]> Daejeon University

62 Daehak-ro, Dong-gu Daejeon 34520 South Korea +82 42 280 4841 yonggeun.hong@gmail.com

Universitat Politecnica de Catalunya/Fundacio i2cat

C/Esteve Terradas, 7 08860 Castelldefels Spain carles.gomez@upc.edu

ETRI

218 Gajeongno, Yuseong Daejeon 34129 South Korea +82 42 860 1429 yhc@etri.re.kr

Wenzhou-Kean University

88 Daxue Road, Ouhai, Wenzhou Zhejiang 325060 P.R. China sangi_bahrian@yahoo.com

San Jose, CA USA samitac.ietf@gmail.com

Internet 6Lo Working Group Internet Draft 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 (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) 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.

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 . For example, many IEEE Std 802.15.4 variants 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 .) 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 specifications that provide an adaptation layer to support IPv6 over IEEE Std 802.15.4 comprising the following functionality:

• Fragmentation and reassembly, address autoconfiguration, and a frame format ,
• IPv6 (and UDP) header compression ,
• Neighbor Discovery Optimization for 6LoWPAN .

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 6LoWPANs" , 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 (see Appendix A). This document provides the applicability and use cases of 6lo, considering the following aspects:

• It covers various IoT-related wired/wireless link layer technologies providing practical information about such technologies.
• It provides a general guideline on how the 6LoWPAN stack can be modified for a given L2 technology.
• Various 6lo use cases and practical deployment examples are described.

6lo Link layer technologies

ITU-T G.9959 The ITU-T G.9959 Recommendation 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 . ITU-T G.9959 can be used for smart home applications and the transmisstion rage is 100 meters per hop.

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 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 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 . 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 .

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. 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 (PP) 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 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 . DECT-ULE can be used for smart metering in a home.

MS/TP MS/TP is a MAC protocol for the RS-485 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. 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 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 .

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 . 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 (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 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 . NFC can be used for secure transfer services where privacy is important.

PLC PLC is a data transmission technique that utilizes power conductors as medium . 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. Some Available Open Standards in PLC

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

IEEE Std 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 Internet, HDTV, audio, gaming. IEEE Std 1901.1 defines a medium frequency band (less than 12 MHz) broadband PLC technology for smart grid applications based on OFDM(Orthogonal Frequency Division Multiplexing). 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. IEEE Std 1901.2 defines a narrowband variant of PLC with lower data rate but significantly higher transmission range that could be used in an indoor or even an outdoor environment. A typical use case of PLC is smart grid. G3-PLC is a narrowband PLC technology that is based on the ITU-T G.9903 Recommendation . 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.

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.

Guidelines for adopting an 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 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. L2-address-derived IPv6 addresses are specified in , but there exist 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. provides such guidelines. For MAC-derived IPv6 addresses, please refer to 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 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/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 , , and for example guidance.
• Mesh or L3-Routing: 6LoWPAN specifications provide mechanisms to support mesh routing at L2, a configuration called mesh-under . It is also possible to use an L3 routing protocol in 6LoWPAN, an approach known as route-over. 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.
• Address Assignment: 6LoWPAN developed a new version of IPv6 Neighbor Discovery . 6LoWPAN Neighbor Discovery 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 which means it should ignore consumed routing headers and Hop-by-Hop options; when operating in a RPL network , it is also beneficial to support IP-in-IP encapsulation . The 6LoWPAN node should also support 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. 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 and for examples of address assignment considerations. In addition, privacy considerations 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) enables Source Address Validation and protects the address ownership against impersonation attacks.
• 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)
• Host-to-Router interface: 6lo has defined registration extensions for 6LoWPAN Neighbor Discovery . 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
• 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) . The latter RFC federates a number of links into a multilink subnet.
• Header Compression: IPv6 header compression is a vital part of IPv6 over low power communication. Examples of header compression over different link-layer specifications are found in , , and . A generic header compression technique is specified in . For 6LoWPAN networks where RPL is the routing protocol, there exist 6LoWPAN header compression extensions which allow also compressing the RPL artifacts used when forwarding packets in the route-over mesh .
• 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 . The relevant IETF working groups should be consulted for application and transport level security. The IETF has worked on address authentication 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 afford it in terms of processing capabilities and energy consumption.
• Additional processing: defines guidelines for ESC dispatch octets use 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.

