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Protocols for Secure Communication in Wireless Sensor Networks

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2.7. Security Requirements 41<br />

teractions between nodes, <strong>for</strong> example radio <strong>in</strong>terference through concurrent<br />

medium access, are not considered. This simplifies the simulation of node processes,<br />

which can be executed strictly sequentially as <strong>in</strong>terleav<strong>in</strong>gs between<br />

concurrent processes do not have to be considered. This allows the simulation<br />

of sensor networks on a much larger scale. A direct comparison between different<br />

simulation environments shows that network-based simulation is able to<br />

handle at least two orders of magnitude more nodes than node-level simulation<br />

[98].<br />

In contrast to node-level simulation, simulation on the network level is more<br />

appropriate <strong>for</strong> evaluat<strong>in</strong>g and test<strong>in</strong>g algorithms and protocols on a higher,<br />

more abstract level. This shifts the focus from implementation details to a<br />

global view, which is more appropriate <strong>for</strong> study<strong>in</strong>g aspects such as collaboration,<br />

accuracy, correctness, failure tolerance, and security on a network-wide<br />

level. For example, Michiardi and Molva [123] study, by network-level simulation,<br />

the impact of malicious node behaviour on rout<strong>in</strong>g quality <strong>in</strong> mobile ad<br />

hoc networks. Their metrics <strong>in</strong>clude the fraction of dropped packets as well as<br />

delays.<br />

In summary, we regard network-level simulation as an important tool <strong>in</strong> the<br />

follow<strong>in</strong>g areas:<br />

• Test<strong>in</strong>g algorithms and protocols <strong>in</strong> large-scale networks dur<strong>in</strong>g the design<br />

phase. Algorithms can be specified on an abstract level without the<br />

obligation of giv<strong>in</strong>g an implementation <strong>for</strong> a concrete plat<strong>for</strong>m. The environment<br />

is idealized, but the effects of natural disruptions, such as connectivity<br />

fluctuations, can be modelled if necessary.<br />

• Study<strong>in</strong>g emergent properties of large-scale networks. Certa<strong>in</strong> properties<br />

emerge only from the <strong>in</strong>teractions of a large number of nodes. They are not<br />

necessarily anticipated dur<strong>in</strong>g the design phase, but could be uncovered by<br />

simulation done <strong>in</strong> an early phase.<br />

• Validation of security assessments. The security of s<strong>in</strong>gle nodes does not<br />

necessarily imply the security of the overall network. It is there<strong>for</strong>e important<br />

to provide means to establish security properties on a network-wide<br />

level. This is the most relevant po<strong>in</strong>t throughout this work.<br />

2.7 Security Requirements<br />

A number of general security vulnerabilities of sensor networks can be identified,<br />

such as <strong>in</strong> the transmission of messages, on the rout<strong>in</strong>g layer, or regard<strong>in</strong>g

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