Sensor networks hold the promise of facilitating large-scale, real-time data processing in complex environments. Their foreseeable applications will help protect and monitor military, environmental, safety-critical, or domestic infrastructures and resources.In these and other vital or security-sensitive deployments, keeping the network available for its intended use is essential. The stakes are high: Denial-of-service (DoS) attacks against such networks may permit real-world damage to the health and safety of people. Without proper security mechanisms, networks will be confined to limited, controlled environments, negating much of the promise they hold. The limited ability of individual sensor nodes to thwart failure or attack makes ensuring network availability more difficult.To identify DoS vulnerabilities, we analyze two effective sensor network protocols that did not initially consider security. These examples demonstrate that consideration of security at design time is the best way to ensure successful network deployment. THEORY AND APPLICATIONAdvances in miniaturization combined with an insatiable appetite for previously unrealizable information gathering have led to the development of new kinds of networks. In many areas, static infrastructures are giving way to dynamic ad hoc networks.One manifestation of these trends is the development of highly application-dependent sensor networks. Developers build sensor networks to collect and analyze low-level data from an environment of interest. Accomplishing the network's goal often depends on local cooperation, aggregation, or data processing because individual nodes have limited capabilities. Physically small, nodes have tiny or irreplaceable power reserves, communicate wirelessly, and may not possess unique identifiers. Further, they must form ad hoc relationships in a dense network with little or no preexisting infrastructure.Protocols and algorithms operating in the network must support large-scale distribution, often with only localized interactions among nodes. The network must continue operating even after significant node failure, and it must meet real-time requirements. In addition to the limitations imposed by applicationdependent deadlines, because it reflects a changing environment, the data the network gathers may intrinsically be valid for only a short time.Sensor networks may be deployed in a host of different environments, and they often figure into military scenarios. These networks may gather intelligence in battlefield conditions, track enemy troop movements, monitor a secured zone for activity, or measure damage and casualties. An airplane or artillery 1 could deploy these networks to otherwise unreachable regions.Although military applications may be the easiest to imagine, much broader opportunities await. Sensor networks could form an impromptu communications network for rescue personnel at disaster sites, or they could themselves help locate casualties. They could monitor conditions at the rim of a volcano, along an earthquake fault, or ...

Wireless Sensor Networks have been proposed for a multitude of location-dependent applications. For such systems, the cost and limitations of the hardware on sensing nodes prevent the use of range-based localization schemes that depend on absolute pointto-point distance estimates. Because coarse accuracy is sufficient for most sensor network applications, solutions in range-free localization are being pursued as a cost-effective alternative to more expensive range-based approaches. In this paper, we present APIT, a novel localization algorithm that is range-free. We show that our APIT scheme performs best when an irregular radio pattern and random node placement are considered, and low communication overhead is desired. We compare our work via extensive simulation, with three state-of-the-art range-free localization schemes to identify the preferable system configurations of each. In addition, we study the effect of location error on routing and tracking performance. We show that routing performance and tracking accuracy are not significantly affected by localization error when the error is less than 0.4 times the communication radio radius.

Wireless Sensor Networks have been proposed for a multitude of location-dependent applications. For such systems, the cost and limitations of the hardware on sensing nodes prevent the use of range-based localization schemes that depend on absolute pointto-point distance estimates. Because coarse accuracy is sufficient for most sensor network applications, solutions in range-free localization are being pursued as a cost-effective alternative to more expensive range-based approaches. In this paper, we present APIT, a novel localization algorithm that is range-free. We show that our APIT scheme performs best when an irregular radio pattern and random node placement are considered, and low communication overhead is desired. We compare our work via extensive simulation, with three state-of-the-art range-free localization schemes to identify the preferable system configurations of each. In addition, we study the effect of location error on routing and tracking performance. We show that routing performance and tracking accuracy are not significantly affected by localization error when the error is less than 0.4 times the communication radio radius.

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