  However, the usage of this broadcast service has not yet
   been standardized for higher layers [RFC8105].  DECT-ULE can be used
   for smart metering in a home.

2.4.  MS/TP

   MS/TP is a MAC protocol for the RS-485 [TIA-485-A] physical layer and
   is used primarily in building automation networks.

   An MS/TP device is typically based on a low-cost microcontroller with
   limited processing power and memory.  These constraints, together
   with low data rates and a small MAC address space, are similar to
   those faced in 6LoWPAN networks.  MS/TP differs significantly from
   6LoWPAN in at least three respects:

   a.  MS/TP devices are typically mains powered.

   b.  All MS/TP devices on a segment can communicate directly, so there
       are no hidden node issues or mesh routing issues.

   c.  The latest MS/TP specification provides support for large
       payloads, eliminating the need for fragmentation and reassembly
       below IPv6.

   MS/TP is designed to enable multidrop networks over shielded twisted
   pair wiring.  It can support network segments up to 1000 meters in
   length at a data rate of 115.2 kbit/s or segments up to 1200 meters
   in length at lower bit rates.  An MS/TP interface requires only a
   Universal Asynchronous Receiver Transmitter (UART), an RS-485
   [TIA-485-A] transceiver with a driver that can be disabled, and a 5
   ms resolution timer.  The MS/TP MAC is typically implemented in
   software.

   Because of its long range (~1 km), MS/TP can be used to connect
   remote devices (such as district heating controllers) to the nearest
   building control infrastructure over a single link [RFC8163].

2.5.  NFC

   NFC technology enables secure interactions between electronic
   devices, allowing consumers to perform contactless transactions,
   access digital content, and connect electronic devices with a single
   touch [LLCP-1.4].  The distance between sender and receiver is 10 cm
   or less.  NFC complements many popular consumer-level wireless
   technologies by utilizing the key elements in existing standards for
   contactless card technology.

   Extending the capability of contactless card technology, NFC also
   enables devices to share information at a distance that is less than
   10 cm with a maximum communication speed of 424 kbps.  Users can
   share business cards, make transactions, access information from a
   smart poster, or provide credentials for access control systems with
   a simple touch.

   NFC's bidirectional communication ability is suitable for
   establishing connections with other technologies by the simplicity of
   touch.  In addition to the easy connection and quick transactions,
   simple data sharing is available [RFC9428].  NFC can be used for
   secure transfer services where privacy is important.

2.6.  PLC

   PLC is a data transmission technique that utilizes power conductors
   as the medium [RFC9354].  Unlike other dedicated communication
   infrastructure, power conductors are widely available indoors and
   outdoors.  Moreover, wired technologies cause less interference to
   the radio medium than wireless technologies and are more reliable
   than their wireless counterparts.

   The table below shows some available open standards defining PLC.

   +=============+=================+============+===========+==========+
   | PLC Systems | Frequency Range |    Type    |    Data   | Distance |
   |             |                 |            |    Rate   |          |
   +=============+=================+============+===========+==========+
   |  IEEE 1901  |    < 100 MHz    | Broadband  |    200    |  1000 m  |
   |             |                 |            |    Mbps   |          |
   +-------------+-----------------+------------+-----------+----------+
   | IEEE 1901.1 |     < 12 MHz    |  PLC-IoT   |     10    |  2000 m  |
   |             |                 |            |    Mbps   |          |
   +-------------+-----------------+------------+-----------+----------+
   | IEEE 1901.2 |    < 500 kHz    | Narrowband |    200    |  3000 m  |
   |             |                 |            |    kbps   |          |
   +-------------+-----------------+------------+-----------+----------+
   |    G3-PLC   |    < 500 kHz    | Narrowband |    234    |  3000 m  |
   |             |                 |            |    kbps   |          |
   +-------------+-----------------+------------+-----------+----------+

               Table 1: Some Available Open Standards in PLC

   IEEE Std 1901 [IEEE-1901] defines a broadband variant of PLC, but it
   is only effective within short range.  This standard addresses the
   requirements of high data rates such as the Internet, HDTV, audio,
   and gaming.

   IEEE Std 1901.1 [IEEE-1901.1] defines a medium frequency band (less
   than 12 MHz) broadband PLC technology for smart grid applications
   based on Orthogonal Frequency Division Multiplexing (OFDM).  By
   achieving an extended communication range with medium speeds, this
   standard can be applied in both indoor and outdoor scenarios, such as
   Advanced Metering Infrastructure (AMI), street lighting, electric
   vehicle charging, and a smart city.

   IEEE Std 1901.2 [IEEE-1901.2] defines a narrowband variant of PLC
   with a lower data rate but a significantly higher transmission range
   that could be used in an indoor or even an outdoor environment.  A
   typical use case of PLC is a smart grid.

   G3-PLC [G3-PLC] is a narrowband PLC technology that is based on the
   ITU-T G.9903 Recommendation [G.9903].  The ITU-T G.9903
   Recommendation contains the physical layer and data link-layer
   specification for the G3-PLC narrowband OFDM power line communication
   transceivers, for communications via alternating current and direct
   current electric power lines over frequency bands below 500 kHz.

2.7.  Comparison between 6lo Link-Layer Technologies

   In the above subsections, various 6lo link-layer technologies are
   described.  The following table shows the dominant parameters of each
   use case corresponding to the 6lo link-layer technology.

