User manual
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The color code extends well beyond that, but since we are only dealing with 4 pairs of wire, you
don’t need to know the entire Bell System color code for terminating a 900 pair distribution
trunk...! What is often confusing is that the pair numbers do not line up with the pin numbers on
the RJ-45 connector. In other words, conductor ONE of the cable (White w/Blue Strip) is NOT
terminated to PIN ONE of the connector. The AT&T connecting standard always uses the middle
pins for the first pair. After that, they are staggered around, primarily to prevent crosstalk between
adjacent pairs. For Ethernet, and for use with the CAB 4n, only the ORANGE and GREEN pairs
are actually used. BUT...it is very important that you build the cable with ALL PAIRS properly
terminated. This will prevent any confusion later, and give your cable a solid mechanical
connection.
Remember, for Ethernet, the BLUE and BROWN pairs are not used. The ORANGE pair is
transmit (TX), and the GREEN pair is receive (RX). There is a positive and negative conductor
for each pair, indicated by the color code. Notice on the chart that the order of the wire pairs does
not follow the connector pins, as mentioned earlier. Don’t let that confuse you. The first wire of a
given pair is always the white wire with a colored stripe and is the positive conductor. The
corresponding colored wire with the white stripe is the negative conductor for that pair.
Crossover Cables
Normal CAT 5 cables are designed to connect the CAB 4n to a
network switch only. You cannot use this type of cable to
connect a CAB directly to a MediaMatrix MM-DSP-cn DPU
card or Nion CM-1 card. For that you need a “crossover”
cable. The pin assignments for a crossover cable, shown in
parentheses on the chart, apply to ONE END of the cable
ONLY!