draft-ietf-lwig-energy-efficient-00.txt   draft-ietf-lwig-energy-efficient-01.txt 
Internet Engineering Task Force Z. Cao Internet Engineering Task Force Z. Cao
Internet-Draft China Mobile Internet-Draft Leibniz University of Hannover
Intended status: Informational C. Gomez Intended status: Informational C. Gomez
Expires: September 22, 2014 Universitat Politecnica de Catalunya/i2CAT Expires: April 30, 2015 Universitat Politecnica de
Catalunya/i2CAT
M. Kovatsch M. Kovatsch
ETH Zurich ETH Zurich
H. Tian H. Tian
China Academy of Telecommunication Research China Academy of
Telecommunication Research
X. He X. He
Hitachi China R&D Corporation Hitachi China R&D
March 21, 2014 Corporation
October 27, 2014
Energy Efficient Implementation of IETF Constrained Protocol Suite Energy Efficient Implementation of IETF Constrained Protocol Suite
draft-ietf-lwig-energy-efficient-00 draft-ietf-lwig-energy-efficient-01
Abstract Abstract
This document summarizes the problems and current practices of energy This document summarizes the problems and current practices of energy
efficient protocol implementation on constrained devices, mostly efficient protocol implementation on constrained devices, mostly
about how to make the protocols within IETF scope behave energy about how to make the protocols within IETF scope behave energy
friendly. This document also summarizes the impact of link layer friendly. This document also summarizes the impact of link layer
protocol power saving behaviors to the upper layer protocols, so that protocol power saving behaviors to the upper layer protocols, so that
they can coordinately make the system energy efficient. they can coordinately make the system energy efficient.
Status of This Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 22, 2014. This Internet-Draft will expire on April 30, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. MAC and Radio Duty Cycling . . . . . . . . . . . . . . . . . 5 3. MAC and Radio Duty Cycling . . . . . . . . . . . . . . . . . . 6
3.1. Power Save Services Provided by IEEE 802.11v . . . . . . 6 3.1. Radio Duty Cycling techniques . . . . . . . . . . . . . . 6
3.2. Power Save Services Provided by Bluetooth Low Energy . . 6 3.2. Latency and buffering . . . . . . . . . . . . . . . . . . 7
3.3. Power Save Services in IEEE 802.15.4 . . . . . . . . . . 7 3.3. Power save services available in example low-power
4. IP Adaptation and Transport Layer . . . . . . . . . . . . . . 9 radios . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Routing Protocols . . . . . . . . . . . . . . . . . . . . . . 10 3.3.1. Power Save Services Provided by IEEE 802.11v . . . . . 8
6. Application Layer . . . . . . . . . . . . . . . . . . . . . . 10 3.3.2. Power Save Services Provided by Bluetooth Low
7. Cross Layer Optimization . . . . . . . . . . . . . . . . . . 11 Energy . . . . . . . . . . . . . . . . . . . . . . . . 9
8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3.3. Power Save Services in IEEE 802.15.4 . . . . . . . . . 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 4. IP Adaptation and Transport Layer . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 5. Routing Protocols . . . . . . . . . . . . . . . . . . . . . . 13
11. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6. Application Layer . . . . . . . . . . . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 7. Cross Layer Optimization . . . . . . . . . . . . . . . . . . . 15
12.1. Normative References . . . . . . . . . . . . . . . . . . 12 8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 14 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
11. Security Considerations . . . . . . . . . . . . . . . . . . . 19
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . . 20
12.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
In many scenarios, the network systems comprises many battery-powered In many scenarios, the network systems comprises many battery-powered
or energy-harvesting devices. For example, in an environmental or energy-harvesting devices. For example, in an environmental
monitoring system or a temperature and humidity monitoring system in monitoring system or a temperature and humidity monitoring system in
the data center, there are no always-on and handy sustained power the data center, there are no always-on and handy sustained power
supplies for the large number of small devices. In such deployment supplies for the large number of small devices. In such deployment
environments, it is necessary to optimize the energy consumption of environments, it is necessary to optimize the energy consumption of
the entire system, including computing, application layer behavior, the entire system, including computing, application layer behavior,
skipping to change at page 3, line 21 skipping to change at page 3, line 37
to summarize the design considerations of making the IETF protocol to summarize the design considerations of making the IETF protocol
suite as energy-efficient as possible. While this document does not suite as energy-efficient as possible. While this document does not
provide detailed and systematic solutions to the energy efficiency provide detailed and systematic solutions to the energy efficiency
problem, it summarizes the design efforts and analyzes the design problem, it summarizes the design efforts and analyzes the design
space of this problem. space of this problem.
After reviewing the energy-efficient design of each layer, an overall After reviewing the energy-efficient design of each layer, an overall
conclusion is summarized. Though the lower layer communication conclusion is summarized. Though the lower layer communication
optimization is the key part of energy efficient design, the protocol optimization is the key part of energy efficient design, the protocol
design at the network and application layers is also important to design at the network and application layers is also important to
make the device battery-friendly. make the device energy-efficient.