6lo Deployment Examples

Wi-SUN usage of 6lo in network layer Wireless Smart Ubiquitous Network (Wi-SUN) is a technology based on IEEE Std 802.15.4g. 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 . The main application domains using Wi-SUN are smart utility and smart city networks. The Wi-SUN Alliance Field Area Network (FAN) covers primarily outdoor networks. The Wi-SUN Field Area Network specification defines an IPv6-based protocol suite including TCP/UDP, IPv6, 6lo adaptation layer, DHCPv6 for IPv6 address management, RPL, and ICMPv6.

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 and IoT platforms, provide end-to-end security, ease development and enable flexible designs . The Thread specification uses the IEEE Std 802.15.4 physical and MAC layers operating at 250 kbps in the 2.4 GHz band. Thread devices use 6LoWPAN, as defined in , 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 . Mesh under routing in Thread is based on a distance vector protocol in a full mesh topology.

G3-PLC usage of 6lo in network layer G3-PLC is a narrowband PLC technology that is based on the ITU-T G.9903 Recommendation . 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 . The ESC dispatch type is used in the G3-PLC to provide fundamental mesh routing and bootstrapping functionalities .

Netricity usage of 6lo in network layer The Netricity program in the HomePlug Powerline Alliance 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 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
• Micro-grids
• 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) objective function based on their own defined Estimated Transmission Time (ETT) metric.

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.

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 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 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) 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.

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 cellular, 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), 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.

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. In this case, additionally, the Fixed Part 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 e.g., 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 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.

Use case of MS/TP: Building Automation Networks The primary use case for IPv6 over MS/TP (6LoBAC) is in building automation networks. is the open, international standard protocol for building automation, and MS/TP is defined in 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, and without the line-of-sight restrictions or hop-by-hop latency of many low-cost wireless solutions.

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. 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 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 cellular connections, the senior citizen 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.

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 segment, whereas connectivity over electricity distribution takes place in the High Voltage segment. Smart grid systems include AMI, Demand Response, Home Energy Management System, 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, 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 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 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 Smart Grid Many sub-systems of 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 sub-system 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 sub-systems.

IANA Considerations There are no IANA considerations related to this document.

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 , , , , , , and . Neighbor Discovery in 6lo links may be susceptible to threats as detailed in . Mesh routing is expected to be common in some 6lo networks, such as ITU-T G.9959 networks, BLE mesh networks and PLC networks. This implies additional threats due to ad hoc routing as per . Most of the L2 technologies considered in this document (i.e., ITU-T G.9959, BLE, 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, TLS/DTLS, object security , and EDHOC(Ephemeral Diffie-Hellman Over COSE) . 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 .

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.