   +=========+========+===========+========+========+========+=========+
   |         | Z-Wave | Bluetooth |DECT-ULE| MS/TP  |  NFC   |   PLC   |
   |         |        |     LE    |        |        |        |         |
   +=========+========+===========+========+========+========+=========+
   |  Usage  |  Home  |  Interact | Meter  |Building| Secure |  Smart  |
   |         | Autom. |  w/ Smart |Reading | Autom. |Transfer|   Grid  |
   |         |        |   Phone   |        |        |        |         |
   +=========+--------+-----------+--------+--------+--------+---------+
   | Topology|L2-mesh |   Star &  | Star,  | MS/TP, |  P2P,  |Star Tree|
   |    &    |   or   |    Mesh   |No mesh |No mesh |L2-mesh |   Mesh  |
   |  Subnet |L3-mesh |           |        |        |        |         |
   +=========+--------+-----------+--------+--------+--------+---------+
   | Mobility|   No   |    Yes    |   No   |   No   |  Yes   |    No   |
   |   Req.  |        |           |        |        |        |         |
   +=========+--------+-----------+--------+--------+--------+---------+
   |Buffering|  Yes   |    Yes    |  Yes   |  Yes   |  Yes   |   Yes   |
   |   Req.  |        |           |        |        |        |         |
   +=========+--------+-----------+--------+--------+--------+---------+
   | Latency,|  Yes   |    Yes    |  Yes   |  Yes   |  Yes   |   Yes   |
   | QoS Req.|        |           |        |        |        |         |
   +=========+--------+-----------+--------+--------+--------+---------+
   | Frequent|   No   |     No    |   No   |  Yes   |   No   |    No   |
   | Tx Req. |        |           |        |        |        |         |
   +=========+--------+-----------+--------+--------+--------+---------+
   |   RFC   |RFC 7428|  RFC 7668 |RFC 8105|RFC 8163|RFC 9428| RFC 9354|
   |         |        |  RFC 9159 |        |        |        |         |
   +=========+--------+-----------+--------+--------+--------+---------+

          Table 2: Comparison between 6lo Link-Layer Technologies

3.  Guidelines for Adopting an IPv6 Stack (6lo)

   6lo aims to reuse and/or adapt existing 6LoWPAN functionality in
   order to efficiently support IPv6 over a variety of IoT L2
   technologies.  The following guideline targets new candidate-
   constrained L2 technologies that may be considered for running a
   modified 6LoWPAN stack on top.  The modification of the 6LoWPAN stack
   should be based on the following:

   Addressing Model:
      The addressing model determines whether the device is capable of
      forming IPv6 link-local and global addresses, and what is the best
      way to derive the IPv6 addresses for the constrained L2 devices.
      IPv6 addresses that are derived from an L2 address are specified
      in [RFC4944], but there are implications for privacy.  The reason
      is that the L2 address in 6lo link-layer technologies is a little
      short, and devices can become vulnerable to the various threats.
      For global usage, a unique IPv6 address must be derived using an
      assigned prefix and a unique interface ID.  [RFC8065] provides
      such guidelines.  For MAC-derived IPv6 addresses, refer to
      [RFC8163] for mapping examples.  Broadcast and multicast support
      are dependent on the L2 networks.  Most low-power L2
      implementations map multicast to broadcast networks.  So care must
      be taken in the design for when to use broadcast, trying to stick
      to unicast messaging whenever possible.

   MTU Considerations:
      The deployment should consider packet maximum transmission unit
      (MTU) needs over the link layer and should consider if
      fragmentation and reassembly of packets are needed at the 6LoWPAN
      layer.  For example, if the link layer supports fragmentation and
      reassembly of packets, then the 6LoWPAN layer may not need to
      support fragmentation and reassembly.  In fact, for greatest
      efficiency, choosing a low-power link layer that can carry
      unfragmented application packets would be optimal for packet
      transmission if the deployment can afford it.  Please refer to 6lo
      RFCs [RFC7668], [RFC8163], and [RFC8105] for example guidance.

   Mesh or L3 Routing:
      6LoWPAN specifications provide mechanisms to support mesh routing
      at L2, a configuration called "mesh-under" [RFC6606].  It is also
      possible to use an L3 routing protocol in 6LoWPAN, an approach
      known as "route-over".  [RFC6550] defines RPL, an L3 routing
      protocol for low-power and lossy networks using directed acyclic
      graphs. 6LoWPAN is routing-protocol-agnostic and does not specify
      any particular L2 or L3 routing protocol to use with a 6LoWPAN
      stack.

   Address Assignment:
      6LoWPAN developed a new version of IPv6 Neighbor Discovery
      [RFC4861] [RFC4862]. 6LoWPAN Neighbor Discovery [RFC6775]
      [RFC8505] inherits from IPv6 Neighbor Discovery for mechanisms
      such as Stateless Address Autoconfiguration (SLAAC) and Neighbor
      Unreachability Detection (NUD).  A 6LoWPAN node is also expected
      to be an IPv6 host per [RFC8200], which means it should ignore
      consumed routing headers and hop-by-hop options.  When operating
      in an RPL network [RFC6550], it is also beneficial to support IP-
      in-IP encapsulation [RFC9008].  The 6LoWPAN node should also
      support the registration extensions defined in [RFC8505] and use
      the mechanism as the default Neighbor Discovery method.  It is the
      responsibility of the deployment to ensure unique global IPv6
      addresses for Internet connectivity.  For local-only connectivity,
      IPv6 Unique Local Address (ULA) may be used.  [RFC6775] and
      [RFC8505] specify the 6LoWPAN Border Router (6LBR), which is
      responsible for prefix assignment to the 6LoWPAN network.  A 6LBR
      can be connected to the Internet or to an enterprise network via
      one of the interfaces.  Please refer to [RFC7668] and [RFC8105]
      for examples of address assignment considerations.  In addition,
      privacy considerations in [RFC8065] must be consulted for
      applicability.  In certain scenarios, the deployment may not
      support IPv6 address autoconfiguration due to regulatory and
      business reasons and may choose to offer a separate address
      assignment service.  Address-Protected Neighbor Discovery
      [RFC8928] enables source address validation [RFC6620] and protects
      the address ownership against impersonation attacks.

   Broadcast Avoidance:
      6LoWPAN Neighbor Discovery aims to reduce the amount of multicast
      traffic of classic Neighbor Discovery, since IP-level multicast
      translates into L2 broadcast in many L2 technologies [RFC6775].
      6LoWPAN Neighbor Discovery relies on a proactive registration to
      avoid the use of multicast for address resolution.  It also uses a
      unicast method for Duplicate Address Detection (DAD) and avoids
      multicast lookups from all nodes by using non-onlink prefixes.
      Router Advertisements (RAs) are also sent in unicast, in response
      to Router Solicitations (RSs).

