A Methodology for Modeling and Evaluating the Reliability of a Radio-communication Network Mohamed-Larbi Rebaiaia*’**, Daoud Ait-Kadi*’**, Arturo Merlano* *Department of Mechanical Engineering, Faculty of Science and Engineering, University of Laval, Quebec (QC), Canada (Tel:1 418-651-6947; e-mail: Mohamed-larbi.rebaiaia@ cirrelt.ca; Arturo.merlano.1@ulaval.ca) ** Interuniversity Research Centre on Enterprise Networks, Logistics and Transportation, Laval University, Quebec, Canada (email:Daoud.Aitkadi@gmc.ulaval.ca) Abstract: To evaluate the performance of a radio-communication network we need to check that communications between users are working normally and that hardware/software system components are up and remain ensuring their mission. The methodological basis of this work consists of modeling and computing the reliability and the availability of a radio-communication network that meets the communication needs of an entire province. A generic multi-components system is postulated to cover our study. We present first the description of the system followed by calculus rules and the reliability evaluation models of components and subsystems. Keywords: Radio communication network, Reliability, Performance indexes, Quality of services.  1. INTRODUCTION When defining the performance of complex and critical systems like radio communication networks, it is important to specify system performance across different concepts. Some of these concepts are commonly named dependability, fault- tolerance, reliability, availability, security and surviviability. They are defined as indicators from which it is possible to measure the performance of a system. In our study we consider the couple reliability and availability as performance indicators. Note that the IEEE 90 standard defines the reliability as the ability or the probability of a system to perform its required functions under stated conditions for a specified period of time and availability may be interpreted as the probability that a system is operational at a given point in time. Maintainability is defined as the probability of performing a successful repair action within a given time. Most frequent mathematical expressions of these probabilities are well-known. The reader is invited to consult Ebeling et al. (2005) for precise details. Nowadays, the analysis of system performance is a crucial test, rough and with major difficulties. This complexity has become indispensable because of the integration of the products of diverse manufactures and technologies (e.g. Motorola, Cisco). Computing the reliability of a system depends of the specification of the reliability of each piece of equipment being powered. Missing one piece will generate false values in computing the system performance and can have dramatic consequences. For instance, a manufacturer of equipment may specify the failure rate estimated using an accelerated degrading testing when no failures statistics are available. In this work we present some of the results recorded in the report of a research project realized by our team as consultants. The project has been entrusted by the telecommunication services of the government of Quebec (Canada). The main objective was to assess the reliability of the radio network covering the entire province of Quebec. This requirement condition was imposed by public and private users for the renewal of their service contracts. As the system is a new network that has just been installed on several stages since early 2000, therefore, the first finding is to be sure that the network as such does not suffer from breakage of certain materials which have not had a disastrous consequence on the functioning of the network. That said, at first sight, it is assumed that the system is correct and one could roughly estimate the reliability of the network on the basis of this assumption. Thus, this finding is not a logical proof to be given to customers that the network is high reliable without giving them an exact value such as 95%. For this purpose, our assessment made sense of quantifying the reliability of the network as a value, the most precise possible. Following our experience in the conduct of the project, it has shown that network failures can occur for a variety of reasons. In most cases, the causes are accidental, inexperienced technicians, natural (wind, frost, ice) and defaults of spare parts. A preliminary description has been published in Rebaiaia et al. (2009). The approach presented herein is comparable with the study done by Willett et al (1988). The difference between the two works is that, their methodology is applied to a shortwave broadcast relay station and is evaluated in term of the number of broadcast hours delivered to the assigned coverage areas. The authors present three models: one for covering the