Abstract – Wireless ad hoc sensor networks (WASNs) are in need of the study of useful applications that will help the researchers view them as distributed physically coupled systems, a collective that estimates the physical environment, and not just energylimited ad hoc networks. We develop this perspective using a large and interesting class of WASN applications called aggregation applications. In particular, we consider the challenging periodic aggregation problem where the WASN provides the user with periodic estimates of the environment, as opposed to simpler and previously studied snapshot aggregation problems. In periodic aggregation our approach allows the spatial-temporal correlation among values sensed at the various nodes to be exploited towards energy-efficient estimation of the aggregated value of interest. Our approach also creates a system level energy vs. accuracy knob whereby the more the estimation error that the user can tolerate, the less is the energy consumed. We present a distributed estimation algorithm that can be applied to explore the energy-accuracy subspace for a sub-class of periodic aggregation problems, and present extensive simulation results that validate our approach. The resulting algorithm, apart from being more flexible in the energy-accuracy subspace and more robust, can also bring considerable energy savings for a typical accuracy requirement (five-fold decrease in energy consumption for 5 % estimation error) compared to repeated snapshot aggregations.

The next generation of high energy physics experiments, such as the Large Hadron Collider (LHC) at CERN, the European Organization for Nuclear Research, pose a challenge to current data handling methodologies, where data tends to be centralised in a single location. Data grids, including the LHC Computing Grid (LCG), are being developed to meet this challenge by unifying computing and storage resources from many sites worldwide and distributing data and computing tasks among them. This thesis describes the data management components of LCG and evaluates the perfor-mance of the LCG File Catalogue, showing it to be performant and scalable enough to meet the experiments ’ needs. File replication can be used to improve a grid’s performance by placing copies of data at strategic locations around the grid. Dy-namic file replication, where replicas are created and deleted automatically according to some strategy, may be especially useful and so the grid simulator OptorSim was developed to investigate different replication strategies. Simulation of several grid scenarios, including LCG, shows that relatively simple replication strategies can lead to significant reductions in data access times and improved usage of grid resources, while a more complex economic model may be useful in future. Gu mo theaghlach-anns a h-uile àite. He reached down from on high and took hold of me; he drew me out of deep waters. He rescued me from my powerful enemy, from my foes, who were too strong for me. They confronted me in the day of my disaster, but the LORD was my support. He brought me out into a spacious place; he rescued me because he delighted in me.

Abstract:- A number of Denial of Service (DoS) attacks in IEEE 802.11 are due to unauthenticated/ unencrypted management and control frames. Current IEEE 802.11 simulators deal with Physical and MAC layers and do not include the exchange of management and control frames, thus making it difficult to simulate an attack (DoS) and its possible solution. A basic IEEE 802.11 network simulator using Verilog is presented. Basic aim is to design a simulator using a hardware description language (HDL) such as Verilog, since the functions and protocols described in state machines are best simulated using a HDL. Besides simulation of a simple wireless network, the paper also presents simulation of a spoofed MAC disassociation DoS attack and one of its possible solutions. The proposed simulator includes the communication setup process and can be used for simulating other DoS attacks and their possible solutions. Key-Words:- Network Simulator, IEEE 802.11, Verilog, Wireless LAN, Link layer simulation.