| Rfc | 6568 |
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| Title | Design and Application Spaces for IPv6 over Low-Power Wireless
Personal Area Networks (6LoWPANs) |
|---|
| Author | E. Kim, D. Kaspar, JP. Vasseur |
|---|
| Date | April 2012 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | INFORMATIONAL |
|---|
|
Internet Engineering Task Force (IETF) E. Kim
Request for Comments: 6568 ETRI
Category: Informational D. Kaspar
ISSN: 2070-1721 Simula Research Laboratory
JP. Vasseur
Cisco Systems, Inc.
April 2012
Design and Application Spaces
for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)
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 Working Group 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
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6568.
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Table of Contents
1. Introduction ....................................................3
1.1. Terminology ................................................5
1.2. Premise of Network Configuration ...........................5
2. Design Space ....................................................6
3. Application Scenarios ...........................................8
3.1. Industrial Monitoring ......................................8
3.1.1. A Use Case and Its Requirements .....................9
3.1.2. 6LoWPAN Applicability ..............................10
3.2. Structural Monitoring .....................................12
3.2.1. A Use Case and Its Requirements ....................12
3.2.2. 6LoWPAN Applicability ..............................14
3.3. Connected Home ............................................15
3.3.1. A Use Case and Its Requirements ....................15
3.3.2. 6LoWPAN Applicability ..............................17
3.4. Healthcare ................................................18
3.4.1. A Use Case and Its Requirements ....................18
3.4.2. 6LoWPAN Applicability ..............................19
3.5. Vehicle Telematics ........................................20
3.5.1. A Use Case and Its Requirements ....................21
3.5.2. 6LoWPAN Applicability ..............................21
3.6. Agricultural Monitoring ...................................22
3.6.1. A Use Case and Its Requirements ....................22
3.6.2. 6LoWPAN Applicability ..............................24
4. Security Considerations ........................................25
5. Acknowledgements ...............................................26
6. References .....................................................26
6.1. Normative References ......................................26
6.2. Informative References ....................................27
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 Power-Line Communication (PLC)). They are
characterized by low speed, low performance, low cost, and unstable
connectivity. A LoWPAN is a particular instance of an LLN, formed by
devices complying with the IEEE 802.15.4 standard [5]. Their typical
characteristics can be summarized as follows:
o Limited Processing Capability: The smallest common LoWPAN nodes
have 8-bit processors with clock rates around 10 MHz. Other
models exist with 16-bit and 32-bit cores (typically ARM7),
running at frequencies on the order of tens of MHz.
o Small Memory Capacity: The smallest common LoWPAN nodes have a few
kilobytes of RAM with a few dozen kilobytes of ROM/flash memory.
While memory sizes of nodes continue to grow (e.g., IMote has 64
KB SRAM, 512 KB 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 radio frequency (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 on 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 250 kbit/s, which is most commonly used in
current deployments. Alternatively, three lower data rates of 20,
40, and 100 kbit/s are defined.
As with any other LLN, a LoWPAN is not necessarily comprised 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.
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 Working Group.
1.1. Terminology
Readers are expected to be familiar with all terms and concepts
discussed in "IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs): Overview, Assumptions, Problem Statement, and Goals" [2],
and "Transmission of IPv6 Packets over IEEE 802.15.4 Networks" [3].
Readers would benefit from reading 6LoWPAN Neighbor Discovery (ND)
[6], 6LoWPAN header compression [7], and 6LoWPAN routing requirements
[8] for details of 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 located at the junction of separate LoWPANs or
between a LoWPAN and another IP network. There may be one or more
LBRs at the LoWPAN boundary. An LBR is the responsible authority
for IPv6 Prefix propagation for the LoWPAN it serves. An isolated
LoWPAN also contains an LBR in the network; the LBR 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 Medium Access Control (MAC)
features that are not always in use, we are not using this
distinction in this document.
6LoWPANs 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" to mean
either a route-over or mesh-under network.
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 on the link layer or as LoWPAN routers, and connect the
entire LoWPAN in a multi-hop fashion. 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 [6] or
by using a coordinator that 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 in 6LoWPAN ND are in [6].
A LoWPAN can be configured as mesh-under or route-over (see
Terminology in [6]). In a route-over configuration, multi-hop
transmission is carried out by LoWPAN routers using IP routing. In a
mesh-under configuration, the link-local scope reaches to the
boundaries of the LoWPAN, and multi-hop transmission is achieved by
forwarding data at the link layer or in a 6LoWPAN adaptation layer.
More information about mesh-under and route-over is in [6] and [8].
