Cabletron Systems BRIM-F6 manual Figure A-9. Optical Bypass Switch

FDDI Devices

BYPASS STATE	OPERATIONAL STATE
Station Power Off	Station Power On

STATION

FDDI Dual

Optical Bypass

Switch

FDDI

RING

STATION

FDDI Dual

Optical Bypass

Switch

FDDI

RING

Figure A-9. Optical Bypass Switch

A concentrator is a hub. It provides connections to the dual ring for single attached stations and controls their access to the ring. The network can optically bypass each main ring connection if the attached station becomes disabled or when the branch cable is disconnected.

Bridging devices for FDDI connect multiple FDDI networks and link an FDDI ring to a network that uses a different MAC layer protocol (Token Ring or Ethernet). A bridge does not expand an existing FDDI ring, it connects rings. Bridges that link two different MAC layer protocols, such as FDDI and Ethernet, typically use one of two bridging techniques, encapsulation or translation.

Translation bridges translate frames from a non-FDDI MAC layer protocol to FDDI, allowing, for instance, an Ethernet station to talk to an FDDI station. Encapsulation bridges enclose the non-FDDI frames within the FDDI protocol. These bridges work in pairs – the sending bridge encapsulates the message and the receiving bridge strips the FDDI protocol, restoring the original frame. The bridge maintains routing information for filtering (prevent frames from crossing the bridge) or forwarding messages across the bridge.

BRIM-F6 User’s Guide Page A-13