1.1. Conventions used in this document 1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] document are to be interpreted as described in [RFC2119]
1.2. Terminology 1.2. Terminology
The terminologies used in this document can be referred to The terminologies used in this document can be referred to [RFC7228].
[I-D.ietf-lwig-terminology].
2. Overview 2. Overview
The IETF has developed multiple protocols to enable end-to-end IP The IETF has developed multiple protocols to enable end-to-end IP
communication between constrained nodes and fully capable nodes. communication between constrained nodes and fully capable nodes.
This work has witnessed the evolution of the traditional Internet This work has witnessed the evolution of the traditional Internet
protocol stack to a light-weight Internet protocol stack. As show in protocol stack to a light-weight Internet protocol stack. As show in
Figure 1 below, the IETF has developed CoAP as the application layer Figure 1 below, the IETF has developed CoAP as the application layer
and 6LoWPAN as the adaption layer to run IPv6 over IEEE 802.15.4 and and 6LoWPAN as the adaption layer to run IPv6 over IEEE 802.15.4 and
Bluetooth Low-Energy, with the support of routing by RPL and Bluetooth Low-Energy, with the support of routing by RPL and
efficient neighbor discovery by 6LoWPAN-ND. efficient neighbor discovery by 6LoWPAN-ND. 6LoWPAN is currently
being adapted by the 6lo working group to support IPv6 over various
other technologies, such as ITU-T G.9959, DECT ULE and MS/TP-BACnet.
+-----+ +-----+ +-----+ +------+ +-----+ +-----+ +-----+ +------+
|http | | ftp | |SNMP | | COAP | |http | | ftp | |SNMP | | COAP |
+-----+ +-----+ +-----+ +------+ +-----+ +-----+ +-----+ +------+
\ / / / \ \ / / / \
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
| tcp | | udp | | tcp | | udp | | tcp | | udp | | tcp | | udp |
+-----+ +-----+ ===> +-----+ +-----+ +-----+ +-----+ ===> +-----+ +-----+
\ / \ / \ / \ /
+-----+ +------+ +-------+ +------+ +-----+ +-----+ +------+ +-------+ +------+ +-----+
skipping to change at page 4, line 27 skipping to change at page 4, line 40
+-------+ +-------+ +----------+ +-------+ +-------+ +----------+
|MAC/PHY| |6lowpan|--|6lowpan-nd| |MAC/PHY| |6lowpan|--|6lowpan-nd|
+-------+ +-------+ +----------+ +-------+ +-------+ +----------+
| |
+-------+ +-------+
|MAC/PHY| |MAC/PHY|
+-------+ +-------+
Figure 1: Traditional and Light-weight Internet Protocol Stack Figure 1: Traditional and Light-weight Internet Protocol Stack
There are comprehensive measurements of wireless communication There are numerous published studies reporting comprehensive
[Powertrace]. Below we list the energy consumption profile of the measurements of wireless communication platforms[Powertrace]. Below
most common atom operations on a prevalent sensor node platform. The we list the energy consumption profile of the most common atom
measurement was based on the Tmote Sky with ContikiMAC as the radio operations on a prevalent sensor node platform. The measurement was
duty cycling algorithm. From the measurement, we can see that based on the Tmote Sky with ContikiMAC as the radio duty cycling
optimized transmissions and reception consume almost the same amount algorithm. From the measurement, we can see that optimized
of energy. For IEEE 802.15.4 and UWB radios, transmitting is transmissions and reception consume almost the same amount of energy.
actually even cheaper than receiving. Only for broadcast and non- For IEEE 802.15.4 and UWB radios, transmitting may actually be even
synchronized communication transmissions become costly in terms of cheaper than receiving. Only for broadcast and non-synchronized
energy because they need to flood the medium for a long time. communication transmissions become costly in terms of energy because
they need to flood the medium for a long time.
+---------------------------------------+---------------+ +---------------------------------------+---------------+
| Activity | Energy (uJ) | | Activity | Energy (uJ) |
+---------------------------------------+---------------+ +---------------------------------------+---------------+
| Broadcast reception | 178 | | Broadcast reception | 178 |
+---------------------------------------+---------------+ +---------------------------------------+---------------+
| Unicast reception | 222 | | Unicast reception | 222 |
+---------------------------------------+---------------+ +---------------------------------------+---------------+
| Broadcast transmission | 1790 | | Broadcast transmission | 1790 |
+---------------------------------------+---------------+ +---------------------------------------+---------------+
skipping to change at page 5, line 29 skipping to change at page 6, line 10
+---------------------------------------+---------------+ +---------------------------------------+---------------+
Figure 2: Power consumption of atom operations on the Tmote Sky with Figure 2: Power consumption of atom operations on the Tmote Sky with
ContikiMAC ContikiMAC
3. MAC and Radio Duty Cycling 3. MAC and Radio Duty Cycling
In low-power wireless networks, communication and power consumption In low-power wireless networks, communication and power consumption
are intertwined. The communication device is typically the most are intertwined. The communication device is typically the most
power-consuming component, but merely refraining from transmissions power-consuming component, but merely refraining from transmissions
is not enough to attain a low power consumption: the radio consumes is not enough to attain a low power consumption: the radio may
as much power in listen mode as when actively transmitting, as show consume as much power in listen mode as when actively transmitting.
in Figure 2 . To reduce power consumption, the radio must be switched This augments the key problem known as idle listening, whereby the
completely off -- duty-cycled -- as much as possible. ContikiMAC is radio of a device may be in receive mode (ready to receive any
a very typical Radio Duty Cycling (RDC) protocol [ContikiMAC]. message), even if no message is being transmitted to that device.
