6LoWPAN Working Group E. Kim
Internet-Draft ETRI
Expires: May 12, 2011 D. Kaspar
Simula Research Laboratory
N. Chevrollier
TNO
JP. Vasseur
Cisco Systems, Inc
November 8, 2010
Design and Application Spaces for 6LoWPANs
draft-ietf-6lowpan-usecases-07
Abstract
This document investigates potential application scenarios and use
cases for low-power wireless personal area networks (LoWPANs). This
document provides dimensions of design space for LoWPAN applications.
A list of use cases and market domains that may benefit and motivate
the work currently done in the 6LoWPAN WG is provided with the
characteristics of each dimension. A complete list of practical use
cases is not the goal of this document.
Status of this Memo
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This Internet-Draft will expire on May 12, 2011.
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Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Basic Network Configuration . . . . . . . . . . . . . . . 5
2. Design Space . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Application Scenarios . . . . . . . . . . . . . . . . . . . . 8
3.1. Industrial Monitoring . . . . . . . . . . . . . . . . . . 8
3.1.1. A Use Case and its Requirements . . . . . . . . . . . 9
3.1.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 10
3.2. Structural Monitoring . . . . . . . . . . . . . . . . . . 12
3.2.1. A Use Case and its Requirements . . . . . . . . . . . 12
3.2.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 13
3.3. Connected Home . . . . . . . . . . . . . . . . . . . . . . 14
3.3.1. A Use Case and its Requirements . . . . . . . . . . . 15
3.3.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 16
3.4. Healthcare . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4.1. A Use Case and its Requirements . . . . . . . . . . . 18
3.4.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 19
3.5. Vehicle Telematics . . . . . . . . . . . . . . . . . . . . 20
3.5.1. A Use Case and its Requirements . . . . . . . . . . . 20
3.5.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 21
3.6. Agricultural Monitoring . . . . . . . . . . . . . . . . . 22
3.6.1. A Use Case and its Requirements . . . . . . . . . . . 22
3.6.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 24
4. Security Considerations . . . . . . . . . . . . . . . . . . . 26
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1. Normative References . . . . . . . . . . . . . . . . . . . 28
6.2. Informative References . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
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1. Introduction
Low-power and lossy networks (LLNs) is the term commonly used to
refer to networks made of highly constrained nodes (limited CPU,
memory, power) interconnected by a variety of "lossy" links (low-
power radio links or powerline communication (PLC)). They are
characterized by low speed, low performance, low cost, and unstable
connectivity. A LoWPAN is a particular instance of an LLN, formed by
devices complying with the IEEE 802.15.4 standard [5]. Their typical
characteristics can be summarized as follows:
o Limited processing capability: the smallest common LoWPAN nodes
have 8-bit processors with clock rates around 10 MHz. Other
models exist with 16-bit and 32-bit cores (typically ARM7),
running at frequencies in the order of tens of MHz.
o Small memory capacity: common RAM sizes for LoWPAN devices consist
of a few kilobytes, usually 4K or 8K bytes. However, a wide
variety of RAM sizes is available, reaching from 1K up to 256K
bytes.
o Low power: wireless radios for LoWPANs are normally battery-
operated. Their RF transceivers often have a current draw of
about 10 to 30 mA, depending on the used transmission power level.
In order to reach common indoor ranges of up to 30 meters and
outdoor ranges of 100 meters, the used transmission power is set
around 0 to 3 dBm. Depending on the processor type, there is an
additional battery current consumption of the CPU itself, commonly
in the order of tens of milliamperes. However, the CPU power
consumption can often be reduced by a thousandfold when switching
to sleep mode.
o Short range: the Personal Operating Space (POS) defined by IEEE
802.15.4 implies a range of 10 meters. For real implementations,
the range of LoWPAN radios is typically measured in tens of
meters, but can reach over 100 meters in line-of-sight situations.
o Low bit rate: the IEEE 802.15.4 standard defines a maximum over-
the-air rate of 250K bit/s, which is most commonly used in current
deployments. Alternatively, three lower data rates of 20K, 40K
and 100K bit/s are defined.
As any other LLN, a LoWPAN does not necessarily comprise of sensor
nodes only, but may also consist of actuators. For instance, in an
agricultural environment, sensor nodes might be used to detect low
soil humidity and then send commands to activate the sprinkler
system.
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After defining common terminology in Section 1.1 and describing the
characteristics of LoWPANs in Section 2, this document provides a
list of use cases and market domains that may benefit and motivate
the work currently done in the 6LoWPAN WG.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [1].
Readers are expected to be familiar with all the terms and concepts
that are discussed in "IPv6 over Low-Power Wireless Personal Area
Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and
Goals" [3], and " Transmission of IPv6 Packets over IEEE 802.15.4
Networks" [4].
Readers would benefit from reading 6LoWPAN ND [6], 6LoWPAN header
compression [7], and 6LoWPAN Routing Requirements [8] for the details
of the 6LoWPAN work.
This document makes extensive use of the same terminology defined in
6LoWPAN ND [6] unless otherwise redefined below.
This document defines additional terms:
LN (LoWPAN Node)
Any host or router participating in a LoWPAN. This term is used
when referring to situations in which either a host or router can
play the role described.
