Dimensioning a policy and charging rules function (PCRF) of a communication system comprises: determining a number of processing nodes of the PCRF at a time; determining a first transaction parameter indicating a number of transactions per second exchanged by the nodes at the time; determining a load parameter indicating processing load of the nodes at the time; based on the first transaction parameter, the load parameter, the number of nodes, and allowable processing load that the nodes are set, determining a second transaction parameter indicating a number of transactions per second expected for exchange at the time by the nodes set at the allowable processing load; forecasting the first and second transaction parameters for a following time thereby obtaining forecasted first and second transaction parameters; and determining a number of nodes required at the following time according to the forecasted first and second transaction parameters.