A valve unit is connected to a fixed member and an external member. The at least one selected shift element of the first group can be actuated in phase or with an overlapping phase displacement or an offset phase displacement with respect to the at least one selected shift element of the second group. The system and method comprising a subscription module for identifying a port type with each notification method added to a description of the synchronous service and for associating a subscription operation with the identified port type. The distance sensing module is used to detect the distance between a body and the displacement detecting device, and then produces a sensing value.