Bypass Switch - Technical Information

Technical Information

Bypass switches increase network reliability through several mechanisms including passive in-line connections, link detection, and Heartbeat packets.

The two network ports in a bypass switch create a fully passive in-line connection that maintains traffic flow even in the absence of power. For fiber links, a normally closed optical switch creates a path for light to flow unimpeded through the device when power is absent. For copper links, micro-relays connect the two ports when power is absent.

The bypass switch monitors the status of the links between its monitor ports and the in-line appliance. If a link goes down, the bypass switch immediately switches into bypass-on mode. When the link comes back up again, the bypass switch returns to bypass-off mode and the appliance resumes receiving traffic.

Some bypass switches send a heartbeat packet through the monitoring appliance in order to ensure that the appliance is passing traffic. If the heartbeat packet does not return to the bypass switch, the appliance is assumed to be down, and the switch goes into bypass-on mode, excluding the appliance from the traffic path. The bypass switch continues to transmit heartbeat packets to the appliance, and when they are again returned by the appliance, the bypass switch changes back to bypass-off mode and the appliance resumes receiving traffic....

Whenever the bypass switch transitions to bypass-on mode for any reason, the link may be temporarily dropped. A good bypass switch reconnects the link in under 1 second, but the network may take several seconds to re-establish communications on link.