draft-ietf-lwig-terminology-05.txt   draft-ietf-lwig-terminology-06.txt 
LWIG Working Group C. Bormann LWIG Working Group C. Bormann
Internet-Draft Universitaet Bremen TZI Internet-Draft Universitaet Bremen TZI
Intended status: Informational M. Ersue Intended status: Informational M. Ersue
Expires: January 10, 2014 Nokia Siemens Networks Expires: June 21, 2014 Nokia Siemens Networks
A. Keranen A. Keranen
Ericsson Ericsson
July 09, 2013 December 18, 2013
Terminology for Constrained Node Networks Terminology for Constrained Node Networks
draft-ietf-lwig-terminology-05 draft-ietf-lwig-terminology-06
Abstract Abstract
The Internet Protocol Suite is increasingly used on small devices The Internet Protocol Suite is increasingly used on small devices
with severe constraints, creating constrained node networks. This with severe constraints on power, memory and processing resources,
document provides a number of basic terms that have turned out to be creating constrained node networks. This document provides a number
useful in the standardization work for constrained environments. of basic terms that have turned out to be useful in the
standardization work for constrained node networks.
Status of This Memo Status of This Memo
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This Internet-Draft will expire on January 10, 2014. This Internet-Draft will expire on June 21, 2014.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Core Terminology . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Constrained Nodes . . . . . . . . . . . . . . . . . . . . 3 2.1. Constrained Nodes . . . . . . . . . . . . . . . . . . . . 4
2.2. Constrained Networks . . . . . . . . . . . . . . . . . . 4 2.2. Constrained Networks . . . . . . . . . . . . . . . . . . 5
2.2.1. Challenged Networks . . . . . . . . . . . . . . . . . 5 2.2.1. Challenged Networks . . . . . . . . . . . . . . . . . 6
2.3. Constrained Node Networks . . . . . . . . . . . . . . . . 5 2.3. Constrained Node Networks . . . . . . . . . . . . . . . . 6
2.3.1. LLN ("low-power lossy network") . . . . . . . . . . . 6 2.3.1. LLN ("low-power lossy network") . . . . . . . . . . . 7
2.3.2. LoWPAN, 6LoWPAN . . . . . . . . . . . . . . . . . . . 6 2.3.2. LoWPAN, 6LoWPAN . . . . . . . . . . . . . . . . . . . 7
3. Classes of Constrained Devices . . . . . . . . . . . . . . . 8 3. Classes of Constrained Devices . . . . . . . . . . . . . . . 8
4. Power Terminology . . . . . . . . . . . . . . . . . . . . . . 10 4. Power Terminology . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Scaling Properties . . . . . . . . . . . . . . . . . . . 10 4.1. Scaling Properties . . . . . . . . . . . . . . . . . . . 10
4.2. Classes of Energy Limitation . . . . . . . . . . . . . . 10 4.2. Classes of Energy Limitation . . . . . . . . . . . . . . 10
4.3. Strategies of Using Power for Communication . . . . . . . 11 4.3. Strategies of Using Power for Communication . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
8. Informative References . . . . . . . . . . . . . . . . . . . 13 8. Informative References . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
Small devices with limited CPU, memory, and power resources, so Small devices with limited CPU, memory, and power resources, so
called constrained devices (also known as sensor, smart object, or called constrained devices (often used as a sensor/actuator, a smart
smart device) can constitute a network, becoming "constrained nodes" object, or a smart device) can form a network, becoming "constrained
in that network. Such a network may itself exhibit constraints, e.g. nodes" in that network. Such a network may itself exhibit
with unreliable or lossy channels, limited and unpredictable constraints, e.g. with unreliable or lossy channels, limited and
bandwidth, and a highly dynamic topology. unpredictable bandwidth, and a highly dynamic topology.
Constrained devices might be in charge of gathering information in Constrained devices might be in charge of gathering information in
diverse settings including natural ecosystems, buildings, and diverse settings including natural ecosystems, buildings, and
factories and sending the information to one or more server stations. factories and sending the information to one or more server stations.
Constrained devices may work under severe resource constraints such They also act on information, by performing some physical action,
as limited battery and computing power, little memory, as well as including displaying it. Constrained devices may work under severe
insufficient wireless bandwidth and ability to communicate. Other resource constraints such as limited battery and computing power,
little memory, as well as insufficient wireless bandwidth and ability
to communicate; these constraints often exacerbate each other. Other
entities on the network, e.g., a base station or controlling server, entities on the network, e.g., a base station or controlling server,
might have more computational and communication resources and could might have more computational and communication resources and could
support the interaction between the constrained devices and support the interaction between the constrained devices and
applications in more traditional networks. applications in more traditional networks.