Idle listening consumes a huge amount of energy unnecessarily. To
reduce power consumption, the radio must be switched completely off
-- duty-cycled -- as much as possible. By applying duty-cycling, the
lifetime of a device operating on a common button battery may be in
the order of years, whereas otherwise the battery may be exhausted in
a few days or even hours. Duty-cycling is a technique generally
exploited by devices that use the P1 strategy [RFC7228], which need
to be able to communicate on a relatively frequent basis. Note that
a more aggressive approach to save energy relies on the P0, Normally-
off strategy, whereby devices sleep for very long periods and
communicate infrequently, even though they spend energy in network
reattachment procedures. ContikiMAC is an example of a very typical
Radio Duty Cycling (RDC) protocol [ContikiMAC].
From the perspective of MAC&RDC, all upper layer protocols, such as From the perspective of MAC&RDC, all upper layer protocols, such as
routing, RESTful communication, adaptation, and management flows, are routing, RESTful communication, adaptation, and management flows, are
all applications. Since the duty cycling algorithm is the key to all applications. Since the duty cycling algorithm is the key to
energy-efficiency of the wireless medium, it synchronizes the TX/RX energy-efficiency of the wireless medium, it synchronizes the TX/RX
request from the higher layer. request from the higher layer.
The MAC&RDC are not in the scope of the IETF, yet lower layer The MAC&RDC are not in the scope of the IETF, yet lower layer
designers and chipset manufactures take great care of the problem. designers and chipset manufactures take great care of the problem.
For the IETF protocol designers, however, it is good to know the For the IETF protocol designers, however, it is good to know the
behaviors of lower layers so that the designed protocols can work behaviors of lower layers so that the designed protocols can work
perfectly with them. perfectly with them.
Once again, the IETF protocols we are going to talk about in the Once again, the IETF protocols we are going to talk about in the
following sections are the customers of the lower layer. If they following sections are the customers of the lower layer. If they
want to get better service in a cooperative way, they should be want to get better service in a cooperative way, they should be
considerate and understand each other. considerate and understand each other.
3.1. Power Save Services Provided by IEEE 802.11v 3.1. Radio Duty Cycling techniques
This subsection describes the main three RDC techniques. Note that
more than one of the presented techniques may be available or can
even be combined in a specific radio technology:
a) Channel sampling. In this solution, the radio interface of a
device periodically monitors the channel for very short time
intervals (i.e. with a low duty cycle) with the aim of detecting
incoming transmissions. In order to make sure that a receiver can
correctly receive a transmitted data unit, the sender may prepend a
preamble of a duration at least the sampling period to the data unit
to be sent. Another option for the sender is to repeatedly transmit
the data unit, instead of sending a preamble before the data unit.
Once a transmission is detected by a receiver, the receiver may stay
awake until the complete reception of the data unit. Examples of
radio technologies that use preamble sampling include ContikiMAC, the
Coordinated Sampled Listening (CSL) mode of IEEE 802.15.4e, and the
Frequently Listening (FL) mode of ITU-T G.9959.
b) Scheduled transmissions. This approach allows a device to know
the instants in which it should be awake (during some time interval)
in order to receive data units. Otherwise, the device may remain in
sleep mode. The decision on the instants that will be used for
communication is reached by means of some form of negotation between
the involved devices. Such negotiation may be performed per
transmission or per session/connection. Bluetooth Low Energy is an
example of a radio technology based on this mechanism.
c) Listen after send. This technique allows a node to remain in
sleep mode by default, wake up and poll a sender (which must be ready
to receive a poll message) for pending transmissions. After sending
the poll message, the node remains in receive mode, ready for a
potential incoming transmission. After a certain time interval, the
node may go back to sleep. The Receiver Initated Transmission (RIT)
mode of 802.15.4e, and the transmission of data between a coordinator
and a device in IEEE 802.15.4-2003 use this technique.
3.2. Latency and buffering
The latency of a data unit transmission to a duty-cycled device is
equal to or greater than the latency of transmitting to an always-on
device. Therefore, duty-cycling leads to a trade-off between energy
consumption and latency. Note that in addition to a latency
increase, RDC may introduce latency variance, since the latency
increase is a random variable (which is uniformly distributed if
duty-cycling follows a periodical behavior).
On the other hand, due to the latency increase of duty-cycling, a
sender waiting for a transmission opportunity may need to store
subsequent outgoing packets in a buffer, increasing memory
requirements and potentially incurring queuing waiting time that
contributes to the packet overall delay and increases the probability
of buffer overflow, leading to losses.
The parameters controlling the radio duty cycle have to be carefully
tuned to achieve the intended application and/or network
requirements. On the other hand, upper layers should take into
account the expected latency behavior due to RDC.
