Internet DRAFT - draft-ietf-6lowpan-usecases
draft-ietf-6lowpan-usecases
6LoWPAN Working Group E. Kim
Internet-Draft ETRI
Intended status: Informational D. Kaspar
Expires: January 28, 2012 Simula Research Laboratory
N. Chevrollier
TNO
JP. Vasseur
Cisco Systems, Inc
July 27, 2011
Design and Application Spaces for 6LoWPANs
draft-ietf-6lowpan-usecases-10
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 January 28, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Premise of network configuration . . . . . . . . . . . . . 5
2. Design Space . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Application Scenarios . . . . . . . . . . . . . . . . . . . . 9
3.1. Industrial Monitoring . . . . . . . . . . . . . . . . . . 9
3.1.1. A Use Case and its Requirements . . . . . . . . . . . 10
3.1.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 11
3.2. Structural Monitoring . . . . . . . . . . . . . . . . . . 13
3.2.1. A Use Case and its Requirements . . . . . . . . . . . 13
3.2.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 14
3.3. Connected Home . . . . . . . . . . . . . . . . . . . . . . 15
3.3.1. A Use Case and its Requirements . . . . . . . . . . . 16
3.3.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 17
3.4. Healthcare . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.1. A Use Case and its Requirements . . . . . . . . . . . 19
3.4.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 20
3.5. Vehicle Telematics . . . . . . . . . . . . . . . . . . . . 21
3.5.1. A Use Case and its Requirements . . . . . . . . . . . 21
3.5.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 22
3.6. Agricultural Monitoring . . . . . . . . . . . . . . . . . 23
3.6.1. A Use Case and its Requirements . . . . . . . . . . . 23
3.6.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 25
4. Security Considerations . . . . . . . . . . . . . . . . . . . 27
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1. Normative References . . . . . . . . . . . . . . . . . . . 31
7.2. Informative References . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33
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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 [6]. 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: the smallest common LoWPAN nodes have a few
kBytes of RAM with a few dozens of kBytes of ROM/flash memory.
While the memory sizes of nodes continue to grow (e.g., IMote has
64K SRAM, 512K Flash memory), the nature of small memory capacity
for LoWPAN nodes remains a challenge.
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
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 [7], 6LoWPAN header
compression [8], and 6LoWPAN Routing Requirements [9] for the details
of the 6LoWPAN work.
This document defines the following terms:
LC (Local Controller)
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. There may be
multiple instances of local controller nodes in a LoWPAN.
LBR (LoWPAN Border Router)
A border router is 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. Premise of 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.
6LoWPAN networks can be deployed using either route-over or mesh-
under architectures. As the choice of route-over or mesh-under does
not affect the applicability of 6LoWPAN technologies to the use cases
described in the document, we will use the term "6LoWPAN network" to
mean either a route-over or mesh-under network.
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Communication to corresponding nodes outside of the LoWPAN is
becoming increasingly important for convenient data collection and
remote control purposes. The intermediate LoWPAN nodes act as packet
forwarders (LM) or LoWPAN routers (LR) and connect the entire LoWPAN
in a multi-hop fashion. LoWPAN Border Routers (LBRs) are used to
interconnect a LoWPAN to other networks, or to form an extended
LoWPAN by connecting multiple LoWPANs. Before LoWPAN nodes obtain
their IPv6 addresses and the network is configured, each LoWPAN
executes a link-layer configuration either by the mechanisms
specified in 6lowpan ND [7] or by using a coordinator who is
responsible for link-layer short address allocation. However, the
link-layer coordinator functionality is out of the scope of this
document. Details of address allocation of 6LoWPAN ND is in [7].
A LoWPAN can be configured as Mesh Under or Route Over (see
Terminology in [7]). In a Route Over configuration, multihop
transmission is carried out by LRs using IP routing. In a Mesh Under
configuration, the link-local scope reaches to the boundaries of the
LoWPAN, and multihop transmission is achieved by forwarding data at
the link layer or in an 6LoWPAN adaptation layer. More information
about Mesh Under and Route Over is in 6LoWPAN ND [7] and 6LoWPAN
Routing Requirements [9].
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2. Design Space
Inspired by [10], 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.
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): QoS issues in LoWPANs may be very
different from the traditional end-to-end QoS as in LoWPAN
applications, one end is not a single sensor node, but often a
group of sensor nodes. Parameters for QoS should consider
collective data for latency, packet loss, data throughput, etc.
