Disclosed is a method of controlling a session in a serving server taking charge of the control plane within a mobile communication network. The control method may include receiving, by the serving server, a tracking area update (TAU) request message of a terminal from a target base station; retrieving, by the serving server, a previous server that has taken charge of the control plane for the terminal; receiving, by the serving server and from the retrieved previous server, a context response message comprising information indicating that a session for the terminal had been established to be passed through a path over the nodes within a fixed network different from a mobile communication network; deciding, by the serving server, whether gateway relocation is needed; releasing, by the serving server, the established session; transmitting, by the serving server, an accept message comprising information for the processing result to the terminal through the target base station; and establishing, by the serving server a session passing through a path over the nodes within a fixed network different from a mobile communication network based on the information.