Common planning practices for network dimensioning, under traffic uncertainty

As a network is dimensioned to cope with future traffic, forecasts have to be used. In this paper we identify some parameters to describe such an uncertain forecast. We distinguish the predicted value for the considered variable (e.g. based on an expert´s view) and an uncertainty level that indicates the doubt there is about the used forecast. Three possible implementations of an uncertain value are presented, which allow us to formalize some common planning practices that use a fixed safety margin to handle uncertainty. We show that it is very difficult to choose an appropriate value for this margin and that a wrong choice may lead to unexpected results. In a case study we consider the dimensioning of a pan-European network subject to uncertain traffic forecasts, under different protection schemes.