Image Processing & Communication, vol. 13,no. 1-2, pp. 1-1 1 Comparing the Reliability of Regular Topologies on a Backbone Network. A Case Study. SERGIO LABEAGA,J OSE GUTIERREZ,TAHIR RIAZ ,J ENS PEDERSEN Networking and Security Section, Department of Electronic Systems, Aalborg University, Niels Jernes Vej 12, 9220, Aalborg, Denmark mailto: sl@es.aau.dk Abstract The aim of this paper is to compare the reliability of regular topologies on a backbone net- work. The study is focused on a large-scale fiber- optic network. Different regular topological solu- tions as single ring, double ring or 4-Regular grid are applied to the case study, and compared in terms of degree, diameter, average distance, economical cost and availability. Furthermore, other non-quantitative parameters such as expandability, embeddability and algorithmic support are introduced. Key words regular topologies, backbone, grid, N2R, double ring, comparison, availability study. 1 Introduction The use of regular topologies in backbone networks has been studied in detail in the past with satisfactory results [1]. Furthermore, year after year, users and companies demand more and more bandwidth, lower delay and higher network availability [2] [3]. Communication networks play an important role in many social and economic activities. Interruptions in data transmission and exchange, even for a short period of time, can suspend critical operations and lead to a significant loss of revenue. Furthermore, new emerging services as telemedicine and e-health care will increase even more, the necessity of design- ing more and more reliable networks [4]. Even though protocols are being developed to en- sure reliability [5], the physical network structures limit the level of reliability that can be offered: two nodes can only communicate if there is a physical link between them. Traditionally, rings have been used as alternatives to tree structures. Rings offer connectivity in case of any single failure. However, given the expected demands of availability, this is likely to become in- sufficient in near future. More information about re- dundancy in ring topologies can be found in [6] and [7]. This document studies the applicability of differ- ent regular topologies as backbone for a regional network. The access technology -in this regional network- was a combination of FTTH and WiMAX technologies. Both qualitative and quantitative parameters are used in the comparison, e.g. connectivity number, economical cost, availability, support to topological routing, etc. The main goal is to evaluate how these regular topologies perform as solutions for back- bones, and compare them to single ring solutions, paying special attention to two key parameters: the economical cost and the availability that they can provide. The three main reasons for analyzing regular topologies are: 1. It is possible to define and document well- known parameters and metrics which ease the network characterization. Besides, based on well-known metrics, it is easy to compare dif-