LTE/EPC is an all-IP mobile system which provides higher data rates and lower latency. Nevertheless guaranteeing the QoS is a real challenge since the LTE/EPC QoS model inherits many characteristics of circuit oriented legacy standards. Contrary to usual QoS models of the fixed internet (IP networks), additional signalling procedures are required in order to establish a dedicated bearer for each desired QoS level. This paper introduces an analytical model to evaluate the impact of such a QoS model in terms of Processing Load. Simulation results are then presented to evaluate the impact of different scenarios of QoS deployment.