LLN Routing Terms: Terms Used in Routing for Low-Power and Lossy Networks
The shared vocabulary for routing in networks of tiny, battery-powered devices.
Vasseur, JP., "Terms Used in Routing for Low-Power and Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 2014, <https://www.rfc-editor.org/info/rfc7102>.
@misc{rfc7102,
series = {Request for Comments},
number = 7102,
howpublished = {RFC 7102},
publisher = {RFC Editor},
doi = {10.17487/RFC7102},
url = {https://www.rfc-editor.org/info/rfc7102},
author = {JP. Vasseur},
title = {{Terms Used in Routing for Low-Power and Lossy Networks}},
pagetotal = 8,
year = 2014,
month = jan,
} RFC text
Contents
Internet Engineering Task Force (IETF) JP. Vasseur
Request for Comments: 7102 Cisco Systems, Inc.
Category: Informational January 2014
ISSN: 2070-1721
Terms Used in Routing for Low-Power and Lossy Networks
Abstract
This document provides a glossary of terminology used in routing
requirements and solutions for networks referred to as Low-Power and
Lossy Networks (LLNs). An LLN is typically composed of many embedded
devices with limited power, memory, and processing resources
interconnected by a variety of links. There is a wide scope of
application areas for LLNs, including industrial monitoring, building
automation (e.g., heating, ventilation, air conditioning, lighting,
access control, fire), connected home, health care, environmental
monitoring, urban sensor networks, energy management, assets
tracking, and refrigeration.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7102.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................3
3. Security Considerations .........................................7
4. Acknowledgements ................................................7
5. Informative References ..........................................7
1. Introduction
This document provides a glossary of terminology used in routing
requirements and solutions for networks referred to as Low-Power and
Lossy Networks (LLNs).
LLNs are 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, air conditioning,
lighting, access control, fire), connected home, health care,
environmental monitoring, urban sensor networks, energy management,
assets tracking, and refrigeration.
Since these applications are usually highly specific (for example,
industrial automation, building automation, etc.), it is not uncommon
to see a number of disparate terms used to describe the same device
or functionality. Thus, in order to avoid confusion or
discrepancies, this document specifies the common terminology to be
used in all ROLL working group documents. The terms defined in this
document are used in [RFC5548], [RFC5673], [RFC5826], and [RFC5867].
Terminology specific to a particular application is out of the scope
of this document.
It is expected that all routing documents defining requirements or
specifying solutions for LLN will use the common terminology
specified in this document. This document should be listed as an
informative reference.
2. Terminology
Actuator: A field device that controls a set of equipment. For
example, an actuator might control and/or modulate the flow of a
gas or liquid, control electricity distribution, perform a
mechanical operation, etc.
AMI: Advanced Metering Infrastructure. Makes use of Smart Grid
technologies. A canonical Smart Grid application is smart-
metering.
Channel: Radio frequency sub-band used to transmit a modulated signal
carrying packets.
Channel Hopping: A procedure by which field devices synchronously
change channels during operation.
Commissioning Tool: Any physical or logical device temporarily added
to the network for the express purpose of setting up the network
and device operational parameters. The commissioning tool can
also be temporarily added to the LLN for scheduled or unscheduled
maintenance.
Closed Loop Control: A procedure whereby a device controller controls
an actuator based on input information sensed by one or more field
devices.
Controller: A field device that can receive sensor input and
automatically change the environment in the facility by
manipulating digital or analog actuators.
DA: Distribution Automation. Part of Smart Grid. Encompasses
technologies for maintenance and management of electrical
distribution systems.
DAG: Directed Acyclic Graph. A directed graph with no directed
cycles (a graph formed by a collection of vertices and directed
edges where each edge connects one vertex to another, such that
there is no way to start at some vertex v and follow a sequence of
edges that eventually loops back to vertex v again).
Data sink: A device that collects data from nodes in an LLN.
Downstream: Data direction traveling from outside of the LLN (e.g.,
traffic coming from a LAN, WAN, or the Internet) via an LLN Border
Router (LBR), or in general, "deeper" in the Directed Acyclic
Graph computed by the routing protocol.
