With a system having no paging function, dead peer detection control and cutoff of a session are implemented as is the case with a system having a paging function. There is provided a method for dead peer detection of a mobile terminal, to be executed in a mobile communications system including a mobile terminal connected to plural wireless systems, a first connection device terminating a first wireless system with access points managing a connection status between the mobile terminal and a wireless link, and a second connection device terminating a second wireless system with access points not managing a connection status between the mobile terminal and a wireless link, said method comprising the steps of the second connection device acquiring the connection status of the mobile terminal in the first wireless system from the first connection device, and the second connection device changing a dead peer detection control process on the basis of the connection status of the mobile terminal, as acquired.