Analysis Of Optimisation Issues In Multi-Period DWDM Network Planning

medium-size national network is optimised using the various techniques, and the results presented in terms of the total number of DWDM systems required and the amount of wavelength-hops (giving an indication toward the number of optical transponders required). Traffic is taken as a mix between unprotected and 1+1 SNCP optical path protected demands. Traffic growth is applied over the 5 year planning horizon to give a tenfold increase in total traffic volume for the final year. A greenfield situation is assumed, yet since deployment occurs over several years, a Present Value calculation is used to estimate total cost, assuming that transponders and systems are only installed when they are due to be 'lit'. A. INTRODUCTION Network operators are currently deploying DWDM-based (Dense Wavelength Division Multiplexing) optical transport networks to meet the tremendous bandwidth requirements caused by the explosive growth in Internet traffic, increased competition forcing down tariffs for voice calls, and corporate Virtual Private Networks spanning the globe. DWDM is seen as an effective solution for this rush for bandwidth. Optical channels can be set up between nodes based on wavelengths within the transmission system. Different rate client signals can also be accommodated, e.g. 2.5GHz and 10GHz, on the same network, as well as very different service types, e.g. SDH and Gigabit Ethernet. A consensus has been reached to implement a channel-associated overhead, to be transmitted as a digital TDM 'wrapper' [1]. This framing means that Optical Transport networks will not be transparent, as originally thought, but gives opportunity for powerful channel management using the optical header, and strong forward error correction to increase the maximum fibre reach and reduce the Optical Amplifier requirement. Current commercially available systems can offer up to 80 optical wavelengths on a single fibre. Many DWDM line systems include modular components, allowing an incremental growth of channels, spreading network investment over the lifetime of the network. Therefore careful optimisation of the network design is required over the typical five year planning horizon to give a cost-effective network meeting any budgetary restrictions for the installation or upgrading of equipment in each annual period. This results in the term Multi-period planning. Towards the end of a planning horizon, the traffic forecasts are at best loose estimates. Flexibility of a network in terms of traffic growth and churn is an important feature. Availability of the network is a key factor to allow the provisioning of service level agreements. …