LR(LoWPAN Router)
An intermediate router in the LoWPAN who can communicate with
other LoWPAN routers in the same LoWPAN. LoWPAN routers are
present only in Route Over topologies.
LM (LoWPAN Mesh Node)
A LoWPAN node that forwards data between arbitrary source-
destination pairs using link-layer addresses and thus only exists
in Mesh Under topologies.
LC(local-controller)
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A logical functional entity that performs the special role of
coordinating and controlling its child nodes for local data
aggregation, status management of local nodes, etc. Thus, the
local controller nodes may be multiple instance in a LoWPAN.
LBR (LoWPAN Border Router)
A border router located at the junction of separate LoWPAN
networks or between a LoWPAN network and another IP network.
There may be one or more LBRs at the LoWPAN network boundary. A
LBR is the responsible authority for IPv6 Prefix propagation for
the LoWPAN network it is serving. An isolated LoWPAN also
contains a LBR in the network, which provides the prefix(es) for
the isolated network.
1.2. Basic Network Configuration
The IEEE 802.15.4 standard distinguishes between two types of nodes,
reduced-function devices (RFDs) and full-function devices (FFDs). As
this distinction is based on some MAC features that are not always in
use, we are not using this distinction in this document.
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2. Design Space
Inspired by [9], this section lists the dimensions used to describe
the design space of wireless sensor networks in the context of the
6LoWPAN Working Group. The design space is already limited by the
unique characteristics of a LoWPAN (e.g., low-power, short range,
low-bit rate) as described in [3]. The possible dimensions for
scenario categorization used in this document are described as
follows:
o Deployment: LoWPAN nodes can be scattered randomly or they may be
deployed in an organized manner in a LoWPAN. The deployment can
occur at once, or as an iterative process. The selected type of
deployment has an impact on node density and location. This
feature affects how to organize (manually or automatically) the
LoWPAN and how to allocate addresses in the network.
o Network Size: The network size takes into account nodes that
provide the intended network capability. The number of nodes
involved in a LoWPAN could be small (10 nodes), moderate (several
100s), or large (over a 1000).
o Power Source: The power source of nodes, whether the nodes are
battery-powered or mains-powered, influences the network design.
The power may also be harvested from solar cells or other sources
of energy. Hybrid solutions are possible where only part of the
network is mains-powered.
o Connectivity: Nodes within a LoWPAN are considered "always
connected" when there is a network connection between any two
given nodes. However, due to external factors (e.g., extreme
environment, mobility) or programmed disconnections (e.g.,
sleeping mode), the network connectivity can be from
"intermittent" (i.e., regular disconnections) to "sporadic" (i.e.,
almost always disconnected network). Differences in L2 duty-
cycling settings may additionally impact the connectivity due to
highly varying bit-rates.
o Multi-hop communication: The multi-hop communication factor
highlights the number of hops that has to be traversed to reach
the edge of the network or a destination node within it. A single
hop may be sufficient for simple star-topologies, but a multi-hop
communication scheme is required for more elaborate topologies,
such as meshes or trees. In previous work by academia and
industry on LoWPANs, various routing mechanisms were introduced,
such as data-centric, event-driven, address-centric, localization-
based, geographical routing, etc. This document does not make use
of such a fine granularity but rather uses topologies and single/
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multi-hop communication.
o Traffic Pattern: several traffic patterns may be used in LoWPANs.
To name a few, Point-to-Multi-Point (P2MP), Multi-Point-to-Point
(MP2P) and Point-to-Point (P2P).
o Security Level: LoWPANs may carry sensitive information and
require high-level security support where the availability,
integrity, and confidentiality of the information are crucial.
This high level of security may be needed in case of structural
monitoring of key infrastructure or health monitoring of patients.
o Mobility: Inherent to the wireless characteristics of LoWPANs,
nodes could move or be moved around. Mobility can be an induced
factor (e.g., sensors in an automobile), hence not predictable, or
a controlled characteristic (e.g., pre-planned movement in a
supply chain).
o Quality of Service (QoS): for mission-critical applications,
support of QoS is mandatory in resource-constrained LoWPANs.
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3. Application Scenarios
This section lists a fundamental set of LoWPAN application scenarios
in terms of system design. A complete list of practical use cases is
not the objective of this document.
3.1. Industrial Monitoring
LoWPAN applications for industrial monitoring can be associated with
a broad range of methods to increase productivity, energy efficiency,
and safety of industrial operations in engineering facilities and
manufacturing plants. Many companies currently use time-consuming
and expensive manual monitoring to predict failures and to schedule
maintenance or replacements in order to avoid costly manufacturing
downtime. LoWPANs can be inexpensively installed to provide more
frequent and more reliable data. The deployment of LoWPANs can
reduce equipment downtime and eliminate manual equipment monitoring
that is costly to be carried out. Additionally, data analysis
functionality can be placed into the network, eliminating the need
for manual data transfer and analysis.
Industrial monitoring can be largely split into the following
application fields:
o Process Monitoring and Control: combining advanced energy metering
and sub-metering technologies with wireless sensor networking in
order to optimize factory operations, reduce peak demand,
ultimately lower costs for energy, avoid machine downtimes, and
increase operation safety.
A plant's monitoring boundary often does not cover the entire
facility but only those areas considered critical to the process.
