A/B switches are network components that connect an optical or electrical primary path to one of two secondary paths. The designation A/B switch is related to the chronological designation of the switch contacts in alphabetical order.
The A/B switch is a toggle switch that connects optical or electrical signals from the primary path to the secondary path, or from A to B.
A/B switches come in mechanical and electromechanical versions that operate manually, automatically, or remotely. The electromechanical versions use bistable relays to maintain a defined switch position in the event of a power failure. An A/B fallback switch, the simplest form of an AB switch, was formerly used to connect two terminals to one modem or one computer to two modems alternatively.
An extended version of an A/B switch is the ABCD switch with four connection options.