The cross-over (or crossover) CAT5 UTP cable has to be one of the most used cables after the classic straight-thru cable. The cross-over cable allows us to connect two computers without needing a hub or switch. If you recall, the hub does the cross-over for you internally, so you only need to use a straight thru cable from the PC to the hub. Since now we don't have a hub, we need to manually do the cross-over.

 

Why do we need an cross-over cable?

When sending or receiving data between two devices (I.E. computers) one will be sending while the other receives. All this is done via the network cable and if you look at a network cable you will notice that it contains multiple cables. Some of these cables are used to send data, while others are used to receive data and this is exactly what we take into account when creating a crossover cable. We basically connect the TX (transmit) of one end to the RX (receive) of the other!

The diagram below shows this in the simplest way possible:

CAT5 Cross-over

There is only one way to make a CAT5e crossover cable and it's pretty simple. Those who read the "Wiring UTP" article know a crossover cable is a 568A on one end and a 568B on the other. If you haven't read the wiring section, don't worry because we’ll provide enough information to help understand about the concept.

As mentioned previously, the purpose of a crossover cable to connect the transmitting side (TX) from one end, to the Receiving side (RX) at the other end, and vice versa.

Let's now have a look at the pinouts of a typical crossover CAT5e cable:

This article covers the commonly known Unshielded Twisted Pair (UTP) cable and shows how many pairs the UTP Cat5, Cat5e, Cat6 & Cat7 cables consists of, the colour coding they follow, the different wiring standard that exist (T-568A & T-568B) plus the pin number designations for both standards.

We will be mainly focussing on the wiring of CAT5e & 6 cables as they are the most popluar cables around! We'll also cover wiring classic CAT1 phone cables. It is very important to understand UTP cabling standards and how to correctly terminate them.

Cabling is the foundation for a solid network, and implementing it correctly the first time will help avoid hours of frustration and troubleshooting. On the other hand, if you are dealing with a poorly cabled network, this knowledge will help you to find the problem and fix it more efficiently.

Wiring the UTP cables

We are now going to look at how UTP cables are wired. There are two popular wiring schemes that most people use today: the T-568A and T-568B. These differ only in which color-coded pairs are connected -- pairs 2 and 3 are reversed. Both work equally well, as long as you don't mix them. If you always use only one version, you're okay, but if you mix A and B in a cable run, you will get crossed pairs.

UTP cables are terminated with standard connectors, jacks and punchdowns. The jack/plug is often referred to as a "RJ-45," but that is really a telephone company designation for the "modular eight-pin connector" terminated with the USOC pinout used for telephones. The male connector on the end of a patch cord is called a "plug" and the receptacle on the wall outlet is a "jack."

Figure 1. A RG-45 Jack and RJ-45 Plug / Connector

 

As already mentioned, UTP has four twisted pairs of wires. The illustration shows the pairs and the color codes they have. As you can see, the four pairs are labeled:

Figure 2. Colour codes & Pairs of UTP CAT 5, CAT 5e, CAT6, CAT7 Cable

Pairs 2 and 3 are used for normal 10/100 Mbps networks, while pairs 1 and 4 are reserved. In Gigabit Ethernet, all four pairs are used.

The picture below shows the end of a CAT5e cable with an RJ-45 connector, commonly used to connect computers to a switch. It also shows a stripped CAT5e cable and identifies the four twisted pairs: