the ras 1 410 when the terminal 400 accesses the first communication system to receive a first communication service it receives the first communication service over the ras 1 410 and the acr 420 if a load occurs in the first communication system while the terminal 400 is receiving the first communication service the terminal 400 accesses the second communication system in order to receive the first communication service over the second communication system in this case the terminal 400 receives the service over the ras 1 410 that provides the first communication service over the ap 1 440 and the apc 450 or the ap 2 442 and the apc 450 and the interworking unit 495 if the terminal 400 performs handover with an intention to receive the second communication service while receiving the first communication service the terminal 400 performs handover to the second communication system using the intact ip address allocated from the first communication system in this case the ras and the ap each have a physical layer structure and a mac layer structure supporting heterogeneous devices next the following description will be made for the exemplary case where the terminal 400 receives the second communication service over the ap 1 440 when the terminal 400 accesses the second communication system to receive the second communication service the terminal 400 receives the second communication service over the ap 1 440 and the apc 450 if a load occurs in the second communication system while the terminal 400 is receiving the second communication service the terminal 400 receives the second communication service over the first communication system that is the terminal 400 accesses the first communication system and receives the service over the apc.