   Host-to-Router Interface:
      6lo has defined registration extensions for 6LoWPAN Neighbor
      Discovery [RFC8505].  This effort provides a host-to-router
      interface by which a host can request its router to ensure
      reachability for the address registered with the router.  Note
      that functionality has been developed to ensure that such a host
      can benefit from routing services in a RPL network [RFC9010].

   Proxy Neighbor Discovery:
      Further functionality also allows a device (e.g., an energy-
      constrained device that needs to sleep most of the time) to
      request proxy Neighbor Discovery services from a 6LoWPAN Backbone
      Router (6BBR) [RFC8505] [RFC8929].  The latter RFC federates a
      number of links into a multi-link subnet.

   Header Compression:
      IPv6 header compression [RFC6282] is a vital part of IPv6 over
      low-power communication.  Examples of header compression over
      different link-layer specifications are found in [RFC7668],
      [RFC8163], and [RFC8105].  A generic header compression technique
      is specified in [RFC7400].  For 6LoWPAN networks where RPL is the
      routing protocol, there are 6LoWPAN header compression extensions
      that allow compressing the RPL artifacts used when forwarding
      packets in the route-over mesh [RFC8138] [RFC9035].

   Security and Encryption:
      Though 6LoWPAN basic specifications do not address security at the
      network layer, the assumption is that L2 security must be present.
      Nevertheless, care must be taken since specific L2 technologies
      may exhibit security gaps.  Typically, 6lo L2 technologies (see
      Section 2) offer security properties such as confidentiality and/
      or message authentication.  In addition, end-to-end security is
      highly desirable.  Protocols such as DTLS/TLS, as well as Object
      Security, are being used in the constrained-node network domain
      [SEC-PROT-COMP].  The relevant IETF working groups should be
      consulted for application and transport level security.  The IETF
      has worked on address authentication [RFC8928], and secure
      bootstrapping is also being discussed in the IETF.  However, there
      may be other security mechanisms available in a deployment through
      other standards, such as hardware-level security or certificates
      for the initial booting process.  In order to use security
      mechanisms, the implementation needs to be able to afford it in
      terms of processing capabilities and energy consumption.

   Additional Processing:
      [RFC8066] defines guidelines for ESC dispatch octets used in the
      6LoWPAN header.  The ESC type is defined to use additional
      dispatch octets in the 6LoWPAN header.  An implementation may take
      advantage of the ESC header to offer a deployment-specific
      processing of 6LoWPAN packets.

4.  6lo Deployment Examples

4.1.  Wi-SUN Usage of 6lo in Network Layer

   Wireless Smart Ubiquitous Network (Wi-SUN) [Wi-SUN] is a technology
   based on IEEE Std 802.15.4g [IEEE-802.15.4].  Wi-SUN networks support
   star and mesh topologies as well as hybrid star/mesh deployments, but
   these are typically laid out in a mesh topology where each node
   relays data for the network to provide network connectivity.  Wi-SUN
   networks are deployed on both grid-powered and battery-operated
   devices [RFC8376].

   The main application domains using Wi-SUN are smart utility and smart
   city networks.  The Wi-SUN Alliance Field Area Network (FAN)
   primarily covers outdoor networks.  The Wi-SUN FAN specification
   defines an IPv6-based protocol suite that includes TCP/UDP, IPv6, 6lo
   adaptation layer, DHCPv6 for IPv6 address management, RPL, and
   ICMPv6.

4.2.  Thread Usage of 6lo in the Network Layer

   Thread is an IPv6-based networking protocol stack built on open
   standards, designed for smart home environments, and based on low-
   power IEEE Std 802.15.4 mesh networks.  Because of its IPv6
   foundation, Thread can support existing popular application layers
   and IoT platforms, provide end-to-end security, ease development, and
   enable flexible designs [Thread].

   The Thread specification uses the IEEE Std 802.15.4 [IEEE-802.15.4]
   physical and MAC layers operating at 250 kbps in the 2.4 GHz band.

   Thread devices use 6LoWPAN, as defined in [RFC4944] and [RFC6282],
   for transmission of IPv6 packets over IEEE Std 802.15.4 networks.
   Header compression is used within the Thread network, and devices
   transmitting messages compress the IPv6 header to minimize the size
   of the transmitted packet.  The mesh header is supported for link-
   layer (i.e., mesh-under) forwarding.  The mesh header as used in
   Thread also allows efficient end-to-end fragmentation of messages
   rather than the hop-by-hop fragmentation specified in [RFC4944].
   Mesh-under routing in Thread is based on a distance vector protocol
   in a full mesh topology.

4.3.  G3-PLC Usage of 6lo in Network Layer

   G3-PLC [G3-PLC] is a narrowband PLC technology that is based on the
   ITU-T G.9903 Recommendation [G.9903].  G3-PLC supports multi-hop mesh
   network topology and facilitates highly reliable, long-range
   communication.  With the abilities to support IPv6 and to cross
   transformers, G3-PLC is regarded as one of the next-generation
   narrowband PLC technologies.  G3-PLC has got massive deployments over
   several countries, e.g., Japan and France.

   The main application domains using G3-PLC are smart grid and smart
   cities.  This includes, but is not limited to, the following
   applications:

   *  smart metering

   *  vehicle-to-grid communication

   *  demand response

   *  distribution automation

   *  home/building energy management systems

   *  smart street lighting

   *  AMI backbone network

   *  wind/solar farm monitoring

   In the G3-PLC specification, the 6lo adaption layer utilizes the
   6LoWPAN functions (e.g., header compression, fragmentation, and
   reassembly).  However, due to the different characteristics of the
   PLC media, the 6LoWPAN adaptation layer cannot perfectly fulfill the
   requirements [RFC9354].  The ESC dispatch type is used in the G3-PLC
   to provide fundamental mesh routing and bootstrapping functionalities
   [RFC8066].

4.4.  Netricity Usage of 6lo in the Network Layer

   The Netricity program in the HomePlug Powerline Alliance [NETRICITY]
   promotes the adoption of products built on the IEEE Std 1901.2 low-
   frequency narrowband PLC standard [IEEE-1901.2], which provides for
   urban and long-distance communications and propagation through
   transformers of the distribution network using frequencies below 500
   kHz.  The technology also addresses requirements that assure
   communication privacy and secure networks.

