LWIG Working Group C. Bormann Internet-Draft Universitaet Bremen TZI Intended status: Informational M. Ersue Expires: May 3, 2018 Nokia Solutions and Networks A. Keranen Ericsson C. Gomez UPC/i2CAT October 30, 2017 Terminology for Constrained-Node Networks draft-bormann-lwig-7228bis-02 Abstract 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. 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 working documents as Internet-Drafts. The list of current Internet- 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 May 3, 2018. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Bormann, et al. Expires May 3, 2018 [Page 1] Internet-Draft CNN Terminology October 2017 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. Core Terminology . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Constrained Nodes . . . . . . . . . . . . . . . . . . . . 4 2.2. Constrained Networks . . . . . . . . . . . . . . . . . . 5 2.2.1. Challenged Networks . . . . . . . . . . . . . . . . . 6 2.3. Constrained-Node Networks . . . . . . . . . . . . . . . . 6 2.3.1. LLN . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3.2. LoWPAN, 6LoWPAN . . . . . . . . . . . . . . . . . . . 7 3. Classes of Constrained Devices . . . . . . . . . . . . . . . 8 4. Power Terminology . . . . . . . . . . . . . . . . . . . . . . 11 4.1. Scaling Properties . . . . . . . . . . . . . . . . . . . 11 4.2. Classes of Energy Limitation . . . . . . . . . . . . . . 12 4.3. Strategies for Using Power for Communication . . . . . . 12 5. Classes of Networks . . . . . . . . . . . . . . . . . . . . . 14 5.1. Classes of link layer MTU size . . . . . . . . . . . . . 14 5.2. Class of Internet Integration . . . . . . . . . . . . . . 15 5.3. Classes of physical layer bit rate . . . . . . . . . . . 16 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 8. Informative References . . . . . . . . . . . . . . . . . . . 17 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 1. Introduction Small devices with limited CPU, memory, and power resources, so- called "constrained devices" (often used as sensors/actuators, smart objects, or smart devices) can form a network, becoming "constrained nodes" in that network. Such a network may itself exhibit constraints, e.g., with unreliable or lossy channels, limited and unpredictable bandwidth, and a highly dynamic topology. Constrained devices might be in charge of gathering information in diverse settings, including natural ecosystems, buildings, and factories, and sending the information to one or more server stations. They might also act on information, by performing some physical action, including displaying it. Constrained devices may work under severe resource constraints such as limited battery and computing power, little memory, and insufficient wireless bandwidth and ability to communicate; these constraints often exacerbate each Bormann, et al. Expires May 3, 2018 [Page 2] Internet-Draft CNN Terminology October 2017 other. Other entities on the network, e.g., a base station or controlling server, might have more computational and communication resources and could support the interaction between the constrained devices and applications in more traditional networks. Today, diverse sizes of constrained devices with different resources and capabilities are becoming connected. Mobile personal gadgets, building-automation devices, cellular phones, machine-to-machine (M2M) devices, and other devices benefit from interacting with other "things" nearby or somewhere in the Internet. With this, the Internet of Things (IoT) becomes a reality, built up out of uniquely identifiable and addressable objects (things). Over the next decade, this could grow to large numbers [FIFTY-BILLION] of Internet- connected constrained devices, greatly increasing the Internet's size and scope. The present document provides a number of basic terms that have been useful in the standardization work for constrained environments. The intention is not to exhaustively cover the field but to make sure a few core terms are used consistently between different groups cooperating in this space. The present document is an update of [RFC7228]. In this document, the term "byte" is used in its now customary sense as a synonym for "octet". Where sizes of semiconductor memory are given, the prefix "kibi" (1024) is combined with "byte" to "kibibyte", abbreviated "KiB", for 1024 bytes [ISQ-13]. In computing, the term "power" is often used for the concept of "computing power" or "processing power", as in CPU performance. In this document, the term stands for electrical power unless explicitly stated otherwise. "Mains-powered" is used as a shorthand for being permanently connected to a stable electrical power grid. 2. Core Terminology There are two important aspects to _scaling_ within the Internet of Things: o scaling up Internet technologies to a large number [FIFTY-BILLION] of inexpensive nodes, while o scaling down the characteristics of each of these nodes and of the networks being built out of them, to make this scaling up economically and physically viable. Bormann, et al. Expires May 3, 2018 [Page 3] Internet-Draft CNN Terminology October 2017 The need for scaling down the characteristics of nodes leads to "constrained nodes". 