Q40: When I should use 568A or 568B or USOC?
A40: It doesn't matter. Both are approved by the TIA/EIA 568. Both have
the same performance. What you need to avoid is terminating one end of
the run in 568A and the other end in 568B. That will cross pair 2 and
3. Both schemes are shown.
Avoid using USOC anywhere in the cable plant. USOC wiring was the pre-data
standard for telecommunications. When a LAN NIC transmits on two wires,
it expects them to be a pair of wires that are twisted together. Ethernet
transmits on pins 1 and 2. Notice that on a USOC cable, they aren't twisted
together.This greatly increases the crosstalk on the line and causes transmission
to be unreliable.
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