The present invention relates to radio communications between a terminal, a radio node and a core network in a radio communication system. A radio node, which can form a radio link to a terminal through a first radio interface by a first radio protocol and a second radio interface by a second radio protocol, may transmit, to the terminal, function structure type information about a mobility management-related function which can be performed through the first radio interface by the first radio protocol, form a radio link to the terminal through the second radio interface by the second radio protocol, establish a connection between the terminal and a core network by a non-access stratum (NAS) protocol if the terminal requests a connection between the terminal and the core network through the second radio interface, release the radio link, and perform the mobility management-related function through the second radio interface by communicating with the terminal.