2.1. Constrained Nodes The term "constrained node" is best defined by contrasting the characteristics of a constrained node with certain widely held expectations on more familiar Internet nodes: Constrained Node: A node where some of the characteristics that are otherwise pretty much taken for granted for Internet nodes at the time of writing are not attainable, often due to cost constraints and/or physical constraints on characteristics such as size, weight, and available power and energy. The tight limits on power, memory, and processing resources lead to hard upper bounds on state, code space, and processing cycles, making optimization of energy and network bandwidth usage a dominating consideration in all design requirements. Also, some layer-2 services such as full connectivity and broadcast/multicast may be lacking. While this is not a rigorous definition, it is grounded in the state of the art and clearly sets apart constrained nodes from server systems, desktop or laptop computers, powerful mobile devices such as smartphones, etc. There may be many design considerations that lead to these constraints, including cost, size, weight, and other scaling factors. (An alternative term, when the properties as a network node are not in focus, is "constrained device".) There are multiple facets to the constraints on nodes, often applying in combination, for example: o constraints on the maximum code complexity (ROM/Flash), o constraints on the size of state and buffers (RAM), o constraints on the amount of computation feasible in a period of time ("processing power"), o constraints on the available power, and o constraints on user interface and accessibility in deployment (ability to set keys, update software, etc.). Section 3 defines a small number of interesting classes ("class-N" for N = 0, 1, 2) of constrained nodes focusing on relevant combinations of the first two constraints. With respect to available Bormann, et al. Expires May 3, 2018 [Page 4] Internet-Draft CNN Terminology October 2017 power, [RFC6606] distinguishes "power-affluent" nodes (mains-powered or regularly recharged) from "power-constrained nodes" that draw their power from primary batteries or by using energy harvesting; more detailed power terminology is given in Section 4. The use of constrained nodes in networks often also leads to constraints on the networks themselves. However, there may also be constraints on networks that are largely independent from those of the nodes. We therefore distinguish "constrained networks" from "constrained-node networks". 2.2. Constrained Networks We define "constrained network" in a similar way: Constrained Network: A network where some of the characteristics pretty much taken for granted with link layers in common use in the Internet at the time of writing are not attainable. Constraints may include: o low achievable bitrate/throughput (including limits on duty cycle), o high packet loss and high variability of packet loss (delivery rate), o highly asymmetric link characteristics, o severe penalties for using larger packets (e.g., high packet loss due to link-layer fragmentation), o limits on reachability over time (a substantial number of devices may power off at any point in time but periodically "wake up" and can communicate for brief periods of time), and o lack of (or severe constraints on) advanced services such as IP multicast. More generally, we speak of constrained networks whenever at least some of the nodes involved in the network exhibit these characteristics. Again, there may be several reasons for this: o cost constraints on the network, o constraints posed by the nodes (for constrained-node networks), Bormann, et al. Expires May 3, 2018 [Page 5] Internet-Draft CNN Terminology October 2017 o physical constraints (e.g., power constraints, environmental constraints, media constraints such as underwater operation, limited spectrum for very high density, electromagnetic compatibility), o regulatory constraints, such as very limited spectrum availability (including limits on effective radiated power and duty cycle) or explosion safety, and o technology constraints, such as older and lower-speed technologies that are still operational and may need to stay in use for some more time. 2.2.1. Challenged Networks A constrained network is not necessarily a "challenged network" [FALL]: Challenged Network: A network that has serious trouble maintaining what an application would today expect of the end-to-end IP model, e.g., by: * not being able to offer end-to-end IP connectivity at all, * exhibiting serious interruptions in end-to-end IP connectivity, or * exhibiting delay well beyond the Maximum Segment Lifetime (MSL) defined by TCP [RFC0793]. All challenged networks are constrained networks in some sense, but not all constrained networks are challenged networks. There is no well-defined boundary between the two, though. Delay-Tolerant Networking (DTN) has been designed to cope with challenged networks [RFC4838]. 2.3. Constrained-Node Networks Constrained-Node Network: A network whose characteristics are influenced by being composed of a significant portion of constrained nodes. A constrained-node network always is a constrained network because of the network constraints stemming from the node constraints, but it may also have other constraints that already make it a constrained network. Bormann, et al. Expires May 3, 2018 [Page 6] Internet-Draft CNN Terminology October 2017 The rest of this subsection introduces two additional terms that are in active use in the area of constrained-node networks, without an intent to define them: LLN and (6)LoWPAN. 2.3.1. LLN A related term that has been used to describe the focus of the IETF ROLL working group is "Low-Power and Lossy Network (LLN)". The ROLL (Routing Over Low-Power and Lossy) terminology document [RFC7102] defines LLNs as follows: LLN: Low-Power and Lossy Network. Typically composed of many embedded devices with limited power, memory, and processing resources interconnected by a variety of links, such as IEEE 802.15.4 or low-power Wi-Fi. There is a wide scope of application areas for LLNs, including industrial monitoring, building automation (heating, ventilation, and air conditioning (HVAC), lighting, access control, fire), connected home, health care, environmental monitoring, urban sensor networks, energy management, assets tracking, and refrigeration. Beyond that, LLNs often exhibit considerable loss at the physical layer, with significant variability of the delivery rate, and some short-term unreliability, coupled with some medium-term stability that makes it worthwhile to both construct directed acyclic graphs that are medium-term stable for routing and do measurements on the edges such as Expected Transmission Count (ETX) [RFC6551]. Not all LLNs comprise low-power nodes [I-D.hui-vasseur-roll-rpl-deployment]. LLNs typically are composed of constrained nodes; this leads to the design of operation modes such as the "non-storing mode" defined by RPL (the IPv6 Routing Protocol for Low-Power and Lossy Networks [RFC6550]). So, in the terminology of the present document, an LLN is a constrained-node network with certain network characteristics, which include constraints on the network as well. 2.3.2. LoWPAN, 6LoWPAN One interesting class of a constrained network often used as a constrained-node network is "LoWPAN" [RFC4919], a term inspired from the name of an IEEE 802.15.4 working group (low-rate wireless personal area networks (LR-WPANs)). The expansion of the LoWPAN acronym, "Low-Power Wireless Personal Area Network", contains a hard- to-justify "Personal" that is due to the history of task group naming in IEEE 802 more than due to an orientation of LoWPANs around a single person. Actually, LoWPANs have been suggested for urban monitoring, control of large buildings, and industrial control applications, so the "Personal" can only be considered a vestige. Bormann, et al. Expires May 3, 2018 [Page 7] Internet-Draft CNN Terminology October 2017 Occasionally, the term is read as "Low-Power Wireless Area Networks" [WEI]. Originally focused on IEEE 802.15.4, "LoWPAN" (or when used for IPv6, "6LoWPAN") also refers to networks built from similarly constrained link-layer technologies [RFC7668] [RFC8105] [RFC7428]. 3. Classes of Constrained Devices Despite the overwhelming variety of Internet-connected devices that can be envisioned, it may be worthwhile to have some succinct terminology for different classes of constrained devices. Before we get to that, let's first distinguish two big rough groups of devices based on their CPU capabilities: o Microcontroller-class devices (ARM term: "M-class" [need ref]). These often (but not always) include RAM and code storage on chip and limit their support for general-purpose operating systems, e.g., they do not have an MMU (memory management unit). They use most of their pins for interfaces to application hardware such as digital in/out (the latter often PWM-controllable), ADC/DACs, etc. Where this hardware is specialized for an application, we may talk about "Systems on a Chip" (SOC). These devices often implement elaborate sleep modes to achieve microwatt- or at least milliwatt- level sustained power usage (Ps, see below). o General-purpose-class devices (ARM term: "A-class"). These usually have RAM and Flash storage on separate chips (not always separate packages), and offer support for general-purpose operating systems such as Linux, e.g. an MMU. Many of the pins on the CPU chip are dedidated to interfacing with RAM and other memory. Some general-purpose-class devices integrate some application hardware such as video controllers, these are often called "Systems on a Chip" (SOC). While these chips also include sleep modes, they are usually more on the watt side of sustained power usage (Ps). If the distinction between these groups needs to be made in this document, we distinguish group "M" (microcontroller) from group "J" (general purpose). In this document, the class designations in Table 1 may be used as rough indications of device capabilities. Note that the classes from 10 upwards are not really constrained devices in the sense of the previous section; they may still be useful to discuss constraints in larger devices: Bormann, et al. Expires May 3, 2018 [Page 8] Internet-Draft CNN Terminology October 2017 +-------+-----------+---------------+-----------------+-------------+ | Group | Name | data size | code size | Examples | | | | (e.g., RAM) | (e.g., Flash) | | +-------+-----------+---------------+-----------------+-------------+ | M | Class 0, | << 10 KiB | << 100 KiB | | | | C0 | | | | | | | | | | | M | Class 1, | ~ 10 KiB | ~ 100 KiB | | | | C1 | | | | | | | | | | | M | Class 2, | ~ 50 KiB | ~ 250 KiB | | | | C2 | | | | | | | | | | | J | Class 10, | 4-8 MiB | (?) | OpenWRT | | | C10 | | | routers | | | | | | | | J | | fill in | J-group classes | | | | | useful | | | | | | | | | | J | Class 13, | 0.5..1 GiB | (lots) | Raspberry | | | C13 | | | PI | | | | | | | | J | Class 15, | 1..2 GiB | (lots) | Smartphones | | | C15 | | | | | | | | | | | J | Class 16, | 4..32 GiB | (lots) | Laptops | | | C16 | | | | | | | | | | | J | Class 19, | (lots) | (lots) | Servers | | | C19 | | | | +-------+-----------+---------------+-----------------+-------------+ Table 1: Classes of Constrained Devices (KiB = 1024 bytes) As of the writing of this document, these characteristics correspond to distinguishable clusters of commercially available chips and design cores for constrained devices. While it is expected that the boundaries of these classes will move over time, Moore's law tends to be less effective in the embedded space than in personal computing devices: gains made available by increases in transistor count and density are more likely to be invested in reductions of cost and power requirements than into continual increases in computing power. Class 0 devices are very constrained sensor-like motes. They are so severely constrained in memory and processing capabilities that most likely they will not have the resources required to communicate directly with the Internet in a secure manner (rare heroic, narrowly targeted implementation efforts notwithstanding). Class 0 devices Bormann, et al. Expires May 3, 2018 [Page 9] Internet-Draft CNN Terminology October 2017 will participate in Internet communications with the help of larger devices acting as proxies, gateways, or servers. Class 0 devices generally cannot be secured or managed comprehensively in the traditional sense. They will most likely be preconfigured (and will be reconfigured rarely, if at all) with a very small data set. For management purposes, they could answer keepalive signals and send on/ off or basic health indications. Class 1 devices are quite constrained in code space and processing capabilities, such that they cannot easily talk to other Internet nodes employing a full protocol stack such as using HTTP, Transport Layer Security (TLS), and related security protocols and XML-based data representations. However, they are capable enough to use a protocol stack specifically designed for constrained nodes (such as the Constrained Application Protocol (CoAP) over UDP [RFC7252]) and participate in meaningful conversations without the help of a gateway node. In particular, they can provide support for the security functions required on a large network. Therefore, they can be integrated as fully developed peers into an IP network, but they need to be parsimonious with state memory, code space, and often power expenditure for protocol and application usage. Class 2 devices are less constrained and fundamentally capable of supporting most of the same protocol stacks as used on notebooks or servers. However, even these devices can benefit from lightweight and energy-efficient protocols and from consuming less bandwidth. Furthermore, using fewer resources for networking leaves more resources available to applications. Thus, using the protocol stacks defined for more constrained devices on Class 2 devices might reduce