Neeli R. Prasad and Ramjee Prasad
Center for TeleInFrastructure (CTIF), Aalborg University, Denmark
Keywords: CRUISE, Environment, Intelligent Sensing, Applications, Mobility
, Security.
Abstract: The recent developments in the research and the technology have brought attention to the wireless sensor
networks as one of the key enabling technologies in the next 10 years. Ubiquitous Intelligent Sensing
Environments have promising future in supporting the everyday life of the European citizens, bringing
important social benefits for each person and for the society as a whole. Taking into account the current
fragmentation in the European research in this field, CRUISE Network of Excellence (NoE) intends to be a
focal point in the coordination of research on communication and application aspects of wireless sensor
networking in Europe. To make a significant contribution to the effectiveness of research, the consortium
will evaluate, update and communicate the State-of-the-Art in wireless sensor networking (WSN) to the
technical community, distilling a path from current technological status to a long term vision. This paper
gives an overview of different research topics in WSN and its open issues.
In the past years, a number of mostly U.S.-based
research projects (Kahn et al., 1999) depicted WSNs
as large-scale networks of homogeneous, tiny,
resource-constraint sensor units. While this
characterization is valid for large class of
applications, an increasing number of sensor
network (SN) applications which are envisaged to
have immense social benefits for each European
citizen and for the society as a whole will play a
profound role in the future Ubiquitous Intelligent
Sensing Environments. WSNs in vehicles, smart
homes, smart offices, applications for road and
traffic safety, for emergency response, health
monitoring of humans, support for elder people,
monitoring of farm animals, etc are mentioned in the
literature (Prasad et al., 2004) (Arampatzis et al.,
2005) (Konrad Lorincz et al., 2004) (Anu Bhargava
et al., 2003). This big diversity of applications
requires different design considerations and
considerable multidisciplinary research efforts in the
areas of communications, electronics, control and
close collaboration between users, application
domain experts and developers.
The potential for innovative user-centric applications
as one of the m
ost exciting aspects of WSN creates a
high motivation for working on the variety of
challenging research topics (Arampatzis et al.,
In this respect, better coordination for the mostly
lated and disconnected research activities on
sensor networks across Europe is essential.
CRUISE (CRUISE, see ref.) Network of Excellence
- CReatin
g Ubiquitous Intelligent Sensing
Environments, is the new project that deals with
WSNs. It actively works against this trend by
promoting discussion and strengthening research
cooperation and coordination between industry and
academia in the topic of communication and
application aspects of WSNs, while maintaining its
academic nature.
The project starts on 1
January 2006 and has
duration of 24 months. 32 internationally recognized
groups from Europe, from academia, from
independent research centers and from industry, are
coordinated by the Center for Telenfrastruktur
(CTIF) at Aalborg University, Denmark.
Convinced that Network of Excellence in this field
is a n
ecessity in this moment, the project partners
share the vision of the ubiquitous intelligent sensing
environments and work to reduce the current
weakness and fragmentation in this research field in
Europe taking into account the immense benefits
that WSNs have to offer to the European society.
R. Prasad N. and Prasad R. (2006).
In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 355-361
The jointly executed program of project activities
has 3 major directions – integration of knowledge
and tools; joint research activities and spreading the
The main focus is the creation of a state-of-the-art
Knowledge Base, available to the European society
and the general public, through information and data
collection, comparison, validation and then
dissemination. To support the research agenda of 6th
and 7th Framework Program of the European
Commission, CRUISE consortium contributes with
identification of the research gaps in the current
research work in all fields related to WSNs; with
creation of visionary scenarios for future
applications of WSNs; with identification of short
and long term benefits, done by stimulation of open
discussions on the issues of standardization and
international collaboration, by broadening the
collaboration with industries and the European
research initiatives active in this field,. CRUISE
partners are to establish frameworks of common
tools and methodologies to accelerate the research
processes and to build sustainable collaboration
links bringing strong commitments to be integrated
within and beyond the boundaries of the consortium.
An important aspect of CRUISE potential impact is
the new contribution to teaching and training in the
field of WSNs. E-learning@CRUISE is the ultimate
goal in promoting the research in Wireless Sensor
Network and in the spreading of the results to the
general public and in particular to the European
industry so that it can compete in this domain.
