To identify whether
an individual patch cord is wired straight through or
cross-over, hold the plug at either end of the cable
aligned side by side with the contacts facing you (up),
the clip down and compare the wire colors from left
to right. The colors should appear in the same order
on both plugs if the cord is wired straight through.
If the colors appear reversed on the second plug right
to left, the cord is cross-over.
There are four basic modular
jack styles. The 8-position modular outlets are commonly
and incorrectly referred to as "RJ45". The
6-position modular jack is commonly referred to as RJ11.
Using these terms can sometimes lead to confusion since
the RJ designations actually refer to very specific
wiring configurations called Universal Service Order
Code (USOC). The designation 'RJ' means Registered Jack.
Each of these basic jack styles can be wired for different
RJ configurations. For example, the 6-position jack
can be wired as an RJ11C (1-pair), RJ14C (2-pair), or
RJ25C (3-pair) configuration. An 8-position jack can
be wired for configurations such as RJ61C (4-pair) and
RJ48C. The keyed 8-position jack can be wired for RJ45S,
RJ46S, and RJ47S. The fourth modular jack style is a
modified version of the 6-position jack (modified modular
jack or MMJ). It was designed by Digital Equipment Corporation®
(DEC) along with the modified modular plug (MMP) to
eliminate the possibility of connecting DEC data equipment
to voice lines and vice versa.