Today diverse sizes of constrained devices with different resources Today diverse sizes of constrained devices with different resources
and capabilities are becoming connected. Mobile personal gadgets, and capabilities are becoming connected. Mobile personal gadgets,
building-automation devices, cellular phones, Machine-to-machine building-automation devices, cellular phones, Machine-to-machine
(M2M) devices, etc. benefit from interacting with other "things" (M2M) devices, etc. benefit from interacting with other "things"
nearby or somewhere in the Internet. With this, the Internet of nearby or somewhere in the Internet. With this, the Internet of
Things (IoT) becomes a reality, built up out of uniquely identifiable Things (IoT) becomes a reality, built up out of uniquely identifiable
and addressable objects (things). And over the next decade, this and addressable objects (things). And over the next decade, this
could grow to large numbers [fifty-billion] of Internet-connected could grow to large numbers [fifty-billion] of Internet-connected
constrained devices, greatly increasing the Internet's size and constrained devices, greatly increasing the Internet's size and
scope. scope.
The present document provides a number of basic terms that have The present document provides a number of basic terms that have
turned out to be useful in the standardization work for constrained turned out to be useful in the standardization work for constrained
environments. The intention is not to exhaustively cover the field, environments. The intention is not to exhaustively cover the field,
but to make sure a few core terms are used consistently between but to make sure a few core terms are used consistently between
different groups cooperating in this space. different groups cooperating in this space.
In this document, the term "byte" is used in its now customary sense In this document, the term "byte" is used in its now customary sense
as a synonym for "octet". Where sizes of semiconductor memory are as a synonym for "octet". Where sizes of semiconductor memory are
given, the prefix "kibi" (1024) is combined with "byte" to given, the prefix "kibi" (1024) is combined with "byte" to
"kibibyte", abbreviated "KiB", for 1024 bytes [ISQ-13]. "kibibyte", abbreviated "KiB", for 1024 bytes [ISQ-13].
2. Terminology In computing, the term "power" is often used for the concept of
"computing power" or "processing power", as in CPU performance.
Unless explicitly stated otherwise, in this document the term stands
for electrical power. "Mains-powered" is used as a short-hand for
being permanently connected to a stable electrical power grid.
The main focus of this field of work appears to be _scaling_: 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] o Scaling up Internet technologies to a large number [fifty-billion]
of inexpensive nodes, while of inexpensive nodes, while
o scaling down the characteristics of each of these nodes and of the o scaling down the characteristics of each of these nodes and of the
networks being built out of them, to make this scaling up networks being built out of them, to make this scaling up
economically and physically viable. economically and physically viable.
The need for scaling down the characteristics of nodes leads to The need for scaling down the characteristics of nodes leads to
_constrained nodes_. _constrained nodes_.
2.1. Constrained Nodes 2.1. Constrained Nodes
The term "constrained node" is best defined by contrasting the The term "constrained node" is best defined by contrasting the
characteristics of a constrained node with certain widely held characteristics of a constrained node with certain widely held
expectations on more familiar Internet nodes: expectations on more familiar Internet nodes:
Constrained Node: A node where some of the characteristics that are Constrained Node: A node where some of the characteristics that are
otherwise pretty much taken for granted for Internet nodes in 2013 otherwise pretty much taken for granted for Internet nodes at the
are not attainable, often due to cost constraints and/or physical time of writing are not attainable, often due to cost constraints
constraints on characteristics such as size, weight, and available and/or physical constraints on characteristics such as size,
power and energy. 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 less than satisfying as a rigorous definition, it is While this is not a rigorous definition, it is grounded in the state
grounded in the state of the art and clearly sets apart constrained of the art and clearly sets apart constrained nodes from server
nodes from server systems, desktop or laptop computers, powerful systems, desktop or laptop computers, powerful mobile devices such as
mobile devices such as smartphones etc. There may be many design smartphones etc. There may be many design considerations that lead
considerations that lead to these constraints, including cost, size, to these constraints, including cost, size, weight, and other scaling
weight, and other scaling factors. factors.
(An alternative name, when the properties as a network node are not (An alternative name, when the properties as a network node are not
in focus, is "constrained device".) in focus, is "constrained device".)
