Connected communication terminal, connecting communication terminal, session management server, and trigger server

The communication system according to the present invention is made up of: a connected communication terminal (1) to which communication is requested; a connecting communication terminal (3) that requests a communication with the connected communication terminal (1); a session management server (4) that manages sessions between the communication terminals; a trigger server (5) that transmits, to the connected communication server (1), the request made by the session management server (4); and routers (6 and 7) that relay between the connecting communication terminal (3) and the connected communication terminal (1), and a network (2). In the system, the connected communication terminal (1) holds a permission list (L) that is a list of communication terminals to which connection is permitted, and the session management server (4) judges, with reference to the permission list (L), whether or not the communication between the connected communication terminal (1) and the connecting communication terminal (3) is permitted.