In a mobile communication network some nodes change location, and are therefore connected to different other nodes at different points in time. We show how such a network can be formally defined and verified using the p-calculus, which is a development of CCS (Calculus of Communicating Systems) allowing port names to be sent as parameters in communication events. An example of a mobile network is the Public Land Mobile Network currently being developed by the European Telecommunication Standards Institute. We concentrate on the handover procedures which controls the dynamic topology of the network