development costs and increase the interoperability. Constrained devices with capabilities significantly beyond Class 2 devices exist. They are less demanding from a standards development point of view as they can largely use existing protocols unchanged. The present document therefore does not make any attempt to define constrained classes beyond Class 2. These devices, and to a certain extent even J-group devices, can still be constrained by a limited energy supply. With respect to examining the capabilities of constrained nodes, particularly for Class 1 devices, it is important to understand what type of applications they are able to run and which protocol mechanisms would be most suitable. Because of memory and other limitations, each specific Class 1 device might be able to support only a few selected functions needed for its intended operation. In other words, the set of functions that can actually be supported is not static per device type: devices with similar constraints might choose to support different functions. Even though Class 2 devices Bormann, et al. Expires May 3, 2018 [Page 10] Internet-Draft CNN Terminology October 2017 have some more functionality available and may be able to provide a more complete set of functions, they still need to be assessed for the type of applications they will be running and the protocol functions they would need. To be able to derive any requirements, the use cases and the involvement of the devices in the application and the operational scenario need to be analyzed. Use cases may combine constrained devices of multiple classes as well as more traditional Internet nodes. 4. Power Terminology Devices not only differ in their computing capabilities but also in available power and/or energy. While it is harder to find recognizable clusters in this space, it is still useful to introduce some common terminology. 4.1. Scaling Properties The power and/or energy available to a device may vastly differ, from kilowatts to microwatts, from essentially unlimited to hundreds of microjoules. Instead of defining classes or clusters, we simply state, using the International System of Units (SI units), an approximate value for one or both of the quantities listed in Table 2: +------+--------------------------------------------------+---------+ | Name | Definition | SI Unit | +------+--------------------------------------------------+---------+ | Ps | Sustainable average power available for the | W | | | device over the time it is functioning | (Watt) | | | | | | Et | Total electrical energy available before the | J | | | energy source is exhausted | (Joule) | +------+--------------------------------------------------+---------+ Table 2: Quantities Relevant to Power and Energy The value of Et may need to be interpreted in conjunction with an indication over which period of time the value is given; see Section 4.2. Some devices enter a "low-power" mode before the energy available in a period is exhausted or even have multiple such steps on the way to exhaustion. For these devices, Ps would need to be given for each of the modes/steps. Bormann, et al. Expires May 3, 2018 [Page 11] Internet-Draft CNN Terminology October 2017 4.2. Classes of Energy Limitation As discussed above, some devices are limited in available energy as opposed to (or in addition to) being limited in available power. Where no relevant limitations exist with respect to energy, the device is classified as E9. The energy limitation may be in total energy available in the usable lifetime of the device (e.g., a device that is discarded when its non-replaceable primary battery is exhausted), classified as E2. Where the relevant limitation is for a specific period, the device is classified as E1, e.g., a solar- powered device with a limited amount of energy available for the night, a device that is manually connected to a charger and has a period of time between recharges, or a device with a periodic (primary) battery replacement interval. Finally, there may be a limited amount of energy available for a specific event, e.g., for a button press in an energy-harvesting light switch; such devices are classified as E0. Note that, in a sense, many E1 devices are also E2, as the rechargeable battery has a limited number of useful recharging cycles. Table 3 provides a summary of the classifications described above. +------+------------------------------+-----------------------------+ | Name | Type of energy limitation | Example Power Source | +------+------------------------------+-----------------------------+ | E0 | Event energy-limited | Event-based harvesting | | | | | | E1 | Period energy-limited | Battery that is | | | | periodically recharged or | | | | replaced | | | | | | E2 | Lifetime energy-limited | Non-replaceable primary | | | | battery | | | | | | E9 | No direct