            !" ##$ !%&’&’"( 129 Case Study: Core Network Design using Graph Theory Method Amer Daeri Computer Engineering Department Zawia University Zawia, Libya ibnjubair1@yahoo.co.uk Rajab Ibsaim Electrical and Electronics Engineering Department Zawia University Zawia, Libya rabsaim@yahoo.com Abstract— In recent years, due to the vast amount of information that is being exchanged between people and the diversity of the type of this information as well as the introduction of the Internet into the public domain in the beginning of the 1990s. The information revolution and the introduction of the Internet made many organizations think about utilizing these benefits for their own use, which ultimately lead to the introduction of the Intranet in the middle of the 1990s, which uses web technology within the boundaries of an organization, This paper is concerned with finding the best method to connect the various faculties and other services in Tripoli University in order to implement an intranet using a unified switched Local Area network, based on the assumption that there exists an infrastructure of underground conduits suitable for laying fiber optical cables. The paper assumed the use of single mode fiber cables to connect the various buildings in the core network. In this paper the graph theory criteria, namely, the hop count, the average path length and the number of geodesics were used as bases to select the most suitable topology. But the result of the graph theory method was not decisive in selecting a topology from the three compared topologies (Star, Ring and Partial Mesh). Hence a management tool known as the Analytic Hierarchy Process (AHP) was employed to reach a decisive decision. The Partial Mesh topology was the selected topology according to the AHP result. KEYWORDS: GRAPH THEORY, SWITCHED NETWORK, TOPOLOGY, PATH LENGTH, GEODESICS, HOP COUNT. I. Introduction In modern network design, the network infrastructure is usually divided to modules for ease of design and visualization. This modular approach known as the hierarchy model. The network is divided to three layers known as the core, distribution and access. These layers are not necessarily to be physically separate, but it is a separation for ease of visualization. This paper is concerned with the core layer of Tripoli university section 'A' proposed network. The work proceeded as follows: o It is started by data collection through personal interviews with the head of the university engineering office and some of the staff to gather information on the existing facilities that can be utilized such as existing cable conduits running between the various faculties and the population for each faculty in the university's section 'A'. o Based on the information collected, the nodes for the network were selected. o A set of measures were applied to the most commonly used topologies namely Star, Ring and Partial Mesh based on graph theory to select the most appropriate alternative of connecting a number of nodes using the analytic hierarchy process method. II. Selected Nodes 9 nodes were selected for the university section 'A' core network. Table (1) shows the list of the selected nodes and their abbreviations. Table (1) Node Name abbreviation Node name Abbreviation Veterinary VET Agriculture AGR Pharmacy & medical technology PH&MT Medicine MED