There are multiple facets to the constraints on nodes, often applying There are multiple facets to the constraints on nodes, often applying
in combination, e.g.: in combination, e.g.:
o constraints on the maximum code complexity (ROM/Flash); o constraints on the maximum code complexity (ROM/Flash);
o constraints on the size of state and buffers (RAM); o constraints on the size of state and buffers (RAM);
o constraints on the available power. o constraints on the amount of computation feasible in a period of
time ("processing power");
o constraints on the available (electrical) power;
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" Section 3 defines a small number of interesting classes ("class-N"
for N=0,1,2) of constrained nodes focusing on relevant combinations for N=0,1,2) of constrained nodes focusing on relevant combinations
of the first two constraints. With respect to available power, of the first two constraints. With respect to available (electrical)
[RFC6606] distinguishes "power-affluent" nodes (mains-powered or power, [RFC6606] distinguishes "power-affluent" nodes (mains-powered
regularly recharged) from "power-constrained nodes" that draw their or regularly recharged) from "power-constrained nodes" that draw
power from primary batteries or by using energy harvesting; more their power from primary batteries or by using energy harvesting;
detailed power terminology is given in Section 4. more detailed power terminology is given in Section 4.
The use of constrained nodes in networks often also leads to The use of constrained nodes in networks often also leads to
constraints on the networks themselves. However, there may also be constraints on the networks themselves. However, there may also be
constraints on networks that are largely independent from those of constraints on networks that are largely independent from those of
the nodes. We therefore distinguish _constrained networks_ and the nodes. We therefore distinguish _constrained networks_ and
_constrained node networks_. _constrained node networks_.
2.2. Constrained Networks 2.2. Constrained Networks
We define "constrained network" in a similar way: We define "constrained network" in a similar way:
Constrained Network: A network where some of the characteristics Constrained Network: A network where some of the characteristics
pretty much taken for granted with link layers in common use in pretty much taken for granted with link layers in common use in
the Internet by 2013, are not attainable. the Internet at the time of writing, are not attainable.
Again, there may be several reasons for this: Again, there may be several reasons for this:
o cost constraints on the network, o cost constraints on the network,
o constraints of the nodes (for constrained node networks), o constraints of the nodes (for constrained node networks),
o physical constraints (e.g., power constraints, environmental o physical constraints (e.g., power constraints, environmental
constraints, media constraints such as underwater operation, constraints, media constraints such as underwater operation,
limited spectrum for very high density, electromagnetic limited spectrum for very high density, electromagnetic
skipping to change at page 5, line 19 skipping to change at page 5, line 52
o technology constraints, such as older and lower speed technologies o technology constraints, such as older and lower speed technologies
that are still operational and may need to stay in use for some that are still operational and may need to stay in use for some
more time. more time.
Constraints may include: Constraints may include:
o low achievable bit rate (including limits on duty cycle), o low achievable bit rate (including limits on duty cycle),
o high packet loss, packet loss (delivery rate) variability, o high packet loss, packet loss (delivery rate) variability,
o highly asymmetric link characteristics,
o severe penalties for using larger packets (e.g., high packet loss o severe penalties for using larger packets (e.g., high packet loss
due to link layer fragmentation), due to link layer fragmentation),
o lack of (or severe constraints on) advanced services such as IP o lack of (or severe constraints on) advanced services such as IP
multicast. multicast.
2.2.1. Challenged Networks 2.2.1. Challenged Networks
A constrained network is not necessarily a _challenged_ network A constrained network is not necessarily a _challenged_ network
[FALL]: [FALL]:
skipping to change at page 6, line 10 skipping to change at page 6, line 43
Constrained Node Network: A network whose characteristics are Constrained Node Network: A network whose characteristics are
influenced by being composed of a significant portion of influenced by being composed of a significant portion of
constrained nodes. constrained nodes.
A constrained node network always is a constrained network because of A constrained node network always is a constrained network because of
the network constraints stemming from the node constraints, but may the network constraints stemming from the node constraints, but may
also have other constraints that already make it a constrained also have other constraints that already make it a constrained
network. network.