quantitative | Mains-powered | | | limitations to available | | | | energy | | +------+------------------------------+-----------------------------+ Table 3: Classes of Energy Limitation 4.3. Strategies for Using Power for Communication Especially when wireless transmission is used, the radio often consumes a big portion of the total energy consumed by the device. Design parameters, such as the available spectrum, the desired range, and the bitrate aimed for, influence the power consumed during transmission and reception; the duration of transmission and Bormann, et al. Expires May 3, 2018 [Page 12] Internet-Draft CNN Terminology October 2017 reception (including potential reception) influence the total energy consumption. Different strategies for power usage and network attachment may be used, based on the type of the energy source (e.g., battery or mains- powered) and the frequency with which a device needs to communicate. The general strategies for power usage can be described as follows: Always-on: This strategy is most applicable if there is no reason for extreme measures for power saving. The device can stay on in the usual manner all the time. It may be useful to employ power- friendly hardware or limit the number of wireless transmissions, CPU speeds, and other aspects for general power-saving and cooling needs, but the device can be connected to the network all the time. Normally-off: Under this strategy, the device sleeps such long periods at a time that once it wakes up, it makes sense for it to not pretend that it has been connected to the network during sleep: the device reattaches to the network as it is woken up. The main optimization goal is to minimize the effort during the reattachment process and any resulting application communications. If the device sleeps for long periods of time and needs to communicate infrequently, the relative increase in energy expenditure during reattachment may be acceptable. Low-power: This strategy is most applicable to devices that need to operate on a very small amount of power but still need to be able to communicate on a relatively frequent basis. This implies that extremely low-power solutions need to be used for the hardware, chosen link-layer mechanisms, and so on. Typically, given the small amount of time between transmissions, despite their sleep state, these devices retain some form of attachment to the network. Techniques used for minimizing power usage for the network communications include minimizing any work from re- establishing communications after waking up and tuning the frequency of communications (including "duty cycling", where components are switched on and off in a regular cycle) and other parameters appropriately. Table 4 provides a summary of the strategies described above. Bormann, et al. Expires May 3, 2018 [Page 13] Internet-Draft CNN Terminology October 2017 +------+--------------+---------------------------------------------+ | Name | Strategy | Ability to communicate | +------+--------------+---------------------------------------------+ | P0 | Normally-off | Reattach when required | | | | | | P1 | Low-power | Appears connected, perhaps with high | | | | latency | | | | | | P9 | Always-on | Always connected | +------+--------------+---------------------------------------------+ Table 4: Strategies of Using Power for Communication Note that the discussion above is at the device level; similar considerations can apply at the communications-interface level. This document does not define terminology for the latter. A term often used to describe power-saving approaches is "duty- cycling". This describes all forms of periodically switching off some function, leaving it on only for a certain percentage of time (the "duty cycle"). [RFC7102] only distinguishes two levels, defining a Non-Sleepy Node as a node that always remains in a fully powered-on state (always awake) where it has the capability to perform communication (P9) and a Sleepy Node as a node that may sometimes go into a sleep mode (a low-power state to conserve power) and temporarily suspend protocol communication (P0); there is no explicit mention of P1. 