Easy to install wireless connectivity extends this line to include
peripheral areas and process measurements that were previously
infeasible or impractical to reach with wired connections.
o Machine Surveillance: ensuring product quality and efficient and
safe equipment operation. Critical equipment parameters such as
vibration, temperature, and electrical signature are analyzed for
abnormalities that are suggestive of impending equipment failure
(see Section 3.2).
o Supply Chain Management and Asset Tracking: with the retail
industry being legally responsible for the quality of sold goods,
early detection of inadequate storage conditions with respect to
temperature will reduce risk and cost to remove products from the
sales channel. Examples include container shipping, product
identification, cargo monitoring, distribution and logistics.
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o Storage Monitoring: sensor systems designed to prevent releases of
regulated substances to ground water, surface water and soil.
This application field may also include theft/tampering prevention
systems for storage facilities or other infrastructure, such as
pipelines.
3.1.1. A Use Case and its Requirements
Example: Hospital Storage Rooms
In a hospital, maintenance of the right temperature in storage rooms
is very critical. Red blood cells need to be stored at 2 to 6
degrees Celsius, blood platelets at 20 to 24 C, and blood plasma
below -18 C. For anti-cancer medicine, maintaining a humidity of 45%
to 55% is required. Storage rooms have temperature sensors and
humidity sensors every 25m to 100m, based on the floor plan and the
location of shelves, as indoor obstacles distort the radio signals.
At each blood pack a sensor tag can be installed to track the
temperature during delivery. A LoWPAN node is installed in each
container of a set of blood packs. In this case, highly dense
networks must be managed.
All nodes are statically deployed and manually configured with either
a single- or multi-hop connection. Different types of LoWPAN nodes
are configured based on the service and network requirements.
All LoWPAN nodes do not move unless the blood packs or a container of
blood packs is moved. Moving nodes get connected by logical
attachment to a new LoWPAN. When containers of blood packs are
transferred to another place of the hospital or by ambulance, the
LoWPAN nodes on the containers associate to a new LoWPAN.
This type of application works based on both periodic and event-
driven notifications. Periodic data is used for monitoring the
temperature and humidity in the storage rooms. The data over or
under a pre-defined threshold is meaningful to report. Blood cannot
be used if it is exposed to the wrong environment for about 30
minutes. Thus, event-driven data sensed on abnormal occurrences is
time-critical and requires secure and reliable transmission.
LoWPANs must be provided with low installation and management costs,
and for the transportation of blood containers, precise location
tracking of containers is important. The hospital network manager or
staff can be provided with an early warning of possible chain
ruptures, for example by conveniently accessing comprehensive online
reports and data management systems.
Dominant parameters in industrial monitoring scenarios:
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o Deployment: pre-planned, manually attached
o Mobility: no (except for asset tracking)
o Network Size: medium to large size, high node density
o Power Source: most of the time battery-operated
o Security Level: business-critical. Secure and reliable
transmission must be guaranteed.
o Multi-hop communication: multi-hop networking
o Connectivity: always on for crucial processes
o QoS: important for time-critical event-driven data
o Traffic Pattern: P2P (actuator control), MP2P (data collection)
o Other Issues: Sensor network management, location tracking, real-
time early warning
3.1.2. 6LoWPAN Applicability
The network configuration of the above use case can differ
substantially by system design. As illustrated in Figure 1, the
simplest way is to build a star topology inside of each storage room,
and connect the storage rooms with one link but overall network
configuration is with mesh topologies. Each LoWPAN node reaches the
LBR by a pre-defined routing/forwarding mechanism. LCs play a role
in aggregation of the sensed data. In the case that the sensed data
from an individual node is important, such as urgent event-driven
data, it will not be accumulated (and further delayed) by the LoWPAN
LCs but immediately relayed. In Route Over topologies, IP forwarding
is used, while link-layer addresses in the mesh-header defined by RFC
4944 [4] are used for transmission in Mesh Under topologies .
Each LoWPAN node configures its link-local address and get a prefix
from its LBR by an 6LoWPAN ND procedure [6]. Based on the layout and
size of the storage room, the LoWPAN can be configured in a different
way of mesh topology as shown in Figure 2. More than one LoWPAN LCs
can be installed in a storage room, and LCs collect data as relay
points to transmit the sensed data toward the LBRs. LoWPAN nodes
need to build a multi-hop connection to reach the LCs and LBR by
either Mesh Under or Route Over. In Mesh Under, more than one LMs
are selected for multi-hop transmission. The nodes MAY also play
role in handling multi-point traffic (multicast) by duplicate
unicasting to the connected nodes. In Route Over, LRs will handle
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multicast traffic to their LoWPAN links.
The data volume is usually not so large in this case, but is
sensitive to delay. Data aggregators can be installed for each
storage room, or just one data aggregator can collect all data. To
make a light transmission, UDP is likely to be chosen, but secure
transmission and security mechanism MUST be added. To increase
security, link-layer mechanisms and/or additional security mechanisms
SHOULD be used.
Because a failure of a LoWPAN node can critically affect the storage
of the blood packs, network management is important in this use-case.
A light weight management mechanism MUST be provided for the
management.
