6LoWPAN Working Group E. Kim
Internet-Draft ETRI
Expires: September 9, 2009 N. Chevrollier
TNO
D. Kaspar
Simula Research Laboratory
JP. Vasseur
Cisco Systems, Inc
March 8, 2009
Design and Application Spaces for 6LoWPANs
draft-ietf-6lowpan-usecases-02
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Abstract
This document investigates potential application scenarios and use
cases for low-power wireless personal area networks (LoWPANs). After
describing the characteristics of a LoWPAN, this document provides a
list of use cases and market domains that may benefit and motivate
the work currently done in the 6LoWPAN WG. A complete list of
practical use cases is not the goal of this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Design Space . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Application Scenarios . . . . . . . . . . . . . . . . . . . . 11
4.1. Industrial Monitoring . . . . . . . . . . . . . . . . . . 11
4.1.1. A Use Case and its Requirements . . . . . . . . . . . 13
4.1.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 14
4.2. Structural Monitoring . . . . . . . . . . . . . . . . . . 16
4.2.1. A Use Case and its Requirements . . . . . . . . . . . 16
4.2.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 18
4.3. Healthcare . . . . . . . . . . . . . . . . . . . . . . . . 19
4.3.1. A Use Case and its Requirements . . . . . . . . . . . 19
4.3.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 21
4.4. Connected Home . . . . . . . . . . . . . . . . . . . . . . 22
4.4.1. A Use Case and its Requirements . . . . . . . . . . . 22
4.4.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 24
4.5. Vehicle Telematics . . . . . . . . . . . . . . . . . . . . 24
4.5.1. A Use Case and its Requirements . . . . . . . . . . . 24
4.5.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 25
4.6. Agricultural Monitoring . . . . . . . . . . . . . . . . . 26
4.6.1. A Use Case and its Requirements . . . . . . . . . . . 26
4.6.2. 6LoWPAN Applicability . . . . . . . . . . . . . . . . 27
5. Security Considerations . . . . . . . . . . . . . . . . . . . 29
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1. Normative References . . . . . . . . . . . . . . . . . . . 31
7.2. Informative References . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
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1. Introduction
LoWPANs are inexpensive, low-performance, wireless communication
networks, and are formed by devices complying with the IEEE 802.15.4
standard [5]. Their typical characteristics can be summarized as
follows:
o Low power: depending on country regulations and used frequency
band, the maximum transmit power levels can be up to 1000 mW [5].
However, typical wireless radios for LoWPANs are battery-operated
and consume between 10 mW and 20 mW [6].
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 go far beyond that in line-of-sight situations
[6].
o Low bit rate: the IEEE 802.15.4 standard defines a maximum over-
the-air rate of 250 kb/s, as well as lower data rates of 40 kb/s
and 20 kb/s for each of the currently defined physical layers (2.4
GHz, 915 MHz and 868 MHz, respectively).
o Small memory capacity: common RAM sizes for LoWPAN devices consist
of a few kilobytes, such as 4 KB.
o Limited processing capability: current LoWPAN nodes usually have
8-bit processors with clock rates around 10 MHz.
LoWPANs do not necessarily comprise of sensor nodes only, but may
also consist of actuators. For instance, in an agricultural
environment, sensor nodes might detect low soil humidity and then
send commands to activate the sprinkler system.
A LoWPAN network can be seen as a network of small star-networks,
each consisting of a single LoWPAN node connected to zero or more
nodes, or a network with mesh topology as shown in Figure 1. It is
noted that it is out of scope of this document to define how mesh
topologies could be obtained and maintained.
Note: The IEEE 802.15.4 standard distinguishes between two types
of nodes, reduced-function devices (RFDs) and full-function
devices (FFDs). This document uses the term LoWPAN node which
includes both type of devices. However, the two device types have
different capabilities, so that the capability requirements of a
LoWPAN node must be considered to choose the type of devices.
Through their inability to transmit MAC layer beacons, RFDs can
only communicate with FFDs in a resulting "master/slave" star
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topology. FFDs are able to communicate with peer FFDs and with
RFDs in the aforementioned relation. FFDs can therefore assume
arbitrary network topologies, such as multi-hop meshes.