References Normative References This document specifies the Neighbor Discovery protocol for IP Version 6. IPv6 nodes on the same link use Neighbor Discovery to discover each other's presence, to determine each other's link-layer addresses, to find routers, and to maintain reachability information about the paths to active neighbors. [STANDARDS-TRACK] This document specifies the steps a host takes in deciding how to autoconfigure its interfaces in IP version 6. The autoconfiguration process includes generating a link-local address, generating global addresses via stateless address autoconfiguration, and the Duplicate Address Detection procedure to verify the uniqueness of the addresses on a link. [STANDARDS-TRACK] This document describes the assumptions, problem statement, and goals for transmitting IP over IEEE 802.15.4 networks. The set of goals enumerated in this document form an initial set only. This memo provides information for the Internet community. This document describes the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on IEEE 802.15.4 networks. Additional specifications include a simple header compression scheme using shared context and provisions for packet delivery in IEEE 802.15.4 meshes. [STANDARDS-TRACK] This document investigates potential application scenarios and use cases for low-power wireless personal area networks (LoWPANs). This document provides dimensions of design space for LoWPAN applications. A list of use cases and market domains that may benefit and motivate the work currently done in the 6LoWPAN Working Group is provided with the characteristics of each dimension. A complete list of practical use cases is not the goal of this document. This document is not an Internet Standards Track specification; it is published for informational purposes. IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) are formed by devices that are compatible with the IEEE 802.15.4 standard. However, neither the IEEE 802.15.4 standard nor the 6LoWPAN format specification defines how mesh topologies could be obtained and maintained. Thus, it should be considered how 6LoWPAN formation and multi-hop routing could be supported. This document provides the problem statement and design space for 6LoWPAN routing. It defines the routing requirements for 6LoWPANs, considering the low-power and other particular characteristics of the devices and links. The purpose of this document is not to recommend specific solutions but to provide general, layer-agnostic guidelines about the design of 6LoWPAN routing that can lead to further analysis and protocol design. This document is intended as input to groups working on routing protocols relevant to 6LoWPANs, such as the IETF ROLL WG. This document is not an Internet Standards Track specification; it is published for informational purposes. The Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks. RFC 6282 defines header compression in 6LoWPAN packets (where "6LoWPAN" refers to "IPv6 over Low-Power Wireless Personal Area Network"). The present document specifies a simple addition that enables the compression of generic headers and header-like payloads, without a need to define a new header compression scheme for each such new header or header-like payload. This document describes the frame format for transmission of IPv6 packets as well as a method of forming IPv6 link-local addresses and statelessly autoconfigured IPv6 addresses on ITU-T G.9959 networks. Bluetooth Smart is the brand name for the Bluetooth low energy feature in the Bluetooth specification defined by the Bluetooth Special Interest Group. The standard Bluetooth radio has been widely implemented and available in mobile phones, notebook computers, audio headsets, and many other devices. The low-power version of Bluetooth is a specification that enables the use of this air interface with devices such as sensors, smart meters, appliances, etc. The low-power variant of Bluetooth has been standardized since revision 4.0 of the Bluetooth specifications, although version 4.1 or newer is required for IPv6. This document describes how IPv6 is transported over Bluetooth low energy using IPv6 over Low-power Wireless Personal Area Network (6LoWPAN) techniques. Digital Enhanced Cordless Telecommunications (DECT) Ultra Low Energy (ULE) is a low-power air interface technology that is proposed by the DECT Forum and is defined and specified by ETSI. The DECT air interface technology has been used worldwide in communication devices for more than 20 years. It has primarily been used to carry voice for cordless telephony but has also been deployed for data-centric services. DECT ULE is a recent addition to the DECT interface primarily intended for low-bandwidth, low-power applications such as sensor devices, smart meters, home automation, etc. As the DECT ULE interface inherits many of the capabilities from DECT, it benefits from operation that is long-range and interference-free, worldwide- reserved frequency band, low silicon prices, and maturity. There is an added value in the ability to communicate with IPv6 over DECT ULE, such as for Internet of Things applications. This document describes how IPv6 is transported over DECT ULE using IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) techniques. Master-Slave/Token-Passing (MS/TP) is a medium access control method for the RS-485 physical layer and is used primarily in building automation networks. This specification defines the frame format for transmission of IPv6 packets and the method of forming link-local and statelessly autoconfigured IPv6 addresses on MS/TP networks. This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. RFC 7668 describes the adaptation of IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) techniques to enable IPv6 over Bluetooth Low Energy (Bluetooth LE) networks that follow the star topology. However, recent Bluetooth specifications allow the formation of extended topologies as well. This document specifies mechanisms that are needed to enable IPv6 mesh over Bluetooth LE links established by using the Bluetooth Internet Protocol Support Profile (IPSP). This document does not specify the routing protocol to be used in an IPv6 mesh over Bluetooth LE links. Power Line Communication (PLC), namely