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11.2 100BASE-FX Components

100BASE-FX Repeaters

The Fast Ethernet standard defines two types of repeater: Class I and Class II. The standard requires that Fast Ethernet repeaters be labeled with the Roman number "I" or "II" centered within a circle.

A Class I repeater is allowed to have larger timing delays, and operates by translating line signals on an incoming port to digital form, and then retranslating them to line signals when sending them out on the other ports. This makes it possible to repeat signals between media segments that use different signalling techniques, such as 100BASE-TX/FX segments and 100BASE-T4 segments, allowing these segment types to be mixed within a single repeater hub. The translation process in Class I repeaters uses up a number of bit times, so that only one Class I repeater can be used in a given collision domain when maximum cable lengths are used.

A Class II repeater is restricted to smaller timing delays, and immediately repeats the incoming signal to all other ports without a translation process. To achieve the smaller timing delay, Class II repeaters connect only to segment types that use the same signalling technique, such as 100BASE-TX and 100BASE-FX segments. A maximum of two Class II repeaters can be used within a given collision domain when maximum cable lengths are used. Segment types with different signalling techniques (e.g. 100BASE-TX/FX and 100BASE-T4) typically cannot be mixed together in a Class II repeater hub.

Quick Reference Guide to 100BASE-FX - 09 SEP 95
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