A simple star topology A mesh topology
n n n n---n n n
\ | / | | | /
ER --- n ---n ER: LoWPAN Edge Router ER---n---n---n---n
/ | \ n: LoWPAN Node /| | | |
n n n n n n n---n
Figure 1: Examples of LoWPAN topologies
Communication to corresponding nodes outside of the LoWPAN is
becoming increasingly important. The intermediate LoWPAN nodes act
as packet forwarders or routers and connect the entire LoWPAN in a
multi-hop fashion. Edge Routers 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 using a single coordinator (named as PAN coordinator in
the link layer) who is responsible for link-layer short address
allocation. However, this link-layer coordinator function is out of
the scope of this document. The term coordinator in this document
does not refer to the PAN coordinator, but is used for a node with
special roles to coordinate neighboring nodes or relay traffic.
A LoWPAN can be configured as Mesh Under or Route Over. In a Mesh
Under configuration, the link-local scope reaches to the boundaries
of the LoWPAN and all nodes in a LoWPAN are included in the scope.
Multihop transmission is achieved by Mesh Under forwarding or routing
mechanisms at the link layer or in an adapatation layer (see
Figure 1). In a Route Over configuration, the link-local scope is
only one radio hop range and includes those nodes which are reachable
over a single radio transmission. Multihop transmission is achieved
using IP routing (see Figure 1).
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h h
| | ER: LoWPAN Edge Router
ER --- m --- m --- h m: LoWPAN Node running Mesh Under
/ \ \ forwarding/routing
h h h
Figure 2: Example of a small Mesh Under LoWPAN
h h
| | ER: LoWPAN Edge Router
ER --- r --- r --- h r: LoWPAN Router
/ \ \ h: LoWPAN Host
h h h
Figure 3: Example of a small Route Over LoWPAN
After defining common terminology in Section 2 and describing the
characteristics of LoWPANs in Section 3, this document provides a
list of use cases and market domains that may benefit and motivate
the work currently done in the 6LoWPAN WG.
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2. 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].
This document defines additional terms:
LoWPAN Coordinator Node
A logical functional entity that performs the special role of
coordinating its child nodes for local data aggregation, status
management of local nodes, etc. Thus, the Coordinator Node does
not need to coincide with a link-layer PAN coordinator and there
may be multiple instance in a LoWPAN.
LoWPAN Mesh Node
A LoWPAN node that forwards data between arbitrary source-
destination pairs in 6LoWPAN adaptation layer using link address
(and thus only exist in Mesh Under LoWPANs). A Mesh Node may also
serve as a LoWPAN Host.
Additionally, in alignment with all other 6LoWPAN drafts, this
document uses the same terms and definitions as provided by the
6LoWPAN ND draft [9]:
LoWPAN Host
A node that only sources or sinks IPv6 datagrams. Referred to as
a host in this document. The term node (see LoWPAN Node) is used
when the differentiation between host and router is not important.
LoWPAN Edge Router
An IPv6 router that interconnects the LoWPAN to another network.
Referred to as an edge router in this document.
LoWPAN Router
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A node that forwards datagrams between arbitrary source-
destination pairs using a single 6LoWPAN interface performing IP
routing (and thus only exist in route over LoWPANs). A LoWPAN
Router may also serve as a LoWPAN Host - both sourcing and sinking
IPv6 datagrams. Referred to as a router in 6LoWPAN documents.
All LoWPAN Routers perform ND message relay on behalf of other
nodes.
LoWPAN Node
A node that composes a LoWPAN. In mesh under, each intermediate
node performs multi-hop forwarding at L2. In route over, each
intermediate node serves as a LoWPAN router performing IP routing.
Mesh Under
A LoWPAN configuration where the link-local scope is defined by
the boundaries of the LoWPAN and includes all nodes within.
Forwarding and multihop routing functions are achieved at L2
between mesh nodes.
Route Over
A LoWPAN configuration where the link-local scope is defined by
those nodes reachable over a single radio transmission. Due to
the time-varying characteristics of wireless communication, the
neighbor set may change over time even when nodes maintain the
same physical locations. Multihop is achieved using IP routing.
Backbone Link
This is an IPv6 link that interconnects two or more edge routers.
It is expected to be deployed as a high speed backbone in order to
federate a potentially large set of LoWPANs.
Extended LoWPAN
This is the aggregation of multiple LoWPANs as defined in [3]
interconnected by a backbone link via Edge Routers and forming a
single subnet.
