Abstract: A network system includes a service providing apparatus; first and second backup apparatuses, each of which is configured to back up at least a part of a function of the service providing apparatus, and is connected with the service providing apparatus through a WAN; and a terminal connected with the service providing apparatus and the first and second backup apparatuses, and configured to receive a service from the service providing apparatus in a normal operation. The service providing apparatus has IP addresses of itself, the first and second backup apparatuses and the terminal, and notifies the IP addresses of the service providing apparatus and the first backup apparatus to the terminal in response to registration of the IP address of the terminal.

Abstract: A network system includes a service providing apparatus; first and second backup apparatuses, each of which is configured to back up at least a part of a function of the service providing apparatus, and is connected with the service providing apparatus through a WAN; and a terminal connected with the service providing apparatus and the first and second backup apparatuses, and configured to receive a service from the service providing apparatus in a normal operation. The service providing apparatus has IP addresses of itself, the first and second backup apparatuses and the terminal, and notifies the IP addresses of the service providing apparatus and the first backup apparatus to the terminal in response to registration of the IP address of the terminal.

Abstract: A high-capacity electronic switching system includes two or more first stage switch modules to each of which one or more subscriber terminals (telephone sets, fax machines, personal computers, etc.) are connected and each of which executes signal switching for signals from/to the subscriber terminals, and a second stage switch module for switching signals between the first stage switch modules. In the high-capacity electronic switching system, each of the first stage switch modules is connected to another one of the first stage switch modules via a special-purpose link for setting a communication link between the first stage switch modules when necessary. For example, the setting of the communication link via the special-purpose link is executed when an abnormal condition of the second stage switch module occurred and normal communication link setting between two first stage switch modules via the second stage switch module is impossible.

Abstract: An IP telephony service system and an accounting method in order to charge for telephony services provided during backup operation. When communications between IP terminals and an IP telephony service providing unit in the main network are interrupted, an IP telephony service backup unit placed in a LAN to which the IP terminals are connected provides IP telephony services to the IP terminals. Information on the services provided to the IP terminals by the IP telephony service backup unit is stored in a backup database. Thus, it becomes possible to charge for the services provided during backup operation.

Abstract: Adapters 10 and 11 implement a mutual conversion of a protocol of a voice signal and a control signal over a telephone network, and voice data and control data over a LAN 30 that are converted into the packet. Thereby, existing digital multi function telephones 40 to 42 and a PBX 20 can be connected to the LAN, and all kinds of the services of utilizing the PBX 20 of the existing multi function telephones in the situation of having been connected to the LAN 30.