2. Design Space
Inspired by [9], this section lists the dimensions used to describe
the design space of wireless sensor networks in the context of the
6LoWPAN Working Group. The design space is already limited by the
unique characteristics of a LoWPAN (e.g., low power, short range, low
bit rate), as described in [2]. 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 (ten), moderate (several
hundred), or large (over a thousand).
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), network connectivity can be from "intermittent"
(i.e., regular disconnections) to "sporadic" (i.e., almost always
disconnected). Differences in L2 duty-cycling settings may
additionally impact connectivity due to highly varying bit rates.
o Multi-Hop Communication: The multi-hop communication factor
highlights the number of hops that have 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 on LoWPANs by academia
and industry, 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/
multi-hop communication.
o Traffic Pattern: Several traffic patterns may be used in LoWPANs
-- Point-to-Multipoint (P2MP), Multipoint-to-Point (MP2P), and
Point-to-Point (P2P), to name a few.
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) -- and 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; these delivery models usually coexist
in LoWPAN applications. QoS issues in LoWPANs are more likely
related to corresponding application-specific data delivery
requirements within resource-constrained LoWPANs.
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 perform. 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: This application field combines
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.
Wireless connectivity that is easy to install extends this line to
include peripheral areas and process measurements that were
previously infeasible or impractical to reach with wired
connections.
o Machine Surveillance: This application field ensures 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.
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 the risk and cost of removing products
from the sales channel. Examples include container shipping,
product identification, cargo monitoring, distribution, and
logistics.
o Storage Monitoring: This application field includes sensor systems
designed to prevent releases of regulated substances into 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 degrees C, and blood
plasma below -18 degrees C. For anti-cancer medicine, maintaining a
humidity of 45% to 55% is required. Storage rooms have temperature
sensors and humidity sensors every 25 to 100 m, 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. In
particular, LCs play a role in aggregation of the sensed data from
blood packs. In the extended networks, more than one LoWPAN LC 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 temperature 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 in 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
temperature and humidity in the storage rooms. The data over or
under a predefined threshold is meaningful to report. Blood cannot
be used if it is exposed to the wrong environment for about 30
minutes. Thus, event-driven data sensed on abnormal occurrences is
time-critical and requires secure and reliable transmission.
LoWPANs must be provided with low installation and management costs,
and for the transportation of blood containers, precise location
tracking of containers is important. The hospital network manager or
staff can be provided with an early warning of possible chain
ruptures, for example, by conveniently accessing comprehensive online
reports and data management systems.
Dominant parameters in industrial monitoring scenarios:
o Deployment: Pre-planned, manually attached.
o Network Size: Medium to large size, high node density.
o Power Source: Battery-operated most of the time.
o Connectivity: Always on for crucial processes.
o Multi-Hop Communication: Multi-hop networking.
o Traffic Pattern: P2P (actuator control), MP2P (data collection).
o Security Level: Business-critical. Secure transmission must be
guaranteed.
o Mobility: None (except for asset tracking).
o QoS: Important for time-critical event-driven data.
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 -- 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 a 6LoWPAN ND procedure [6]. LoWPAN
nodes need to build a multi-hop connection to reach the LCs and LBR.
Secure data transmission and authentication are crucial in a hospital
scenario, to prevent personal information from being 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.
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 a 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 lightweight management mechanism must be provided for this
management.
The service quality of this case is highly related to effective
handling of event-driven data that is delay intolerant and mission
critical. Wrong humidity and wrong temperature are events that need
to be detected as quickly and reliably 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 [12]. It can be considered to
provide appropriate data aggregation for minimizing delay and
maximizing accuracy of delivery by using power-affluent nodes, or can
be aided by middleware or other types of network elements.
When a container is moved out of the storage room and connected to
another 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 the 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 (e.g., beds moved in the
hospital, 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
+------------+-----------+
| | | 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
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 1000-m-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 100-m 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 for the pillars, there are no special obstacles
causing attenuation of 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
points of the LoWPAN hosts at the pillar and act as local
coordinators.
This use case can be extended to medium or large sensor networks to
monitor a building or, for instance, the safety status of highways
and tunnels. Larger networks of the same kind still have similar
characteristics, such as static node placement and manual deployment;
depending on the blueprint 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 Network Size: Small (dozens of nodes) to large.
o Power Source: Mains-powered nodes are mixed with battery-powered
nodes. (Mains-powered nodes will be used for local coordination
or relays.)
o Connectivity: Always connected, or intermittent via sleeping mode
scheduling.
o Multi-Hop Communication: It is recommended that multi-hop mesh
networking be supported.
o Traffic Pattern: MP2P (data collection), P2P (localized querying).
o Security Level: Safety-critical. Secure transmission must be
guaranteed. Only authenticated users must be able to access and
handle the data.
o Mobility: None.
