Packet switching networks are an attractive way of transmitting bursty data traffic, due to the extensive resource sharing they allow. This sharing, however, has to be done in an orderly way, securing a fair access to the network resources by all users. In this work, a detailed analysis of all existing fairness definitions is first made and then two new techniques to evaluate fairness are proposed. One scheme is conceptually more rigorous and assumes that the ratio between a penalty measure and a congestion measure should be constant for all network users. The second method employs only the penalty measure but it requires much less computing time. Both techniques assume that the network operates with window flow control. One important feature of the two schemes proposed is that they allow the users to select which parameter, delay or throughput, is more important for them. Several examples illustrating the behavior of the two methods are also presented.