IPv6 over Constrained Node Networks (6lo) Applicability & Use cases
draft-ietf-6lo-use-cases-11

Document Type Active Internet-Draft (6lo WG)
Authors Yong-Geun Hong  , Carles Gomez  , Abdur Sangi  , Samita Chakrabarti 
Last updated 2021-07-12
Stream Internet Engineering Task Force (IETF)
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Send notices to Gabriel Montenegro <Gabriel.Montenegro@microsoft.com>
6Lo Working Group                                              Y-G. Hong
Internet-Draft                                        Daejeon University
Intended status: Informational                                  C. Gomez
Expires: January 13, 2022                                            UPC
                                                               Y-H. Choi
                                                                    ETRI
                                                               AR. Sangi
                                         Huaiyin Institute of Technology
                                                          S. Chakrabarti
                                                           July 12, 2021

  IPv6 over Constrained Node Networks (6lo) Applicability & Use cases
                      draft-ietf-6lo-use-cases-11

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 such
   as ITU-T G.9959 (Z-Wave), Bluetooth Low Energy, DECT-ULE, MS/TP, NFC,
   and PLC are used as examples.  The 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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 13, 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  6lo Link layer technologies . . . . . . . . . . . . . . . . .   4
     2.1.  ITU-T G.9959  . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Bluetooth LE  . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  DECT-ULE  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.4.  MS/TP . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.5.  NFC . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.6.  PLC . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.7.  Comparison between 6lo link layer technologies  . . . . .   8
   3.  Guidelines for adopting IPv6 stack (6lo)  . . . . . . . . . .   9
   4.  6lo Deployment Scenarios  . . . . . . . . . . . . . . . . . .  11
     4.1.  Wi-SUN usage of 6lo in network layer  . . . . . . . . . .  11
     4.2.  Thread usage of 6lo in network layer  . . . . . . . . . .  12
     4.3.  G3-PLC usage of 6lo in network layer  . . . . . . . . . .  13
     4.4.  Netricity usage of 6lo in network layer . . . . . . . . .  14
   5.  6lo Use Case Examples . . . . . . . . . . . . . . . . . . . .  15
     5.1.  Use case of ITU-T G.9959: Smart Home  . . . . . . . . . .  15
     5.2.  Use case of Bluetooth LE: Smartphone-based Interaction  .  16
     5.3.  Use case of DECT-ULE: Smart Home  . . . . . . . . . . . .  16
     5.4.  Use case of MS/TP: Building Automation Networks . . . . .  17
     5.5.  Use case of NFC: Alternative Secure Transfer  . . . . . .  18
     5.6.  Use case of PLC: Smart Grid . . . . . . . . . . . . . . .  18
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  20
   Appendix A.  Design Space Dimensions for 6lo Deployment . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

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, low cost, and large number of devices, among
   others [RFC4919][RFC7228].  For example, many IEEE Std 802.15.4
   variants [IEEE802154] exhibit a frame size of 127 octets, whereas

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   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 802.15.9-2016 provides multiplexing and fragmentation layer for
   the IEEE Std 802.15.4[IEEE802159].)  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 WPAN (6LoWPAN)
   working group published a suite of specification that provide an
   adaptation layer to support IPv6 over IEEE Std 802.15.4 comprising
   the following functionality:

   o  Fragmentation and reassembly, address autoconfiguration, and a
      frame format [RFC4944],

   o  IPv6 (and UDP) header compression [RFC6282],

   o  Neighbor Discovery Optimization for 6LoWPAN [RFC6775][RFC8505].

   As Internet of Things (IoT) services become more popular, the IETF
   6lo working group [IETF_6lo] 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 6LoWPANs" [RFC6568], which describes potential
   application scenarios and use cases for low-power wireless personal
   area networks.  The present document aims to provide guidance to an
   audience who are 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 cases
   examples.  In addition, it considers various network design space
   dimensions such as deployment, network size, power source,
   connectivity, multi-hop communication, traffic pattern, security
   level, mobility, and QoS requirements etc.

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

   o  It covers various IoT-related wired/wireless link layer
      technologies providing practical information of such technologies.