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 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 via 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 in 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
addresses can be used for IPv6 link-local addresses [3].
Each pillar might have one LC for data collection. 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 address allocation.
This type of application works based on periodic, query-driven, and
event-driven notifications. The data over or under a predefined
threshold is meaningful to report. Event-driven data sensed on
abnormal occurrences is time-critical and requires secure and
reliable transmission. Alternatively, 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-affluent or
mains-powered node that 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 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 without 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 Section 3.4)
o Smart appliances and home entertainment systems
In home environments, LoWPANs typically comprise a few dozen and,
probably in the near future, a few hundred nodes of various types:
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.), as well as home control (activate 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 emergence of "Smart Grid" applications, the LoWPAN may also
have direct interactions with the Grid itself via the Internet to
report the amount of kilowatts 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 a
Demand-Response application. Another service, known as Demand-Side
Management (DSM), could be provided by utilities to monitor and
report to the user his energy consumption, with a fine granularity
(on a per-device basis). A user can also receive other inputs from
the utility, such as dynamic pricing; according to local policy, the
utility may then turn some appliances on or off in order to reduce
its energy bill.
In terms of home safety and security, the LoWPAN is made up of motion
sensors and audio sensors, sensors at doors and windows, and video
cameras; additional sensors can be added for safety (gas, water, CO,
Radon, smoke detection). The LoWPAN is typically comprised of 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 simplest 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 may be
activated to send a video stream to a cell phone via a gateway.
Ergonomics in connected homes is key, and the LoWPAN must be
self-managed and easy to install. Traffic patterns may vary greatly,
depending on applicability; 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, the
response time and network delays must still be on the order of a few
hundred milliseconds for optimal 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
LoWPANs usually do not require multi-topology or QoS routing. Fairly
simple QoS mechanisms are enough for handling emergency data; they
can be programmed to alarm via actuators or to operate sprinklers.
Dominant parameters for home automation applications:
o Deployment: Multi-hop topologies.
o Network Size: Medium number of nodes, potentially high density.
o Power Source: Mix of battery-powered and mains-powered devices.
o Connectivity: Intermittent (usage-dependent sleep modes).
o Multi-Hop Communication: No requirement for multi-topology or QoS
routing.
o Traffic Pattern: P2P (inter-device), P2MP, and MP2P (polling).
o Security Level: Authentication and encryption required.
o Mobility: Some degree of mobility.
o QoS: Support of limited QoS for emergency data (alarm).
3.3.2. 6LoWPAN Applicability
In the home automation use case, the network topology is made of a
mix of battery-operated and mains-powered nodes that communicate with
each other. An LBR provides connectivity to the outside world for
control management (Figure 4).
In the 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, traffic will be sent to a LC for processing; the
LC may in turn decide on local actions (switch a light on, ...). In
other scenarios, all devices will send their data to the LCs, which
in turn may also act as the LBR for data processing and potential
relay of data outside of the LoWPAN. It does not mean that all
devices communicate with each other via the LC and LBR. 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 send data
once enough data has been accumulated (e.g., energy consumption for
the past 6 hours for a set of appliances), or trigger an alarm that
is 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 path of 2-3
hops (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 applications (e.g., fire,
gas-leak detection, health monitoring), whereas other applications
may not be critical (e.g., humidity monitoring). Such emergency data
has the same QoS issues as does event-driven data in other
applications and can be delivered by pre-defined paths through
mains-powered nodes without being stored in intermediate nodes such
as LCs. Similarly, some information may require the use of security
mechanisms for authentication and confidentiality.
3.4. Healthcare
LoWPANs are envisioned to be heavily used in healthcare environments.
They have a high potential for easing the deployment of new services
by getting rid of cumbersome wires and simplifying patient care in
hospitals and at home (home care). In healthcare environments,
delayed or lost information may be a matter of life or death.
Various systems, ranging from simple wearable remote controls for
tele-assistance or intermediate systems with wearable sensor nodes
monitoring various metrics to more complex systems for studying life
dynamics, can be supported by LoWPANs. In the latter category, a
large amount of data from various LoWPAN nodes can be collected:
movement pattern observation, checks that medicaments have been
taken, object tracking, and more. An example of such a deployment is
described in [10] using the concept of "personal networks".
