One of the most essential and time critical mobility functions in a mobile system is handover. The main function performed during handover is the connections' switching. In the system under consideration, this function for the network side is allocated in an additional network node, a mobility server, attached to a standard B-ISDN switch. In this paper1 we discuss various algorithms for the implementation of the switching function for the hard handover case. Particularly, the case where there is not sufficient time for establishing the new fixed connections to support the handover is studied. This might happen in environments where the radio link degrades rapidly and so the mobile terminal has to switch to a new base station in order to continue a call. The main focus is on the execution of switching at the network side, inside the mobility server. Alternative cases are studied and an investigation of the time and the places where data losses occur is made. At the end, a first attempt is made to specify a process capable of handling the switching algorithms described.