The use of Ethernet protocol for railway vehicle on-board networks is considered. It is shown that a single Ethernet network can carry real-time control data, thus replacing existing train control networks. In addition, this network can also carry entertainment data for passengers as well as data coming from mobile wireless devices carried on-board. OPNET simulations are used to estimate the maximum allowable entertainment traffic that can be carried by the network while satisfying the real-time constraints of the control traffic.