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   o  It provides a general guideline on how the 6LoWPAN stack can be
      modified for a given L2 technology.

   o  Various 6lo use cases and practical deployment examples are
      described.

2.  6lo Link layer technologies

2.1.  ITU-T G.9959

   The ITU-T G.9959 Recommendation [G.9959] targets low-power Wireless
   Personal Area Networks (WPANs), 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].  The ITU-T G.9959 can be used for smart home
   applications.

2.2.  Bluetooth LE

   Bluetooth LE was introduced in Bluetooth 4.0, enhanced in Bluetooth
   4.1, and developed further in successive versions.  Bluetooth SIG has
   also published the Internet Protocol Support Profile (IPSP).  The
   IPSP enables discovery of IP-enabled devices and establishment of
   link-layer connection for transporting IPv6 packets.  IPv6 over
   Bluetooth LE is dependent on both Bluetooth 4.1 and IPSP 1.0 or
   newer.

   Many devices such as mobile phones, notebooks, tablets and other
   handheld computing devices which 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 is being developed
   [I-D.ietf-6lo-blemesh]

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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.

   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 FDMA/TDMA/TDD techniques.

   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 (PP) attached.  The Medium Access Control
   (MAC) layer supports traditional DECT as this is used for services
   like discovery, pairing, security features etc.  All these features
   have been reused from DECT.

   The DECT-ULE device can switch to the ULE mode of operation,
   utilizing the new 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 or mesh routing issues, and c)
   the latest MS/TP specification provides support for large payloads,
   eliminating the need for fragmentation and reassembly below IPv6.

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   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 superior "range" (~1 km) compared to many low power
   wireless data links, MS/TP may be suitable 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 simple and safe two-way interactions between
   electronic devices, allowing consumers to perform contactless
   transactions, access digital content, and connect electronic devices
   with a single touch.  NFC complements many popular consumer level
   wireless technologies, by utilizing the key elements in existing
   standards for contactless card technology (ISO/IEC 14443 A&B and
   JIS-X 6319-4).

   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 ideal for establishing
   connections with other technologies by the simplicity of touch.  In
   addition to the easy connection and quick transactions, simple data
   sharing is also available [I-D.ietf-6lo-nfc].  NFC can be used for
   secure transfer in healthcare services.

2.6.  PLC

   PLC is a data transmission technique that utilizes power conductors
   as medium [I-D.ietf-6lo-plc].  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 below table shows some available open standards defining PLC.

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   +-------------+-----------------+------------+-----------+----------+
   | PLC Systems | Frequency Range |    Type    | Data Rate | Distance |
   +-------------+-----------------+------------+-----------+----------+
   |   IEEE1901  |     <100MHz     | Broadband  |  200Mbps  |  1000m   |
   |             |                 |            |           |          |
   |  IEEE1901.1 |      <12MHz     |  PLC-IoT   |   10Mbps  |  2000m   |
   |             |                 |            |           |          |
   |  IEEE1901.2 |     <500kHz     | Narrowband |  200kbps  |  3000m   |
   |             |                 |            |           |          |
   |    G3-PLC   |     <500kHz     | Narrowband |  234kbps  |  3000m   |
   +-------------+-----------------+------------+-----------+----------+

               Table 1: Some Available Open Standards in PLC

   IEEE Std 1901 [IEEE1901] defines a broadband variant of PLC but is
   effective within short range.  This standard addresses the
   requirements of applications with high data rate such as: Internet,
   HDTV, Audio, Gaming etc.  Broadband operates on Orthogonal Frequency
   Division Multiplexing (OFDM) modulation.

   IEEE Std 1901.1 [IEEE1901.1] defines a medium frequency band (less
   than 12 MHz) broadband PLC technology for smart grid applications
   based on OFDM.  By achieving an extended communication range with
   medium speeds, this standard can be applied both in indoor and
   outdoor scenarios, such as Advanced Metering Infrastructure (AMI),
   street lighting, electric vehicle charging, smart city etc.

