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.