5. Classes of Networks 5.1. Classes of link layer MTU size Link layer technologies used by constrained devices can be categorized on the basis of link layer MTU size. Depending on this parameter, the fragmentation techniques needed (if any) to support the IPv6 MTU requirement may vary. We define the following classes of link layer MTU size: Bormann, et al. Expires May 3, 2018 [Page 14] Internet-Draft CNN Terminology October 2017 +------+---------------------+------------------------------------+ | Name | L2 MTU size (bytes) | 6LoWPAN Fragmentation applicable*? | +------+---------------------+------------------------------------+ | S0 | 3 - 12 | need new kind of fragmentation | | | | | | S1 | 13 - 127 | yes | | | | | | S2 | 128 - 1279 | yes | | | | | | S2 | >= 1280 | no fragmentation needed | +------+---------------------+------------------------------------+ *if no link layer fragmentation is available (note: 'Sx' stands for 'Size x') S0 technologies require fragmentation to support the IPv6 MTU requirement. If no link layer fragmentation is available, fragmentation is needed at the adaptation layer below IPv6. However, 6LoWPAN fragmentation [RFC4944] cannot be used for these technologies, given the extremely reduced link layer MTU. In this case, lightweight fragmentation formats must be used (e.g. [I-D.ietf-lpwan-ipv6-static-context-hc]). S1 and S2 technologies require fragmentation at the subnetwork level to support the IPv6 MTU requirement. If link layer fragmentation is unavailable or insufficient, fragmentation is needed at the adaptation layer below IPv6. 6LoWPAN fragmentation [RFC4944] can be used to carry 1280-byte IPv6 packets over these technologies. S3 technologies do not require fragmentation to support the IPv6 MTU requirement. 5.2. Class of Internet Integration The term "Internet of Things" is sometimes confusingly used for connected devices that are not actually employing Internet technology. Some devices do use Internet technology, but only use it to exchange packets with a fixed communication partner ("device-to- cloud" scenarios, [RFC7452]). More general devices are prepared to communicate with other nodes in the Internet as well. We define the following classes of Internet technology level: Bormann, et al. Expires May 3, 2018 [Page 15] Internet-Draft CNN Terminology October 2017 +------+--------------------------------------+ | Name | Internet technology | +------+--------------------------------------+ | I0 | none (local interconnect only) | | | | | I1 | device-to-cloud only | | | | | I9 | full Internet connectivity supported | +------+--------------------------------------+ 5.3. Classes of physical layer bit rate [This section is a trial balloon. We could also talk about burst rate, sustained rate; bits/s, messages/s, ...] Physical layer technologies used by constrained devices can be categorized on the basis of physical layer (PHY) bit rate. The PHY bit rate class of a technology has important implications with regard to compatibility with existing protocols and mechanisms on the Internet, responsiveness to frame transmissions and need for header compression techniques. We define the following classes of PHY bit rate: +------+------------+-----------------------------------------------+ | Name | PHY bit | Comment | | | rate | | | | (bit/s) | | +------+------------+-----------------------------------------------+ | B0 | < 10 | Tx time of 150-byte frame > MSL | | | | | | B1 | 10 - 10^3 | Unresponsiveness if human expects reaction to | | | | sent frame (frame size > 62.5 byte) | | | | | | B2 | 10^3 - | Responsiveness if human expects reaction to | | | 10^6 | sent frame, but header compression still | | | | needed | | | | | | B3 | > 10^6 | Header compression yields relatively low | | | | performance benefits | +------+------------+-----------------------------------------------+ (note: 'Bx' stands for 'Bit rate x') B0 technologies lead to very high transmission times, which may be close to or even greater than the Maximum Segment Lifetime (MSL) assumed on the Internet [RFC0793]. Many Internet protocols and mechanisms will fail when transmit times are greater than the MSL. Bormann, et al. Expires May 3, 2018 [Page 16] Internet-Draft CNN Terminology October 2017 B0 technologies lead to a frame transmission time greater than the MSL for a frame size greater than 150 bytes. B1 technologies offer transmission times which are lower than the MSL (for a frame size greater than 150 bytes). However, transmission times for B1 technologies are still significant if a human expects a reaction to the transmission of a frame. With B1 technologies, the transmission time of a frame greater than 62.5 bytes exceeds 0.5 seconds, i.e. a threshold time beyond which any response or reaction to a frame transmission will appear not to be immediate [RFC5826]. B2 technologies do not incur responsiveness problems, but still benefit from using header compression techniques (e.g. [RFC6282]) to achieve performance improvements. Over B3 technologies, the relative performance benefits of header compression are low. For example, in a duty-cycled technology offering B3 PHY bit rates, energy consumption decrease due to header compression may be comparable with the energy consumed while in a sleep interval. On the other hand, for B3 PHY bit rates, a human user will not be able to perceive whether header compression has been used or not in a frame transmission. 