   The main application domains using Netricity are smart grid and smart
   cities.  This includes, but is not limited to, the following
   applications:

   *  utility grid modernization

   *  distribution automation

   *  meter-to-grid connectivity

   *  microgrids

   *  grid sensor communications

   *  load control

   *  demand response

   *  net metering

   *  street lighting control

   *  photovoltaic panel monitoring

   The Netricity system architecture is based on the physical and MAC
   layers of IEEE Std 1901.2.  Regarding the 6lo adaptation layer and an
   IPv6 network layer, Netricity utilizes IPv6 protocol suite including
   6lo/6LoWPAN header compression, DHCPv6 for IP address management, RPL
   routing protocol, ICMPv6, and unicast/multicast forwarding.  Note
   that the L3 routing in Netricity uses RPL in non-storing mode with
   the MRHOF (Minimum Rank with Hysteresis Objective Function) based on
   their own defined Estimated Transmission Time (ETT) metric.

5.  6lo Use-Case Examples

   As IPv6 stacks for constrained-node networks use a variation of the
   6LoWPAN stack applied to each particular link-layer technology,
   various 6lo use cases can be provided.  In this section, various 6lo
   use cases, which are based on different link-layer technologies, are
   described.

5.1.  Use Case of ITU-T G.9959: Smart Home

   Z-Wave is one of the main technologies that may be used to enable
   smart home applications.  Born as a proprietary technology, Z-Wave
   was specifically designed for this particular use case.  Recently,
   the Z-Wave radio interface (physical and MAC layers) has been
   standardized as the ITU-T G.9959 specification [G.9959].

   Example: Use of ITU-T G.9959 for Home Automation

      A variety of home devices (e.g., light dimmers/switches, plugs,
      thermostats, blinds/curtains, and remote controls) are augmented
      with ITU-T G.9959 interfaces.  A user may turn home appliances on
      and off, or the user may control them by pressing a wall switch or
      a button on a remote control.  Scenes may be programmed so that
      the home devices adopt a specific configuration after a given
      event.  Sensors may also periodically send measurements of several
      parameters (e.g., gas presence, light, temperature, humidity),
      which are collected at a sink device, or may generate commands for
      actuators (e.g., a smoke sensor may send an alarm message to a
      safety system).

   The devices involved in the described scenario are nodes of a network
   that follows the mesh topology, which is suitable for path diversity
   to face indoor multipath propagation issues.  The multi-hop paradigm
   allows end-to-end connectivity when direct range communication is not
   possible.

5.2.  Use Case of Bluetooth LE: Smartphone-Based Interaction

   The key feature behind the current high Bluetooth LE momentum is its
   support in a large majority of smartphones in the market.  Bluetooth
   LE can be used to allow interaction between a smartphone and
   surrounding sensors or actuators.  Furthermore, Bluetooth LE is also
   the main radio interface currently available in wearables.  Since a
   smartphone typically has several radio interfaces that provide
   Internet access, such as Wi-Fi or cellular, a smartphone can act as a
   gateway for nearby devices, such as sensors, actuators, or wearables.
   Bluetooth LE may be used in several domains, including healthcare,
   sports/wellness, and home automation.

   Example: Use of a Body Area Network Based on Bluetooth LE for Fitness

      A person wears a smartwatch for fitness purposes.  The smartwatch
      has several sensors (e.g., heart rate, accelerometer, gyrometer,
      GPS, and temperature), a display, and a Bluetooth LE radio
      interface.  The smartwatch can show fitness-related statistics on
      its display.  However, when a paired smartphone is in range of the
      smartwatch, the latter can report almost real-time measurements of
      its sensors to the smartphone, which can forward the data to a
      cloud service on the Internet. 6lo enables this use case by
      providing efficient end-to-end IPv6 support.  In addition, the
      smartwatch can receive notifications (e.g., alarm signals) from
      the cloud service via the smartphone.  On the other hand, the
      smartphone may locally generate messages for the smartwatch, such
      as e-mail reception or calendar notifications.

   The functionality supported by the smartwatch may be complemented by
   other devices, such as other on-body sensors, wireless headsets, or
   head-mounted displays.  All such devices may connect to the
   smartphone, creating a star topology network whereby the smartphone
   is the central component.  Support for extended network topologies
   (e.g., mesh networks) is being developed as of the writing of this
   document.

5.3.  Use Case of DECT-ULE: Smart Home

   DECT is a technology widely used for wireless telephone
   communications in residential scenarios.  Since DECT-ULE is a low-
   power variant of DECT, DECT-ULE can be used to connect constrained
   devices (such as sensors and actuators) to a Fixed Part (FP), a
   device that typically acts as a base station for wireless telephones.
   In this case, additionally, the FP must have a data network
   connection.  Therefore, DECT-ULE is especially suitable for the
   connected home space in application areas such as home automation,
   smart metering, safety, and healthcare.  Since DECT-ULE uses
   dedicated bandwidth, it avoids this coexistence issues suffered by
   other technologies that use, for example, Industrial, Scientific, and
   Medical (ISM) frequency bands.

   Example: Use of DECT-ULE for Smart Metering

      The smart electricity meter of a home is equipped with a DECT-ULE
      transceiver.  This device is in the coverage range of the FP of
      the home.  The FP can act as a router connected to the Internet.
      This way, the smart meter can transmit electricity consumption
      readings through the DECT-ULE link with the FP, and the latter can
      forward such readings to the utility company using Wide Area
      Network (WAN) links.  The meter can also receive queries from the
      utility company or from an advanced energy control system
      controlled by the user, which may also be connected to the FP via
      DECT-ULE.