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 ("low-power lossy network") 2.3.1. LLN ("low-power lossy network")
A related term that has been used recently is "low-power lossy A related term that has been used to describe the focus of the IETF
network" (LLN). In its terminology document, the ROLL working group working group on Routing Over Low power and Lossy networks (ROLL) is
is saying [I-D.ietf-roll-terminology]: "low-power lossy network" (LLN). The ROLL terminology document
[I-D.ietf-roll-terminology] defines LLNs as follows:
LLN: Low power and Lossy networks (LLNs) are typically composed of LLN: Low power and Lossy networks (LLNs) are typically composed of
many embedded devices with limited power, memory, and processing many embedded devices with limited power, memory, and processing
resources interconnected by a variety of links, such as IEEE resources interconnected by a variety of links, such as IEEE
802.15.4 or Low Power WiFi. There is a wide scope of application 802.15.4 or Low Power WiFi. There is a wide scope of application
areas for LLNs, including industrial monitoring, building areas for LLNs, including industrial monitoring, building
automation (HVAC, lighting, access control, fire), connected home, automation (HVAC, lighting, access control, fire), connected home,
healthcare, environmental monitoring, urban sensor networks, healthcare, environmental monitoring, urban sensor networks,
energy management, assets tracking and refrigeration.. [sic] energy management, assets tracking and refrigeration.. [sic]
In common usage, LLN often stands for "the network characteristics Beyond that, LLNs often exhibit considerable loss at the physical
that RPL has been designed for". Beyond what is said in the ROLL layer, with significant variability of the delivery rate, and some
terminology document, LLNs do appear to have significant loss at the short-term unreliability, coupled with some medium term stability
physical layer, with significant variability of the delivery rate, that makes it worthwhile to construct medium-term stable directed
and some short-term unreliability, coupled with some medium term acyclic graphs for routing and do measurements on the edges such as
stability that makes it worthwhile to construct medium-term stable ETX [RFC6551]. Actual "low power" does not seem to be a defining
directed acyclic graphs for routing and do measurements on the edges characteristic for an LLN [I-D.hui-vasseur-roll-rpl-deployment].
such as ETX [RFC6551]. Actual "low power" does not seem to be
required for an LLN [I-D.hui-vasseur-roll-rpl-deployment], and the
positions on scaling of LLNs appear to vary widely
[I-D.clausen-lln-rpl-experiences].
The ROLL terminology document states that LLNs typically are composed LLNs typically are composed of constrained nodes; this leads to the
of constrained nodes; this is also supported by the design of design of operation modes such as the "non-storing mode" defined by
operation modes such as RPL's "non-storing mode". So, in the RPL (the IPv6 Routing Protocol for Low-Power and Lossy Networks
terminology of the present document, an LLN seems to be a constrained [RFC6650]). So, in the terminology of the present document, an LLN
node network with certain network characteristics, which include is a constrained node network with certain network characteristics,
constraints on the network as well. which include constraints on the network as well.
2.3.2. LoWPAN, 6LoWPAN 2.3.2. LoWPAN, 6LoWPAN
One interesting class of a constrained network often used as a One interesting class of a constrained network often used as a
constrained node network is the "LoWPAN" [RFC4919], a term inspired constrained node network is the "LoWPAN" [RFC4919], a term inspired
from the name of the IEEE 802.15.4 working group (low-rate wireless from the name of the IEEE 802.15.4 working group (low-rate wireless
personal area networks (LR-WPANs)). The expansion of that acronym, personal area networks (LR-WPANs)). The expansion of that acronym,
"Low-Power Wireless Personal Area Network" contains a hard to justify "Low-Power Wireless Personal Area Network" contains a hard to justify
"Personal" that is due to the history of task group naming in IEEE "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 802 more than due to an orientation of LoWPANs around a single
person. Actually, LoWPANs have been suggested for urban monitoring, person. Actually, LoWPANs have been suggested for urban monitoring,
control of large buildings, and industrial control applications, so control of large buildings, and industrial control applications, so
the "Personal" can only be considered a vestige. Maybe the term is the "Personal" can only be considered a vestige. Occasionally the
best read as "Low-Power Wireless Area Networks" (LoWPANs) [WEI]. term is read as "Low-Power Wireless Area Networks" (LoWPANs) [WEI].
Originally focused on IEEE 802.15.4, "LoWPAN" (or when used for IPv6, Originally focused on IEEE 802.15.4, "LoWPAN" (or when used for IPv6,
"6LoWPAN") is now also being used for networks built from similarly "6LoWPAN") also refers to networks built from similarly constrained
constrained link layer technologies [I-D.ietf-6lowpan-btle] link layer technologies [I-D.ietf-6lowpan-btle]
[I-D.mariager-6lowpan-v6over-dect-ule] [I-D.brandt-6man-lowpanz]. [I-D.mariager-6lowpan-v6over-dect-ule] [I-D.brandt-6man-lowpanz].
