Switched Ethernet is now considered as an attractive enabling technology for supporting factory communication needs. This paper deals with the modelling of an Ethernet switch and the performance evaluation of its real-time features. For multiple priority periodic and single priority aperiodic input traffic, methods for calculating respectively the worst case buffering delay and buffering delay probability distribution are given, allowing thus to estimate both hard real-time and soft real-time guarantees. Moreover for aperiodic traffic, Binomial input is compared to the Poisson one and we numerically showed that the Poisson case could be used as an approximation model to upper bounds the buffering delay of the actual switch. This allowed us to further consider the priorities for buffering delay evaluation using classic results of M/G/1 queue