Straight-through or reversed (crossover) wiring?

Modular cords are used for two basic applications.

One application uses them for patching between modular patch panels. When used in this manner modular cords should always be wired "straight-through" (pin 1 to pin 1, pin 2 to pin 2, pin 3 to pin 3, etc.).

The second major application uses modular cords to connect the workstation equipment (PC, phone, FAX, etc.) to the modular jack.

Modular cords may either be wired "straight-through" or "reversed," sometimes called "crossover" (pin 1 to pin 6, pin 2 to pin 5, pin 3 to pin 4, etc.) depending on the system manufacturer's specifications. This "reversed" wiring is typically used for phone systems. "Straight-through" is normally used for data.

How to Read a Modular Cord

Align the plugs side-by-side with the contacts facing you and compare the wire colors from left to right. If the colors appear in the same order on both plugs, the cord is wired "straight-through". If the colors appear reversed on the second plug (from right to left), the cord is wired "reversed".

(info & diagram from Siemon)