5.4.  Use Case of MS/TP: Building Automation Networks

   The primary use case for IPv6 over MS/TP (6LoBAC) is in building
   automation networks.  [BACnet] is the open, international standard
   protocol for building automation, and MS/TP is defined in [BACnet]
   Clause 9.  MS/TP was designed to be a low-cost, multi-drop field bus
   to interconnect the most numerous elements (sensors and actuators) of
   a building automation network to their controllers.  A key aspect of
   6LoBAC is that it is designed to co-exist with BACnet MS/TP on the
   same link, easing the ultimate transition of some BACnet networks to
   fundamental end-to-end IPv6 transport protocols.  New applications
   for 6LoBAC may be found in other domains where low cost, long
   distance, and low latency are required.  Note that BACnet comprises
   various networking solutions other than MS/TP, including the recently
   emerged BACnet IP.  However, the latter is based on high-speed
   Ethernet infrastructure, and it is outside of the constrained-node
   network scope.

   Example: Use of 6LoBAC in Building Automation Networks

      The majority of installations for MS/TP are for "terminal" or
      "unitary" controllers, i.e., single zone or room controllers that
      may connect to HVAC or other controls such as lighting or blinds.
      The economics of daisy chaining a single twisted pair between
      multiple devices is often preferred over home-run, Cat-5-style
      wiring.

   A multi-zone controller might be implemented as an IP router between
   a classical Ethernet link and several 6LoBAC links, fanning out to
   multiple terminal controllers.

   The superior distance capabilities of MS/TP (~1 km) compared to other
   6lo media may suggest its use in applications to connect remote
   devices to the nearest building infrastructure.  For example, remote
   pumping or measuring stations with moderate bandwidth requirements
   can benefit from the low-cost and robust capabilities of MS/TP over
   other wired technologies such as DSL, without the line-of-sight
   restrictions or hop-by-hop latency of many low-cost wireless
   solutions.

5.5.  Use Case of NFC: Alternative Secure Transfer

   In different applications, a variety of secured data can be handled
   and transferred.  Depending on the security level of the data,
   different transfer methods can be alternatively selected.

   Example: Use of NFC for Secure Transfer in Healthcare Services with
   Tele-Assistance

      An older adult who lives alone wears one to several wearable 6lo
      devices to measure heartbeat, pulse rate, etc.  Other 6lo devices
      are densely installed at home for movement detection.  A 6LBR at
      home will send the sensed information to a connected healthcare
      center.  Portable base stations with displays may be used to check
      the data at home, as well.  Data is gathered in both periodic and
      event-driven fashion.  In this application, event-driven data can
      be very time critical.  In addition, privacy becomes a serious
      issue in this case, as the sensed data is very personal.

   While the older adult is provided audio and video healthcare services
   by a tele-assistance based on cellular connections, the older adult
   can alternatively use NFC connections to transfer the personal sensed
   data to the tele-assistance.  Hackers can overhear the data based on
   the cellular connection, but they cannot gather the personal data
   over the NFC connection.

5.6.  Use Case of PLC: Smart Grid

   The smart grid concept is based on deploying numerous operational and
   energy measuring subsystems in an electricity grid system.  It
   comprises multiple administrative levels and segments to provide
   connectivity among these numerous components.  Last mile connectivity
   is established over the Low-Voltage segment, whereas connectivity
   over electricity distribution takes place over the High-Voltage
   segment.  Smart grid systems include AMI, Demand Response, Home
   Energy Management System, and Wide Area Situational Awareness (WASA),
   among others.

   Although other wired and wireless technologies are also used in a
   smart grid, PLC benefits from reliable data communication over
   electrical power lines that are already present, and the deployment
   cost can be comparable to wireless technologies.  The 6lo-related
   scenarios for PLC mainly lie in the Low-Voltage PLC networks with
   most applications in the area of advanced metering infrastructure,
   vehicle-to-grid communications, in-home energy management, and smart
   street lighting.

   Example: Use of PLC for AMI

      Household electricity meters transmit time-based data of electric
      power consumption through PLC.  Data concentrators receive all the
      meter data in their corresponding living districts and send them
      to the Meter Data Management System through a WAN network (e.g.,
      Medium-Voltage PLC, Ethernet, or General Packet Radio Service
      (GPRS)) for storage and analysis.  Two-way communications are
      enabled, which means smart meters can perform actions like
      notification of electricity charges according to the commands from
      the utility company.

   With the existing power line infrastructure as a communication
   medium, the cost of building up the PLC network is naturally saved,
   and more importantly, labor and operational costs can be minimized
   from a long-term perspective.  Furthermore, this AMI application
   speeds up electricity charging, reduces losses by restraining power
   theft, and helps to manage the health of the grid based on line loss
   analysis.

   Example: Use of PLC (IEEE Std 1901.1) for WASA in a Smart Grid

      Many subsystems of a smart grid require low data rates, and
      narrowband variants (e.g., IEEE Std 1901.1) of PLC fulfill such
      requirements.  Recently, more complex scenarios are emerging that
      require higher data rates.

   A WASA subsystem is an appropriate example that collects large
   amounts of information about the current state of the grid over a
   wide area from electric substations as well as power transmission
   lines.  The collected feedback is used for monitoring, controlling,
   and protecting all the subsystems.

6.  IANA Considerations

   This document has no IANA actions.

7.  Security Considerations

   This document does not create security concerns in addition to those
   described in the Security Considerations sections of the 6lo
   adaptation layers considered in this document [RFC7428], [RFC7668],
   [RFC8105], [RFC8163], [RFC9159], [RFC9428], and [RFC9354].

   Neighbor Discovery in 6lo links may be susceptible to threats as
   detailed in [RFC3756].  Mesh routing is expected to be common in some
   6lo networks, such as ITU-T G.9959 networks, Bluetooth LE mesh
   networks, and PLC networks.  This implies additional threats due to
   ad hoc routing as per [KW03].  Most of the L2 technologies considered
   in this document (i.e., ITU-T G.9959, Bluetooth LE, DECT-ULE, and
   PLC) support link-layer security.  Making use of such provisions will
   alleviate the threats mentioned above.  Note that NFC is often
   considered to offer intrinsic security properties due to its short
   link range.  MS/TP does not support link-layer security, since in its
   original BACnet protocol stack, security is provided at the network
   layer; thus, alternative security functionality needs to be used for
   a 6lo-based protocol stack over MS/TP.

