1. Field of the Invention
This invention relates generally to computer networks and specifically to failover or redundancy in network switches or routers.
2. Related Art
It is often desirable for network equipment, such as that equipment used for switching or routing of information packets between network devices, to remain in operational condition for continuous periods of time. Failure of network equipment can be inconvenient and costly. Active-passive operation is sometimes used to minimize the effects of equipment failure. In active-passive operation, sometimes referred to as failover or redundancy, two components have overlapping capabilities. An active component performs a particular task, but in the event that the active component fails, the passive component takes over performance of the task.
One application of active-passive operation is in networking equipment. More specifically, two switches may be dedicated to route packets between network devices. One switch is configured to be active and one switch is configured to be passive. Prior art techniques for providing active-passive operation require physically switching the signal wires that are connected to the active unit and passive units. This scheme, however, presents several drawbacks. First, each network port requires a minimum of 4 signal wires to be switched from the active unit to the passive unit. Hence a large number of circuits need to be physically switched. Second, the switching requires the use of electromechanical relays since the signal levels are very low (in the tens to hundreds of millivolts range) and very high frequency (hundreds of megahertz). Third, electromechanical relays are bulky, costly, prone to high failure rates, and not as reliable as passive devices or silicon integrated circuits. Fourth, the control signal that switches the relay from one unit to another introduces a single point of failure, namely in the event of a failure in the control signal, the entire active-passive combination may become inoperative, even if the active and passive units themselves remain operational. Finally, the relays require a power source, which introduces yet another possible point of failure in the configuration.
There is thus need for a network flow switching system that utilizes an active-passive configuration to provide redundancy without relying on electromechanical relays.