Field Device: A field device is a physical device placed in the
network's operating environment (e.g., plant, urban area, or
home). Field devices include sensors and actuators as well as
routers and Low-Power and Lossy Network Border Routers (LBRs). A
field device is usually (but not always) a device with constrained
CPU, memory footprint, storage capacity, bandwidth, and sometimes
power (battery operated). At the time of writing, for the sake of
illustration, a typical sensor or actuator would have a few
Kilobytes of RAM, a few dozens of Kilobytes of ROM/Flash memory, a
8-/16-/32-bit microcontroller, and communication capabilities
ranging from a few kbits/s to a few hundred kbits/s. Although
continuous improvement of hardware and software technologies is
expected, such devices will likely continue to be seen as
resource-constrained devices compared to computers and routers
used in the rest of the Internet.
Flash Memory: non-volatile memory that can be re-programmed.
FMS: Facility Management System. A global term applied across all
the vertical designations within a building, including heating,
ventilation, and air conditioning (also referred to as HVAC),
fire, security, lighting, and elevator control.
HART: Highway Addressable Remote Transducer. A group of
specifications for industrial process and control devices
administered by the HART Foundation (see [HART]). The latest
version for the specifications is HART7, which includes the
additions for WirelessHART.
HVAC: Heating, Ventilation, and Air Conditioning. A term applied to
mechanisms used to maintain the comfort level of an internal
space.
ISA: International Society of Automation. An ANSI accredited
standards-making society. ISA100 is an ISA committee whose
charter includes defining a family of standards for industrial
automation. [ISA100.11a] is a working group within ISA100 that is
working on a standard for monitoring and non-critical process-
control applications.
LAN: Local Area Network.
LBR: Low-Power and Lossy Network Border Router. A device that
connects the Low-Power and Lossy Network to another routing domain
such as a LAN, a WAN, or the Internet where a different routing
protocol may be in operation. The LBR acts as a routing device
and may possibly host other functions such as data collector or
aggregator.
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 (HVAC, lighting, access control, fire), connected home,
health care, environmental monitoring, urban sensor networks,
energy management, assets tracking, and refrigeration.
MP2P: Multipoint-to-Point. Used to describe a particular traffic
pattern (e.g., MP2P flows collecting information from many nodes
flowing upstream towards a collecting sink or an LBR).
MAC: Medium Access Control. Refers to algorithms and procedures used
by the data link layer to coordinate use of the physical layer.
Non-Sleepy Node: A node that always remains in a fully powered-on
state (i.e., always awake) where it has the capability to perform
communication.
Open Loop Control: A process whereby a plant operator manually
manipulates an actuator over the network where the decision is
influenced by information sensed by field devices.
PER: Packet Error Rate. A ratio of the number of unusable packets
(not received at all or received in error, even after any
applicable error correction has been applied) to the total number
of packets that would have been received in the absence of errors.
P2P: Point To Point. Refers to traffic exchanged between two nodes
(regardless of the number of hops between the two nodes).
P2MP: Point-to-Multipoint. Refers to traffic between one node and a
set of nodes. This is similar to the P2MP concept in Multicast or
MPLS Traffic Engineering ([RFC4461]and [RFC4875]). A common use
case for the Routing Protocol for Low-Power and Lossy Networks
(RPL) involves P2MP flows from or through a DAG root outward
towards other nodes contained in the DAG.
RAM: Random Access Memory. A volatile memory.
RFID: Radio Frequency IDentification.
ROM: Read-Only Memory.
ROLL: Routing Over Low-Power and Lossy Networks.
RPL: An IPv6 Routing Protocol for Low-Power and Lossy Networks that
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. RPL also supports point-to-
point traffic between any arbitrary nodes in the LLN.
RPL Domain: A collection of RPL routers under the control of a single
administration. The boundaries of routing domains are defined by
network management by setting some links to be exterior, or inter-
domain, links.
Schedule: An agreed execution, wake-up, transmission, reception,
etc., timetable between two or more field devices.
Sensor: A device that measures a physical quantity and converts it to
an analog or digital signal that can be read by a program or a
user. Sensed data can be of many types: electromagnetic (e.g.,
current, voltage, power, or resistance), mechanical (e.g.,
pressure, flow, liquid density, or humidity), chemical (e.g.,
oxygen or carbon monoxide), acoustic (e.g., noise or ultrasound),
etc.
Sleepy Node: A node that may sometimes go into a sleep mode (i.e., go
into a low-power state to conserve power) and temporarily suspend
protocol communication. When not in sleep mode, the sleepy node
is in a fully powered-on state where it has the capability to
perform communication.
Smart Grid: A broad class of applications to network and automate
utility infrastructure.
Timeslot: A fixed time interval that may be used for the transmission
or reception of a packet between two field devices. A timeslot
used for communications is associated with a slotted-link.