3.3. Power save services available in example low-power radios
This subsection presents power save services and techniques used in a
few relevant examples of wireless low-power radios: IEEE 802.11v,
Bluetooth Low Energy and IEEE 802.15.4. For a more detailed overview
of each technology, the reader may refer to the literature or to the
corresponding specifications.
3.3.1. Power Save Services Provided by IEEE 802.11v
IEEE 802.11v [IEEE80211v] defines mechanisms and services for power IEEE 802.11v [IEEE80211v] defines mechanisms and services for power
save of stations/nodes that include flexible multicast service (FMS), save of stations/nodes that include flexible multicast service (FMS),
proxy ARP advertisement, extended sleep modes, traffic filtering. It proxy ARP advertisement, extended sleep modes, traffic filtering. It
would be useful if upper layer protocols knows such capabilities would be useful if upper layer protocols knows such capabilities
provided by the lower layer, so that they can coordinate with each provided by the lower layer, so that they can coordinate with each
other. other.
These services include: These services include:
skipping to change at page 6, line 45 skipping to change at page 9, line 9
traffic filters specified by the non-AP STA. traffic filters specified by the non-AP STA.
Using the above services provided by the lower layer, the constrained Using the above services provided by the lower layer, the constrained
nodes can achieve either client initiated power save (via TFS) or nodes can achieve either client initiated power save (via TFS) or
network assisted power save (Proxy-ARP, BSS Max Idel Period and FMS). network assisted power save (Proxy-ARP, BSS Max Idel Period and FMS).
Upper layer protocols would better synchronize with the parameters Upper layer protocols would better synchronize with the parameters
such as FMS interval and BSS MAX Idle Period, so that the wireless such as FMS interval and BSS MAX Idle Period, so that the wireless
transmissions are not triggered periodically. transmissions are not triggered periodically.
3.2. Power Save Services Provided by Bluetooth Low Energy 3.3.2. Power Save Services Provided by Bluetooth Low Energy
Bluetooth Low Energy (BT-LE) is a wireless low-power communications Bluetooth Low Energy (Bluetooth LE) is a wireless low-power
technology that is the hallmark component of the Bluetooth 4.0 communications technology that is the hallmark component of the
specification. BT-LE has been designed for the goal of ultra-low- Bluetooth 4.0 and Bluetooth 4.1 specifications [Bluetooth41]"/>.
power consumption. Currently, it is possible to run IPv6 over BT-LE BT-LE has been designed for the goal of ultra-low-power consumption.
networks by using a 6LoWPAN variant adapted to BT-LE Currently, it is possible to run IPv6 over BT-LE networks by using a
[I-D.ietf-6lowpan-btle]. 6LoWPAN variant adapted to BT-LE [I-D.ietf-6lowpan-btle].
BT-LE networks comprise a master and one or more slaves which are Bluetooth LE networks comprise a master and one or more slaves which
connected to the master. The BT-LE master is assumed to be a are connected to the master. The Bluetooth LE master is assumed to
relatively powerful device, whereas a slave is typically a be a relatively powerful device, whereas a slave is typically a
constrained device (e.g. a class 1 device). constrained device (e.g. a class 1 device).
Medium access in BT-LE is based on a TDMA scheme which is coordinated Medium access in Bluetooth LE is based on a TDMA scheme which is
by the master. This device determines the start of connection coordinated by the master. This device determines the start of
events, in which communication between the master and a slave takes connection events, in which communication between the master and a
place. At the beginning of a connection event, the master sends a slave takes place. At the beginning of a connection event, the
poll message, which may encapsulate data, to the slave. The latter master sends a poll message, which may encapsulate data, to the
must send a response, which may also contain data. The master and slave. The latter must send a response, which may also contain data.
the slave may continue exchanging data until the end of the The master and the slave may continue exchanging data until the end
connection event. The next opportunity for communication between the of the connection event. The next opportunity for communication
master and the slave will be in the next connection event scheduled between the master and the slave will be in the next connection event
for the slave. scheduled for the slave.
The time between consecutive connection events is defined by the The time between consecutive connection events is defined by the
connInterval parameter, which may range between 7.5 ms and 4 s. The connInterval parameter, which may range between 7.5 ms and 4 s. The
slave may remain in sleep mode since the end of its last connection slave may remain in sleep mode since the end of its last connection
event until the beginning of its next connection event. Therefore, event until the beginning of its next connection event. Therefore,
BT-LE is duty-cycled by nature. Furthermore, after having replied to Bluetooth LE is duty-cycled by nature. Furthermore, after having
the master, a slave is not required to listen to the master (and thus replied to the master, a slave is not required to listen to the
may keep the radio in sleep mode) for connSlaveLatency consecutive master (and thus may keep the radio in sleep mode) for
connection events. connSlaveLatency is an integer parameter between 0 connSlaveLatency consecutive connection events. connSlaveLatency is
and 499 which should not cause link inactivity for more than an integer parameter between 0 and 499 which should not cause link
connSupervisionTimeout time. The connSupervisionTimeout parameter is inactivity for more than connSupervisionTimeout time. The
in the range between 100 ms and 32 s. connSupervisionTimeout parameter is in the range between 100 ms and
32 s.
