The ILP model is supposed to calculate the optimal required number of donors by running over a 7-day planning horizon. At the same time, the DES would account for the uncertainty in supply and demand, based on probability distribution fitted from historical data routinely collected in all blood centres. The system state is updated at the begging of each day where the ILP algorithm will run the calculations for the next seven days. The DES will handle simulations of the centre's operations on that day, distributing blood to several demand points. The proposed method can be classified as an "alternative Optimisation-based Simulation (IOS)". The ILP model optimised a cost function composed of production costs, penalties for expired unites, number of stockouts and violation of the blood groups proportionality constraints (Osorio 2016).