Cabletron Systems 100BASE-FX, Cabling Manual

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Ethernet Media
4-8 Cabling Types
Twenty-Five Pair Cable
UTP cabling in large installations requiring several cable runs between two points
is often 25-pair cable. This is a heavier, thicker form of UTP. The wires within the
plastic jacket are of the same construction, and are twisted around associated
wires to form pairs, but there are 50 individual wires twisted into 25 pairs in these
larger cables. In most cases, 25-pair cable is used to connect wiring closets to one
another, or to distribute large amounts of cable to intermediate distribution
points, from which four-pair cable is run to the end stations.
Table 4-1. 10BASE-T/100BASE-TX Four-Pair Wire Use
Wire Color EIA/TIA Pair
Ethernet Signal Use
568A 568B
White/Blue (W-BL)
Pair 1 Not Used
Blue (BL)
White/Orange (W-OR)
Pair 2
RX+ TX+
Orange (OR) RX- TX-
White/Green (W-GR)
Pair 3
TX+ RX+
Green (GR) TX- RX-
White/Brown (W-BR)
Pair 4 Not Used
Brown (BR)
NOTE
Do not split pairs in a twisted pair installation. While you may
consider combining your voice and data cabling into one piece
of horizontal facility cabling, the Crosstalk and interference
produced by this practice greatly reduces the viability of the
cable for either application. The use of the pairs of cabling in
this fashion can also prevent the future usage of advanced
networking technologies such as FDDI TP-PMD and
100BASE-T4, that require the use of all four pairs in a twisted
pair cable.