Upstream: Data direction traveling from the LLN via the LBR to
outside of the LLN (LAN, WAN, or Internet) or generally closer to
the root of the DAG computed by the routing protocol.
WAN: Wide Area Network.
3. Security Considerations
Since this document specifies terminology and does not specify new
procedures or protocols, it raises no new security issues.
4. Acknowledgements
The authors would like to thank Christian Jacquenet, Tim Winter,
Pieter De Mil, David Meyer, Mukul Goyal, and Abdussalam Baryun for
their valuable feedback.
5. Informative References
[HART] HART Communication Foundation, <http://www.hartcomm.org>.
[ISA100.11a]
ISA, "Wireless systems for industrial automation: Process
control and related applications", ISA 100.11a, May 2008,
<http://www.isa.org/Community/
SP100WirelessSystemsforAutomation>.
[RFC4461] Yasukawa, S., Ed., "Signaling Requirements for Point-to-
Multipoint Traffic-Engineered MPLS Label Switched Paths
(LSPs)", RFC 4461, April 2006.
[RFC4875] Aggarwal, R., Ed., Papadimitriou, D., Ed., and S. Yasukawa,
Ed., "Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC5548] Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and D.
Barthel, Ed., "Routing Requirements for Urban Low-Power and
Lossy Networks", RFC 5548, May 2009.
[RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
Phinney, "Industrial Routing Requirements in Low-Power and
Lossy Networks", RFC 5673, October 2009.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks", RFC
5826, April 2010.
[RFC5867] Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, June 2010.
Author's Address
JP. Vasseur
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
US
EMail: jpv@cisco.com
ISO Plain Language
On this page
§1Why a Shared Word List
The document provides a glossary of the terminology used in routing requirements and solutions for networks referred to as Low-Power and Lossy Networks. Such a network is 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, including industrial monitoring, building automation for heating, ventilation, air conditioning, lighting, access control and fire, connected home, health care, environmental monitoring, urban sensor networks, energy management, assets tracking, and refrigeration. Since these applications are usually highly specific, it is not uncommon to see a number of disparate terms used to describe the same device or functionality. To avoid confusion or discrepancies, the document specifies the common terminology to be used in all the documents of the routing working group, and the terms it defines are already used in the routing requirement documents for urban, industrial, home and building networks.
Terminology specific to a particular application is out of scope. The expectation is that all routing documents defining requirements or specifying solutions for these networks will use the common terminology, and that this document should be listed as an informative reference.
Every industry calls the same little box a different name. Once you are writing about how such devices route their messages, you need one set of names, and this RFC is that set.
§2The Devices and the Network
A field device is a physical device placed in the network's operating environment, such as a plant, an urban area or a home. Field devices include sensors and actuators as well as routers and border routers, and are usually, though not always, constrained in processor, memory footprint, storage capacity, bandwidth and sometimes power. For illustration, a typical sensor or actuator would have a few kilobytes of RAM, a few dozens of kilobytes of read-only or flash memory, an 8-, 16- or 32-bit microcontroller, and communication capabilities ranging from a few kilobits per second to a few hundred kilobits per second. Even as hardware improves, such devices are likely to keep looking resource-constrained next to the computers and routers used in the rest of the internet.
A sensor measures a physical quantity and converts it into an analogue or digital signal that can be read by a program or a person, of many kinds: electromagnetic, such as current, voltage, power or resistance, mechanical, such as pressure, flow, liquid density or humidity, chemical, such as oxygen or carbon monoxide, and acoustic, such as noise or ultrasound. An actuator is a field device that controls a set of equipment, for example modulating the flow of a gas or liquid, controlling electricity distribution, or performing a mechanical operation. A controller is a field device that can receive sensor input and automatically change the environment in the facility by manipulating digital or analogue actuators. A data sink is a device that collects data from nodes in the network.
The border router of a low-power and lossy network connects that network to another routing domain, such as a local area network, a wide area network or the internet, where a different routing protocol may be in operation. It acts as a routing device and may also host other functions such as a data collector or aggregator. The routing structure itself is a directed acyclic graph: a collection of vertices and directed edges where each edge connects one vertex to another, such that there is no way to start at some vertex and follow a sequence of edges that eventually loops back to where you started. RPL is the IPv6 routing protocol for these networks. It supports multipoint-to-point traffic from devices inside the network towards a central control point, point-to-multipoint traffic from that control point back out to the devices, and point-to-point traffic between any two nodes. An RPL domain is a collection of RPL routers under the control of a single administration, with the boundaries of routing domains set by network management marking some links as exterior or inter-domain links.
