Engineering planar separator algorithms

We consider classical linear-time planar separator algorithms, determining for a given planar graph a small subset of the nodes whose removal separates the graph into two components of similar size. These algorithms are based upon Planar Separator Theorems, which guarantee separators of size asymptotically in the square root of the number of nodes n and remaining components of size less than 2n/3. In this work, we present a comprehensive experimental study of the algorithms applied to a large variety of graphs, where the main goal is to find separators that do not only satisfy upper bounds but also possess other desirable qualities with respect to separator size and component balance. We propose the usage of fundamental cycles, whose size is at most twice the diameter of the graph, as planar separators: For graphs of small diameter the guaranteed bound is better than the bounds of the classical algorithms, and it turns out that this simple strategy almost always outperforms the other algorithms, even for graphs with large diameter

Attack propagation in networks

A new model for intrusion and its propagation through various attack schemes in networks is considered. The model is characterized by the number of network nodes n, and two parameters f and g. Parameter f represents the probability of failure of an attack to a node and is a gross measure of the level of security of the attacked system and perhaps of the intruder’s skills; g represents a limit on the number of attacks that the intrusion software can ever try, due to the danger of being discovered, when it issues them from a particular (broken) network node. The success of the attack scheme is characterized by two factors: the number of nodes captured (the spread factor) and the number of virtual links that a defense mechanism has to trace from any node where the attack is active to the origin of the intrusion (the traceability factor). The goal of an intruder is to maximize both factors. In our model we present four different ways (attack schemes) by which an intruder can organize his attacks. Using analytic and experimental methods, we first show that for any 0 < f < 1, there exists a constant g for which any of our attack schemes can achieve a �(n) spread and traceability factor with high probability, given sufficient propagation time. We also show for three of our attack schemes that the spread and the traceability factors are, with high probability, linearly related during the whole duration of the attack propagation. This implies that it will not be easy for a detection mechanism to trace the origin of the intrusion, since it will have to trace a number of links proportional to the nodes captured

Dap: A generic platform for the simulation of distributed algorithms

DAP (Distributed Algorithms Platform) is a generic and homogeneous simulation environment aiming at the implementation, simulation, and testing of distributed algorithms for wired and wireless networks. In this work, we present its architecture, the most important design decisions, and discuss its distinct features and functionalities. DAP allows the algorithm designer to implement a distributed protocol by creating his own customized environment, and programming in a standard programming language in a style very similar to that of a real-world application. DAP provides a graphical user interface that allows the designer to monitor and control the execution of simulations, visualize algorithms, as well as gather statistics and other information for their experimental analysis and testing. 1