3. Classes of Constrained Devices 3. Classes of Constrained Devices
Despite the overwhelming variety of Internet-connected devices that Despite the overwhelming variety of Internet-connected devices that
can be envisioned, it may be worthwhile to have some succinct can be envisioned, it may be worthwhile to have some succinct
terminology for different classes of constrained devices. In this terminology for different classes of constrained devices. In this
document, the class designations in Table 1 may be used as rough document, the class designations in Table 1 may be used as rough
indications of device capabilities: indications of device capabilities:
skipping to change at page 8, line 48 skipping to change at page 8, line 48
gateways or servers. Class 0 devices generally cannot be secured or gateways or servers. Class 0 devices generally cannot be secured or
managed comprehensively in the traditional sense. They will most managed comprehensively in the traditional sense. They will most
likely be preconfigured (and will be reconfigured rarely, if at all), likely be preconfigured (and will be reconfigured rarely, if at all),
with a very small data set. For management purposes, they could with a very small data set. For management purposes, they could
answer keepalive signals and send on/off or basic health indications. answer keepalive signals and send on/off or basic health indications.
Class 1 devices cannot easily talk to other Internet nodes employing Class 1 devices cannot easily talk to other Internet nodes employing
a full protocol stack such as using HTTP, TLS and related security a full protocol stack such as using HTTP, TLS and related security
protocols and XML-based data representations. However, they have protocols and XML-based data representations. However, they have
enough power to use a protocol stack specifically designed for enough power to use a protocol stack specifically designed for
constrained nodes (e.g., CoAP over UDP) and participate in meaningful constrained nodes (such as CoAP over UDP [I-D.ietf-core-coap]) and
conversations without the help of a gateway node. In particular, participate in meaningful conversations without the help of a gateway
they can provide support for the security functions required on a node. In particular, they can provide support for the security
large network. Therefore, they can be integrated as fully developed functions required on a large network. Therefore, they can be
peers into an IP network, but they need to be parsimonious with state integrated as fully developed peers into an IP network, but they need
memory, code space, and often power expenditure for protocol and to be parsimonious with state memory, code space, and often power
application usage. expenditure for protocol and application usage.
Class 2 can already support mostly the same protocol stacks as used Class 2 can already support mostly the same protocol stacks as used
on notebooks or servers. However, even these devices can benefit on notebooks or servers. However, even these devices can benefit
from lightweight and energy-efficient protocols and from consuming from lightweight and energy-efficient protocols and from consuming
less bandwidth. Furthermore, using fewer resources for networking less bandwidth. Furthermore, using fewer resources for networking
leaves more resources available to applications. Thus, using the leaves more resources available to applications. Thus, using the
protocol stacks defined for very constrained devices also on Class 2 protocol stacks defined for very constrained devices also on Class 2
devices might reduce development costs and increase the devices might reduce development costs and increase the
interoperability. interoperability.
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available electrical power and/or energy. While it is harder to find available electrical power and/or energy. While it is harder to find
recognizable clusters in this space, it is still useful to introduce recognizable clusters in this space, it is still useful to introduce
some common terminology. some common terminology.
4.1. Scaling Properties 4.1. Scaling Properties
The power and/or energy available to a device may vastly differ, from The power and/or energy available to a device may vastly differ, from
kilowatts to microwatts, from essentially unlimited to hundreds of kilowatts to microwatts, from essentially unlimited to hundreds of
microjoules. microjoules.
Instead of defining classes or clusters, we propose simply stating, Instead of defining classes or clusters, we simply state, in SI
in SI units, an approximate value for one or both of the quantities units, an approximate value for one or both of the quantities listed
listed in Table 2: in Table 2:
+--------+---------------------------------------------+------------+ +--------+---------------------------------------------+------------+
| Name | Definition | SI Unit | | Name | Definition | SI Unit |
+--------+---------------------------------------------+------------+ +--------+---------------------------------------------+------------+
| Ps | Sustainable average power available for the | W (Watt) | | Ps | Sustainable average power available for the | W (Watt) |
| | device over the time it is functioning | | | | device over the time it is functioning | |
| | | | | | | |
| Et | Total electrical energy available before | J (Joule) | | Et | Total electrical energy available before | J (Joule) |
| | the energy source is exhausted | | | | the energy source is exhausted | |
+--------+---------------------------------------------+------------+ +--------+---------------------------------------------+------------+
Table 2: Quantities Relevant to Power and Energy Table 2: Quantities Relevant to Power and Energy
The value of Et may need to be interpreted in conjunction with an The value of Et may need to be interpreted in conjunction with an
indication over which period of time the value is given; see the next indication over which period of time the value is given; see the next
subsection. subsection.
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.
4.2. Classes of Energy Limitation 4.2. Classes of Energy Limitation
As discussed above, some devices are limited in available energy as As discussed above, some devices are limited in available energy as
opposed to (or in addition to) being limited in available power. opposed to (or in addition to) being limited in available power.