LoWPAN Link
A low-power wireless link which is shared by a link-local scope in
a LoWPAN. In a LoWPAN, a link can be a very instable set of
nodes, for instance the set of nodes that can receive a packet
that is broadcast over the air in a route over LoWPAN, or the set
of nodes currently reachable in an L2 mesh in a mesh under LoWPAN.
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Such a set may vary from one packet to the next as the nodes move
or as the radio propagation conditions change.
LoWPAN Subnet
A subnet including a LoWPAN or an Extended LoWPAN, together with
the backbone link with the same subnet prefix and prefix length.
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3. Design Space
Inspired by [7], this section describes the potential dimensions that
could be used to describe the design space of wireless sensor
networks in the context of the 6LoWPAN WG. 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: In a LoWPAN, sensor nodes can be scattered randomly or
they may be deployed in an organized manner. 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
sensor network 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 sensor nodes
are battery-powered or mains-powered, influences the network
design. A hybrid solution is also 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 disconnection) to "sporadic" (i.e.,
almost always disconnected network).
o Routing: The routing 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 needed for simple star-
topologies or a multi-hop communication scheme for more elaborate
topologies, such as meshes or trees. From previous work by
academia and industry on LoWPANs, various routing mechanisms have
been 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/multi-hop communication when referring
to the routing categorization.
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o Traffic Pattern: several traffic patterns may be used in sensor
networks. To name a few, Point-to-Multi-Point (P2MP), Multi-
Point-to-Point (MP2P) and Point-to-Point (P2P).
o Security Level: sensor networks may carry sensitive information
and require high-level security support where the availability,
integrity, and confidentiality of the information are primordial.
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,
sensor 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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4. 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 goal of this document. The characteristics of the scenarios
described in this section do not reflect the characteristics that
every LoWPAN must have in a particular environment (e.g.,
healthcare).
4.1. Industrial Monitoring
Sensor network 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. Wireless sensor networks can be
inexpensively installed and provide more frequent and more reliable
data. The deployment of wireless sensor networks 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, and
ultimately lower costs for energy.
Manufacturing plants and engineering facilities, such as product
assembly lines and engine rooms, can be drastically optimized
using wireless sensor technology in order to ensure product
quality, control energy consumption, avoid machine downtimes, and
increase operation safety. In industrial settings, sensors such
as vibration detectors can be used to continuously monitor
equipment and predict equipment failure and to detect the need for
maintenance, with far greater precision. This allows companies to
avoid costly equipment failures or shutdowns of production lines
and therefore increase their productivity.
Greater access to process parameters gives engineers better
visibility and ultimately better decision making power. Various
sensor measurements, such as gas pressure, the flow of liquids and
gases, room temperature and humidity, or tank charging levels may
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be used together with controllers and actuators to improve a
plant's productivity in a continuous self-controlling loop, in
which instruments can be upgraded, calibrated, and reconfigured as
needed via the wireless channel.
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 4.2).
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.
Global supply chain and transportation applications increasingly
require real-time sensor and location information about their
supplies and assets. Wireless sensor networks meet these
requirements efficiently with low installation and management
costs, providing benefits such as reduced inventory, increased
asset utilization, and precise location tracking of containers,
goods, and mobile equipment. Clients can be provided with an
early warning of possible chain ruptures, for example by using
call centers or conveniently accessing comprehensive on-line
reports and data management systems. Such reports could include
monitoring of current states, the history of goods with critical
conservation conditions, and in critical areas the monitoring
status of oil containers, or verification of chemical gas
substance concentration.
For instance, thousands of cargo ships loaded with millions of
containers are sailing the oceans today. However, supply and
demand are not equally distributed around the world, which results
in high costs for shipping empty containers. Sophisticated IT
systems try to circumnavigate this problem and precision planning
is critical in any case: the customer always expects containers to
arrive just in time. Wireless sensor networks have a great
potential of making this growing market even more efficient by
allowing more reliable tracking and identification of containers,
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and cargo monitoring for hazardous freight detection or
identification of illegal shipment.
Also, the process of loading and unloading can be implemented more
efficiently. For example, after a crane operator has lifted a
container from the deck, its content is identified and taken to
the corresponding warehouse -- on a driverless truck whose
movements are controlled at centimeter precision by transponders
under the asphalt.
o Storage Monitoring: sensory 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.
4.1.1. A Use Case and its Requirements
Example: Storage Monitoring (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. The network configuration and routing
tables are not changed in the storage room unless node failure
occurs.