The project consortium is consulted by External
advisory board (EAB) on international developments
especially desires for (new) actions, projects and
activities in the area of wireless sensor networks and
applications. EAB consist of international experts in
the field of WSNs from all over the world (USA,
Turkey, Canada, Australia, Japan, The Netherlands,
UK, Switzerland, Portugal), from industry and
This paper is organized as follows: section II
provides overview of the Applications and
scenarios; section III discussed the mobility in
WSN, section IV gives the insight of security issues
in WSN and finally the paper is concluded in section
Within the next few years, distributed sensing and
computing will be everywhere, i.e., homes, offices,
factories, automobiles, shopping centers,
supermarkets, farms, forests, rivers, lakes, and even
Some of the immediate commercial applications of
WSN are
Industrial automation (process control)
Environmental (ecology system monitoring)
Defense (unattended sensors, real-time
Utilities (automated meter reading),
Weather prediction (temperature, humidity)
Security (smart building, tracking, car theft
Building automation (HVAC controllers).
Disaster relief operations (earthquake,
Medical monitoring and instrumentation (remote
sensing and health care)
Intelligent transportation (unmanned driving)
Research Challenges
Numerous unattended and resource-constrained
sensors, deployed at high density in regions
requiring surveillance and monitoring. Network
topology is unknown due to unexpected node
Sensors are memory as well as energy
constrained, and power consumption in WSN can
be divided into three domains:
Communication, Data Processing, and Sensing
A sensor expends maximum energy in data
communication (both for transmission and
reception), and the transceiver circuitry has both
active and start-up power consumption.
Power consumption in data processing is much
less than in communication, so local data
processing is crucial in minimizing power
consumption in a multi-hop network.
Tradeoff between energy and QoS
Prolong network lifetime by sacrificing
application requirements, such as delay,
throughput, reliability, data fidelity.
The existing state-of-the-art can be organized, on
one hand, into the analysis of different sensors,
depending on the application and on the other hand,
the processing algorithms involved taking into
account the constrains of the devices (motes), the
monitoring process and the trade-off between delay
and throughput.
For the targeted applications, environmental
monitoring and road traffic monitoring, we have
different approaches in the state-of-the-art. For
environmental monitoring: U.S. NSF (US NSF, see
ref.) , DARPA (DARPA, see ref.) and INTEL
(INTEL, see ref.) , in U.S.; IBM Zurich (IBM , see
ref), EPFL (MICS, see ref.) in Switzerland;
Australian Research Council (Australian Research
Council, see ref.) and for road traffic monitoring:
Pravin Varaiya’s Group (Berkeley) (Pravin
Varaiya’s Group, see ref.) and Cartel People (MIT)
(Cartel People (MIT), see ref.).
Different sources of mobility are:
Node mobility
A node participating as source/sink (or
destination) or a relay node might move around
Deliberately, self-propelled or by external force;
targeted or at random
Happens in both WSN and MANET
Sink mobility
In WSN, a sink that is not part of the WSN
might move
Mobile requester
Event mobility
In WSN, event that is to be observed moves
around (or extends, shrinks)
Different WSN nodes become “responsible” for
surveillance of such an event
The processing algorithms to optimize sensors in
environment application and scenario within the
WSN framework can be determined by the objective
of these applications such as:
For environmental monitoring:
Watershed and quality water monitoring, where
data is used to: a) analyze the effect of pollution in
water and soil conditions, b) track groundwater
Early detection of forest fires, where WSNs will
include temperature, light, soil moisture and air
humidity sensors to estimate evaporation, as well
as sensors to measure wind speed and direction,
allowing inferring fire risk levels and probable fire
For road traffic monitoring:
Vehicle tracking, detection and classification (e.g.
length, speed, etc.), using acoustic, magnetic and
infrared sensors and tiny cameras
Intelligent & efficient parking on public streets,
finding free parking spots for drivers, decreasing
the risk of possible accidents and pollution
Mobility can be described along two-axis: location
coordinate and time
Mobile enabled WSN will provide time-varying
topological view to task managers
Mobility maybe can be leveraged to realize the
divide and conquer” idea, i.e. not acting until
appropriate opportunity
Mobility management in WSN requires nano-
scale location management and topology
Sensor relocation can assist the deployment of
sensor network to meet certain coverage
requirement. Sensor mobility provides a time-
varying coverage that is of benefit to monitor
moving intrusion target. Mobile sink can collect
information from vicinal sensors and make decision
about its mobility pattern. The sink’s mobility
pattern can be learned and leveraged by sensors to
dynamically choose best route and finally, mobile
relay is another alternative to alleviate the burden of
energy consumption bottleneck of the sensor nodes
around the sink.
When designing a secure WSN, the following
security requirements should be considered:
authentication, integrity, freshness, availability,
confidentiality, robustness, autonomous recovery,
privacy protection, trust establishment. In the
following paragraphs, state-of-the-art for each of
them is provided and open research issues are
The broadcast nature of the transmission medium
makes information more vulnerable than in wired
applications. Thus, security mechanisms such as
encryption and authentication are essential to protect
information transfers.