When a container is moved out from the storage room, and connected to
the other hospital system (if the hospital buildings are fully or
partly covered with LoWPANs), a mechanism to rebind to a new parent
node and a new LoWPAN MUST be supported. In the case that it is
moved by an ambulance, it will be connected to an LBR in the vehicle.
This type of mobility is supported by 6LoWPAN ND and routing
mechanism.
LoWPANs MUST be provided with low installation and management costs,
providing benefits such as reduced inventory, and precise location
tracking of containers, and mobile equipment (moving beds at the
hospital or ambulances).
LBR
| LBR: LoWPAN Border Router
LC----------LC----------LC LC: Local Controller node
/ | \ / | \ / | \ (Data Aggregator)
n n n n n n n n n n: LoWPAN node
Figure 1: Storage rooms with a simple star topology
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+------------+-----------+
| | | LBR: LoWPAN Border Router
LBR LBR LBR(LC) LC: Local Controller node
| | | (Data Aggregator)
LC - n LC - n n n: LoWPAN Node
/ | | | | / \
n n - LC n - n - n n - n
| | \ | |\
n n n - n n n n
Figure 2: Storage rooms with a mesh topology
3.2. Structural Monitoring
Intelligent monitoring in facility management can make safety checks
and periodic monitoring of the architecture status highly efficient.
Mains-powered nodes can be included in the design phase of a
construction or battery-equipped nodes can be added afterwards. All
nodes are static and manually deployed. Some data is not critical
for security protection (such as normal room temperature), but event-
driven emergency data (such as a fire alarm) MUST be handled in a
very critical manner.
3.2.1. A Use Case and its Requirements
Example: Bridge Safety Monitoring
A 1000m long concrete bridge with 10 pillars is described. Each
pillar and the bridge body contain 5 sensors to measure the water
level, and 5 vibration sensors are used to monitor its structural
health. The LoWPAN nodes are deployed to have 100m line-of-sight
distance from each other. All nodes are placed statically and
manually configured with a single-hop connection to the local
coordinator. All LoWPAN nodes are immobile while the service is
provided. Except from the pillars, there are no special obstacles of
attenuation to the node signals, but careful configuration is needed
to prevent signal interference between LoWPAN nodes.
The physical network topology is changed in case of node failure. On
the top part of each pillar, an sink node is placed to collect the
sensed data. The sink nodes of each pillar become data gathering
point of the LoWPAN hosts at the pillar as local coordinators.
This use case can be extended to medium or large size sensor networks
to monitor a building or for instance the safety status of highways
and tunnels. Larger networks of the same kind still have similar
characteristics such as static node placement, manual deployment and
dependent on the blue print of the structure, mesh topologies will be
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built with mains-powered relay points. Periodic and event-driven
real-time data gathering is performed and the emergency event-driven
data MUST be delivered without delay.
Dominant parameters in structural monitoring applications:
o Deployment: static, organized, pre-planned
o Mobility: none
o Network Size: small (dozens of nodes) to large
o Power Source: mains-powered nodes are mixed with battery powered
(mains-power nodes will be used for local coordination or relays).
o Security Level: safety-critical. Secure transmission must be
guaranteed. Only authenticated users must be able to access and
handle the data.
o Multi-hop communication: multi-hop mesh networking is recommended
to be supported.
o Connectivity: always connected or intermittent by sleeping mode
scheduling.
o QoS: Emergency notification (fire, over-threshold vibrations,
water level, etc.) is required to have priority of delivery and
must be transmitted in a highly reliable manner.
o Traffic Pattern: MP2P (data collection), P2P (localized querying)
o Other Issues: accurate sensing and reliable transmission are
important. In addition, sensor status reports should be
maintained in a reliable monitoring system.
3.2.2. 6LoWPAN Applicability
The network configuration of this use case can be done by simple
topologies, but there are many extended use cases for more complex
structures. The example bridge monitoring case may be the simplest
case.
The LoWPAN Nodes are installed on the place after manual optimization
of their location. Static data paths to the data gathering points
can be set in the commissioning phase. Address configuration and
LoWPAN formation are achieved by 6LoWPAN HC [7] and 6LoWPAN ND [6].
Each pillar network may be built as a stub network, so that 16-bit
addresses can be utilized (see Section 3 in [7]). Globally routable
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addresses must be allocated to communicate with other LoWPAN nodes.
If the network does not use a Route Over mechanism, the 6LoWPAN mesh-
header described in RFC 4944 [4] may be used for static data
forwarding, unless other mesh under mechanisms are provided.
Each pillar may have one LC for data collection from each pillar.
The logical entity for data gathering can be implemented as a
separate node or in a LR or LM. Communication schedules must be set
up between leaf nodes and their LC to efficiently gather the
different types of sensed data. Each data packet may include meta-
information about its data, or the type of sensors could be encoded
in its address during the address allocation. The data gathering
entity can be programmed to trigger actuators installed in the
infrastructure, when a certain threshold value has been reached.
This type of application works based on both periodic and event-
driven notifications. The data over or under a pre-defined threshold
is meaningful to report. Event-driven data sensed on abnormal
occurrences is time-critical and requires secure and reliable
transmission. For energy conservation, all nodes may have periodic
and long sleep modes but wake up on certain events.