In addition, QoS requirements can be different based on the data
delivery model such as event-driven, query-driven, continuous
real-time, or continuous non-real-time delivery model, which
usually coexist in LoWPAN applications. QoS issues in LoWPANs are
more likely related to corresponding application specific data
delivery requirements within 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.
Especially, LCs play a role in aggregation of the sensed data from
blood packs. In the extended networks, more than one LoWPAN LCs can
be installed in a storage room. In the case that the sensed data
from an individual node is urgent event-driven data such as outrange
of temparature or humidity, it will not be accumulated (and further
delayed) by the LCs but immediately relayed.
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
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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:
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 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.
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.
Each LoWPAN node may reach the LBR by a predefined routing/forwarding
mechanism. Each LoWPAN node configures its link-local address and
obtains a prefix from its LBR by an 6LoWPAN ND procedure [7]. LoWPAN
nodes need to build a multi-hop connection to reach the LCs and LBR.
Secure data transmission and authentication is crucial in a hospital
scenario to prevent personal information to be retrieved by an
adversary. Confidential data must be encrypted not only in
transmission, but also when stored on nodes, because nodes can
potentially be stolen.
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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.
The service quality of this case is highly related to effective
handling of event-driven data which is delay intolerant and mission
critical. The event of wrong humidity and temperature needs to be
detected as quickly and reliable as possible. It is important to
provide efficient resource usage for such data with consideration of
minimal usage of energy. Energy aware QoS support in wireless sensor
networks is a challenging issue [13]. It can be considered to
provide appropriate data aggreation for minimizing the delay,
maximizing the accuracy of the delivery by using power-affluent
nodes, or aided by middleware or other types of network elements.
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 periodic or query-driven
notification of 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, a 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 and act 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
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characteristics such as static node placement, manual deployment and
dependent on the blue print of the structure, mesh topologies will be
built with mains-powered relay points. Periodic, query-driven, 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, however, there are many extended use cases for more
complex structures. The example bridge monitoring case may be the
simplest case (an example topology is illustrated in Figure 3).
The LoWPAN Nodes are installed on the place after manual optimization
of their location. As the communication of the leaf LoWPAN nodes may
be limited to the data gathering points, both 16-bit and 64-bit can
be used for IPv6 link-local addresses [4].
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Each pillar might have one LC for data collection from each pillar.
Communication schedules should 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.
This type of application works based on periodic, query-driven 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. Conflictly, for energy conservation, all
nodes may have periodic and long sleep modes but wake up on certain
events. To ensure the reliability of such emergency event-driven
data, such data is immediately relayed to a power-affluet or mains-
power node which usually takes a LoWPAN router role, and does not go
into a long sleep status. The data gathering entity can be
programmed to trigger actuators installed in the infrastructure, when
a certain threshold value has been reached.
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 must 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 bridge monitoring scenario
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
o Healthcare (see above section)
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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.
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
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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. Fairly simple QoS mechanisms are enough for
handling emergency data. It can be programmed to alarm by actuators
or to operate sprinklers.
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 for emergency data (alarm)
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
outside of world for control management (Figure 4).
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In home network, installation and management must be 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
| | 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
(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 (e.g humidity monitoring). Such emergency data has the
same QoS issues with the event-driven data in the other applications,
and can be delivered by pre-defined paths through mains-powered node
without being stored in intermidiate nodes such as LCs. 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 [11] 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. A small set of secret keys can be shared
within the sensor nodes during bootstapping procedures in order to
build a secure link without using much of memory and energy. 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 reliability 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.
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-
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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, LoWPAN Nodes are included in roads during their
construction for motion monitoring. When a car passes 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
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are most likely mains-powered, LoWPAN Nodes in the roads run on
battery. Power saving 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: pre-planned (road, vehicle)
o Mobility: none (road infrastructure), high (vehicle)
o Network Size: large (road infrastructure), small (vehicle)
o Power Source: hybrid
o Security Level: handling physical damage and link failure
o Multi-hop communication: multi-hop, especially ad-hoc
o Connectivity: intermittent
o Traffic Pattern: mostly Multi-Point-to-Point (MP2P), 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
(Figure 6). 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.
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+-----+
| 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: Telematics scenario.
Given the fact that nodes are incorporated in the road, tampering
with sensors is difficult for an adversary. However, the application
must be robust against possible attacks and node failures. Sensed
data should thus be used primarily for monitoring purposes, not to
instruct (and potentially mislead) traffic participants.