The vocabulary covers the sensors that read the world, the actuators that change it, the controllers that connect the two, the little routers in between, and the border router that joins the whole thing to the internet.
- ApplicationWhat the sensor or actuator is actually for
- Low-power and lossy networkField devices joined by links such as IEEE 802.15.4
- Border routerConnects the network to another routing domain
- LAN, WAN or the internetThe rest of the world, with a different routing protocol
- Field deviceA physical device in the operating environment, usually with very little memory, processor and power.
- SensorMeasures a physical quantity and turns it into a signal a program can read.
- ActuatorControls equipment, such as the flow of a gas or an electric supply.
- ControllerTakes sensor input and changes the environment by driving actuators.
- Border routerConnects the network to another routing domain, and may collect data as well.
- Data sinkThe device that collects data from the nodes in the network.
§2Direction, Traffic Patterns and Sleeping Devices
Direction is defined relative to the network. Upstream is the data direction travelling from inside the network out through the border router to a local area network, a wide area network or the internet, or generally closer to the root of the directed acyclic graph computed by the routing protocol. Downstream is the opposite: data travelling from outside the network in through the border router, or generally deeper into the graph.
Three traffic patterns are named. Point to point is traffic exchanged between two nodes, whatever the number of hops between them. Point-to-multipoint is traffic between one node and a set of nodes, a concept much like the one used in multicast or in MPLS traffic engineering; a common use of RPL involves point-to-multipoint flows from or through the root of the graph outwards towards the other nodes. Multipoint-to-point describes a traffic pattern such as flows collecting information from many nodes and flowing upstream towards a collecting sink or a border router.
Because the devices have so little power, they sleep. A sleepy node may sometimes go into a sleep mode, a low-power state that conserves power, and temporarily suspend protocol communication; when it is not asleep it is fully powered on and able to communicate. A non-sleepy node is always fully powered on and always able to communicate. Around this sit the radio terms. A channel is a radio frequency sub-band used to transmit a modulated signal carrying packets, and channel hopping is the procedure by which field devices synchronously change channels while operating. A timeslot is a fixed time interval that may be used for the transmission or reception of a packet between two field devices, and a timeslot used for communications is associated with a slotted link. A schedule is an agreed execution, wake-up, transmission or reception timetable between two or more field devices. The packet error rate is the ratio of the number of unusable packets, whether not received at all or received in error after any applicable error correction, to the total number that would have been received without errors.
The same terms are used for which way data is going and for how the radios share the air. Nodes spend most of their time asleep, so the routing has to work with devices that are only occasionally listening.
§2The Vocabulary of Particular Industries
Several terms belong to the application areas rather than to routing. Advanced metering infrastructure uses smart grid technologies, and a canonical smart grid application is smart metering. Distribution automation is part of the smart grid and encompasses technologies for the maintenance and management of electrical distribution systems. A smart grid is a broad class of applications that network and automate utility infrastructure. The facility management system is a global term applied across all the vertical designations within a building, including heating, ventilation and air conditioning, fire, security, lighting and elevator control. The Highway Addressable Remote Transducer group of specifications covers industrial process and control devices, and its latest version, HART7, includes the additions for WirelessHART. The International Society of Automation is an accredited standards-making society, and ISA100 is one of its committees, whose charter includes defining a family of standards for industrial automation, with a working group inside it working on a standard for monitoring and non-critical process-control applications.
Two control models are distinguished. Under closed loop control, a device controller controls an actuator based on input information sensed by one or more field devices. Under open loop control, a plant operator manually manipulates an actuator over the network, with the decision influenced by information sensed by field devices. A commissioning tool is any physical or logical device temporarily added to the network for the express purpose of setting up the network and the device operational parameters, and it can also be added temporarily for scheduled or unscheduled maintenance. The document also names radio frequency identification, the medium access control algorithms used by the data link layer to coordinate use of the physical layer, and the memory types the devices use: RAM is volatile, ROM is read-only, and flash memory is non-volatile but can be re-programmed.
Some of the words belong to a particular industry: what a smart meter is called, what a plant operator does differently from a controller, and what a maintenance laptop is called when it is plugged in for an afternoon.
§3Security
The RFC is one paragraph long on security. Since the document specifies terminology and does not specify new procedures or protocols, it raises no new security issues.
A word list cannot introduce a security problem, because it introduces no behaviour. The document says exactly that and stops there.