Due to the safety-critical data of the structure, authentication and
security are important issues here. Only authenticated users MUST be
allowed to access the data. Additional security SHOULD be provided
at the LBR for restricting the access from outside of the LoWPAN.
The LBR may take charge of authentication of LoWPAN nodes. Reliable
and secure data transmission should be guaranteed.
LBR - LC ----- LC ------ LC LBR: LoWPAN Border Router
/| | | LC: Local Controller node
n n n - n - n n - n n: LoWPAN Node
/\ | | | |
n n n - n n - n - n
Figure 3: A LoWPAN with a mesh topology
3.3. Connected Home
The "Connected" Home or "Smart" home is with no doubt an area where
LoWPANs can be used to support an increasing number of services:
o Home safety/security
o Home Automation and Control
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o Healthcare (see above section)
o Smart appliances and home entertainment systems
In home environments LoWPAN networks typically comprise a few dozen
and probably in the near future a few hundreds of nodes of various
nature: sensors, actuators and connected objects.
3.3.1. A Use Case and its Requirements
Example: Home Automation
The home automation and control system LoWPAN offers a wide range of
services: local or remote access from the Internet (via a secured
edge router) to monitor the home (temperature, humidity, activation
of remote video surveillance, status of the doors (locked or open),
etc.) but also for home control (activate the air conditioning/
heating, door locks, sprinkler systems, etc.). Fairly sophisticated
systems can also optimize the level of energy consumption thanks to a
wide range of input from various sensors connected to the LoWPAN:
light sensors, presence detection, temperature, etc. in order to
control electric window shades, chillers, air flow control, air
conditioning and heating with the objective to optimize energy
consumption.
With the emergence of "Smart Grid" applications, the LoWPAN may also
have direct interactions with the Grid itself via the Internet to
report the amount of KWatts that could be load shed (Home to Grid)
and to receive dynamic load shedding information if/when required
(Grid to home): this application is also referred to as Demand-
Response application. Another service known as Demand Side
Management (DSM) could be provided by utilities to monitor and report
to the user its energy consumption with a fine granularity (on a per
device basis). Other inputs such as dynamic pricing can also be
received by the user from the utility that can then turn on and off
some appliances according to its local policy in order to reduce its
energy bill.
In terms of home safety and security, the LoWPAN is made of motion-
and audio-sensors, sensors at doors and windows, and video cameras to
which additional sensors can be added for safety (gas, water, CO,
Radon, smoke detection). The LoWPAN typically comprises a few dozen
nodes forming an ad-hoc network with multi-hop routing since the
nodes may not be in direct range. It is worth mentioning that the
number of devices tends to grow considering the number of new
applications for the home. In its most simple form, all nodes are
static and communicate with a central control module but more
sophisticated scenarios may also involve inter-device communication.
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For example, a motion/presence sensor may send a multicast message to
a group of lights to be switched on, or a video camera will be
activated sending a video stream to a gateway that can be received on
a cell phone.
Ergonomics in Connected Homes is a key and the LoWPAN must be self-
managed and easy to install. Traffic patterns may greatly vary
depending on the applicability and so does the level of reliability
and QoS expected from the LoWPAN. Humidity sensing is typically not
critical and requires no immediate action whereas tele-assistance or
gas leak detection is critical and requires a high degree of
reliability. Furthermore, although some actions may not involve
critical data, still the response time and network delays must be on
the order of a few hundreds of milliseconds to preserve the user
experience (e.g. use a remote control to switch a light on). A
minority of nodes are mobile (with slow motion). With the emergence
of energy related applications it becomes crucial to preserve data
confidentiality. Connected Home LoWPAN usually do not require multi-
topology or QoS routing and fairly simple QoS mechanisms must be
supported by the LoWPAN (the number of Class of Services is usually
limited).
Dominant parameters for home automation applications:
o Deployment: multi-hop topologies
o Mobility: some degree of mobility
o Network Size: medium number of nodes, potentially high density
o Power Source: mix of battery and mains-powered devices
o Security Level: authentication and encryption required
o Multi-hop communication: no requirement for multi-topology or QoS
routing
o Connectivity: intermittent (usage-dependent sleep modes)
o QoS: support of limited QoS (small number of Class of Service)
o Traffic Pattern: P2P (inter-device), P2MP and MP2P (polling)
3.3.2. 6LoWPAN Applicability
In the home automation use case, the network topology is made of a
mix of a battery operated and mains-powered nodes that both
communication with each other and a LBR provides connectivity to the
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outside of world for control management.
In home network, installation and management must as extremely simple
for the user. Link local IPv6 addresses can be used by nodes with no
external communication and the LBR allocates routable addresses to
communicate with other LoWPAN nodes not reachable over a single radio
transmission.
n --- n I: Internet
| | LBR: LoWPAN Border Router
Internet/ ------- LBR/LC -- n --- n ---- LC LC: Local controller node
Utility network | | /|\ n: LoWPAN Node
n ---- n n n n
(outside) (home automation system)
Figure 4: Home Automation scenario
In some scenarios, the traffic will be sent to a LC for processing
that may in turn decide of local actions (switch a light on, ...).