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, and 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
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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
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: depending on business-purpose. Light-weight
security or a simple shared 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 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 [2]) to connect the outside of the LoWPAN, the LoWPAN Nodes
operate a more energy-considering ND described in [7], which includes
basic bootstrapping and address assignment. Each LBR can have
predefined forward management information to a central data
aggregation point, if necessary.
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 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: Automated vineyard scenario.
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4. Security Considerations
Relevant security considerations are listed by application scenario
in Section 3 and the security considerations in RFC 4919 [3] and RFC
4944 [4] apply as well.
The physical exposure of LoWPAN nodes (especially in outdoor
networks) allows an adversary to capture, clone, tamper with, or even
destroy these devices. Given the safety issues involved in some use
cases, these threats place high demands for resiliency and
survivability upon the LoWPAN. The generally wireless channels of
LoWPANs are susceptible to several security threats. Without proper
security measures, confidential information might be snooped by a
"man in the middle". An attacker might also modify or introduce data
packets into the network, for example to manipulate sensor readings
or to take control over sensors and actuators. This specification
expects that the link layer is sufficiently protected, either by
means of physical or IP security for the backbone link or with MAC
sublayer cryptography. However, link-layer encryption and
authentication may not be sufficient to provide confidentiality,
authentication, integrity, and freshness to both data and signaling
packets.
Due to their low-power nature, LoWPANs are especially vulnerable to
denial-of-service (DoS) type attacks. Example DoS attacks include
attempts to drain a node's battery by excessive querying or to
introduce a high-power jamming signal that makes LoWPAN nodes
dysfunctional. Security solutions must therefore be lightweight and
support node authentication, so that message integrity can be
guaranteed and misbehaving nodes can be denied participation in the
network. A node must authenticate itself to trusted nodes before
taking part in the LoWPAN.
While IPsec is mandatory with IPv6 [4], considering the power
constraints and limited processing capabilities of IEEE802.15.4
devices, IPsec is computationally expensive; Internet key exchange
(IKEv2) messaging described in [5] is not suited for LoWPANs as the
amount of signaling in these networks should be minimized. Thus,
LoWPANs may need to define their own keying management method that
requires minimum overhead in terms of packet size and message
exchange [12]. IPsec provides authentication and confidentiality
between end nodes and across multiple LoWPAN links, and may be useful
only when two nodes want to apply security to all exchanged messages.
However, in many cases, the security may be requested at the
application layer as needed, while other messages can flow in the
network without security overhead.
Security requirements may differ by use case. For example,
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industrial and structural monitoring applications are safety-critical
and secure transmission must be guaranteed, so that only
authenticated users are able to access and handle the data. In
health care systems, data privacy is an important issue. Encryption
is required, and role-based access control is needed for proper
authentication. In home automation scenarios, critical applications
such as door locks, require a high security and robustness against
intrusion. On the other hand, a remote controlled light switch has
no critical security threats.
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5. IANA Considerations
This document contains no actions for IANA.
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6. Acknowledgements
Thanks for David Cypher for giving more insight on the IEEE 802.15.4
standard, and Irene Fernandez, Shoichi Sakane and Paul Chilton for
review and valuable comments.
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7. References
7.1. Normative References
[1] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
[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] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, "Internet Key
Exchange Protocol Version 2 (IKEv2)", RFC 5996, September 2010.
[6] IEEE Computer Society, "IEEE Std. 802.15.4-2006 (as amended)",
2007.
7.2. Informative References
[7] Shelby, Z., Chakrabarti, S., and E. Nordmark, "Neighbor
Discovery Optimization for Low Power and Lossy Networks
(6LoWPAN)", draft-ietf-6lowpan-nd-17 (work in progress),
June 2011.
[8] Hui, J. and P. Thubert, "Compression Format for IPv6 Datagrams
in Low Power and Lossy Networks (6LoWPAN)",
draft-ietf-6lowpan-hc-15 (work in progress), February 2011.
[9] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for 6LoWPAN Routing",
draft-ietf-6lowpan-routing-requirements-09 (work in progress),
February 2011.
[10] Roemer, K. and F. Mattern, "The Design Space of Wireless Sensor
Networks", December 2004.
[11] den Hartog, F., Schmidt, J., and A. de Vries, "On the Potential
of Personal Networks for Hospitals", May 2006.
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[12] Dutertre, B., Cheung, S., and J. Levy, "Lightweight key
management in wireless sensor networks by leveraging initial
trust", April 2004.
[13] Chen, D. and P. K. Varshney, "QoS Support in Wireless Sensor
Networks: A survey", June 2004.
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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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