FDDI Devices
BRIM-F6 User’s Guide
Page A-13
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.
STATION
FDDI
RING
FDDI Dual
Optical Bypass
Switch
STATION
FDDI
RING
FDDI Dual
Optical Bypass
Switch
BYPASS STATE
OPERATIONAL STATE
Station Power Off
Station Power On
BRIM-F Book Page 13 Monday, January 29, 1996 9:26 AM