Upper layer protocols should take into account the medium access and Upper layer protocols should take into account the medium access and
duty-cycling behavior of BT-LE. In particular, connInterval, duty-cycling behavior of Bluetooth LE. In particular, connInterval,
connSlaveLatency and connSupervisionTimeout determine the time connSlaveLatency and connSupervisionTimeout determine the time
between two consecutive connection events for a given slave. The between two consecutive connection events for a given slave. The
upper layer packet generation pattern and rate should be consistent upper layer packet generation pattern and rate should be consistent
with the settings of the aforementioned parameters (and vice versa). with the settings of the aforementioned parameters (and vice versa).
3.3. Power Save Services in IEEE 802.15.4 3.3.3. Power Save Services in IEEE 802.15.4
IEEE 802.15.4 is a family of standard radio interfaces for low-rate, IEEE 802.15.4 is a family of standard radio interfaces for low-rate,
low-power wireless networking. Since the publication of its first low-power wireless networking [fifteendotfour]. Since the
version in 2003, IEEE 802.15.4 has become the de-facto choice for a publication of its first version in 2003, IEEE 802.15.4 has become
wide range of constrained node network application domains and has the de-facto choice for a wide range of constrained node network
been a primary target technology of various IETF working groups such application domains and has been a primary target technology of
as 6LoWPAN [RFC6282],[RFC6775],[RFC4944] and 6TiSCH various IETF working groups such as 6LoWPAN
[RFC6282],[RFC6775],[RFC4944] and 6TiSCH
[I-D.ietf-6tisch-architecture]. IEEE 802.15.4 specifies PHY and MAC [I-D.ietf-6tisch-architecture]. IEEE 802.15.4 specifies PHY and MAC
layer functionality. layer functionality.
IEEE 802.15.4 defines three roles called device, coordinator and PAN IEEE 802.15.4 defines three roles called device, coordinator and PAN
coordinator. The device role is adequate for nodes that do not coordinator. The device role is adequate for nodes that do not
implement the complete IEEE 802.15.4 functionality, and is mainly implement the complete IEEE 802.15.4 functionality, and is mainly
targeted for constrained nodes with a limited energy source. The targeted for constrained nodes with a limited energy source. The
coordinator role includes synchronization capabilities and is coordinator role includes synchronization capabilities and is
suitable for nodes that do not suffer severe constraints (e.g. a suitable for nodes that do not suffer severe constraints (e.g. a
mains-powered node). The PAN coordinator is a special type of mains-powered node). The PAN coordinator is a special type of
coordinator that acts as a principal controller in an IEEE 802.15.4 coordinator that acts as a principal controller in an IEEE 802.15.4
network. network.
IEEE 802.15.4 has mainly defined two types of networks depending on IEEE 802.15.4 has mainly defined two types of networks depending on
their configuration: beacon-enabled and nonbeacon-enabled networks. their configuration: beacon-enabled and nonbeacon-enabled networks.
In the first network type, coordinators periodically transmit In the first network type, coordinators periodically transmit
beacons. The time between beacons is divided in three main parts: beacons. The time between beacons is divided in three main parts:
the Contention Access Period (CAP), the Contention Free Period (CFP) the Contention Access Period (CAP), the Contention Free Period (CFP)
and an inactive period. In the first period, nodes use slotted CSMA/ and an inactive period. In the first period, nodes use slotted
CA for data communication. In the second one, a TDMA scheme controls CSMA/CA for data communication. In the second one, a TDMA scheme
medium access. During the idle period, communication does not take controls medium access. During the idle period, communication does
place, thus the inactive period is a good opportunity for nodes to not take place, thus the inactive period is a good opportunity for
turn the radio off and save energy. The coordinator announces in nodes to turn the radio off and save energy. The coordinator
each beacon the list of nodes for which data will be sent in the announces in each beacon the list of nodes for which data will be
subsequent period. Therefore, devices may remain in sleep mode by sent in the subsequent period. Therefore, devices may remain in
default and wake up periodically to listen to the beacons sent by sleep mode by default and wake up periodically to listen to the
their coordinator. If a device wants to transmit data, or learns beacons sent by their coordinator. If a device wants to transmit
from a beacon that it is an intended destination, then it will data, or learns from a beacon that it is an intended destination,
exchange messages with the coordinator and will thus consume energy. then it will exchange messages with the coordinator and will thus
An underlying assumption is that when a message is sent to a consume energy. An underlying assumption is that when a message is
coordinator, the radio of the latter will be ready to receive the sent to a coordinator, the radio of the latter will be ready to
message. receive the message.
The beacon interval and the duration of the beacon interval active The beacon interval and the duration of the beacon interval active
portion (i.e. the CAP and the CFP), and thus the duty cycle, can be portion (i.e. the CAP and the CFP), and thus the duty cycle, can be
configured. The parameters that control these times are called configured. The parameters that control these times are called
macBeaconOrder and macSuperframeOrder, respectively. As an example, macBeaconOrder and macSuperframeOrder, respectively. As an example,
when IEEE 802.15.4 operates in the 2.4 GHz PHY, both times can be when IEEE 802.15.4 operates in the 2.4 GHz PHY, both times can be
(independently) set to values in the range between 15.36 ms and 251.6 (independently) set to values in the range between 15.36 ms and 251.6
s. s.
