Terms Used in Routing for Low-Power and Lossy Networks
Standardized terminology for routing in networks of tiny, power-constrained 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.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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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
AI ELI5
On this page
§1What Are Low-Power and Lossy Networks?
A Low-Power and Lossy Network (LLN) is a collection of many small embedded devices connected by radio links, with severe constraints on power, memory, and processing capacity. These networks power real-world applications: temperature and humidity sensors in building HVAC systems, industrial equipment monitoring, home lighting control, power meter reporting, environmental monitoring, and more.
An LLN device might have kilobytes of RAM, tens of kilobytes of Flash memory, and a 8- or 16-bit processor. Many run on batteries and sleep for long periods to conserve power. Radio links are lossy—packets sometimes fail to arrive—and have limited bandwidth, often just a few tens of kilobits per second.
Because these devices are very different from traditional routers and servers, they need specialized routing approaches. The IETF Routing Over Low-power and Lossy networks (ROLL) working group developed terminology to describe these approaches consistently across different application domains.
Sensor networks are networks of tiny, battery-powered gadgets with weak radios. They work differently from regular routers, so they need their own vocabulary.
- ApplicationsBuilding control, environmental monitoring, industrial systems
- RPL Routing ProtocolBuilds and maintains the LLN topology structure
- IP (IPv6)Network layer addressing and forwarding
- Link LayerIEEE 802.15.4, low-power WiFi, or other wireless medium
- PhysicalRadio hardware, antennas, power management
§2Field Devices: Sensors, Actuators, and Routers
An LLN is built from field devices: physical devices placed in the network's operating environment. Field devices include sensors (devices that measure something—temperature, pressure, light—and report it), actuators (devices that control something—a valve, switch, or motor), and routers (devices that relay traffic for others).
A sleepy node is a field device that saves power by sleeping (radio off, processor halted) for periods and waking up to listen for messages. A non-sleepy node always stays powered on. Sleepy nodes are common in battery-powered sensors; non-sleepy nodes are common in plugged-in equipment or nodes that must respond immediately.
An LLN Border Router (LBR) connects the LLN to the outside world (the Internet, a company network, or a central control system). It runs standard IP routing and translates between the LLN's specialized routing protocol and wider networks.
Field devices are the tiny machines. Some sleep to save batteries, some stay awake. The border router is the gateway connecting the tiny network to the big one.
§3Routing Model: DAG and RPL
LLN routing often builds on a Directed Acyclic Graph (DAG)—a network structure with no loops where traffic flows toward a root (usually the LBR). A RPL (Routing Protocol for Low-Power and Lossy Networks) is the main IETF protocol for LLNs that builds and maintains this structure.
In RPL, traffic patterns are naturally asymmetric. Multipoint-to-Point (MP2P) traffic flows upward from many sensors to a central data sink (the LBR): a temperature reading from a sensor in the warehouse to the control center. Point-to-Multipoint (P2MP) traffic flows downward from the root to many nodes: a command to all lights in a building to turn on. Point-to-Point (P2P) traffic goes between any two nodes, often requiring multi-hop paths.
The root of the DAG typically computes rank values (hop count or cost) that determine the forwarding structure, ensuring efficient paths without loops.
Messages usually flow up to a central hub (like reports to a manager) or down from it (like orders to workers). The network structure is a tree with no circles.
§4Application Domains and Use Cases
LLNs are deployed in diverse domains, each with different requirements. Building automation controls heating, ventilation, air conditioning, lighting, fire alarms, and access. Devices are often plugged in but still power-conscious. Industrial monitoring observes equipment health and processes, sometimes in harsh environments. Smart Grid applications (Advanced Metering Infrastructure, Distribution Automation) manage electrical generation, transmission, and consumption. Connected home includes appliances, security, and home automation. Healthcare monitors patients and environmental conditions. Environmental monitoring tracks pollution, weather, and wildlife.
Each domain has different trade-offs: Industrial applications may tolerate higher latency but need high reliability. Smart metering requires infrequent but reliable message delivery. Building automation often allows longer response times but must cover large areas.
These networks are everywhere: controlling your office building's temperature, reading your electric meter, monitoring a factory, or watching weather. Each has its own priorities.
§5Terminology for Consistency
RFC 7102 defines terms consistently so that when a specification says 'sleepy node' or 'non-sleepy node,' all engineers understand the same thing. Terms are grouped by concept: basic devices (field device, sensor, actuator), network devices (LBR, DAG, RPL), infrastructure terms (channel, timeslot, schedule), and application categories (building automation, industrial, Smart Grid).
The glossary explicitly excludes application-specific terminology to keep it broadly useful across all LLN domains. It is intended to be referenced by all IETF routing documents that involve LLNs, making standards work clearer and reducing ambiguity.
One consistent vocabulary across all tiny-network standards so everyone talks about the same thing.