A GENETIC ALGORITHM APPROACH TO OPTIMAL TOPOLOGICAL DESIGN OF ALL TERMINAL NETWORKS BERNA DENGIZ AND FULYA ALTIPARMAK Department of Industrial Engineering Gazi University, Ankara, TURKEY 06570 ALICE E. SMITH 1 Department of Industrial Engineering University of Pittsburgh, Pittsburgh, PA 15261 ABSTRACT: In the design of communication networks, one of the fundamental considerations is the reliability and availability of communication paths between all terminals. Together, these form the network system reliability. The other important aspect is the layout of paths to minimize cost while meeting a reliability criterion. In this paper, a new heuristic search algorithm based on Genetic Algorithms (GA) is presented to optimize the design of large scale network topologies subject to a reliability constraint. The search works with an improved Monte Carlo simulation technique to estimate the system reliability of a network topology. 1 Corresponding author. INTRODUCTION An important part of network design is to find the best way to layout the components (nodes and arcs) to minimize cost while meeting a performance criterion such as transmission delay, throughput or reliability. This design stage is called “Network Topological Optimization”. In a topological network design problem, a main concern is to design networks which operate effectively and without interruption in the presence of component failures. Reliability is concerned with the ability of a network to carry out desired network operations. Generally, a large scale network has a multilevel, hierarchical structure consisting of a backbone network and several local access networks (Boorstyn et al, 1977). Therefore, designing the topology of a large scale network can be divided into two problems, the backbone network design and the local network design. This study is mainly interested in large scale backbone network design. For backbone network design, an important connectivity measure is reliability. In a communication network, all terminal network reliability can be defined as the probability that every pair of nodes can communicate with each other (Jan et al, 1993; Colbourn, 1987). Many studies have considered topological optimization with a network reliability criterion. For example, Jan et al (1993) used a decomposition method based on branch and bound to minimize total network cost under a system reliability