Patent ID: 7685284

Claim:
A network, comprising: a plurality of network terminal devices; first and second system control devices which can control each of said plurality of network terminal devices; and an address management device for managing IP (Internet Protocol) addresses of said plurality of network terminal devices, wherein said first system control device and said address management device are connected to a first station; said second system control device and said plurality of network terminal devices are connected to a second station; each of said plurality of network terminal devices is connected to and operable by each of said first system control device and said second system control device; and each of said network terminal devices has a storage unit for storing an IP address acquired from said address management device, and a management unit for using the IP address stored in said storage unit when a malfunction has occurred in the connection between said first station and said second station, and re-registering the address in the system control device to which that network terminal devices are connected; said second system control device of said second station acts as a backup system control device when said first station is a main-station and said second station is a remote station; said address management device has a DHCP (Dynamic Host Configuration Protocol) server, and time-limited IP addresses are assigned to said plurality of network terminal devices; each of said plurality of network terminal devices uses as a terminal IP address an IP address acquired from said DHCP server previously saved in said storage unit when said IP address could not be acquired from said DHCP server at the time of registration in said backup system control device; and each said plurality of network terminal devices connects to the second system control device of the second station other than the first station to which said DHCP server is connected when the IP addresses acquired from said DHCP server previously saved in said storage unit are used.