This type of application works based on both periodic and event-
driven notifications. Periodic data is used for monitoring the right
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
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time-critical and requires secure and reliable transmission. Due to
the time-critical sensing data, reliable and secure data transmission
is highly important.
Dominant parameters in industrial monitoring scenarios:
o Deployment: pre-planned, manually attached
o Mobility: no (except for the asset tracking case)
o Network Size: medium to large size, high node density
o Power Source: all battery-operated
o Security Level: business-critical. Secure and reliable
transmission must be guaranteed. An extra key mechanism can be
used.
o Routing: single- to multi-hop. Routing tables are merely changed
after configuration, except in the asset tracking case. Node
failure or indoor obstacles will cause the changes.
o Connectivity: always on for crucial processes, otherwise
intermittent
o QoS: important for time-critical event-driven data
o Traffic Pattern: P2P (actuator control), MP2P (data collection)
o Other Issues: Sensor network management
4.1.2. 6LoWPAN Applicability
The network configuration of the above use-case can differ
substantially by system design. As illustrated in Figure 4, the
simplest way is to build up a star topology inside of one storage
room, and connect the storage rooms with one link. Each LoWPAN node
reaches the Edge Router (ER) by pre-defined routing/forwarding
mechanism. the LoWPAN Coordinator Nodes (CNs) play role in
aggregation of the sensed data at each storage room and transmit the
data. It is noted that the LoWPAN CN is a logical entity so that it
can be implemented together with an LoWPAN Edge Router or a LoWPAN
Node. In case data from an individual node is important, such as
urgent event-driven data, it will not be accumulated (and further
delayed) by the LoWPAN CN but immediately relayed. In Mesh under,
link-layer addresses in mesh-header defined in RFC 4944[4] are used
for transmission, and in Route Over, IP forwarding is used.
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Based on the layout and size of the storage room, the LoWPAN can be
configured in mesh topology as shown in Figure 5. More than one
LoWPAN CNs can be installed in a storage room, and CNs collect data
and become relay points to send it to the LoWPAN ERs. LoWPAN Nodes
need to build a multi-hop connection to reach the CNs and ER by ether
Mesh Under or Route Over. In Mesh Under, more than one CNs can be
installed in the LoWPAN and the nodes play role in transmission
multi-point traffic (multicast) to unicast method, not only role in
data collection. In Route Over, LoWPAN Routers will handle multicast
traffic to their LoWPAN Link.
Each LoWPAN node configures its link-local address and may get a
prefix from its default router by an 6LoWPAN ND procedure (ND
optimization is on-going work in the WG [9]). Inside of the storage
room, each node does not need to get a globally unique IPv6 address.
However, containers can be moved inside or outside of the hospital,
so that globally unique addresses may be needed depending on the
purpose of the system and service. Address auto-configuration is
explained in Chapter 6 of RFC 4944 [4]. When the system is only used
within a link-local scope, 16-bit addresses can be utilized, but 64-
bit addresses are recommended for globally unique addressing.
The data volume is usually not so big in this case, but it is
sensitive for 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 (encapsulated in 6LoWPAN header or as
it is) will be chosen, but secure transmission and security mechanism
should be added. To increase security, MAC layer mechanisms or
additional security mechanisms can 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.
SNMP-lite or other mechanism SHOULD be provided for the management.
When a container is moved out from the storage room, and connected to
the hospital system (if the hospital buildings are fully or partly
covered with 6LoWPANs), it should rebind to a new parent and a new
LoWPAN. 6LoWPAN ND[9] will support this procedure. In case that it
is moved by an ambulance, it will be connected to an edge router in
vehicle.
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ER
| ER: LoWPAN Edge Router
CN----------CN----------CN CN: Coordinator Node
/ | \ / | \ / | \ n: LoWPAN Node
n n n n n n n n n
Figure 4: Storage rooms with simple star topology
GW
+------------+-----------+ GW: Gateway
| | | ER: LoWPAN Edge Router
ER ER ER(CN) CN: Coordinator Node
| | | (Data Aggregator)
n -- CN -- n CN -- n n n: LoWPAN Node
/ | \ | /|\
n CN n n -- n --CN n n n
/ | \ /|\
n n n -- n n n n
Figure 5: Storage rooms with mesh topology
4.2. 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 MUST be handled in very critical manner.
