In an industrial or technical context, some of the communications are strongly time-constrained. Our objective is to evaluate the service offered by a switched Ethernet architecture. We have chosen the network calculus theory because it gives a good representation of the exchanges and enables to determine the maximum end to end delays. Previous models implementing a strict priority policy presented in [A formal method to guarantee a deterministic behaviour of switched Ethernet networks for time-critical applications] are improved in order to take into account the Weighted Fair Queueing mechanism which enables to balance the allocation of the network to the different traffics regarding the time contraints they have to respect. This paper also presents the new analytical formulas which upper bound the maximum end-to-end delays of the time-critical messages over the whole network. This enables to determine the optimal bandwith dedicated to both critical and best effort traffics. On an industrial scenario, Strict Priority and Weighted Fair Queueing policies are finally compared.