   IEEE Std 1901.2 [IEEE1901.2] defines a narrowband variant of PLC with
   less data rate but significantly higher transmission range that could
   be used in an indoor or even an outdoor environment.  It is
   applicable to typical IoT applications such as: Building Automation,
   Renewable Energy, Advanced Metering, Street Lighting, Electric
   Vehicle, Smart Grid etc.  Moreover, IEEE Std 1901.2 standard is based
   on the 802.15.4 MAC sub-layer and fully endorses the security scheme
   defined in 802.15.4 [RFC8036].  A typical use case of PLC is 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 frequencies below 500 kHz.

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2.7.  Comparison between 6lo link layer technologies

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

+--------------+---------+---------+---------+---------+---------+---------+
|              |  Z-Wave |   BLE   | DECT-ULE|  MS/TP  |   NFC   |   PLC   |
+--------------+---------+---------+---------+---------+---------+---------+
|              |  Home   | Interact|         | Building| Health- |         |
|     Usage    |  Auto-  | w/ Smart|  Meter  |  Auto-  |  care   |  Smart  |
|              | mation  |  Phone  | Reading | mation  | Service |  Grid   |
+--------------+---------+---------+---------+---------+---------+---------+
|   Topology   | L2-mesh |  Star   |  Star   |  MS/TP  |  P2P    |  Star   |
|      &       |    or   |    &    |         |         |         |  Tree   |
|    Subnet    | L3-mesh |  Mesh   | No mesh | No mesh | L2-mesh |  Mesh   |
+--------------+---------+---------+---------+---------+---------+---------+
|              |         |         |         |         |         |         |
|   Mobility   |   No    |   Low   |   No    |   No    | Moderate|   No    |
|  Requirement |         |         |         |         |         |         |
+--------------+---------+---------+---------+---------+---------+---------+
|              |  High + |         |  High + |  High + |         |  High + |
|   Security   | Privacy |Partially| Privacy | Authen. |  High   | Encrypt.|
|  Requirement | required|         | required| required|         | required|
+--------------+---------+---------+---------+---------+---------+---------+
|              |         |         |         |         |         |         |
|   Buffering  |   Low   |   Low   |   Low   |   Low   |   Low   |   Low   |
|  Requirement |         |         |         |         |         |         |
+--------------+---------+---------+---------+---------+---------+---------+
|   Latency,   |         |         |         |         |         |         |
|     QoS      |   High  |   Low   |   Low   |   High  |   High  |   Low   |
|  Requirement |         |         |         |         |         |         |
+--------------+---------+---------+---------+---------+---------+---------+
|              |         |         |         |         |         |         |
|     Data     | Infrequ-| Infrequ-| Infrequ-| Frequent|  Small  | Infrequ-|
|     Rate     |   ent   |   ent   |   ent   |         |         |   ent   |
+--------------+---------+---------+---------+---------+---------+---------+
|     RFC #    |         | RFC7668,|         |         |  draft- |  draft- |
|      or      | RFC7428 | ietf-6lo| RFC8105 | RFC8163 | ietf-6lo| ietf-6lo|
|     Draft    |         | -blemesh|         |         |   -nfc  |   -plc  |
+--------------+---------+---------+---------+---------+---------+---------+

            Table 2: Comparison between 6lo link layer technologies

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3.  Guidelines for adopting IPv6 stack (6lo)

   6lo aims at reusing and/or adapting 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 6LoWPAN stack
   should be based on the following:

   o  Addressing Model: 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.  L2-address-derived IPv6 addresses are
      specified in [RFC4944], but there exist implications for privacy.
      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, please refer to
      [RFC8163] for IPv6 address 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 when to use broadcast and try to
      stick to unicast messaging whenever possible.

   o  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/reassembly.  In fact, for
      most efficiency, choosing a low-power link layer that can carry
      unfragmented application packets would be optimum for packet
      transmission if the deployment can afford it.  Please refer to 6lo
      RFCs [RFC7668], [RFC8163], [RFC8105] for example guidance.

   o  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,
      a 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.