Where no relevant limitations exist with respect to energy, the Where no relevant limitations exist with respect to energy, the
device is classified as E3. The energy limitation may be in total 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 energy available in the usable lifetime of the device (e.g. a device
with a non-replaceable primary battery, which is discarded when this with a non-replaceable primary battery, which is discarded when this
battery is exhausted), classified as E2. Where the relevant battery is exhausted), classified as E2. Where the relevant
limitation is for a specific period, this is classified as E1, e.g. limitation is for a specific period, this is classified as E1, e.g. a
a limited amount of energy available for the night with a solar- limited amount of energy available for the night with a solar-powered
powered device, or for the period between recharges with a device device, or for the period between recharges with a device that is
that is manually connected to a charger, or by a periodic (primary) manually connected to a charger, or by a periodic (primary) battery
battery replacement interval. Finally, there may be a limited amount replacement interval. Finally, there may be a limited amount of
of energy available for a specific event, e.g. for a button press in energy available for a specific event, e.g. for a button press in an
an energy harvesting light switch; this is classified as E0. Note energy harvesting light switch; this is classified as E0. Note that
that many E1 devices in a sense also are E2, as the rechargeable many E1 devices in a sense also are E2, as the rechargeable battery
battery has a limited number of useful recharging cycles. has a limited number of useful recharging cycles.
In summary, we distinguish (Table 3): In summary, we distinguish (Table 3):
+------+------------------------------+-----------------------------+ +------+------------------------------+-----------------------------+
| Name | Type of energy limitation | Example Power Source | | Name | Type of energy limitation | Example Power Source |
+------+------------------------------+-----------------------------+ +------+------------------------------+-----------------------------+
| E0 | Event energy-limited | Event-based harvesting | | E0 | Event energy-limited | Event-based harvesting |
| | | | | | | |
| E1 | Period energy-limited | Battery that is | | E1 | Period energy-limited | Battery that is |
| | | periodically recharged or | | | | periodically recharged or |
| | | replaced | | | | replaced |
| | | | | | | |
| E2 | Lifetime energy-limited | Non-replaceable primary | | E2 | Lifetime energy-limited | Non-replaceable primary |
| | | battery | | | | battery |
| | | | | | | |
| E3 | No direct quantitative | Mains powered | | E9 | No direct quantitative | Mains powered |
| | limitations to available | | | | limitations to available | |
| | energy | | | | energy | |
+------+------------------------------+-----------------------------+ +------+------------------------------+-----------------------------+
Table 3: Classes of Energy Limitation Table 3: Classes of Energy Limitation
4.3. Strategies of Using Power for Communication 4.3. Strategies of Using Power for Communication
Especially when wireless transmission is used, the radio often Especially when wireless transmission is used, the radio often
consumes a big portion of the total energy consumed by the device. consumes a big portion of the total energy consumed by the device.
skipping to change at page 12, line 5 skipping to change at page 12, line 10
The general strategies for power usage can be described as follows: The general strategies for power usage can be described as follows:
Always-on: This strategy is most applicable if there is no reason Always-on: This strategy is most applicable if there is no reason
for extreme measures for power saving. The device can stay on in 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- the usual manner all the time. It may be useful to employ power-
friendly hardware or limit the number of wireless transmissions, friendly hardware or limit the number of wireless transmissions,
CPU speeds, and other aspects for general power saving and cooling CPU speeds, and other aspects for general power saving and cooling
needs, but the device can be connected to the network all the needs, but the device can be connected to the network all the
time. time.
Always-off: Under this strategy, the device sleeps such long periods Normally-off: Under this strategy, the device sleeps such long
at a time that once it wakes up, it makes sense for it to not periods at a time that once it wakes up, it makes sense for it to
pretend that it has been connected to the network during sleep: not pretend that it has been connected to the network during
The device re-attaches to the network as it is woken up. The main sleep: The device re-attaches to the network as it is woken up.
optimization goal is to minimize the effort during such re- The main optimization goal is to minimize the effort during such
attachment process and any resulting application communications. re-attachment process and any resulting application
communications.
If the device sleeps for long periods of time, and needs to If the device sleeps for long periods of time, and needs to
communicate infrequently, the relative increase in energy communicate infrequently, the relative increase in energy
expenditure during reattachment may be acceptable. expenditure during reattachment may be acceptable.
