1. Field of the Invention
The present invention relates to a method for switching central devices when a failure occurs in a cable modem system, which forms a local area network (LAN) by using a CATV transmission path, and a cable modem system using the method.
2. Description of the Related Art
In recent years, cable modem systems have been put in practical use, where a CATV transmission path is taken as an access network, and users can connect from their homes to Internet through a LAN interface.
These systems target for services to general public. Therefore, there is a need for obtaining a license as the first-class communication service. To get the license, high reliability is required as a system.
The conventional LAN system will be now considered. In the conventional LAN system, although a main section for inter-routers connection can be formed having redundancy, it is impossible to form sub sections directly accommodating terminals to have redundancy. The reason is because it is possible to detect a failure on a router to be connected and automatically set a bypass route by transmitting and receiving a routing protocol, such as a RIP, between routers.
However, it is general that such the routing protocol is not supported for a terminal such as a personal computer. Therefore, LAN connections are not set according to gateway definition of which settings can be changed manually.
Therefore, when a failure occurs on a router for directly storing terminals, it is impossible to perform the LAN connections by using the bypass route without changing settings of the terminal.
Accordingly, it is an object of the present invention to provide a method for switching central devices to maintain a LAN connection by using a redundancy central device without changing settings of terminals, when a failure occurs on a central device having a router function, which directly accommodates the terminals and a cable modem system using the method.
The above-described object is achieved by a cable modem center device having a plurality of central devices including N working central devices and one protection central device of a N+1 redundancy structure provided on a LAN center, to the CATV transmission path side of which terminal devices are connected each through a cable modem, and having router functions forming segments respectively at the sides of the LAN center and the CATV transmission path, and a working central device transmitting routing information of the segment on the CATV transmission path side to inform the LAN center segment of an existence of the segment on said transmission path side, so that the terminal devices are connected to appropriate networks via the LAN center, the cable modem center device comprising a switch device provided between said plurality of central device and said CATV transmission path for switching a failed one of the plurality of central devices to said protection central device and connecting said plurality of center devices and said CATV transmission path.
The cable modem center devices further comprises a monitor device for monitoring said plurality of central devices, maintaining control information of the plurality of working central devices and the protection central device to be monitored, detecting failure of a working central device by regularly polling the N working central devices, switching the detected, failed working central device to the protection central device to connect the plurality of central devices to the CATV transmission path, transferring the maintained control information of the failed central device to the protection central device, and setting the protection central device to an active status according to the transferred control information.
Further, in one preferred mode, it is another feature that the control information of the plural working central devices and the protection device to be monitor device includes a network address of a segment on the CATV transmission path and control information of a cable modem stored under the plural working central devices and the protection devices.
Alternatively, in another mode, the monitor device includes a physical address (MAC address) of the segment on the transmission path of the working central device as the maintained information and the information transferred to the protection central device, and said protection central device additionally uses said physical address to activate.
Furthermore, in one mode, the failed central device stops sending routing information after a failure is informed.
Alternatively, it is a further feature that distance (HOP number) or cost data of the routing information the switched protection central device sends is made to be smaller than that of the information the working central device sends.
Further, in one embodiment, it is informed to the data sender that the failed central device is switched to the protection central device according to an internet control message protocol (ICMP) redirect message when receiving the data to the segment on the CATV transmission path after a failure is informed.
It is other feature that a resumption confirmation is performed by connecting the terminal and the failed central device, the control information of the protection central device is transferred from the monitor device to the failed central device, and the failed central device is made to be active according to the transferred information after the failure on the failed central device is restored.
Further, objects and features of the present invention become clear by the description for explaining embodiments according to the attached drawings.