In the beaconless mode, nodes use unslotted CSMA/CA for data In the beaconless mode, nodes use unslotted CSMA/CA for data
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the 6TiSCH working group has been recently created. TSCH is based on the 6TiSCH working group has been recently created. TSCH is based on
a TDMA schedule whereby a set of time slots are used for frame a TDMA schedule whereby a set of time slots are used for frame
transmission and reception, and other time slots are unscheduled. transmission and reception, and other time slots are unscheduled.
The latter time slots may be used by a dynamic scheduling mechanism, The latter time slots may be used by a dynamic scheduling mechanism,
otherwise nodes may keep the radio off during the unscheduled time otherwise nodes may keep the radio off during the unscheduled time
slots, thus saving energy. The minimal schedule configuration slots, thus saving energy. The minimal schedule configuration
specified in [I-D.ietf-6tisch-minimal] comprises 101 time slots, specified in [I-D.ietf-6tisch-minimal] comprises 101 time slots,
whereby 95 of these time slots are unscheduled and the time slot whereby 95 of these time slots are unscheduled and the time slot
duration is 15 ms. duration is 15 ms.
Other 802.15.4e modes, which are in fact designed for low energy, are
the previously mentioned CSL and RIT.
4. IP Adaptation and Transport Layer 4. IP Adaptation and Transport Layer
6LoWPAN is the adaption layer to run IPv6 over IEEE 802.15.4 MAC&PHY. 6LoWPAN is the adaption layer to run IPv6 over IEEE 802.15.4 MAC&PHY.
It was born to fill the gap that the IPv6 layer does not support It was born to fill the gap that the IPv6 layer does not support
fragmentation and assembly of <1280-byte packets while IEEE 802.15.4 fragmentation and assembly of <1280-byte packets while IEEE 802.15.4
only supports a MTU of 127 bytes. only supports a MTU of 127 bytes.
IPv6 is the basis for the higher layer protocols, including both TCP/ IPv6 is the basis for the higher layer protocols, including both TCP/
UDP transport and applications. So they are quite ignorant of the UDP transport and applications. So they are quite ignorant of the
lower layers, and are almost neutral to the energy-efficiency lower layers, and are almost neutral to the energy-efficiency
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The authors of the Powertrace tool [Powertrace] studied the power The authors of the Powertrace tool [Powertrace] studied the power
profile of RPL. It divides the routing protocol into control and profile of RPL. It divides the routing protocol into control and
data traffic. The control channel uses ICMP messages to establish data traffic. The control channel uses ICMP messages to establish
and maintain the routing states. The data channel is any application and maintain the routing states. The data channel is any application
that uses RPL for routing packets. The study has shown that the that uses RPL for routing packets. The study has shown that the
power consumption of the control traffic goes down over time and data power consumption of the control traffic goes down over time and data
traffic stays relatively constant. The study also reflects that the traffic stays relatively constant. The study also reflects that the
routing protocol should keep the control traffic as low as possible routing protocol should keep the control traffic as low as possible
to make it energy-friendly. The amount of RPL control traffic can be to make it energy-friendly. The amount of RPL control traffic can be
tuned by setting the Trickle algorithm parameters (i.e. Imin, Imax tuned by setting the Trickle algorithm parameters (i.e. Imin, Imax
and k) to adequate values. However, there exists a trade-off between and k) to adequate values. However, there exists a trade-off between
energy consumption and other performance parameters such as network energy consumption and other performance parameters such as network
convergence time and robustness. convergence time and robustness.
Todo: more discussion of energy efficient routing. RFC 6551 [RFC6551] defines routing metrics and constraints to be used
by RPL in route computation. Among others, RFC 6551 specifies a Node
Energy object that allows to provide information related to node
energy, such as the energy source type or the estimated percentage of
remaining energy. Appropriate use of energy-based routing metrics
may help to balance energy consumption of network nodes, minimize
network partitioning and increase network lifetime.
6. Application Layer 6. Application Layer
CoAP [I-D.ietf-core-coap]was designed as a RESTful application CoAP [RFC7252] was designed as a RESTful application protocol,
protocol, connecting the services of smart devices to the World Wide connecting the services of smart devices to the World Wide Web. CoAP
Web. CoAP is not a chatty protocol, it provides basic communication is not a chatty protocol, it provides basic communication services
services such as service discovery and GET/POST/PUT/DELETE methods such as service discovery and GET/POST/PUT/DELETE methods with a
with a binary header. binary header.
The energy-efficient design is implicitly included in the CoAP The energy-efficient design is implicitly included in the CoAP
protocol design. To reduce regular and frequent queries of the protocol design. CoAP uses a fixed-length binary header of only four
resources, CoAP provides an observe mode, in which the requester bytes that may be followed by binary options. To reduce regular and
registers its interest of a certain resource and the responder will frequent queries of the resources, CoAP provides an observe mode, in
report the value whenever it was updated. This reduces the request which the requester registers its interest of a certain resource and
response roundtrip while keeping information exchange a ubiquitous the responder will report the value whenever it was updated. This
service. reduces the request response roundtrip while keeping information
exchange a ubiquitous service and, most importantly, it allows an
energy-constrained server to remain in sleep mode during the period
between observe notification transmissions.