In other scenarios, all devices will send their data to the LCs that
may also act as the LBR for data processing and potential relay of
data to outside of the LoWPAN. It does not mean that every device
gets through the LC and LBR for communicating each other. For the
sake of illustration, some of the data may be processed to trigger
local action (e.g. switch off an appliance), simply store and sent
once enough data has been accumulated (e.g. energy consumption for
the past 6 hours for a set of appliances) or could trigger an alarm
immediately sent to a datacenter (e.g. gas leak detection).
Although in the majority of cases nodes within the LoWPAN will be in
direct range, some nodes will reach the LBR/LC with a 2-3 hops path
using Mesh Under or very likely a Route Over solution (with the
emergence of several low power media such as low power PLC) in which
case LoWPAN routers will be deployed in the home to interconnect the
various IPv6 links.
The home LoWPAN must be able to provide extremely reliable
communication in support of some specific application (e.g. fire, gas
leak detection, health monitoring) whereas other application may not
be critical at all (e.g humidity monitoring). Similarly some
information may require the use of security mechanisms for
authentication, confidentiality.
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3.4. Healthcare
LoWPANs are envisioned to be heavily used in healthcare environments.
They have a big potential to ease the deployment of new services by
getting rid of cumbersome wires and simplify patient care in
hospitals and for home care. In healthcare environments, delayed or
lost information may be a matter of life or death.
Various systems, ranging from simple wearable remote controls for
tele-assistance or intermediate systems with wearable sensor nodes
monitoring various metrics to more complex systems for studying life
dynamics, can be supported by LoWPANs. In the latter category, a
large amount of data from various LoWPAN nodes can be collected:
movement pattern observation, checks that medicaments have been
taken, object tracking, and more. An example of such a deployment is
described in [10] using the concept of Personal Networks.
3.4.1. A Use Case and its Requirements
Example: healthcare at home by tele-assistance
A senior citizen who lives alone wears one to few wearable LoWPAN
nodes to measure heartbeat, pulse rate, etc. Dozens of LoWPAN nodes
are densely installed at home for movement detection. A LBR at home
will send the sensed information to a connected healthcare center.
Portable base stations with LCDs may be used to check the data at
home, as well. The different roles of devices have different duty-
cycles, which affect node management.
Multipath interference may often occur due to the mobility of the
patients at home, where there are many walls and obstacles. Even
during sleeping, the change of the body position may affect the radio
propagation.
Data is gathered both periodically and event-driven. In this
application, event-driven data can be very time-critical. Thus,
real-time and reliable transmission must be guaranteed.
Privacy also becomes an serious issue in this case, as the sensed
data is very personal. In addition, different data will be provided
to the hospital system from what is given to a patient's family
members. Role-based access control is needed to support such
services, thus support of authorization and authentication is
important.
Dominant parameters in healthcare applications:
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o Deployment: pre-planned
o Mobility: moderate (patient's mobility)
o Network Size: small, high node density
o Power Source: hybrid
o Security Level: Data privacy and security MUST be provided.
Encryption is required. Role based access control is required to
be supported by light weight authentication mechanism
o Multi-hop communication: multi-hop for homecare devices, star
topology on patients body. Multipath interference due to walls
and obstacles at home must be considered.
o Connectivity: always on
o QoS: high level of support (life and death implication), role-
based
o Traffic Pattern: MP2P/P2MP (data collection), P2P (local
diagnostic)
o Other issues: Plug-and-play configuration is required for mainly
non-technical end-users. Real-time data acquisition and analysis
are important. Efficient data management is needed for various
devices which have different duty-cycles, and for role-based data
control. Reliability and robustness of the network are also
essential.
3.4.2. 6LoWPAN Applicability
In this use case, the local network size is rather small (less than
10s of nodes). The home care system is statically configured with
multi-hop paths and the patient's body network can be built as a star
topology. The LBR at home is the sink node in the routing path from
sources on the patient's body. A plug-and-play configuration is
required. As the communication of the system is limited to a home
environment, both 16-bit and 64-bit can be used for IPv6 link-local
addresses [4]. An example topology is provided in Figure 5.
Multi-hop communication can be achieved by either Mesh Under or Route
Over mechanisms. When a Route Over routing mechanism is used, the
routers deployed in the home environment will form a mesh of IPv6
links. In Mesh Under, more than one LMs in the LoWPAN play role in
multi-hop transmission in link layer and in transmission multi-point
traffic (multicast) to unicast method. In Route Over, LRs will
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handle multicast traffic to their LoWPAN link.
The patient's body network can be simply configured as a star
topology with a LC dealing with data aggregation and dynamic network
attachment when the patient moves around at home. As multipath
interference may often occur due to the patients' mobility at home,
the deployment of LoWPAN nodes and transmission paths should be well
considered. At home, some nodes can be installed with power-
affluence status, and those LoWPAN nodes can be used for relaying
points or data aggregation points.
The sensed information MUST be maintained with the identification of
the patient no matter if the patient visits the connected hospital or
stays at home. If the patient's LoWPAN uses globally unique IPv6
address, the address can be used for the identification. However, it
causes cost for privacy and security. The hospital LoWPAN where the
patient's information is transferring needs to operate additional
identification system together with strong authority and
authentication mechanism. The connection between the LBR at home and
the LBR at Hospital must be reliable and secure, as the data is
privacy-critical. To achieve this, additional policy for security is
recommended between the two LoWPAN.
n - n I: Internet
| | LBR: Edge Router
LBR --- I -- LBR - n - n - LC LC: Local controller node
/|\ | | /|\ n: LoWPAN Node
.. . .. n -- n n n n
(hospital) (home system) (patient)
Figure 5: A mobile healthcare scenario.