   o  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

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      expected to be an IPv6 host per [RFC8200] which means it should
      ignore consumed routing headers and Hop-by-Hop options; when
      operating in a RPL network [RFC6550], it is also beneficial to
      support IP-in-IP encapsulation [RFC9008].  The 6LoWPAN node should
      also support [RFC8505] and use it 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][RFC8505] specifies 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 [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 Protection for 6LoWPAN
      Neighbor Discovery (AP-ND) [RFC8928] enables Source Address
      Validation [RFC6620] and protects the address ownership against
      impersonation attacks.

   o  Broadcast Avoidance: 6LoWPAN Neighbor Discovery aims at reducing
      the amount of multicast traffic of classical Neighbor Discovery,
      since IP-level multicast translates into L2 broadcast in many L2
      technologies. 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)

   o  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]

   o  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
      federates a number of links into a multilink subnet.

   o  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

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      [RFC7668], [RFC8163], [RFC8105].  A generic header compression
      technique is specified in [RFC7400].  For 6LoWPAN networks where
      RPL is the routing protocol, there exist 6LoWPAN header
      compression extensions which allow to compress also the RPL
      artifacts used when forwarding packets in the route-over mesh
      [RFC8138] [RFC9035]

   o  Security and Encryption: Though 6LoWPAN basic specifications do
      not address security at the network layer, the assumption is that
      L2 security must be present.  In addition, application-level
      security is highly desirable.  The working groups [IETF_ace] and
      [IETF_core] should be consulted for application and transport
      level security. 6lo working group is working on address
      authentication [RFC8928] and secure bootstrapping is also being
      discussed at IETF.  However, there may be different levels of
      security available in a deployment through other standards such as
      hardware-level security or certificates for initial booting
      process.  Encryption is important if the implementation can afford
      it.

   o  Additional processing: [RFC8066] defines guidelines for ESC
      dispatch octets use in the 6LoWPAN header.  An implementation may
      take advantage of ESC header to offer a deployment specific
      processing of 6LoWPAN packets.

4.  6lo Deployment Scenarios

4.1.  Wi-SUN usage of 6lo in network layer

   Wireless Smart Ubiquitous Network (Wi-SUN)[Wi-SUN] is a technology
   based on the IEEE Std 802.15.4g standard.  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 powered and battery-operated devices
   [RFC8376].

   The main application domains targeted by Wi-SUN are smart utility and
   smart city networks.  This includes, but is not limited to the
   following applications:

   o  Advanced Metering Infrastructure

   o  Distribution Automation

   o  Home Energy Management

   o  Infrastructure Management

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   o  Intelligent Transportation Systems

   o  Smart Street Lighting

   o  Agriculture

   o  Structural health (bridges, buildings)

   o  Monitoring and Asset Management

   o  Smart Thermostats, Air Conditioning and Heat Controls

   o  Energy Usage Information Displays

   The Wi-SUN Alliance Field Area Network (FAN) covers primarily outdoor
   networks, and its specification is oriented towards meeting the more
   rigorous challenges of these environments.  It has the following
   features:

   o  Open standards based on IEEE802, IETF, TIA, ETSI

   o  Architecture based on an IPv6 frequency hopping wireless mesh
      network with enterprise-level security

   o  Simple infrastructure of low cost, low complexity

   o  Enhanced network robustness, reliability, and resilience to
      interference, due to high redundancy and frequency hopping

   o  Enhanced scalability, long range, and energy friendliness

   o  Supports multiple global license-exempt sub-GHz bands

   o  Multi-vendor interoperability

   o  Very low power modes in development permitting long term battery
      operation of network nodes

   The Wi-SUN FAN specification defines an IPv6-based protocol suite
   including TCP/UDP, IPv6, 6lo adaptation layer, DHCPv6 for IPv6
   address management, RPL, and ICMPv6.

4.2.  Thread usage of 6lo in 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

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   and IoT platforms, provide end-to-end security, ease development and
   enable flexible and future-proof designs [Thread].

   The Thread specification uses the IEEE Std 802.15.4 [IEEE802154]
   physical and MAC layers operating at 250 kbps in the 2.4 GHz band.