Furthermore, [RFC7252] defines CoAP proxies which can cache resource
representations previously provided by sleepy CoAP servers. The
proxies themselves may respond to client requests if the
corresponding server is sleeping and the resource representation is
recent enough. Otherwise, a proxy may attempt to obtain the resource
from the sleepy server.
Beyond these features of CoAP, there have been a number of proposals
to further support sleepy nodes at the application layer by
leveraging CoAP mechanisms. A good summary of such proposals can be
found in [I-D.rahman-core-sleepy-nodes-do-we-need]. The different
approaches include exploiting the use of proxies, leveraging the
Resource Directory [I-D.ietf-core-resource-directory] or signaling
when a node is awake to the interested nodes. As of the writing,
none of these proposals has been adopted by the CoRE working group.
CoAP offers mechanisms for reliable communication between two CoAP CoAP offers mechanisms for reliable communication between two CoAP
endpoints. A CoAP message may be signaled as a confirmable (CON) endpoints. A CoAP message may be signaled as a confirmable (CON)
message, and an acknowledgment (ACK) is issued by the receiver if the message, and an acknowledgment (ACK) is issued by the receiver if the
CON message is correctly received. The sender starts a CON message is correctly received. The sender starts a
Retransmission TimeOut (RTO) for every CON message sent. The initial Retransmission TimeOut (RTO) for every CON message sent. The initial
RTO value is chosen randomly between 2 and 3 s. If an RTO expires, RTO value is chosen randomly between 2 and 3 s. If an RTO expires,
the new RTO value is doubled (unless a limit on the number of the new RTO value is doubled (unless a limit on the number of
retransmissions has been reached). Since duty-cycling at the link retransmissions has been reached). Since duty-cycling at the link
layer may lead to long latency (i.e. even greater than the initial layer may lead to long latency (i.e. even greater than the initial
RTO value), CoAP RTO parameters should be tuned accordingly in order RTO value), CoAP RTO parameters should be tuned accordingly in order
to avoid spurious RTOs which would unnecessarily waste node energy to avoid spurious RTOs which would unnecessarily waste node energy
and other resources. and other resources.
7. Cross Layer Optimization 7. Cross Layer Optimization
The cross layer optimization is a technique used in many The cross layer optimization is a technique used in many
skipping to change at page 12, line 44 skipping to change at page 20, line 11
This document discusses the energy efficient protocol design, and This document discusses the energy efficient protocol design, and
does not incur any changes or challenges on security issues besides does not incur any changes or challenges on security issues besides
what the protocol specifications have analyzed. what the protocol specifications have analyzed.
12. References 12. References
12.1. Normative References 12.1. Normative References
[Announcementlayer] [Announcementlayer]
Dunkels, A., "The Announcement Layer: Beacon Coordination Dunkels, A., "The Announcement Layer: Beacon Coordination
for the Sensornet Stack. In Proceedings of EWSN 2011", . for the Sensornet Stack. In Proceedings of EWSN 2011".
[Bluetooth41]
"Bluetooth Core Specification Version 4.1", 2013.
[ContikiMAC] [ContikiMAC]
Dunkels, A., "The ContikiMAC Radio Duty Cycling Protocol, Dunkels, A., "The ContikiMAC Radio Duty Cycling Protocol,
SICS Technical Report T2011:13", December 2011. SICS Technical Report T2011:13", December 2011.
[Cross-layer-Optimization] [Cross-layer-Optimization]
Le, and Hossain, "Cross-Layer Optimization Frameworks for Le and Hossain, "Cross-Layer Optimization Frameworks for
Multihop Wireless Networks Using Cooperative Diversity", Multihop Wireless Networks Using Cooperative Diversity",
July 2008. July 2008.
[Cross-layer-design] [Cross-layer-design]
Chen, , Low, , and Doyle, "Cross-layer design in multihop Chen, Low, and Doyle, "Cross-layer design in multihop
wireless networks", 2011. wireless networks", 2011.
[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-6man-impatient-nud] [I-D.ietf-6man-impatient-nud]
Nordmark, E. and I. Gashinsky, "Neighbor Unreachability Nordmark, E. and I. Gashinsky, "Neighbor Unreachability
Detection is too impatient", draft-ietf-6man-impatient- Detection is too impatient",
nud-07 (work in progress), October 2013. draft-ietf-6man-impatient-nud-07 (work in progress),
October 2013.
[I-D.ietf-6tisch-architecture] [I-D.ietf-6tisch-architecture]
Thubert, P., Watteyne, T., and R. Assimiti, "An Thubert, P., Watteyne, T., and R. Assimiti, "An
Architecture for IPv6 over the TSCH mode of IEEE Architecture for IPv6 over the TSCH mode of IEEE
802.15.4e", draft-ietf-6tisch-architecture-01 (work in 802.15.4e", draft-ietf-6tisch-architecture-03 (work in
progress), February 2014. progress), July 2014.