3.5. Vehicle Telematics
LoWPANs play an important role in intelligent transportation systems.
Incorporated in roads, vehicles, and traffic signals, they contribute
to the improvement of safety of transporting systems. Through
traffic or air-quality monitoring, they increase the possibilities in
terms of traffic flow optimization and help reducing road congestion.
3.5.1. A Use Case and its Requirements
Example: Telematics
As shown in Figure 6, scattered LoWPAN Nodes are included in roads
during their construction for motion monitoring. When a car passes
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over these nodes, the possibility is then given to track the
trajectory and velocity of cars for safety purposes. The lifetime of
the LoWPAN Nodes incorporated into roads is expected to be as long as
the life time of the roads (about 10 years). Multi-hop communication
is possible between LoWPAN Nodes, and the network should be able to
cope with the deterioration over time of the node density due to
power fails. Sink nodes placed at the side of road are mains-
powered, LoWPAN Nodes in the roads run on battery. Power savings
schemes might intermittently disconnect the nodes. A rough estimate
of 4 nodes per square meter is needed. Other applications may
involve car-to-car communication for increased road safety.
Dominant parameters in vehicle telematics applications:
o Deployment: scattered, pre-planned
o Mobility: none (road infrastructure), high (vehicle)
o Network Size: large (road infrastructure), small (vehicle)
o Power Source: hybrid
o Security Level: low
o Multi-hop communication: multi-hop, especially ad-hoc
o Connectivity: intermittent
o QoS: support of limited QoS
o Traffic Pattern: mostly Point-to-Point (P2P), Point-to-Multi-Point
(P2MP)
3.5.2. 6LoWPAN Applicability
For this use case, the network topology includes fixed LBRs that are
mains-powered and have a connection to high speed networks (e.g.,
Internet) in order to reach the transportation control center. These
LBRs may be logically combined with LC as a data sink to gather
sensed data from a number of LoWPAN Nodes inserted in the tarmac of
the road.
In the road infrastructure, a LoWPAN with one LBR forms a fixed
network and the LoWPAN nodes are installed by manual optimization of
their location. Static data paths to the data gathering point can be
set in the commissioning phase. If the network does not use a Route
Over mechanism, the 6LoWPAN mesh under forwarding is used.
Forwarding/Routing tables are not changed unless a node failure
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occurs.
+-----+
| LBR |----------------------------- LBR ...
+-----+ (at the road side)
-------|------------------------------
|
n -- n --- n --- n +---|---+ LBR: LoWPAN Border Router
/ \ | | n-n-n | n: LoWPAN Node
n n n +---|---+
(cars)
--------------------------------------
Figure 6: Multi-hop LoWPAN combined with mobile star LoWPAN.
3.6. Agricultural Monitoring
Accurate temporal and spatial monitoring can significantly increase
agricultural productivity. Due to natural limitations, such as a
farmers' inability to check the crop at all times of day or
inadequate measurement tools, luck often plays a too large role in
the success of harvests. Using a network of strategically placed
sensors, indicators such as temperature, humidity, soil condition,
can be automatically monitored without labor intensive field
measurements. For example, sensor networks could provide precise
information about crops in real time, enabling businesses to reduce
water, energy, and pesticide usage and enhancing environment
protection. The sensing data can be used to find optimal
environments for the plants. In addition, the data on the planting
condition can be saved by sensor tags, which can be used in supply
chain management.
3.6.1. A Use Case and its Requirements
Example: Automated Vineyard
In a vineyard with medium to large geographical size, a number of 50
to 100 LC nodes are manually deployed in order to provide full signal
coverage over the study area. An additional number of 100 to 1000
leaf nodes with (possibly heterogeneous) specialized sensors (i.e.,
humidity, temperature, soil condition, sunlight) are attached to the
LCs in local wireless star topologies, periodically reporting
measurements to the associated LCs. For example, in a 20-acre
vineyard with 8 parcels of land, 10 LoWPAN Nodes are placed within
each parcel to provide readings on temperature and soil moisture.
The LoWPAN Nodes are able to support a multi-hop forwarding/routing
scheme to enable data transmission to a sink node at the edge of the
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vineyard. Each of the 8 parcels contains one data aggregator to
collect the sensed data.
Localization is important for this type of LoWPAN where installed in
a geographically large area, for pinning down where an event
occurred, and for combining gathered data with their actual position.
Using manual deployment, device addresses can be used for identifying
the position and localization. For randomly deployed nodes, a
localization algorithm needs to be applied.
There might be various types of sensor devices deployed in a single
LoWPAN, each providing raw data with different semantics. Thus, an
additional method is required to correctly interpret sensor readings.
Each data packet may include meta-information about its data, or a
type of a sensor could be encoded in its address during address
allocation.