using electric power lines for indoor and outdoor communications, has been widely applied to support Advanced Metering Infrastructure (AMI), especially smart meters for electricity. The existing electricity infrastructure facilitates the expansion of PLC deployments due to its potential advantages in terms of cost and convenience. Moreover, a wide variety of accessible devices raises the potential demand of IPv6 for future applications. This document describes how IPv6 packets are transported over constrained PLC networks, such as those described in ITU-T G.9903, IEEE 1901.1, and IEEE 1901.2. Informative References Electronics and Telecommunications Research Institute Daejon University DONG-EUI University Near Field Communication (NFC) is a set of standards for smartphones and portable devices to establish radio communication with each other by touching them together or bringing them into proximity, usually no more than 10 cm apart. NFC standards cover communications protocols and data exchange formats, and are based on existing radio-frequency identification (RFID) standards including ISO/IEC 14443 and FeliCa. The standards include ISO/IEC 18092 and those defined by the NFC Forum. The NFC technology has been widely implemented and available in mobile phones, laptop computers, and many other devices. This document describes how IPv6 is transmitted over NFC using 6LoWPAN techniques. Ericsson AB Ericsson AB INRIA This document analyzes and compares the sizes of key exchange flights and the per-packet message size overheads when using different security protocols to secure CoAP. Small message sizes are very important for reducing energy consumption, latency, and time to completion in constrained radio network such as Low-Power Wide Area Networks (LPWANs). The analyzed security protocols are DTLS 1.2, DTLS 1.3, TLS 1.2, TLS 1.3, cTLS, EDHOC, OSCORE, and Group OSCORE. The DTLS and TLS record layers are analyzed with and without 6LoWPAN- GHC compression. DTLS is analyzed with and without Connection ID. The existing IETF standards specify that IPv6 Neighbor Discovery (ND) and Address Autoconfiguration mechanisms may be protected with IPsec Authentication Header (AH). However, the current specifications limit the security solutions to manual keying due to practical problems faced with automatic key management. This document specifies three different trust models and discusses the threats pertinent to IPv6 Neighbor Discovery. The purpose of this discussion is to define the requirements for Securing IPv6 Neighbor Discovery. This memo provides information for the Internet community. This document updates RFC 4944, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks". This document specifies an IPv6 header compression format for IPv6 packet delivery in Low Power Wireless Personal Area Networks (6LoWPANs). The compression format relies on shared context to allow compression of arbitrary prefixes. How the information is maintained in that shared context is out of scope. This document specifies compression of multicast addresses and a framework for compressing next headers. UDP header compression is specified within this framework. [STANDARDS-TRACK] Low-Power and Lossy Networks (LLNs) are a class of network in which both the routers and their interconnect are constrained. LLN routers typically operate with constraints on processing power, memory, and energy (battery power). Their interconnects are characterized by high loss rates, low data rates, and instability. LLNs are comprised of anything from a few dozen to thousands of routers. Supported traffic flows include point-to-point (between devices inside the LLN), point-to-multipoint (from a central control point to a subset of devices inside the LLN), and multipoint-to-point (from devices inside the LLN towards a central control point). This document specifies the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL), which provides a mechanism whereby multipoint-to-point traffic from devices inside the LLN towards a central control point as well as point-to-multipoint traffic from the central control point to the devices inside the LLN are supported. Support for point-to-point traffic is also available. [STANDARDS-TRACK] This memo describes First-Come, First-Served Source Address Validation Improvement (FCFS SAVI), a mechanism that provides source address validation for IPv6 networks using the FCFS principle. The proposed mechanism is intended to complement ingress filtering techniques to help detect and prevent source address spoofing. [STANDARDS-TRACK] The IETF work in IPv6 over Low-power Wireless Personal Area Network (6LoWPAN) defines 6LoWPANs such as IEEE 802.15.4. This and other similar link technologies have limited or no usage of multicast signaling due to energy conservation. In addition, the wireless network may not strictly follow the traditional concept of IP subnets and IP links. IPv6 Neighbor Discovery was not designed for non- transitive wireless links, as its reliance on the traditional IPv6 link concept and its heavy use of multicast make it inefficient and sometimes impractical in a low-power and lossy network. This document describes simple optimizations to IPv6 Neighbor Discovery, its addressing mechanisms, and duplicate address detection for Low- power Wireless Personal Area Networks and similar networks. The document thus updates RFC 4944 to specify the use of the optimizations defined here. [STANDARDS-TRACK] This document discusses how a number of privacy threats apply to technologies designed for IPv6 over various link-layer protocols, and it provides advice to protocol designers on how to address such threats in adaptation-layer specifications for IPv6 over such links. RFC 4944 defines the ESC dispatch type to allow additional dispatch octets in the 6LoWPAN header. The value of the ESC dispatch type was updated by RFC 6282; however, its usage was not defined in either RFC 6282 or RFC 4944. This document updates RFC 4944 and RFC 6282 by defining the ESC extension octet code points and listing registration entries for known use cases at the time of writing of this document. This specification introduces a new IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) dispatch type for use in 6LoWPAN route-over