Front-end device connected network system, communication method thereof on the network system and management system for network devices

A communication method of an intermediary device in a network system and a network device management system are provided to solve a problem that a management server can not request connections to devices connected to a network because of a firewall, and to enable the management server to request connections to the devices and to be connected to the devices when necessary without waiting till the plural devices are connected to the management server. An intermediary device connected to a grouped network attempts to be connected to a management server, and transmits registration information to the management server and requests registration to the management server if it is connected to the management server(S1). The management server stores the transmitted registration information at a database, and transmits registration acknowledgement and schedule information to the intermediary device(S2). The first device among plural devices attempts a connection, and transmits registration information to the management server(S3). The management server stores the transmitted registration information at a database, and transmits registration acknowledgement and schedule information to the first device(S4). If at least one among the plural devices and the intermediary device are connected to and are registered at the management server, the management server selects one among the registered devices and designates the selected device as a real intermediary device(S5). The selected intermediary device transmits a designation acknowledgement, expressing receipt of packets, to the management server and maintains a connection to the management server(S6). If the management server wants a connection to the first device among the plural devices, the management server transmits a connection request message to the intermediary device(S7). The intermediary device forwards the received connection request message to the first device(S8). The first device is connected to the management server in response to the connection request message and communicates with the management server(S9).