   End-to-end communication is expected to be secured by means of common
   mechanisms, such as IPsec, DTLS/TLS, Object Security [RFC8613], and
   Ephemeral Diffie-Hellman Over COSE (EDHOC) [EDHOC].

   The 6lo stack uses the IPv6 addressing model.  The implications for
   privacy and network performance of using L2-address-derived IPv6
   addresses need to be considered [RFC8065].

8.  References

8.1.  Normative References

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.

   [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,
              <https://www.rfc-editor.org/info/rfc4919>.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
              <https://www.rfc-editor.org/info/rfc4944>.

   [RFC6568]  Kim, E., Kaspar, D., and JP. Vasseur, "Design and
              Application Spaces for IPv6 over Low-Power Wireless
              Personal Area Networks (6LoWPANs)", RFC 6568,
              DOI 10.17487/RFC6568, April 2012,
              <https://www.rfc-editor.org/info/rfc6568>.

   [RFC6606]  Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
              Statement and Requirements for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Routing",
              RFC 6606, DOI 10.17487/RFC6606, May 2012,
              <https://www.rfc-editor.org/info/rfc6606>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.

   [RFC7400]  Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
              IPv6 over Low-Power Wireless Personal Area Networks
              (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
              2014, <https://www.rfc-editor.org/info/rfc7400>.

   [RFC7428]  Brandt, A. and J. Buron, "Transmission of IPv6 Packets
              over ITU-T G.9959 Networks", RFC 7428,
              DOI 10.17487/RFC7428, February 2015,
              <https://www.rfc-editor.org/info/rfc7428>.

   [RFC7668]  Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
              Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
              Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
              <https://www.rfc-editor.org/info/rfc7668>.

   [RFC8105]  Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt,
              M., and D. Barthel, "Transmission of IPv6 Packets over
              Digital Enhanced Cordless Telecommunications (DECT) Ultra
              Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May
              2017, <https://www.rfc-editor.org/info/rfc8105>.

   [RFC8163]  Lynn, K., Ed., Martocci, J., Neilson, C., and S.
              Donaldson, "Transmission of IPv6 over Master-Slave/Token-
              Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163,
              May 2017, <https://www.rfc-editor.org/info/rfc8163>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC9159]  Gomez, C., Darroudi, S.M., Savolainen, T., and M. Spoerk,
              "IPv6 Mesh over BLUETOOTH(R) Low Energy Using the Internet
              Protocol Support Profile (IPSP)", RFC 9159,
              DOI 10.17487/RFC9159, December 2021,
              <https://www.rfc-editor.org/info/rfc9159>.

   [RFC9354]  Hou, J., Liu, B., Hong, Y-G., Tang, X., and C. Perkins,
              "Transmission of IPv6 Packets over Power Line
              Communication (PLC) Networks", RFC 9354,
              DOI 10.17487/RFC9354, January 2023,
              <https://www.rfc-editor.org/info/rfc9354>.

8.2.  Informative References

   [BACnet]   ASHRAE, "BACnet-A Data Communication Protocol for Building
              Automation and Control Networks (ANSI Approved)", ASHRAE
              Standard 135-2020, October 2020,
              <https://www.techstreet.com/standards/ashrae-
              135-2020?product_id=2191852>.

   [BTCorev5.4]
              Bluetooth, "Core Specification Version 5.4", January 2012,
              <https://www.bluetooth.com/specifications/specs/core-
              specification-5-4/>.

   [EDHOC]    Selander, G., Preuß Mattsson, J., and F. Palombini,
              "Ephemeral Diffie-Hellman Over COSE (EDHOC)", Work in
              Progress, Internet-Draft, draft-ietf-lake-edhoc-22, 25
              August 2023, <https://datatracker.ietf.org/doc/html/draft-
              ietf-lake-edhoc-22>.

   [G.9903]   ITU-T, "Narrowband orthogonal frequency division
              multiplexing power line communication transceivers for
              G3-PLC networks", ITU-T Recommendation G.9903, August
              2017, <https://www.itu.int/rec/T-REC-G.9903-201708-I/en>.

   [G.9959]   ITU-T, "Short range narrow-band digital radiocommunication
              transceivers - PHY, MAC, SAR and LLC layer
              specifications", ITU-T Recommendation G.9959, January
              2015, <https://www.itu.int/rec/T-REC-G.9959-201501-I/en>.

   [G3-PLC]   "G3-Alliance", <https://g3-plc.com>.

   [IEEE-1901]
              IEEE, "IEEE Standard for Broadband over Power Line
              Networks: Medium Access Control and Physical Layer
              Specifications", DOI 10.1109/IEEESTD.2010.5678772, IEEE
              Std 1901-2010, December 2010,
              <https://standards.ieee.org/ieee/1901/4953/>.

   [IEEE-1901.1]
              IEEE, "IEEE Standard for Medium Frequency (less than 12
              MHz) Power Line Communications for Smart Grid
              Applications", DOI 10.1109/IEEESTD.2018.8360785, IEEE
              Std 1901.1-2018, May 2018,
              <https://ieeexplore.ieee.org/document/8360785>.

   [IEEE-1901.2]
              IEEE, "IEEE Standard for Low-Frequency (less than 500 kHz)
              Narrowband Power Line Communications for Smart Grid
              Applications", DOI 10.1109/IEEESTD.2013.6679210, IEEE
              Std 1901.2-2013, December 2013,
              <https://standards.ieee.org/ieee/1901.2/4833/>.

   [IEEE-802.15.4]
              IEEE, "IEEE Standard for Low-Rate Wireless Networks",
              DOI 10.1109/IEEESTD.2020.9144691, IEEE Std 802.15.4-2020,
              July 2020,
              <https://standards.ieee.org/ieee/802.15.4/7029/>.

   [IEEE-802.15.9]
              IEEE, "IEEE Standard for Transport of Key Management
              Protocol (KMP) Datagrams",
              DOI 10.1109/IEEESTD.2022.9690134, IEEE Std 802.15.9-2021,
              January 2022,
              <https://ieeexplore.ieee.org/document/9690134>.

   [IPSP]     Bluetooth, "Internet Protocol Support Profile 1.0",
              December 2014,
              <https://www.bluetooth.com/specifications/specs/internet-
              protocol-support-profile-1-0/>.