topologies, which initially covers the needs of Routing Protocol for Low-Power and Lossy Networks (RPL) data packet compression (RFC 6550). Using this dispatch type, this specification defines a method to compress the RPL Option (RFC 6553) information and Routing Header type 3 (RFC 6554), an efficient IP-in-IP technique, and is extensible for more applications. This document describes the challenges for energy-efficient protocol operation on constrained devices and the current practices used to overcome those challenges. It summarizes the main link-layer techniques used for energy-efficient networking, and it highlights the impact of such techniques on the upper-layer protocols so that they can together achieve an energy-efficient behavior. The document also provides an overview of energy-efficient mechanisms available at each layer of the IETF protocol suite specified for constrained-node networks. Low-Power Wide Area Networks (LPWANs) are wireless technologies with characteristics such as large coverage areas, low bandwidth, possibly very small packet and application-layer data sizes, and long battery life operation. This memo is an informational overview of the set of LPWAN technologies being considered in the IETF and of the gaps that exist between the needs of those technologies and the goal of running IP in LPWANs. This specification updates RFC 6775 -- the Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor Discovery specification -- to clarify the role of the protocol as a registration technique and simplify the registration operation in 6LoWPAN routers, as well as to provide enhancements to the registration capabilities and mobility detection for different network topologies, including the Routing Registrars performing routing for host routes and/or proxy Neighbor Discovery in a low-power network. This document defines Object Security for Constrained RESTful Environments (OSCORE), a method for application-layer protection of the Constrained Application Protocol (CoAP), using CBOR Object Signing and Encryption (COSE). OSCORE provides end-to-end protection between endpoints communicating using CoAP or CoAP-mappable HTTP. OSCORE is designed for constrained nodes and networks supporting a range of proxy operations, including translation between different transport protocols. Although an optional functionality of CoAP, OSCORE alters CoAP options processing and IANA registration. Therefore, this document updates RFC 7252. This document updates the IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor Discovery (ND) protocol defined in RFCs 6775 and 8505. The new extension is called Address-Protected Neighbor Discovery (AP-ND), and it protects the owner of an address against address theft and impersonation attacks in a Low-Power and Lossy Network (LLN). Nodes supporting this extension compute a cryptographic identifier (Crypto-ID), and use it with one or more of their Registered Addresses. The Crypto-ID identifies the owner of the Registered Address and can be used to provide proof of ownership of the Registered Addresses. Once an address is registered with the Crypto-ID and a proof of ownership is provided, only the owner of that address can modify the registration information, thereby enforcing Source Address Validation. This document updates RFCs 6775 and 8505 in order to enable proxy services for IPv6 Neighbor Discovery by Routing Registrars called "Backbone Routers". Backbone Routers are placed along the wireless edge of a backbone and federate multiple wireless links to form a single Multi-Link Subnet (MLSN). This document looks at different data flows through Low-Power and Lossy Networks (LLN) where RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks) is used to establish routing. The document enumerates the cases where RPL Packet Information (RPI) Option Type (RFC 6553), RPL Source Route Header (RFC 6554), and IPv6-in-IPv6 encapsulation are required in the data plane. This analysis provides the basis upon which to design efficient compression of these headers. This document updates RFC 6553 by adding a change to the RPI Option Type. Additionally, this document updates RFC 6550 by defining a flag in the DODAG Information Object (DIO) Configuration option to indicate this change and updates RFC 8138 as well to consider the new Option Type when the RPL Option is decompressed. This specification provides a mechanism for a host that implements a routing-agnostic interface based on IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor Discovery to obtain reachability services across a network that leverages RFC 6550 for its routing operations. It updates RFCs 6550, 6775, and 8505. This document updates RFC 8138 by defining a bit in the Routing Protocol for Low-Power and Lossy Networks (RPL) Destination-Oriented Directed Acyclic Graph (DODAG) Configuration option to indicate whether compression is used within the RPL Instance and to specify the behavior of nodes compliant with RFC 8138 when the bit is set and unset. Ericsson AB Ericsson AB Ericsson AB Work in Progress Bluetooth Special Interest Group Bluetooth Special Interest Group ETSI ETSI

Design Space Dimensions for 6lo Deployment 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 , 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:

• 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 support.
• Multi-link subnet, single subnet: The selection of multi-link subnet and single subnet depends on connectivity and the number of 6lo nodes.
• 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.
• Buffering requirements: Some 6lo use case may require 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 case 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 case related to health service, the measured data must be recorded with exact time.
• Reliability and QoS: Some 6lo use case requires 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 case 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 . Each link layer technology defines a particular power use strategy which may be tuned . Readers are expected to be familiar with terminology.
• Update firmware requirements: Most 6lo use cases will need a mechanism for updating 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/wireless technologies.