3.4.1. A Use Case and Its Requirements
Example: Healthcare at Home by Tele-Assistance
A senior citizen who lives alone wears one to several wearable LoWPAN
nodes to measure heartbeat, pulse rate, etc. Dozens of LoWPAN nodes
are densely installed at home for movement detection. An 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
patients at home, where there are many walls and obstacles. Even
during sleep, the change of body position may affect radio
propagation.
Data is gathered in both periodic and event-driven fashion. In this
application, event-driven data can be very time-critical. Thus,
real-time and reliable transmission must be guaranteed.
Privacy also becomes a 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 bootstrapping procedures in order to build a
secure link without using much memory and energy. In addition,
different data will be provided to the hospital system from that
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 Network Size: Small, high node density.
o Power Source: Hybrid.
o Connectivity: Always on.
o Multi-Hop Communication: Multi-hop for home-care devices;
patient's body network is star topology. Multipath interference
due to walls and obstacles at home must be considered.
o Traffic Pattern: MP2P/P2MP (data collection), P2P (local
diagnostic).
o Security Level: Data privacy and security must be provided.
Encryption is required. It is required that role-based access
control be supported by a lightweight authentication mechanism.
o Mobility: Moderate (patient's mobility).
o QoS: High level of reliability support (life-or-death
implication), role-based.
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 that 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 (say, 10
nodes or less). 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 addresses can be used for IPv6
link-local addresses [3]. 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 patient's mobility at home,
the deployment of LoWPAN nodes and transmission paths should be well
considered. At home, some nodes can be installed with
power-affluence status, and those LoWPAN nodes can be used for
relaying points or data aggregation points.
The sensed information must be maintained with the identification of
the patient, no matter whether the patient visits the connected
hospital or stays at home. If the patient's LoWPAN uses a globally
unique IPv6 address, the address can be used for patient
identification. However, this incurs a cost in terms of privacy and
security. The hospital LoWPAN to which the patient's information is
transferred needs to operate an additional identification system,
together with a strong authority and authentication mechanism. The
connection between the LBR at home and the LBR at the hospital must
be reliable and secure, as the data is privacy-critical. To achieve
this, an additional policy for security between the two LoWPANs is
recommended.
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 into roads, vehicles, and traffic signals, they
contribute to the improvement of safety in transportation systems.
Through traffic or air-quality monitoring, they increase the
possibility of traffic flow optimization, and they help reduce road
congestion.
3.5.1. A Use Case and Its Requirements
Example: Telematics
As shown in Figure 6, LoWPAN nodes for motion monitoring are
incorporated into roads during road construction. When a car passes
over these nodes, it is then possible to track, for safety purposes,
the trajectory (path) and velocity of the car.
The lifetime of LoWPAN nodes incorporated into roads is expected to
be as long as the lifetime 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 node
density due to power failures. Sink nodes placed at the side of the
road are most likely mains-powered; LoWPAN nodes in the roads run on
batteries. 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 Network Size: Large (road infrastructure), small (vehicle).
o Power Source: Hybrid.
o Connectivity: Intermittent.
o Multi-Hop Communication: Multi-hop, especially ad hoc.
o Traffic Pattern: Mostly MP2P, P2MP.
o Security Level: Handling physical damage and link failure.
o Mobility: None (road infrastructure), high (vehicle).
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., the
Internet) in order to reach the transportation control center
(Figure 6). These LBRs may be logically combined with a LC as a data
sink to gather sensed data from a number of LoWPAN nodes inserted in
the road pavement. 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.
+-----+
| LBR |--------------------------- LBR ...
+-----+ (at the roadside)
-------|------------------------------
|
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 into 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
farmer's inability to check crops at all times of the day, or
inadequate measurement tools, luck often plays too large a 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 environmental
protection. The sensing data can be used to find optimal
environments for the plants. In addition, the data on planting
conditions 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 of medium to large geographical size, between 50 and
100 LC nodes are manually deployed in order to provide full signal
coverage over the study area. An additional 100 to 1000 leaf nodes
with (possibly heterogeneous) specialized sensors (i.e., humidity,
temperature, soil condition, sunlight) are attached to the LCs in
local wireless star topologies, periodically reporting measurements
to the associated LCs. For example, in a 20-acre vineyard with 8
parcels of land, 10 LoWPAN nodes are placed within each parcel to
provide readings on temperature and soil moisture. The LoWPAN nodes
are able to support a multi-hop forwarding/routing scheme to enable
data transmission to a sink node at the edge of the vineyard. Each
of the 8 parcels contains one data aggregator to collect the sensed
data.
