A network system connected with one or more master devices and a method for operating the same. The system and method enable a new master device to be automatically connected to a network, when the network system is newly constructed or when the new master device is additionally connected to the network with which at least one master device has already been connected. A plurality of slave devices are connected to the network constructed within a building to transmit and receive data through the network. At least one master device controls the slave devices. A network manager automatically assigns a network address to the master device to appropriately connect the master device to the network when the master device is newly connected to the network or additionally connected to the network with which an existing master device is connected. Therefore, a network connection and a setting task associated with the master device are automatically performed, thereby easily and conveniently managing the network and hence reducing costs for managing the network.