4.2.1. A Use Case and its Requirements
Example: Bridge Safety Monitoring
A 1000m long 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
sensor 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 coordinator. All sensor nodes do
not move while the service is provided. The network configuration
and routing tables are changed only in case of node failure. Except
from the pillars, there are no special obstacles of attenuation to
the sensor signals, but careful configuration is needed to prevent
signal interference between sensors.
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The network configuration and routing tables are changed only in case
of node failure. On the top part of each pillar, an "infrastructure"
sink node is placed to collect the sensed data. The sink nodes of
each pillar become data gathering point of the sensor nodes at the
pillar.
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 nodes, manual deployment, and mostly
star (or multi-level of star) topologies (see Figure 6), but
dependent on the blue print of the structure, mesh topologies will be
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 coordinators or relays)
o Security Level: safety-critical. Secure transmission must be
guaranteed. Only authenticated users should be able to access and
handle the data. Lightweight key mechanisms can be used.
o Routing: star-topology (potentially hierarchical) In case of
hierarchical case, reorganization of routing tree may be the
issue. However, routing table may merely be changed after
configuration. Node failure or indoor obstacles will cause the
changes.
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 may be needed to
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maintain a reliable monitoring system.
4.2.2. 6LoWPAN Applicability
The network configuration of this use case can be very simple, but
there are many extended use-cases for more complex structures. The
example bridge monitoring case may be the simplest case. Dependent
on the bridge size, the network will be configured by multiple stars
or a mesh topology.
Each LoWPAN node configures its link-local address and may get a
prefix from its default router by an 6LoWPAN ND procedure [9]). Each
pillar may have one LoWPAN Coordinator Node(CN) for data collection
from each pillar. Each node does not need to get a globally unique
IPv6 address, as the main communication is from/to the LoWPAN CN of
each pillar. In this manner, this system is likely to be built as a
stub network, so that 16-bit addresses can be utilized, but 64-bit
addresses are recommended for the new header format [10]. Globally
unique addresses MAY be allocated depending on the purpose of the
system.
The LoWPAN Nodes are installed on the place after 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-header described in RFC 4944
[4] is used for static data forwarding. In Mesh Under, a IPv6 link
is shared by all nodes in the LoWPAN, but for Route Over, an IPv6
link is only shared by nodes that lie in radio transmission range.
A logical entity of data gathering can be implemented in each LoWPAN
CN. Communication schedules must be set up between leaf nodes and
their CN 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 should
be allowed to access the data. Additional security should be
provided at the LoWPAN ER for restricting the access from outside of
the LoWPAN. The LoWPAN ER may take charge of authentication of
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LoWPAN nodes. Reliable and secure data transmission SHOULD be
guaranteed.
n n n
\ | / ER: LoWPAN Edge Router
n ---CN --- ER --- n CN: LoWPAN Coordinator Node
/ | \ and Data Aggregator
n n n n: LoWPAN Node
Figure 6: A LoWPAN with a simple star topology.
ER ---CN ------CN -------CN ER: Edge Router
/| / | \ | C: LoWPAN Coordinator Node
h r(m) h r(m) h r(m)-r(m)-h r: LoWPAN Router (Route Over)
/\ | | m: Mesh Node (Mesh Under)
h h h r(m) -- h h: LoWPAN Host
Figure 7: A LoWPAN with a mesh topology
4.3. 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 [8] using the concept of Personal Networks.
4.3.1. A Use Case and its Requirements
Example: Healthcare at Home by Tele-Assistance
An old 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 LoWPAN Edge
Router at home will send the sensed information to a connected
healthcare center. Portable base stations with LCDs may be used to
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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 patients' mobility
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 issue in this case, as the sensing data is
very personal. In addition, different data will be provided to the
hospital system than 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:
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 support by proper authentication mechanism
o Routing: multihop 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
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control. Reliability and robustness of the network are also
essential.
4.3.2. 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 LoWPAN Edge Router(ER) at home is the sink node in the
routing path from sources on the patient's body. A plug-and-play
configuration is required. Each home system node will get a link-
local IPv6 address according to the auto-configuration described in
RFC 4944 [4]. 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. However, 64-bit address is recommended to perform
the 6LoWPAN ND [9] and new header format in [10]. An example
topology is provided in Figure 8.
Multi-hop communication can be achieved by either Mesh Under or Route
Over routing mechanisms. In case the Mesh Under mechanism is
implemented, the LoWPAN ER becomes the only router of the home
network, and ND is done as [9] describes. When 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 CNs can be
installed in the LoWPAN and the nodes play role in transmission
multi-point traffic (multicast) to unicast method. In Route Over,
LoWPAN Routers will handle multicast traffic to their LoWPAN Link.