Localization is important for this type of LoWPAN when installed in a
geographically large area, in order to pin down where an event
occurred, and to combine gathered data with the actual positions of
the devices. Using manual deployment, device addresses can be used
for identifying their 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 the
type of 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, and dust, in dynamic environments of
moving people and machinery, and with growing crops and foliage.
LoWPAN nodes can be deployed in a predefined manner, with
consideration given to harsh environments.
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 Connectivity: Intermittent (many sleeping nodes).
o Multi-Hop Communication: Mesh topology with local star
connections.
o Traffic Pattern: Mainly MP2P/P2MP. P2P actuator triggering.
o Security Level: Depends on purpose of the business. Lightweight
security or simple shared-key management can be used, depending on
the purpose of the business.
o Mobility: All static.
o Other Issues: Time synchronization among sensors is required, but
the traffic interval may not be frequent (e.g., once every 30 to
60 minutes).
3.6.2. 6LoWPAN Applicability
The network configuration in this use case might, in the simplest
case, look like the configuration illustrated in Figure 7. This
static scenario consists of one or more fixed LBRs that are
mains-powered and have a high-bandwidth connection to a backbone
link, which might be placed in a control center or connected 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 [1]) to connect to the outside of the LoWPAN, the LoWPAN
nodes operate a more energy-conserving ND described in [6], which
includes basic bootstrapping and address assignment. Each LBR can
have predefined forward management information to a central data
aggregation point, if necessary.
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 at the
application level are necessary.
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
4. Security Considerations
Relevant security considerations are listed by application scenario
in Section 3. The security considerations in RFC 4919 [2] and
RFC 4944 [3] 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 of 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) 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.
Considering the power constraints and limited processing capabilities
of IEEE 802.15.4 devices, IPsec is computationally expensive;
Internet key exchange (IKEv2) messaging as described in [4] is not
suited for LoWPANs, as the amount of signaling in these networks
should be minimized. Thus, LoWPANs may need to define their own
key-management method that requires minimum overhead in terms of
packet size and message exchange [11]. 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. Recent work [13]
shows some promise for minimal IKEv2 implementations.
Security requirements may differ by use case. For example,
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
healthcare 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 high security and robustness against
intrusion. On the other hand, a remote-controlled light switch has
no critical security threats.
5. Acknowledgements
Special thanks to Nicolas Chevrollier for participating in the
initial design of the document. Also, thanks to David Cypher for
giving more insight on the IEEE 802.15.4 standard, and to Irene
Fernandez, Shoichi Sakane, and Paul Chilton for their review and
valuable comments.
6. References
6.1. Normative References
[1] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[2] 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.
[3] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4 Networks",
RFC 4944, September 2007.
[4] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, "Internet Key
Exchange Protocol Version 2 (IKEv2)", RFC 5996, September 2010.
[5] IEEE Computer Society, "IEEE Standard for Local and
Metropolitan Area Networks -- Part 15.4: Low-Rate Wireless
Personal Area Networks (LR-WPANs)", IEEE Std. 802.15.4-2011,
September 2011.
6.2. Informative References
[6] Shelby, Z., Ed., Chakrabarti, S., and E. Nordmark, "Neighbor
Discovery Optimization for Low Power and Lossy Networks
(6LoWPAN)", Work in Progress, October 2011.
[7] Hui, J., Ed., and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
September 2011.
[8] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for 6LoWPAN Routing", Work
in Progress, November 2011.
[9] Roemer, K. and F. Mattern, "The Design Space of Wireless Sensor
Networks", IEEE Wireless Communications, Vol. 11, No. 6,
pp. 54-61, December 2004.
[10] den Hartog, F., Schmidt, J., and A. de Vries, "On the potential
of personal networks for hospitals", International Journal of
Medical Informatics, 75, pp. 658-663, May 2006.
[11] Dutertre, B., Cheung, S., and J. Levy, "Lightweight Key
Management in Wireless Sensor Networks by Leveraging Initial
Trust", SDL Technical Report SRI-SDL-04-02, April 2004.
[12] Chen, D. and P.K. Varshney, "QoS Support in Wireless Sensor
Networks: A Survey", Proc. 2004 Int. Conf. Wireless
Networks (ICWN 2004), June 2004.
[13] Kivinen, T., "Minimal IKEv2", Work in Progress, February 2011.
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: +47-6782-8200
EMail: dokaspar.ietf@gmail.com
JP. Vasseur
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
EMail: jpv@cisco.com