Key management protocol:
Symmetric encryption/decryption algorithms and
hashing functions are between two to four orders of
magnitude faster than Public-key algorithms, such as
RSA, and constitute the basic tools for securing
sensor networks communications.
In (Tassos Dimitriou et al., 2005) a localized
algorithm for key establishment between a source
node and the base station suitable for sensor network
deployment is proposed. The protocol provides
security against a large number of attacks and
guarantees that data securely reaches the base station
in an energy efficient manner.
Encryption algorithms:
TEA, SEAL, RC4, RC5 (Xiaohua Luo et al.,
2004).These encryption algorithms are suitable for
sensor networks with harsh resource constraints.
According to the comparison performed in (Xiaohua
Luo et al., 2004). TEA is the most perfect encryption
algorithm to minimize memory footprint and
maximize speed. Disadvantage of SEAL - it requires
several kilobytes of RAM space and rather intensive
RC4 is widely used in many applications and is
generally regarded to be secure.
µTesla (John Kelsey et al., 1997): Broadcast
authentication is a critical security service in sensor
networks; it allows a sender to broadcast messages
to multiple nodes in an authenticated way. µTESLA
and multi-level µTESLA have been proposed to
provide such services for sensor networks. The
propose approach removes the authentication delay
as well as the vulnerability to DOS attacks during
the distribution of µTESLA parameters, and at the
same time allows a large number of senders but
requires loosely time synchronization between
senders and receivers.
The danger is that information could be altered when
exchanged over insecure networks. An attacker can
perform a wide variety of attacks (once the attacker
compromised the base station or the aggregators, the
attacker could perform a denial-of-service attack and
stop responding to any queries). Since it is assumed
that a compromised node is under the full control of
the attacker, there is nothing to prevent the attacker
from mounting such denial-of-service attacks.
The approach introduced in (Bartosz Przydatek et
al., 2004) against stealthy attack is for of secure
information aggregation in sensor networks, with
analysis of the attack model and security
requirements. It proposes the aggregate-commit-
prove framework for designing secure information
aggregation protocols; proposes the approach of
forward secure authentication to ensure that even if
an attacker corrupts a sensor node at a point in time,
it will not be able to change any previous readings
the sensor has recorded locally.
Verifying physical presence of a neighbor in
wireless networks is one of the key components in
developing protocols resilient to replay-based
attacks. One of the key issues is how to verify
whether the given two neighbors are actually within
each other’s transmission range or not without
increasing the complexity or requiring additional
hardware; if this fundamental question can be
addressed in an efficient and scalable manner, then
the replay-based attacks can easily be determined
and eliminated by canceling fake neighboring
The Two methods proposed in (Turgay Korkmaz,
2005) are possible solutions with the objective of
increasing the rate of making correct decisions when
checking neighboring relations, supporting and
justifying the proposed ideas.
Focusing on RTS/CTS patterns in a given
neighborhood and analyze them with the objective
of detecting physically impossible neighboring
In a sensor network many risks can result in a loss of
availability such as denial of service attacks etc. In
(Wood et al., 2002) a geographic routing protocol
for sinkhole and wormholes attack is proposed.
Sinkhole and wormholes attacks: geographic
routing protocol - Sensor networks are susceptible
to sinkhole attacks because of their specific
communication pattern, and also because all packets
share the same ultimate destination (in networks
with only one base station). Wormholes are hard to
detect because they use a private, out-of-band
channel invisible to the underlying sensor network.
Sinkholes are difficult to defend against in protocols
that use advertised information such as remaining
energy or an estimate of end-to-end reliability to
construct a routing topology because this
information is hard to verify. The situation becomes
worse when the two are used in combination.
One class of protocols resistant to these attacks is
geographic routing protocols. Geographic protocols
construct a topology on demand using only localized
interactions and information and without initiation
from the base station. Because traffic is naturally
routed towards the physical location of a base
station, it is difficult to attract it elsewhere to create
a sinkhole.
Sybil attack (Karlof et al., 2002) - In a Sybil attack,
a single node presents multiple identities to other
nodes in the network. The Sybil attack can
significantly reduce the effectiveness of fault-
tolerant schemes such as distributed storage, and
multipath. Sybil attacks also pose a significant threat
to geographic routing protocols. Location aware
routing often requires nodes to exchange coordinate
information with their neighbors to efficiently route
geographically addressed packets because by using
the sybil attack, an adversary can “be in more than
one place at once”.
Intrusion and Misbehavior detection:
In sensor networks, many potential sources of faulty
packets exist. The source may be benign, such as a
malfunctioning sensor reporting impossible data, or
the source may be malicious - an outside attacker
performing a denial-of-service by injecting garbage
data, or a compromised node triggering false alarms
or misleading data. As possible solution, Sensor
Node Traceback Scheme (SNTS) to trace malicious
packets into the network is proposed in (Damon
Smith et al., 2004).