   [KW03]     Karlof, C. and D. Wagner, "Secure routing in wireless
              sensor networks: attacks and countermeasures", Volume 1,
              Issues 2-3, Pages 293-315,
              DOI 10.1016/S1570-8705(03)00008-8, September 2003,
              <https://doi.org/10.1016/S1570-8705(03)00008-8>.

   [LLCP-1.4] NFC Forum, "Logical Link Control Protocol Technical
              Specification", Version 1.4, December 2022, <https://nfc-
              forum.org/build/specifications/logical-link-control-
              protocol-technical-specification/>.

   [NETRICITY]
              Netricity, "The Netricity program addresses the need for
              long range powerline networking for outside-the-home,
              smart meter-to-grid, and industrial control applications",
              <https://www.netricity.org/>.

   [RFC3756]  Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
              Neighbor Discovery (ND) Trust Models and Threats",
              RFC 3756, DOI 10.17487/RFC3756, May 2004,
              <https://www.rfc-editor.org/info/rfc3756>.

   [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              DOI 10.17487/RFC6282, September 2011,
              <https://www.rfc-editor.org/info/rfc6282>.

   [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,
              <https://www.rfc-editor.org/info/rfc6550>.

   [RFC6620]  Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS
              SAVI: First-Come, First-Served Source Address Validation
              Improvement for Locally Assigned IPv6 Addresses",
              RFC 6620, DOI 10.17487/RFC6620, May 2012,
              <https://www.rfc-editor.org/info/rfc6620>.

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <https://www.rfc-editor.org/info/rfc6775>.

   [RFC8065]  Thaler, D., "Privacy Considerations for IPv6 Adaptation-
              Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065,
              February 2017, <https://www.rfc-editor.org/info/rfc8065>.

   [RFC8066]  Chakrabarti, S., Montenegro, G., Droms, R., and J.
              Woodyatt, "IPv6 over Low-Power Wireless Personal Area
              Network (6LoWPAN) ESC Dispatch Code Points and
              Guidelines", RFC 8066, DOI 10.17487/RFC8066, February
              2017, <https://www.rfc-editor.org/info/rfc8066>.

   [RFC8138]  Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
              "IPv6 over Low-Power Wireless Personal Area Network
              (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
              April 2017, <https://www.rfc-editor.org/info/rfc8138>.

   [RFC8352]  Gomez, C., Kovatsch, M., Tian, H., and Z. Cao, Ed.,
              "Energy-Efficient Features of Internet of Things
              Protocols", RFC 8352, DOI 10.17487/RFC8352, April 2018,
              <https://www.rfc-editor.org/info/rfc8352>.

   [RFC8376]  Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
              Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
              <https://www.rfc-editor.org/info/rfc8376>.

   [RFC8505]  Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Neighbor
              Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
              <https://www.rfc-editor.org/info/rfc8505>.

   [RFC8613]  Selander, G., Preuß Mattsson, J., Palombini, F., and L.
              Seitz, "Object Security for Constrained RESTful
              Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613,
              July 2019, <https://www.rfc-editor.org/info/rfc8613>.

   [RFC8928]  Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik,
              "Address-Protected Neighbor Discovery for Low-Power and
              Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November
              2020, <https://www.rfc-editor.org/info/rfc8928>.

   [RFC8929]  Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli,
              "IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929,
              November 2020, <https://www.rfc-editor.org/info/rfc8929>.

   [RFC9008]  Robles, M.I., Richardson, M., and P. Thubert, "Using RPI
              Option Type, Routing Header for Source Routes, and IPv6-
              in-IPv6 Encapsulation in the RPL Data Plane", RFC 9008,
              DOI 10.17487/RFC9008, April 2021,
              <https://www.rfc-editor.org/info/rfc9008>.

   [RFC9010]  Thubert, P., Ed. and M. Richardson, "Routing for RPL
              (Routing Protocol for Low-Power and Lossy Networks)
              Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021,
              <https://www.rfc-editor.org/info/rfc9010>.

   [RFC9035]  Thubert, P., Ed. and L. Zhao, "A Routing Protocol for Low-
              Power and Lossy Networks (RPL) Destination-Oriented
              Directed Acyclic Graph (DODAG) Configuration Option for
              the 6LoWPAN Routing Header", RFC 9035,
              DOI 10.17487/RFC9035, April 2021,
              <https://www.rfc-editor.org/info/rfc9035>.

   [RFC9428]  Choi, Y., Ed., Hong, Y., and J. Youn, "Transmission of
              IPv6 Packets over Near Field Communication", RFC 9428,
              DOI 10.17487/RFC9428, July 2023,
              <https://www.rfc-editor.org/info/rfc9428>.

   [SEC-PROT-COMP]
              Preuß Mattsson, J., Palombini, F., and M. Vučinić,
              "Comparison of CoAP Security Protocols", Work in Progress,
              Internet-Draft, draft-ietf-iotops-security-protocol-
              comparison-02, 11 April 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-iotops-
              security-protocol-comparison-02>.

   [Thread]   Thread, "Resources",
              <https://www.threadgroup.org/Support>.

   [TIA-485-A]
              TIA, "Electrical Characteristics of Generators and
              Receivers for Use in Balanced Digital Multipoint Systems",
              TIA-485-A, Revision of TIA-485, March 1998,
              <https://global.ihs.com/
              doc_detail.cfm?item_s_key=00032964>.

   [TS102.939-1]
              ETSI, "Digital Enhanced Cordless Telecommunications
              (DECT); Ultra Low Energy (ULE); Machine to Machine
              Communications; Part 1: Home Automation Network (phase
              1)", V1.2.1, ETSI-TS 102 939-1, March 2015,
              <https://www.etsi.org/deliver/
              etsi_ts/102900_102999/10293901/01.02.01_60/
              ts_10293901v010201p.pdf>.

   [TS102.939-2]
              ETSI, "Digital Enhanced Cordless Telecommunications
              (DECT); Ultra Low Energy (ULE); Machine to Machine
              Communications; Part 2: Home Automation Network (phase
              2)", V1.1.1, ETSI TS 102 939-2, March 2015,
              <https://www.etsi.org/deliver/
              etsi_ts/102900_102999/10293902/01.01.01_60/
              ts_10293902v010101p.pdf>.