   Thread devices use 6LoWPAN, as defined in [RFC4944][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 targeted by G3-PLC are smart grid and
   smart cities.  This includes, but is not limited to the following
   applications:

   o  Smart Metering

   o  Vehicle-to-Grid Communication

   o  Demand Response

   o  Distribution Automation

   o  Home/Building Energy Management Systems

   o  Smart Street Lighting

   o  Advanced Metering Infrastructure (AMI) backbone network

   o  Wind/Solar Farm Monitoring

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   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 [I-D.ietf-6lo-plc].  The ESC dispatch type is used in
   the G3-PLC to provide native mesh routing and bootstrapping
   functionalities [RFC8066].

4.4.  Netricity usage of 6lo in network layer

   The Netricity program in HomePlug Powerline Alliance [NETRICITY]
   promotes the adoption of products built on the IEEE Std 1901.2 low-
   frequency narrowband PLC standard, 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 targeted by Netricity are smart grid and
   smart cities.  This includes, but is not limited to the following
   applications:

   o  Utility grid modernization

   o  Distribution automation

   o  Meter-to-Grid connectivity

   o  Micro-grids

   o  Grid sensor communications

   o  Load control

   o  Demand response

   o  Net metering

   o  Street Lighting control

   o  Photovoltaic panel monitoring

   Netricity system architecture is based on the physical and MAC layers
   of IEEE Std 1901.2 PLC standard.  Regarding the 6lo adaptation layer
   and 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-

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   storing mode with the MRHOF objective function based on the 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.

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

   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 on/off or may control home
   appliances by pressing a wall switch or by pressing a button in a
   remote control.  Scenes may be programmed, so that after a given
   event, the home devices adopt a specific configuration.  Sensors may
   also periodically send measurements of several parameters (e.g. gas
   presence, light, temperature, humidity, etc.) 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 multihop paradigm
   allows end-to-end connectivity when direct range communication is not
   possible.  Security support is required, specially for safety-related
   communication.  When a user interaction (e.g. a button press)
   triggers a message that encapsulates a command, if the message is
   lost, the user may have to perform further interactions to achieve
   the desired effect (e.g. turning off a light).  A reaction to a user
   interaction will be perceived by the user as immediate as long as the
   reaction takes place within 0.5 seconds [RFC5826].

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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 the interaction between the 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 4G, the 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 Bluetooth LE-based Body Area Network for fitness

   A person wears a smartwatch for fitness purposes.  The smartwatch has
   several sensors (e.g. heart rate, accelerometer, gyrometer, GPS,
   temperature, etc.), 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 the 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.

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, a device that
   typically acts as a base station for wireless telephones.  Therefore,
   DECT-ULE is specially suitable for the connected home space in
   application areas such as home automation, smart metering, safety,
   healthcare, etc.  Since DECT-ULE uses dedicated bandwidth, it avoids
   the coexistence issues suffered by other technologies that use e.g.
   ISM frequency bands.

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   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 Fixed Part
   of the home.  The Fixed Part 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 Fixed Part,
   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 Fixed Part
   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 inter-connect 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
   native 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 thus it falls 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 traditional 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

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   other wired technologies such as DSL, and 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

   A senior citizen who lives alone wears one to several wearable 6lo
   devices to measure heartbeat, pulse rate, etc.  The 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 LCDs 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 also becomes a serious issue in this
   case, as the sensed data is very personal.

   While the senior citizen is provided audio and video healthcare
   services by a tele-assistance based on LTE connections, the senior
   citizen can alternatively use NFC connections to transfer the
   personal sensed data to the tele-assistance.  Hidden hackers can
   overhear the data based on the LTE 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 sub-systems in an electricity grid system.  It
   comprises multiple administrative levels/segments to provide
   connectivity among these numerous components.  Last mile connectivity
   is established over the Low Voltage (LV) segment, whereas
   connectivity over electricity distribution takes place in the High
   Voltage (HV) segment.  Smart grid systems include Advanced Metering
   Infrastructure (AMI), Demand Response (DR), Home Energy Management
   System (HEMS), Wide Area Situational Awareness (WASA), among others.

