Three configurations of Ethernet networks that operate in duplex mode at relatively low load of transmission media are investigated. Configurations differ by number of collision domains and switches used in the network. To investigate the dependences among basic parameters, analytic models of the functioning of such networks are elaborated. Calculations made for a relatively large set of values of initial data confirm the necessity of case dependent special investigations on the physical configuration of concrete Ethernet networks. It has been determined, for example, that the fragmentation doesn't necessarily permit to increase the number of stations in the network; it may be even vice versa.