The patient's body network can be simply configured as a star
topology with a LoWPAN Coordinator Node(CN) 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.
It should be maintained the sensed information with the
identification of the patient wherever 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, the home system itself does not require
globally unique IPv6 address but could be run with link-local IPv6
address. In this case, the hospital LoWPAN needs to operate
additional identification system.
The connection with the LoWPAN Edge Router at home and the ER at
Hospital must provide reliable and secure transmission, as the data
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is privacy-critical. To achieve this, additional policy for security
is recommended between the two LoWPAN.
n --- n I: Internet
| | ER: Edge Router
ER --- I --- ER --- n --- n --- CN CN: Coordinator Node
/|\ | | /|\ n: LoWPAN Node
.. . .. n --- n h h h h: LoWPAN Host
(hospital) (home system) (patient)
Figure 8: A mobile healthcare scenario.
4.4. 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)
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.
4.4.1. A Use Case and its Requirements
Example: Home Automation
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 security (gas, water, CO,
Radon, smoke detection). The LoWPAN typically comprises a few dozen
of nodes forming an ad-hoc network with multi-hop routing since the
nodes may not be in direct range. 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
activated sending a video stream to a gateway that can be received on
a cell phone.
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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),
...) but also for home control (activate the air conditioning/
heating, door locks, sprinkler systems, ...). 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, ... in order to
control electric window shades, chillers, air flow control, air
conditioning and heating with the objective to optimize energy
consumption.
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). 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: small degree of mobility
o Network Size: medium number of nodes, potentially high density
o Power Source: mix of battery and AC powered devices
o Security Level: authentication and encryption required
o Routing: 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)
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4.4.2. 6LoWPAN Applicability
(TBD)
4.5. 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.
4.5.1. A Use Case and its Requirements
Example: Telematics
As shown in Figure 9, scattered LoWPAN Nodes are included in roads
during their construction for motion monitoring. When a car passes
over of 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 (10 years). Multihop 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
failures. Sinks placed at the road side are mains-powered, LoWPAN
Nodes in the roads run on battery. Power savings schemes might
intermittently disconnect the LoWPAN 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: mostly battery powered
o Security Level: low
o Routing: multi-hop, especially ad-hoc
o Connectivity: intermittent
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o QoS: support of limited QoS
o Traffic Pattern: mostly Point-to-Point (P2P), Point-to-Multi-Point
(P2MP)
4.5.2. 6LoWPAN Applicability
For this use case, the network topology includes fixed LoWPAN Edge
Routers that are mains-powered and have a connection to a gateway in
order to reach the transportation control center. These LoWPAN ERs
are logically combined with LoWPAN Coordinator Nodes (CNs) as data
sinks for a number of LoWPAN Nodes inserted in the tarmac of the
road.
In contrast to the LoWPAN ERs, the LoWPAN Nodes can generally operate
with link-local IPv6 addresses as no direct access from outside the
LoWPAN is established to the LoWPAN Nodes. Based on the purpose of
the service, globally unique IPv6 address can be allocated during the
network setup procedure described in RFC 4944[4] and 6LoWPAN ND [9].
In Infrastructure LoWPANs, each ER is connected by a backbone link
and additional registration procedures may be required for management
of multiple LoWPANs. Details of this registration is described in
6LoWPAN ND .
In this topology, a LoWPAN with one LoWPAN ER 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-header described in RFC 4944 [4] is used
for static data forwarding. Routing tables are not changed unless a
node failure occurs.
+----+
| ER |----------------------------- ER ...
+----+ (at the road side)
-------|------------------------------
|
n -- n --- n --- n +---|---+ ER: LoWPAN Edge Router
/ \ | | h-n-h | n: LoWPAN Node
n n n +---|---+ h: LoWPAN Host
(cars)
--------------------------------------
Figure 9: Multi-hop LoWPAN combined with mobile star LoWPAN.
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4.6. 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.
4.6.1. A Use Case and its Requirements
Example: Automated Vineyard
In a vineyard with medium to large geographical size, a number of 50
to 100 LoWPAN Coordinator 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 LoWPAN CNs in local wireless star
topologies, periodically reporting measurements to the associated
LoWPAN CNs. 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 routing scheme to enable data forwarding to a
sink node at the edge of the vineyard. Each of the 8 parcels
contains one data aggregator to collect the sensed data. Ten
intermediate nodes are used to connect the sinks to the main gateway.