As the same time reliable and timely detection of
deviation from legitimate protocol operation is
recognized as a prerequisite for ensuring efficient
use of resources and minimizing performance losses.
The basic feature of attack and misbehavior
strategies is that they are entirely unpredictable. The
random nature of protocol operation together with
the inherent difficulty of monitoring in the open and
highly volatile wireless medium poses significant
Resilience to node capture and ensuring
By using cryptography in the sensors, it is easy to
prevent attacks by unauthorized intruders. On the
other side, cryptography by itself cannot prevent
node capture or inside attackers because in this case
the attacker would have the full control over the
sensor, including the cryptographic keys.
One-time sensors - In (Kemal Bicakci et al., 2005)
the concept of one-time sensors to mitigate node-
capture attacks is proposed by utilizing the low-cost
property of sensor nodes. The idea is to preload
every sensor with a single cryptographic token
before deployment, so that any node can only insert
one legitimate message. If the sensor is captured,
this sensor can only inject a single malicious
message in the sensor network.
However this approach is not an appropriate choice
for applications that require sensors to send arbitrary
messages and the integrity and/or confidentiality of
these messages should be protected, in particular
dealing with medical care sensors.
Robustness against attacks:
WSN protocols need to be able to identify failed
neighbor nodes in real time and to adjust
accordingly to the updated topology. At the network
level, the routing protocol should be made aware of
faulty nodes to ensure that faulty nodes are routed
Self diagnosing sensor nodes - A method of
introducing a level of fault tolerance into wireless
sensor networks is proposed in (Harte et al., 2005),
performed by monitoring the hardware and detecting
the status of physical malfunctions, caused by
impacts or incorrect orientation.
Software analysis is performed on the raw data from
the accelerometers to determine the orientation of
the node and to detect impacts.
Event boundary detection - The main purpose is to
identify the faulty sensors and detection of the reach
of events in sensor networks with faulty sensors.
Two novel algorithms for faulty sensor identification
and fault-tolerant event boundary detection are
proposed and analyzed in (Ding et al., 2005). These
algorithms are purely localized and thus scale well
to large sensor networks. The computational
overhead is low, since only simple numerical
operations are involved. The algorithms can be
applied as long as the “events” can be modeled by
numerical numbers.
Modeling and Detection of Misbehavior in
The pervasiveness of wireless sensor devices and the
architectural organization of wireless sensor
networks in distributed communities, where no trust
can be assumed, are the main reasons for the
growing interest in the issue of compliance to
protocol rules. Reliable and timely detection of
deviation from legitimate protocol operation is
recognized as a prerequisite for ensuring efficient
use of resources and minimizing performance losses.
The basic feature of attack and misbehavior
strategies is that they are entirely unpredictable. In
the presence of such uncertainty, it is meaningful to
seek models and decision rules that are robust,
namely they perform well for a wide range of
uncertainty conditions. One useful design
philosophy is to identify the rule that optimizes
worst-case performance over the class of allowed
uncertainty conditions. The situation is challenging
because several protocols operate in a non-
deterministic manner. Thus the distinction of normal
behavior from occasional misbehavior is not
In a wireless network, information about the
behavior of nodes is available to immediate
neighbors through direct observations. If these
measurements are compared with their counterparts
for normal protocol operation, it is then contingent
upon the detection rule to decide whether the
protocol is normally executed or not. Furthermore,
we propose to study the interaction between the
detection system and the attacker as players
participating in a zero-sum game. On the one hand,
the detection system would like to devise a detection
rule that minimizes detection time of the attacker.
On the other hand, the attacker would like to behave
so as to prolong detection as much as possible.
Therefore, the objective function in that aspect
would be detection time.
The CRUISE project marks the start of a long-term
research and education co-operation initiative among
leading European universities and research institutes
in the field of wireless sensor networks and
applications. The results of CRUISE will be
available to interested European research
organizations, industry, SMEs and to the wide
Wireless sensor networks are a reality. The market
for ZigBee devices, including smart dust, will grow
to 150 million units by 2008 creating a billion dollar
business. Much research has been done. TinyOS is a
good research platform, but not an industry strength
WSNs need killer application. It is not clear what the
killer application is. But certainly environment
monitoring is not.
Nomadic user based WSN routing and Mobile
WSNs represent new challenges to do research and
development in this exciting area. Mobility in
wireless sensor networks poses unique challenges to
the medium access control (MAC) protocol design.
Previous MAC protocols for sensor networks
assume static sensor nodes and focus on energy
This work has been performed in the framework of
the IST-4-027738 NoE CRUISE, which is partly
funded by the European Union. The authors would
like to acknowledge the contribution of their
colleagues from the consortium.
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