100BASE-T4 Crossover Wiring

A signal crossover is required between devices connected to a 100BASE-T4 segment, so that the TX data pins and bi-directional data pins on the device at one end of the segment are connected to the RX data pins and bi-directional data pins on the device at the other end, and vice versa. The standard recommends that the crossover be done internally in the repeater port. If the crossover function is done inside a repeater, then the port on the repeater must be marked with an "X."

If two stations are linked together with a single 100BASE-T4 segment, or if the repeater hub does not implement the signal crossover internally, then a special crossover cable must be provided.

FIGURE 12.2 100BASE-T4 crossover cable wiring

As shown in the figure, a crossover cable for a 100BASE-T4 segment must be wired so that the TX pair at one end of the cable is connected to the RX pair at the other end of the cable, and vice versa. In addition, the BI_D3 pair at one end of the cable is connected to the BI_D4 pair at the other end, and vice versa.

Quick Reference Guide to 100BASE-T4 - 09 SEP 95

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