One of the most common and most puzzling problems a network engineer/technician may face is what is the PROPER way to make up a 10BaseT, 100BaseT or 1000BaseT (You need CAT 5e for gigabit data transmission) cable for basic 10/100 functionality. Since the overwhelming bulk of network cabling done today uses Unshielded Twisted Pair (UTP) wiring. The process begins with the selection of the proper wiring level or category. Today it is basically inexcusable to use or install anything at less than Level V or Category 5. While technically Category 5 and Level V are not the same, they are identical in tradition. Both support up to 100 megabit per second data transmission and their physical cable assembly requirements are the same. We will refer to them both as CAT5. When you buy a CAT5 UTP cable you will receive a cable containing 4 twisted pairs of wires, a total of 8 wires.
Proper Ordering Pairs
The pairs of wires in UTP cable are colored so that you can identify the same wire at each end. They are usually color coded by pair so that the pairs can also be identified from end to end. Typical CAT5 UTP cables contain 4 pairs made up of a solid color and the same solid color striped onto a white background. The most common color scheme is the one that corresponds to the (EIA/TIA) Electronic Industry Association/Telecommunications Industry Association's Standard.
Connectors
The cable connectors and jacks that are most commonly used with CAT5 UTP cables are RJ45. The RJ simply means Registered Jack and the 45 designation specifies the pin numbering scheme.
10Base T / 100Base T Straight through
10BaseT and 100BaseT are most common mode of LAN. You can use UTP category-5 cable for both modes. A straight cable is used to connect a computer to a hub. You can use it to connect 2 hubs in the case one of the hub has an uplink port (and you use normal port on the other hub).
10Base T / 100Base T Crossover
A cross cable for 10BaseT and 100BaseT is used to connect 2 computers directly (with ONLY the UTP cable). It is also used when you connect 2 hubs with a normal port on both hubs. (In other words, the cross cable is used relatively in a rare case.)
(See also: Network cable color coding)