   Although other wired and wireless technologies are also used in Smart
   Grid, PLC enjoys the advantage of 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 LV PLC networks with most
   applications in the area of Advanced Metering Infrastructure,

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   Vehicle-to-Grid communications, in-home energy management and smart
   street lighting.

   Example: Use of PLC for Advanced Metering Infrastructure

   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 (MDMS) through WAN network (e.g.
   Medium-Voltage PLC, Ethernet or GPRS) for storage and analysis.  Two-
   way communications are enabled which means smart meters can do
   actions like notification of electricity charges according to the
   commands from the utility company.

   With the existing power line infrastructure as communication medium,
   cost on building up the PLC network is naturally saved, and more
   importantly, labor operational costs can be minimized from a long-
   term perspective.  Furthermore, this AMI application speeds up
   electricity charge, 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 Smart Grid

   Many sub-systems of Smart Grid require low data rate 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.

   WASA sub-system is an appropriate example that collects large amount
   of information about the current state of the grid over wide area
   from electric substations as well as power transmission lines.  The
   collected feedback is used for monitoring, controlling and protecting
   all the sub-systems.

6.  IANA Considerations

   There are no IANA considerations related to this document.

7.  Security Considerations

   Security considerations are not directly applicable to this document.
   For the use cases, the security requirements described in the
   protocol specifications apply.

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8.  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, and by Secretaria
   d'Universitats i Recerca del Departament d'Empresa i Coneixement de
   la Generalitat de Catalunya 2017 through grant SGR 376.  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 draft.

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

   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.

9.  Informative References

   [BACnet]   "ASHRAE, "BACnet-A Data Communication Protocol for
              Building Automation and Control Networks", ANSI/ASHRAE
              Standard 135-2016", January 2016,
              <http://www.techstreet.com/ashrae/standards/ashrae-
              135-2016?product_id=1918140#jumps>.

   [G.9903]   "International Telecommunication Union, "Narrowband
              orthogonal frequency division multiplexing power line
              communication transceivers for G3-PLC networks", ITU-T
              Recommendation", August 2017.

   [G.9959]   "International Telecommunication Union, "Short range
              narrow-band digital radiocommunication transceivers - PHY
              and MAC layer specifications", ITU-T Recommendation",
              January 2015.

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

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   [IEEE1901]
              "IEEE Standard, IEEE Std 1901-2010 - IEEE Standard for
              Broadband over Power Line Networks: Medium Access Control
              and Physical Layer Specifications", 2010,
              <https://standards.ieee.org/findstds/
              standard/1901-2010.html>.

   [IEEE1901.1]
              "IEEE Standard, IEEE Std 1901.1-2018 - IEEE Standard for
              Medium Frequency (less than 12 MHz) Power Line
              Communications for Smart Grid Applications", 2018,
              <https://ieeexplore.ieee.org/document/8360785>.

   [IEEE1901.2]
              "IEEE Standard, IEEE Std 1901.2-2013 - IEEE Standard for
              Low-Frequency (less than 500 kHz) Narrowband Power Line
              Communications for Smart Grid Applications", 2013,
              <https://standards.ieee.org/findstds/
              standard/1901.2-2013.html>.

   [IEEE802154]
              IEEE standard for Information Technology, "IEEE Standard
              for Low-Rate Wireless Networks".

   [IEEE802159]
              IEEE standard for Information Technology, "IEEE Std
              802.15.9-2016 - IEEE Recommended Practice for Transport of
              Key Management Protocol (KMP) Datagrams".

   [I-D.ietf-6lo-blemesh]
              Gomez, C., Darroudi, S., Savolainen, T., and M. Spoerk,
              "IPv6 Mesh over BLUETOOTH(R) Low Energy using IPSP",
              draft-ietf-6lo-blemesh-10 (work in progress), April 2021.

   [I-D.ietf-6lo-nfc]
              Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi,
              "Transmission of IPv6 Packets over Near Field
              Communication", draft-ietf-6lo-nfc-17 (work in progress),
              August 2020.

   [I-D.ietf-6lo-plc]
              Hou, J., Liu, B., Hong, Y., Tang, X., and C. Perkins,
              "Transmission of IPv6 Packets over PLC Networks", draft-
              ietf-6lo-plc-06 (work in progress), April 2021.

