Each FIP (FDDI Interface Processor) provides a single network interface for both multimode and single-mode FDDI networks, and provides the interface for connection to a Class A dual attachment station (DAS) with primary and secondary rings, or to a Class B single attachment station (SAS) with only a primary ring.The single-mode/single-mode FIP (CX-FIP-SS) and multimode/multimode FIP (CX-FIP-MM) each provide a control port for an optical bypass switch, which allows the light signal to pass directly through the bypass switch, completely bypassing the FIP transceivers when the interface is shut down.