Dominant parameters in agricultural monitoring:
o Deployment: pre-planned
The nodes are installed outdoors or in a greenhouse with high
exposure to water, soil, dust, in dynamic environments of moving
people and machinery, with growing crop and foliage. LoWPAN nodes
can be deployed in a pre-defined manner, considering the harsh
environment.
o Mobility: all static
o Network Size: medium to large, low to medium density
o Power Source: all nodes are battery-powered except the sink, or
energy harvesting
o Security Level: business-critical. Light-weight security or a
global key management can be used depending on the business
purpose.
o Multi-hop communication: mesh topology with local star
connections.
o Connectivity: intermittent (many sleeping nodes)
o QoS: support of limited QoS (small number of Class of Service)
o Traffic Pattern: Mainly MP2P/P2MP. P2P actuator triggering.
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o Other issues: Time synchronization among sensors are required, but
the traffic interval may not be frequent (e.g. once in 30 minutes
to 1 hour).
3.6.2. 6LoWPAN Applicability
The network configuration in this use case might, in the most simple
case, look like illustrated in Figure 7. This static scenario
consists of one or more fixed LBR that are mains-powered and have a
high-bandwidth connection to a backbone link, which might be placed
in a control center, or connect to the Internet. The LBRs are
strategically located at the border of vineyard parcels, acting as
data sinks. A number of LCs are placed along a row of plants with
individual LoWPAN nodes spread around them.
While the LBRs implement the IPv6 Neighbor Discovery protocol (RFC
4861) to connect the outside of the LoWPAN, the LoWPAN Nodes operate
a more energy-considering ND described in [6], which includes basic
bootstrapping and address assignment. Each LBR can have predefined
forward management information to a central data aggregation point,
if necessary.
The intermediate nodes must implement a multi-hop forwarding/routing
protocol and they are responsible to transmit the measured data at
the LoWPAN nodes to the LBRs. In this simplest case, the LRs or LMs
can build static forwarding/routing paths, and all end-nodes can be
placed in one radio hop distance from its forwarder. In more
advanced setups, mesh routing is used for data distribution.
LoWPAN nodes may send event-driven notifications when readings exceed
certain thresholds, such as low soil humidity; which may
automatically trigger a water sprinkler in the local environment.
For increased energy efficiency, all LoWPAN Nodes are in periodic
sleep state. However, the LCs need to be aware of sudden events from
the leaf nodes. Their sleep periods should therefore be set to
shorter intervals. Communication schedules must be set up between
master and leaf nodes, and global time synchronization is needed to
account for clock drift.
Also, the result of data collection may activate actuators. Context-
awareness, node identification and data collection on the application
level are necessary.
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I
|
| n n n n n n n n n I: Internet
| \|/ \|/ \|/ LBR: LoWPAN Border Router
LBR----LC------LC------LC LC: Local Controller node
| /|\ /|\ /|\ n: LoWPAN node
| n n n n n n n n n
|
LBR
...
Figure 7: An aligned multi-hop LoWPAN.
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4. Security Considerations
Security requirements differ by use case. For example, industrial
and structural monitoring applications are safety-critical. Secure
transmission MUST be guaranteed, and only authenticated users MUST be
able to access and handle the data. Lightweight key mechanisms can
be used. In health care system, data privacy is an important issue.
Encryption is required, and role-based access control is required to
be supported by a proper authentication mechanism.
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5. Acknowledgements
Thanks to David Cypher for giving more insight on the IEEE 802.15.4
standard and to Irene Fernandez for her review and valuable comments.
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6. References
6.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[3] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs): Overview,
Assumptions, Problem Statement, and Goals", RFC 4919,
August 2007.
[4] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4 Networks",
RFC 4944, September 2007.
[5] IEEE Computer Society, "IEEE Std. 802.15.4-2006 (as amended)",
2007.
6.2. Informative References
[6] Shelby, Z., Chakrabarti, S., and E. Nordmark, "Neighbor
Discovery Optimization for Low-power and Lossy Networks",
draft-ietf-6lowpan-nd-14 (work in progress), October 2010.
[7] Hui, J. and P. Thubert, "Compression Format for IPv6 Datagrams
in 6LoWPAN Networks", draft-ietf-6lowpan-hc-13 (work in
progress), September 2010.
[8] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for 6LoWPAN Routing",
draft-ietf-6lowpan-routing-requirements-07 (work in progress),
August 2010.
[9] Roemer, K. and F. Mattern, "The Design Space of Wireless Sensor
Networks", December 2004.
[10] den Hartog, F., Schmidt, J., and A. de Vries, "On the Potential
of Personal Networks for Hospitals", May 2006.
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Authors' Addresses
Eunsook Kim
ETRI
161 Gajeong-dong
Yuseong-gu
Daejeon 305-700
Korea
Phone: +82-42-860-6124
Email: eunah.ietf@gmail.com
Dominik Kaspar
Simula Research Laboratory
Martin Linges v 17
Snaroya 1367
Norway
Phone: +47-4748-9307
Email: dokaspar.ietf@gmail.com
Nicolas G. Chevrollier
TNO
Brassersplein 2
P.O. Box 5050
Delft 2600
The Netherlands
Phone: +31-15-285-7354
Email: nicolas.chevrollier@tno.nl
JP Vasseur
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough MA 01719
USA
Phone:
Email: jpv@cisco.com
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