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   [IETF_6lo]
              "IETF IPv6 over Networks of Resource-constrained Nodes
              (6lo) working group",
              <https://datatracker.ietf.org/wg/6lo/charter/>.

   [IETF_ace]
              "IETF Authentication and Authorization for Constrained
              Environments (ace) working group",
              <https://datatracker.ietf.org/wg/ace/charter/>.

   [IETF_core]
              "IETF Constrained RESTful Environments (core) working
              group", <https://datatracker.ietf.org/wg/core/charter/>.

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

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

   [NETRICITY]
              "Netricity program in HomePlug Powerline Alliance",
              <http://groups.homeplug.org/tech/Netricity>.

   [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>.

   [RFC5826]  Brandt, A., Buron, J., and G. Porcu, "Home Automation
              Routing Requirements in Low-Power and Lossy Networks",
              RFC 5826, DOI 10.17487/RFC5826, April 2010,
              <https://www.rfc-editor.org/info/rfc5826>.

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   [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>.

   [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>.

   [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>.

   [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>.

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   [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>.

   [RFC8036]  Cam-Winget, N., Ed., Hui, J., and D. Popa, "Applicability
              Statement for the Routing Protocol for Low-Power and Lossy
              Networks (RPL) in Advanced Metering Infrastructure (AMI)
              Networks", RFC 8036, DOI 10.17487/RFC8036, January 2017,
              <https://www.rfc-editor.org/info/rfc8036>.

   [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>.

   [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>.

   [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>.

   [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>.

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   [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>.

   [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., 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., 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>.

   [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 2003,
              <https://global.ihs.com/
              doc_detail.cfm?item_s_key=00032964>.

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Appendix A.  Design Space Dimensions for 6lo Deployment

   The [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 [RFC6568], the following design space dimensions are
   described: Deployment, Network size, Power source, Connectivity,
   Multi-hop communication, Traffic pattern, Mobility, Quality of
   Service (QoS).  However, in this document, the following design space
   dimensions are considered:

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

   o  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.

   o  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 support.

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

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

   o  Buffering requirements: Some 6lo use case may require more data
      rate than the link layer technology support.  In this case, a
      buffering mechanism to manage the data is required.

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

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

   o  Time synchronization requirements: The requirement of time
      synchronization of the upper layer service is dependent on the 6lo
      use case.  For some 6lo use case related to health service, the

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      measured data must be recorded with exact time and must be
      transferred with time synchronization.

   o  Reliability and QoS: Some 6lo use case requires high reliability,
      for example real-time service or health-related services.

   o  Traffic patterns: 6lo use cases may involve various traffic
      patterns.  For example, some 6lo use case may require short data
      length and random transmission.  Some 6lo use case may require
      continuous data and periodic data transmission.

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

   o  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 which may
      be tuned [RFC8352].  Readers are expected to be familiar with
      [RFC7228] terminology.

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

   o  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
      requirement of 6lo use cases and the characteristics of wired/
      wireless technologies.  For example, some 6lo use cases may
      require easy and quick deployment, whereas others may need a
      continuous source of power.

Authors' Addresses

   Yong-Geun Hong
   Daejeon University
   62 Daehak-ro, Dong-gu
   Daejeon  34520
   Korea

   Phone: +82 42 280 4841
   Email: yonggeun.hong@gmail.com

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   Carles Gomez
   Universitat Politecnica de Catalunya/Fundacio i2cat
   C/Esteve Terradas, 7
   Castelldefels  08860
   Spain

   Email: carlesgo@entel.upc.edu

   Younghwan Choi
   ETRI
   218 Gajeongno, Yuseong
   Daejeon  34129
   Korea

   Phone: +82 42 860 1429
   Email: yhc@etri.re.kr

   Abdur Rashid Sangi
   Huaiyin Institute of Technology
   No.89 North Beijing Road, Qinghe District
   Huaian  223001
   P.R. China

   Email: sangi_bahrian@yahoo.com

   Samita Chakrabarti
   San Jose, CA
   USA

   Email: samitac.ietf@gmail.com

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