Quick Reference Guide to 10BASE-FL Fiber Optic Ethernet

6.2 Old and New Fiber Link Segments

The original FOIRL specification from the Ethernet standard of the early 1980s provided a link segment of up to 1000 meters between two repeaters only. As the cost of repeaters dropped and more and more multiport repeater hubs were used, it became cost-effective to link individual computers to a fiber optic port on a repeater hub. Vendors created outboard FOIRL MAUs to allow this, although a repeater-to-DTE fiber connection was not specifically described in the FOIRL standard.

To deal with this and other aspects of fiber optic Ethernet, a set of fiber optic media standards, called 10BASE-F, was developed. This set of fiber standards includes revised specifications for a fiber optic link segment that allow direct attachments to computers. The full set of 10BASE-F specifications includes three segment types:

• 10BASE-FL. The 10BASE-FL standard replaces the older FOIRL specifications, and is designed to interoperate with existing FOIRL-based equipment. 10BASE-FL provides a fiber optic link segment that may be up to 2000 meters long, providing that only 10BASE-FL equipment is used in the segment. If 10BASE-FL equipment is mixed with FOIRL equipment, then the maximum segment length may be 1000 meters.
  • A 10BASE-FL segment may be attached between two computers, or two repeaters, or between a computer and a repeater port. Because of the widespread use of fiber links, 10BASE-FL is the most widely used portion of the 10BASE-F fiber optic specifications, and equipment is available from a large number of vendors.

• 10BASE-FB. The 10BASE-FB specifications describe a synchronous signaling backbone segment that allows the limit on the number of repeaters that may be used in a given 10-Mbps Ethernet system to be exceeded. 10BASE-FB links typically attach to repeater hubs, and are used to link special 10BASE-FB synchronous signalling repeater hubs together in a repeated backbone system that can span long distances. Individual 10BASE-FB links may be up to 2000 meters in length. This system has a limited market and equipment is available from only a few vendors.

• 10BASE-FP. The Fiber Passive system provides a set of specifications for a fiber optic mixing segment that links multiple computers on a fiber optic media system without using repeaters. 10BASE-FP segments may be up to 500 meters long, and a single 10BASE-FP fiber optic passive star coupler may link up to 33 computers. This system has not been widely adopted and equipment does not appear to be generally available.

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