[I-D.ietf-6tisch-minimal] [I-D.ietf-6tisch-minimal]
Vilajosana, X. and K. Pister, "Minimal 6TiSCH Vilajosana, X. and K. Pister, "Minimal 6TiSCH
Configuration", draft-ietf-6tisch-minimal-00 (work in Configuration", draft-ietf-6tisch-minimal-02 (work in
progress), November 2013. progress), July 2014.
[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-core-resource-directory]
Shelby, Z., Bormann, C., and S. Krco, "CoRE Resource
Directory", draft-ietf-core-resource-directory-01 (work in
progress), December 2013.
[I-D.ietf-lwig-terminology] [I-D.ietf-lwig-terminology]
Bormann, C., Ersue, M., and A. Keranen, "Terminology for Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained Node Networks", draft-ietf-lwig-terminology-07 Constrained Node Networks", draft-ietf-lwig-terminology-07
(work in progress), February 2014. (work in progress), February 2014.
[I-D.kovatsch-lwig-class1-coap] [I-D.kovatsch-lwig-class1-coap]
Kovatsch, M., "Implementing CoAP for Class 1 Devices", Kovatsch, M., "Implementing CoAP for Class 1 Devices",
draft-kovatsch-lwig-class1-coap-00 (work in progress), draft-kovatsch-lwig-class1-coap-00 (work in progress),
October 2012. October 2012.
[I-D.rahman-core-sleepy-nodes-do-we-need]
Rahman, A., "Sleepy Devices: Do we need to Support them in
CORE?", draft-rahman-core-sleepy-nodes-do-we-need-01 (work
in progress), February 2014.
[IEEE80211v] [IEEE80211v]
IEEE, , "Part 11: Wireless LAN Medium Access Control (MAC) IEEE, "Part 11: Wireless LAN Medium Access Control (MAC)
and Physical Layer (PHY) specifications, Amendment 8: IEEE and Physical Layer (PHY) specifications, Amendment 8: IEEE
802.11 Wireless Network Management.", February 2012. 802.11 Wireless Network Management.", February 2012.
[Powertrace] [Powertrace]
Dunkels, , Eriksson, , Finne, , and Tsiftes, "Powertrace: Dunkels, Eriksson, Finne, and Tsiftes, "Powertrace:
Network-level Power Profiling for Low-power Wireless Network-level Power Profiling for Low-power Wireless
Networks", March 2011. Networks", March 2011.
[fifteendotfour]
"802.15.4-2011", 2011.
12.2. Informative References 12.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4 "Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007. Networks", RFC 4944, September 2007.
[RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 [RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
September 2011. September 2011.
[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., [RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
Lossy Networks", RFC 6550, March 2012. Lossy Networks", RFC 6550, March 2012.
[RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D.
Barthel, "Routing Metrics Used for Path Calculation in
Low-Power and Lossy Networks", RFC 6551, March 2012.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, August 2012.
[RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann, [RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
"Neighbor Discovery Optimization for IPv6 over Low-Power "Neighbor Discovery Optimization for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)", RFC 6775, Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
November 2012. November 2012.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, May 2014.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, June 2014.
Authors' Addresses Authors' Addresses
Zhen Cao (Ed.) Zhen Cao (Ed.)
China Mobile Leibniz University of Hannover
Xuanwumenxi Ave. No.32
Beijing 100871
P.R.China P.R.China
Email: zehn.cao@gmail.com, caozhen@chinamobile.com Phone:
Email: zhencao.ietf@gmail.com
Carles Gomez Carles Gomez
Universitat Politecnica de Catalunya/i2CAT Universitat Politecnica de Catalunya/i2CAT
C/Esteve Terradas, 7 C/Esteve Terradas, 7
Castelldefels 08860 Castelldefels, 08860
Spain Spain
Phone:
Fax:
Email: carlesgo@entel.upc.edu Email: carlesgo@entel.upc.edu
URI:
Matthias Kovatsch Matthias Kovatsch
ETH Zurich ETH Zurich
Universitaetstrasse 6 Universitaetstrasse 6
Zurich, CH-8092 Zurich, CH-8092
Switzerland Switzerland
Phone:
Fax:
Email: kovatsch@inf.ethz.ch Email: kovatsch@inf.ethz.ch
URI:
Hui Tian Hui Tian
China Academy of Telecommunication Research China Academy of Telecommunication Research
Huayuanbeilu No.52 Huayuanbeilu No.52
Beijing, Haidian District 100191 Beijing, Haidian District 100191
China China
Phone:
Fax:
Email: tianhui@mail.ritt.com.cn Email: tianhui@mail.ritt.com.cn
URI:
Xuan He Xuan He
Hitachi China R&D Corporation Hitachi China R&D Corporation
301, Tower C North, Raycom, 2 Kexuyuan Nanlu, Haidian District 301, Tower C North, Raycom, 2 Kexuyuan Nanlu, Haidian District
Beijing 100190 Beijing, 100190
P.R.China P.R.China
Phone:
Fax:
Email: xhe@hitachi.cn Email: xhe@hitachi.cn
URI:
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