Low-power: This strategy is most applicable to devices that need to 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 operate on a very small amount of power, but still need to be able
to communicate on a relatively frequent basis. This implies that to communicate on a relatively frequent basis. This implies that
extremely low power solutions needs to be used for the hardware, extremely low power solutions needs to be used for the hardware,
chosen link layer mechanisms, and so on. Typically, given the chosen link layer mechanisms, and so on. Typically, given the
small amount of time between transmissions, despite their sleep small amount of time between transmissions, despite their sleep
state these devices retain some form of network attachment to the state these devices retain some form of network attachment to the
network. Techniques used for minimizing power usage for the network. Techniques used for minimizing power usage for the
network communications include minimizing any work from re- network communications include minimizing any work from re-
establishing communications after waking up, tuning the frequency establishing communications after waking up, tuning the frequency
of communications, and other parameters appropriately. of communications (including "duty cycling", where components are
switched on and off in a regular cycle), and other parameters
appropriately.
In summary, we distinguish (Table 4): In summary, we distinguish (Table 4):
+------+------------+----------------------------------------------+ +--------+--------------------+-------------------------------------+
| Name | Strategy | Ability to communicate | | Name | Strategy | Ability to communicate |
+------+------------+----------------------------------------------+ +--------+--------------------+-------------------------------------+
| S0 | Always-off | Re-attach when required | | P0 | Normally-off | Re-attach when required |
| | | | | | | |
| S1 | Low-power | Appears connected, perhaps with high latency | | P1 | Low-power | Appears connected, perhaps with |
| | | | | | | high latency |
| S2 | Always-on | Always connected | | | | |
+------+------------+----------------------------------------------+ | P9 | Always-on | Always connected |
+--------+--------------------+-------------------------------------+
Table 4: Strategies of Using Power for Communication Table 4: Strategies of Using Power for Communication
Note that the discussion above is at the device level; similar Note that the discussion above is at the device level; similar
considerations can apply at the communications interface level. This considerations can apply at the communications interface level. This
document does not define terminology for the latter. 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").
[I-D.ietf-roll-terminology] 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. Security Considerations 5. Security Considerations
This document introduces common terminology that does not raise any This document introduces common terminology that does not raise any
new security issue. Security considerations arising from the new security issue. Security considerations arising from the
constraints discussed in this document need to be discussed in the constraints discussed in this document need to be discussed in the
context of specific protocols. For instance, [I-D.ietf-core-coap] context of specific protocols. For instance, [I-D.ietf-core-coap]
section 11.6, "Constrained node considerations", discusses section 11.6, "Constrained node considerations", discusses
implications of specific constraints on the security mechanisms implications of specific constraints on the security mechanisms
employed. employed. A wider view at security in constrained node networks is
provided in [I-D.garcia-core-security].
6. IANA Considerations 6. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
7. Acknowledgements 7. Acknowledgements
Dominique Barthel and Peter van der Stok provided useful comments; Dominique Barthel and Peter van der Stok provided useful comments;
Charles Palmer provided a full editorial review. Charles Palmer provided a full editorial review.
Peter van der Stok insisted that we should have power terminology, Peter van der Stok insisted that we should have power terminology,
hence Section 4. The text for Section 4.3 is mostly lifted from hence Section 4. The text for Section 4.3 is mostly lifted from a
[I-D.arkko-lwig-cellular] and has been adapted for this document. previous version of [I-D.ietf-lwig-cellular] and has been adapted for
this document.
8. Informative References 8. Informative References
[FALL] Fall, K., "A Delay-Tolerant Network Architecture for [FALL] Fall, K., "A Delay-Tolerant Network Architecture for
Challenged Internets", SIGCOMM 2003, 2003. Challenged Internets", SIGCOMM 2003, 2003.
[I-D.arkko-lwig-cellular]
Arkko, J., Eriksson, A., and A. Keraenen, "Building Power-
Efficient CoAP Devices for Cellular Networks", draft-
arkko-lwig-cellular-00 (work in progress), February 2013.
[I-D.brandt-6man-lowpanz] [I-D.brandt-6man-lowpanz]
Brandt, A. and J. Buron, "Transmission of IPv6 packets Brandt, A. and J. Buron, "Transmission of IPv6 packets
over ITU-T G.9959 Networks", draft-brandt-6man-lowpanz-02 over ITU-T G.9959 Networks", draft-brandt-6man-lowpanz-02
(work in progress), June 2013. (work in progress), June 2013.
[I-D.clausen-lln-rpl-experiences] [I-D.garcia-core-security]
Clausen, T., Verdiere, A., Yi, J., Herberg, U., and Y. Garcia-Morchon, O., Kumar, S., Keoh, S., Hummen, R., and
Igarashi, "Observations of RPL: IPv6 Routing Protocol for R. Struik, "Security Considerations in the IP-based
Low power and Lossy Networks", draft-clausen-lln-rpl- Internet of Things", draft-garcia-core-security-06 (work
experiences-06 (work in progress), February 2013. in progress), September 2013.