Sensor localization is important for geographical routing, 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 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.
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Dominant parameters in agricultural monitoring:
o Deployment: pre-planned
The sensor 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.
Sensor 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
o Security Level: business-critical. Light-weight security or a
global key management can be used depending on the business
purpose.
o Routing: mesh topology with local star connections. Routing table
is merely changed after configuration. Node failure or indoor
obstacles will cause the changes.
o Connectivity: intermittent (many sleeping nodes)
o QoS: not critical
o Traffic Pattern: Mainly MP2P/P2MP. P2P for Gateway communication
or actuator triggering.
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).
4.6.2. 6LoWPAN Applicability
The network configuration in this use case might, in the most simple
case, look like illustrated in Figure 10. This static scenario
consists of one or more fixed edge routers that are mains-powered and
have a high-bandwidth connection to a gateway via a backbone link,
which might be placed in a control center, or connect to the
Internet. The LoWPAN Edge Routers are strategically located at the
border of vineyard parcels, acting as data sinks. A number LoWPAN
Coordinator Nodes are placed along a row of plants with individual
LoWPAN Hosts spread around them.
While the LoWPAN ERs implement the IPv6 Neighbor Discovery protocol
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(RFC 4861), the LoWPAN Nodes need a more energy-efficient mechanism.
They instead follow LoWPAN Neighbor Discovery as described in [9],
which includes basic bootstrapping and address assignment. Link-
local addresses are used for communication within the network. Each
LoWPAN ER can have predefined forward management information, if
necessary.
The intermediate nodes must implement a multi-hop routing protocol
(Mesh Under or Route Over) and they are responsible for forwarding
measurement data of the LoWPAN hosts towards the LoWPAN ERs. In this
simplest case, the LoWPAN Routers (not edge routers) or Mesh Nodes
can build static routing (or forwarding) paths, and all end-nodes can
be placed in one radio hop distance from its forwarder. Packets can
be forwarded to each router or mesh node and relayed to the LoWPAN ER
by link-layer forwarding using the 6LoWPAN mesh-header or Route Over
routing.
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 LoWPAN CNs 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.
+----+
| GW | GW: Gateway
+----+ ER: LoWPAN Edge Router
| h h h h h h h h h CN: LoWPAN Coordinator Node
| \|/ \|/ \|/ r: Route Over (LoWPAN Router)
ER----CN(r,m)--CN(r,m)--CN(r,m) m: Mesh Under(forwarding node)
| /|\ /|\ /|\ h: LoWPAN Host
| h h h h h h h h h
ER
...
Figure 10: An aligned multi-hop LoWPAN.
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5. Security Considerations
Security requirements are differ by use-cases. For example, industry
monitoring an structure monitoring applications are safety-critical.
Secure transmission must be guaranteed, and only authenticated users
should 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 support by proper authentication mechanism.
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6. 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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7. References
7.1. 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.
7.2. Informative References
[6] Bulusu, N. and S. Jha, "Wireless Sensor Networks", July 2005.
[7] Roemer, K. and F. Mattern, "The Design Space of Wireless Sensor
Networks", December 2004.
[8] den Hartog, F., Schmidt, J., and A. de Vries, "On the Potential
of Personal Networks for Hospitals", May 2006.
[9] Shelby, Z., Thubert, P., Hui, C., Chakrabarti, S., and E.
Nordmark, "Neighbor Discovery for 6LoWPAN,
draft-shelby-6lowpan-nd-00 (work in progress)", October 2008.
[10] Hui, J. and P. Thubert, "Compression Format for IPv6 Datagrams
in 6LoWPAN Networks, draft-ietf-6lowpan-hc-04 (work in
progress)", December 2008.
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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
Nicolas G. Chevrollier
TNO
Brassersplein 2
P.O. Box 5050
Delft 2600
The Netherlands
Phone: +31-15-285-7354
Email: nicolas.chevrollier@tno.nl
Dominik Kaspar
Simula Research Laboratory
Martin Linges v 17
Snaroya 1367
Norway
Phone: +47-4748-9307
Email: dokaspar.ietf@gmail.com
JP Vasseur
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough MA 01719
USA
Phone:
Email: jpv@cisco.com
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