Cabletron Systems BRIM-F6 manual A-12

APPENDIX A: BASIC FDDI NETWORKS

Optical bypass switches, concentrators, and bridges exist throughout FDDI networks. These devices allow creation of ring topologies that meet the specific needs of different network applications.

Repeaters, often found in other network topologies, do not exist as entities for FDDI networks. This is because all devices that attach to the FDDI main ring must comply with FDDI protocol. In other words, they must dual attach to the ring and have, as a minimum, two PMD and PHY entities and one MAC and SMT entity.

Since a DAS or DAC can match this configuration, either could serve as a repeater when a main ring segment must extend beyond the 2 km maximum between nodes.

Together with Figure A-10, the following descriptions provide a brief introduction to several FDDI components and their network functions. In many cases, specific functions combine in a single device.

An optical bypass switch allows insertion between a station and the FDDI ring connections without having to remove the station from the ring and disturbing ring continuity. These devices, often electrically actuated, provide passive optical switching of both the primary and secondary ring cables. Figure A-9 shows the data paths through the switch in both the bypass and operational (non-bypassed) states.

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