[I-D.hui-vasseur-roll-rpl-deployment] [I-D.hui-vasseur-roll-rpl-deployment]
Vasseur, J., Hui, J., Dasgupta, S., and G. Yoon, "RPL Vasseur, J., Hui, J., Dasgupta, S., and G. Yoon, "RPL
deployment experience in large scale networks", draft-hui- deployment experience in large scale networks", draft-hui-
vasseur-roll-rpl-deployment-01 (work in progress), July vasseur-roll-rpl-deployment-01 (work in progress), July
2012. 2012.
[I-D.ietf-6lowpan-btle] [I-D.ietf-6lowpan-btle]
Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "Transmission of IPv6 Packets Shelby, Z., and C. Gomez, "Transmission of IPv6 Packets
over BLUETOOTH Low Energy", draft-ietf-6lowpan-btle-12 over BLUETOOTH Low Energy", draft-ietf-6lowpan-btle-12
(work in progress), February 2013. (work in progress), February 2013.
[I-D.ietf-core-coap] [I-D.ietf-core-coap]
Shelby, Z., Hartke, K., and C. Bormann, "Constrained Shelby, Z., Hartke, K., and C. Bormann, "Constrained
Application Protocol (CoAP)", draft-ietf-core-coap-18 Application Protocol (CoAP)", draft-ietf-core-coap-18
(work in progress), June 2013. (work in progress), June 2013.
[I-D.ietf-lwig-cellular]
Arkko, J., Eriksson, A., and A. Keranen, "Building Power-
Efficient CoAP Devices for Cellular Networks", draft-ietf-
lwig-cellular-00 (work in progress), August 2013.
[I-D.ietf-roll-terminology] [I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy Vasseur, J., "Terms used in Routing for Low power And
Networks", draft-ietf-roll-terminology-12 (work in Lossy Networks", draft-ietf-roll-terminology-13 (work in
progress), March 2013. progress), October 2013.
[I-D.mariager-6lowpan-v6over-dect-ule] [I-D.mariager-6lowpan-v6over-dect-ule]
Mariager, P. and J. Petersen, "Transmission of IPv6 Mariager, P., Petersen, J., and Z. Shelby, "Transmission
Packets over DECT Ultra Low Energy", draft-mariager- of IPv6 Packets over DECT Ultra Low Energy", draft-
6lowpan-v6over-dect-ule-02 (work in progress), May 2012. mariager-6lowpan-v6over-dect-ule-03 (work in progress),
July 2013.
[ISQ-13] International Electrotechnical Commission, "International [ISQ-13] International Electrotechnical Commission, "International
Standard -- Quantities and units -- Part 13: Information Standard -- Quantities and units -- Part 13: Information
science and technology", IEC 80000-13, March 2008. science and technology", IEC 80000-13, March 2008.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981. 793, September 1981.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, [RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
skipping to change at page 15, line 7 skipping to change at page 16, line 7
[RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D. [RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D.
Barthel, "Routing Metrics Used for Path Calculation in Barthel, "Routing Metrics Used for Path Calculation in
Low-Power and Lossy Networks", RFC 6551, March 2012. Low-Power and Lossy Networks", RFC 6551, March 2012.
[RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for IPv6 over Low-Power Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing", RFC Wireless Personal Area Network (6LoWPAN) Routing", RFC
6606, May 2012. 6606, May 2012.
[RFC6650] Falk, J. and M. Kucherawy, "Creation and Use of Email
Feedback Reports: An Applicability Statement for the Abuse
Reporting Format (ARF)", RFC 6650, June 2012.
[WEI] Shelby, Z. and C. Bormann, "6LoWPAN: the Wireless Embedded [WEI] Shelby, Z. and C. Bormann, "6LoWPAN: the Wireless Embedded
Internet", ISBN 9780470747995, 2009. Internet", ISBN 9780470747995, 2009.
[fifty-billion] [fifty-billion]
Ericsson, "More Than 50 Billion Connected Devices", Ericsson, "More Than 50 Billion Connected Devices",
Ericsson White Paper 284 23-3149 Uen, February 2011, Ericsson White Paper 284 23-3149 Uen, February 2011,
<http://www.ericsson.com/res/docs/whitepapers/ <http://www.ericsson.com/res/docs/whitepapers/
wp-50-billions.pdf>. wp-50-billions.pdf>.
Authors' Addresses Authors' Addresses
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