Bum-Joo Park

Representing the Voronoi diagram of a simple polygon using rational quadratic Bézier curves

Abstract The Voronoi diagram of a set of geometric entities on a plane, such as points, line segments, or arcs, is a collection of Voronoi polygons associated with each entity, where the Voronoi polygon of an entity is a set of points which are closer to the associated entity than any other entity. A Voronoi diagram is one of the most fundamental geometrical constructs, and it is well known for its theoretical elegance and the wealth of applications. Various geometric problems can be solved with the aid of Voronoi diagrams. The paper discusses an algorithm to construct the Voronoi diagram of the interior of a simple polygon which consists of simple curves such as line segments as well as arcs in a plane with O(N log N) time complexity by the use of a divide-and-conquer scheme. Particular emphasis is placed on the parameterization of bisectors using a rational quadratic Bezier curve representation which unifies four different bisector cases.

A self-healing mechanism for an intrusion tolerance system

The dependability analysis of an ITS (Intrusion Tolerance System – a system that performs continuously minimal essential services even when the computer system is partially compromised because of intrusions) is essential for the design of the ITS. In this paper, we applied self-healing mechanism, the core technology of autonomic computing to analyze the dependability of the ITS. In other words, we described the state transition of the ITS composed of a primary server and a backup server utilizing two factors of self-healing mechanism (fault model and system response) and analyzed it using M/G/1 queuing technique. We also evaluated the availability of the ITS through simulation experiments.

A Mechanism for Improving Web Server Performance Using Fuzzy Concept

This paper presents a mechanism to improve Web server performance with fuzzy-based techniques. A load balancing mechanism based on the fuzzy control technique is developed in such a way that ambiguous situations caused by workload estimation of cluster- based Web servers, client request rates, and dynamic request rates can be represented in an effective way. Extensive experiments show that the fuzzy-based performance isolation technique improves the performance of Web servers in terms of the 95- percentile response times.

A Survivability Model of an Intrusion Tolerance System

There have been large concerns about survivability defined as the capability of a system to perform a mission-critical role, in a timely manner, in the presence of attacks, failures. In particular, One of the most important core technologies required for the design of the ITS(Intrusion Tolerance System) that performs continuously minimal essential services even when the computer system is partially compromised because of intrusions is the survivability one of In included the dependability analysis of a reliability and availability etc. quantitative dependability analysis of the In. In this Paper, we applied self-healing mechanism utilizing two factors of self-healing mechanism (fault model and system response), the core technology of autonomic computing to secure the protection power of the ITS and consisted of a state transition diagram of the ITS composed of a primary server and a backup server. We also defined the survivability, availability, and downtime cost of the ITS, and then performed studies on simulation experiments and two cases of vulnerability attack. Simulation results show that intrusion tolerance capability at the initial state is more important than coping capability at the attack state in terms of the dependability enhancement.