   [Wi-SUN]   "Wi-SUN Alliance", <https://www.wi-sun.org>.

Appendix A.  Design Space Dimensions for 6lo Deployment

   [RFC6568] lists the dimensions used to describe the design space of
   wireless sensor networks in the context of the 6LoWPAN Working Group.
   The design space is already limited by the unique characteristics of
   a LoWPAN (e.g., low power, short range, low bit rate).  In Section 2
   of [RFC6568], the following design space dimensions are described:
   Deployment, Network Size, Power Source, Connectivity, Multi-Hop
   Communication, Traffic Pattern, Mobility, and Quality of Service
   (QoS).  However, in this document, the following design space
   dimensions are considered:

   Deployment/Bootstrapping:
      6lo nodes can be connected randomly or in an organized manner.
      The bootstrapping has different characteristics for each link-
      layer technology.

   Topology:
      Topology of 6lo networks may inherently follow the characteristics
      of each link-layer technology.  Point-to-point, star, tree, or
      mesh topologies can be configured, depending on the link-layer
      technology considered.

   L2-mesh or L3-mesh:
      L2-mesh and L3-mesh may inherently follow the characteristics of
      each link-layer technology.  Some link-layer technologies may
      support L2-mesh and some may not.

   Multi-link Subnet and Single Subnet:
      The selection of a multi-link subnet and a single subnet depends
      on connectivity and the number of 6lo nodes.

   Data Rate:
      Typically, the link-layer technologies of 6lo have a low rate of
      data transmission.  However, by adjusting the MTU, it can deliver
      a higher upper-layer data rate.

   Buffering Requirements:
      Some 6lo use case may require a higher data rate than the link-
      layer technology support.  In this case, a buffering mechanism,
      telling the application to throttle its generation of data, and
      compression of the data are possible to manage the data.

   Security and Privacy Requirements:
      Some 6lo use cases can involve transferring some important and
      personal data between 6lo nodes.  In this case, high-level
      security support is required.

   Mobility across 6lo Networks and Subnets:
      The movement of 6lo nodes depends on the 6lo use case.  If the 6lo
      nodes can move or be moved around, a mobility management mechanism
      is required.

   Time Synchronization Requirements:
      The requirement of time synchronization of the upper-layer service
      is dependent on the use case.  For some 6lo use cases related to
      health service, the measured data must be recorded with the exact
      time.

   Reliability and QoS:
      Some 6lo use cases require high reliability, for example, real-
      time or health-related services.

   Traffic Patterns:
      6lo use cases may involve various traffic patterns.  For example,
      some 6lo use cases may require short data lengths and random
      transmission.  Some 6lo use cases may require continuous data
      transmission and discontinuous data transmission.

   Security Bootstrapping:
      Without the external operations, 6lo nodes must have a security
      bootstrapping mechanism.

   Power Use Strategy:
      To enable certain use cases, there may be requirements on the
      class of energy availability and the strategy followed for using
      power for communication [RFC7228].  Each link-layer technology
      defines a particular power use strategy that may be tuned
      [RFC8352].  Readers are expected to be familiar with the
      terminology found in [RFC7228].

   Update Firmware Requirements:
      Most 6lo use cases will need a mechanism to update firmware.  In
      these cases, support for over-the-air updates is required,
      probably in a broadcast mode when bandwidth is low and the number
      of identical devices is high.

   Wired vs. Wireless:
      Plenty of 6lo link-layer technologies are wireless, except MS/TP
      and PLC.  The selection of wired or wireless link-layer technology
      is mainly dependent on the requirements of the 6lo use cases and
      the characteristics of wired and wireless technologies.

Acknowledgements

   Carles Gomez has been funded in part by the Spanish Government
   through the Jose Castillejo CAS15/00336 grant, the TEC2016-79988-P
   grant, and the PID2019-106808RA-I00 grant as well as by Secretaria
   d'Universitats i Recerca del Departament d'Empresa i Coneixement de
   la Generalitat de Catalunya through grants 2017 SGR 376 and 2021 SGR
   00330.  His contribution to this work has been carried out in part
   during his stay as a visiting scholar at the Computer Laboratory of
   the University of Cambridge.

   Thomas Watteyne, Pascal Thubert, Xavier Vilajosana, Daniel Migault,
   Jianqiang Hou, Kerry Lynn, S.V.R. Anand, and Seyed Mahdi Darroudi
   have provided valuable feedback for this document.

   Das Subir and Michel Veillette have provided valuable information of
   jupiterMesh, and Paul Duffy has provided valuable information of Wi-
   SUN for this document.  Also, Jianqiang Hou has provided valuable
   information of G3-PLC and Netricity for this document.  Take
   Aanstoot, Kerry Lynn, and Dave Robin have provided valuable
   information of MS/TP and practical use case of MS/TP for this
   document.

   Deoknyong Ko has provided relevant text of LTE-MTC, and he shared his
   experience to deploy IPv6 and 6lo technologies over LTE MTC in SK
   Telecom.

Authors' Addresses

   Yong-Geun Hong
   Daejeon University
   62 Daehak-ro, Dong-gu
   Daejeon
   34520
   South Korea
   Phone: +82 42 280 4841
   Email: yonggeun.hong@gmail.com


   Carles Gomez
   Universitat Politecnica de Catalunya
   C/Esteve Terradas, 7
   08860 Castelldefels
   Spain
   Email: carles.gomez@upc.edu


   Younghwan Choi
   ETRI
   218 Gajeongno, Yuseong
   Daejeon
   34129
   South Korea
   Phone: +82 42 860 1429
   Email: yhc@etri.re.kr


   Abdur Rashid Sangi
   Wenzhou-Kean University
   88 Daxue Road, Ouhai, Wenzhou
   Zhejiang
   325060
   China
   Email: sangi_bahrian@yahoo.com


   Samita Chakrabarti
   Verizon
   Bedminster, NJ
   United States of America
   Email: samita.chakrabarti@verizon.com
