Method for handover between heterogeneous communications networks

The present invention relates to the method of maintaining communication between the 2nd unit (2) that communicates through the 1st mobile unit (1) and 2nd communication network (A2) that communicate through the 1st communication network (A1), a computer program product, and the medium that can be computer read. The 1st unit (1) contains the 1st protocol stack (12), and the 2nd unit (2) contains the 2nd protocol stack (22). The 1st unit (1) contains the 1st session layer (11) that conforms so that it may function as an interface between the 1st protocol stack (12) and the 1st software component (15) that operates within the 1st unit (1). Similarly, the 2nd unit (2) contains the 2nd session layer (21) that conforms so that it may function as an interface between the 2nd protocol stack (22) and the 2nd software component (25) that operates within the 2nd unit (1). The 1st unit (1) contains one or the 1st two communication hardwares or more (13a, 13b, 13c, 13d) relevant to the drive routine (12a, 12b, 12c, 12d) which suited a different communication network (A1, A2, A3, A4). When the 1st unit (1) performs the change (A1*3) to the 3rd communication network (A3) from the 1st communication network (A1), the 1st session layer (11), By choosing the 1st communication hardware (13b) and drive routine (14b) that are needed for the 3rd communication network (A3), it functions as maintaining communication. Each identification information of the 1st and 2nd units (1, 2) is held by the 1st and 2nd session layers (11, 21), and these identification information is maintained during the change of the communication network by the 1st unit (1).