The 6000 A/B switch connects port A or port B to port C, through latching relays. The switches are designed to fit into a 4U high 19-inch rack. The rack has 18 slots, two of which areused by the A/B Switch Controller /External Power Supply card. The 16 remaining slots can hold up to 16 rack A/B switch cards. Each A/B switch card can be individually switched, or the entire rack can be switched from the A/B switch controller card. The 4U rack has a keyed switch to enable and disable switching from this rack. The controller has two RJ11 ports, used to daisy chain up to 64 racks into a single system, allowing a single rack to control all racks in the system. The A/B switch controller can be controlled with a +/- 12 VDC signal, or a remote toggle switch. The A/B switch controller is available in three options: (Logic Only, Processor, and SNMP). The Logic Only version allows Rack and System Gang Switching, in addition to the individual switching allowed on each A/B Switch Card. The Processor version allows all features of the Logic Only version, with the addition of RS-232 communication on the gang-in and gang-out connectors. This allows racks to be addressed, and individual A/B Switch Cards within the rack to be switched with serial commands. The SNMP version allows all features of the Processor version, with the addition of an Ethernet port for SNMP commands. There can only be one SNMP capable card in the system, and it must be in the first rack in the system.The Fibre Optic A/B switch uses the same latching relays to control an optical switch. The optical switch however is not latching. Therefore, if power is lost, the optical switch will connect port A to port C. When power is re-applied, the latching relay will cause the optical switch to reconnect the port selected prior to the loss of power.