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.


The TIA and AT&T wiring schems are the two that have been adopted by EIA/TIA-568A. They are nearly identical except that pairs two and three are reversed. TIA (T568A) is the perferred scheme because it is compatible with 1 or 2-pair USOC Systems. Either configuration can be used for integrated Services Digital Network (ISDN) application.

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.

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