Design modeling and simulation of a repeaterless optical fiber network for Sri Lanka

Abstract

A reliable and wideband telecommunication network is a vital infrastructure development, where wide band services such as ATM, ADSL and IP based services could be supported. In Sri Lanka, the requirement of this kind of an optical network is very significant as other operators also can share the capacity of the network for transporting their traffic. On the other hand the network problems such as excessive BER (Bit Error Rate) etc are experienced after its construction. In order to avoid such limitations in the network, the network needs to be modeled on appropriate software tools and run with designed network parameters, so that the desired BER could be ensured. During the initial phase of the study, the total telephone demand by year 20If was estimated as nearly 2 million subscribers. This was estimated through the world trend for telephone subscribers together with economic indicators such as GNP and GDP. The Nodes of the Network was determined based on the present distribution of customers in the County. In this case all the Tertiary Switching Center areas and the Secondary Center Areas where the customer base is more than 2.5% of total customers were taken as the main nodes of the network. In addition Jaffna and Baticaloa were also taken as nodes considering the potential growth of traffic in northern and eastern parts of the Island. The Gravity model and Earlang's E formula, traffic tables, were used to find the traffic between nodes and the number of circuits between nodes. Based on the traffic distribution between nodes, a part of the network was proposed as a fully reliable Ring Network, while other nodes are connected through extended links. The IP traffic, which is thought to be the major traffic flow in the future, were estimated considering the broadband Internet growth in the country. Also the traffic, which are expected to be migrated from traditional PSTN to IP Network were identified and estimated to find the total bandwidth requirement of the network by year 2015 The number of wavelengths in the proposed Network were decided based on the final bandwidth requirement. This resulted an island wide network consisting of WDM Ring Network having 08 wavelengths that basically covers the southern part of the country and two other extensions having a wavelength each to northern and eastern parts of the country. The Colombo and the Kandy nodes were selected as Full Fiber Terminal Stations as most of the traffic flow between these two nodes. Wavelengths are added and dropped at each branch station based on the traffic volumes between these nodes. The wavelengths were selected such that the. space between adjacent wavelengths is 0.8rm to avoid nonlinear effects and cross talks. The G-655 non-zero dispersion fiber was selected to mange the dispersion and non-linear effects. DFB and APD are the Source and the Detector respectively to suit long I ransmissions having arrow pectra widths and also I o meet better sensitivity at the receiver.