Abstract: A call control device including: a memory, and a processor coupled to the memory and configured to: receive a call request from a communication device, a source of the call request being a terminal, the call request being transferred by the communication device when the terminal is registered in a management device, and request the management device to deregister the terminal when the call control device is determined that the call control device is attacked from the terminal based on the call request.

Abstract: A first call control server transmits line information of a line to be used by a terminal device calls of which are controlled by the first call control server to a second call control server when congestion is detected. The first call control server receives the line information to be used in call control from the second call control server, and establishes a connection with the terminal device using the received line information. The second call control server receives the line information from the first call control server, and receives a call control request for the terminal device, the call control request being addressed to the first call control server. The second call control server responds to the first call control server with the received line information, when the call control request is received.

Abstract: A call control device including: a memory, and a processor coupled to the memory and configured to: receive a call request from a communication device, a source of the call request being a terminal, the call request being transferred by the communication device when the terminal is registered in a management device, and request the management device to deregister the terminal when the call control device is determined that the call control device is attacked from the terminal based on the call request.

Abstract: A first call control server transmits line information of a line to be used by a terminal device calls of which are controlled by the first call control server to a second call control server when congestion is detected. The first call control server receives the line information to be used in call control from the second call control server, and establishes a connection with the terminal device using the received line information. The second call control server receives the line information from the first call control server, and receives a call control request for the terminal device, the call control request being addressed to the first call control server. The second call control server responds to the first call control server with the received line information, when the call control request is received.

Abstract: A call management method makes a call management system perform a process of releasing resources that are secured for a terminal device that has become a communication disable state among resources in the call management system that are secured for each of the terminal devices under speech communication (#103 and #108), and sending a message for finishing speech communication to a terminal device on the other end of the speech communication without transmitting it to the terminal device that has become a communication disable state (#112), when it is detected that one of the terminal devices under speech communication with each other has become a communication disable state in a mobile communication network (#102).

Abstract: A call management method makes a call management system perform a process of releasing resources that are secured for a terminal device that has become a communication disable state among resources in the call management system that are secured for each of the terminal devices under speech communication (#103 and #108), and sending a message for finishing speech communication to a terminal device on the other end of the speech communication without transmitting it to the terminal device that has become a communication disable state (#112), when it is detected that one of the terminal devices under speech communication with each other has become a communication disable state in a mobile communication network (#102).

Abstract: A server capable of reducing an overloaded state even if a refreshing message is frequently generated. A central processing unit receives a first message transmitted from a terminal to establish a session. The central processing unit, when receiving the first message from the terminal, allocates to itself and the other plural central processing units the subsequent message transmission and reception between the terminal and a terminal as a communication partner. The central processing unit allocates to itself and the other plural central processing units the message transmission and reception between the terminals, for example, in a round robin fashion.