6. IANA Considerations This document makes no requests of IANA. 7. Security Considerations This document introduces common terminology that does not raise any new security issues. Security considerations arising from the constraints discussed in this document need to be discussed in the context of specific protocols. For instance, Section 11.6 of [RFC7252], "Constrained node considerations", discusses implications of specific constraints on the security mechanisms employed. [RFC7416] provides a security threat analysis for the RPL routing protocol. Implementation considerations for security protocols on constrained nodes are discussed in [RFC7815] and [I-D.ietf-lwig-tls-minimal]. A wider view of security in constrained-node networks is provided in [I-D.irtf-t2trg-iot-seccons]. 8. Informative References [FALL] Fall, K., "A Delay-Tolerant Network Architecture for Challenged Internets", SIGCOMM 2003, DOI 10.1145/863955.863960, 2003. Bormann, et al. Expires May 3, 2018 [Page 17] Internet-Draft CNN Terminology October 2017 [FIFTY-BILLION] Ericsson, "More Than 50 Billion Connected Devices", Ericsson White Paper 284 23-3149 Uen, February 2011, . [I-D.hui-vasseur-roll-rpl-deployment] Vasseur, J., Hui, J., Dasgupta, S., and G. Yoon, "RPL deployment experience in large scale networks", draft-hui- vasseur-roll-rpl-deployment-01 (work in progress), July 2012. [I-D.ietf-lpwan-ipv6-static-context-hc] Minaburo, A., Toutain, L., and C. Gomez, "LPWAN Static Context Header Compression (SCHC) and fragmentation for IPv6 and UDP", draft-ietf-lpwan-ipv6-static-context-hc-07 (work in progress), October 2017. [I-D.ietf-lwig-tls-minimal] Kumar, S., Keoh, S., and H. Tschofenig, "A Hitchhiker's Guide to the (Datagram) Transport Layer Security Protocol for Smart Objects and Constrained Node Networks", draft- ietf-lwig-tls-minimal-01 (work in progress), March 2014. [I-D.irtf-t2trg-iot-seccons] Garcia-Morchon, O., Kumar, S., and M. Sethi, "State-of- the-Art and Challenges for the Internet of Things Security", draft-irtf-t2trg-iot-seccons-08 (work in progress), October 2017. [ISQ-13] International Electrotechnical Commission, "International Standard -- Quantities and units -- Part 13: Information science and technology", IEC 80000-13, March 2008. [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, . [RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant Networking Architecture", RFC 4838, DOI 10.17487/RFC4838, April 2007, . [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, . Bormann, et al. Expires May 3, 2018 [Page 18] Internet-Draft CNN Terminology October 2017 [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, . [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, . [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, . [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, . [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., and D. Barthel, "Routing Metrics Used for Path Calculation in Low-Power and Lossy Networks", RFC 6551, DOI 10.17487/RFC6551, March 2012, . [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, . [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 2014, . [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . Bormann, et al. Expires May 3, 2018 [Page 19] Internet-Draft CNN Terminology October 2017 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., and M. Richardson, Ed., "A Security Threat Analysis for the Routing Protocol for Low-Power and Lossy Networks (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, . [RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets over ITU-T G.9959 Networks", RFC 7428, DOI 10.17487/RFC7428, February 2015, . [RFC7452] Tschofenig, H., Arkko, J., Thaler, D., and D. McPherson, "Architectural Considerations in Smart Object Networking", RFC 7452, DOI 10.17487/RFC7452, March 2015, . [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, . [RFC7815] Kivinen, T., "Minimal Internet Key Exchange Version 2 (IKEv2) Initiator Implementation", RFC 7815, DOI 10.17487/RFC7815, March 2016, . [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, . [WEI] Shelby, Z. and C. Bormann, "6LoWPAN: the Wireless Embedded Internet", Wiley-Blackwell monograph, DOI 10.1002/9780470686218, ISBN 9780470747995, 2009. Bormann, et al. Expires May 3, 2018 [Page 20] Internet-Draft CNN Terminology October 2017 Acknowledgements TBD Authors' Addresses Carsten Bormann Universitaet Bremen TZI Postfach 330440 Bremen D-28359 Germany Phone: +49-421-218-63921 EMail: cabo@tzi.org Mehmet Ersue Nokia Solutions and Networks St.-Martinstrasse 76 Munich 81541 Germany Phone: +49 172 8432301 EMail: mehmet.ersue@nsn.com Ari Keranen Ericsson Hirsalantie 11 Jorvas 02420 Finland EMail: ari.keranen@ericsson.com Carles Gomez UPC/i2CAT Escola d'Enginyeria de Telecomunicacio i Aeroespacial de Castelldefels C/Esteve Terradas, 7 Castelldefels 08860 Spain Phone: +34-93-413-7206 EMail: carlesgo@entel.upc.edu Bormann, et al. Expires May 3, 2018 [Page 21]