The Basics of Ethernet Cabling

by David Davis - January 7, 2009

Almost anyone who has connected to the Internet through a broadband connection, such as cable or DSL, has used an Ethernet cable to do it. You have connected your PC's network interface card (NIC) to your cable modem, DSL modem, or home router with an Ethernet cable.

Because of the commonality of this, if I say "use an Ethernet cable," then you have a picture of a cable in your mind. However, you should know that there is more than one type of Ethernet cable.

When you start learning about Cisco equipment and get further into networking, different types of Ethernet cabling will come up. In fact, Ethernet cabling is an important topic on Cisco's CCNA exam. So what do you need to know about Ethernet cabling? Let's find out.

Ethernet Cabling Basics

Ethernet Cabling Types

To begin, you should know that not all Ethernet cabling is the same. If you go to a store, then you may find several different cabling categories. These categories tell you the quality of the cabling. The quality determines how much the cable can handle. The following outlines the categories that you need to know:

Cat 3 – used for voice cabling and 10Mb Ethernet

Cat 5 – used for 10/100Mb Ethernet and works for voice as well

Cat 5E – Enhanced Cat 5 cabling that helps to prevent cross-talk, works for 10/100Mb and 1000Mb (or Gigabit Ethernet)

Cat 6 – Like Cat 5E but with larger gauge wires, works for 10/100/1000Mb. This cable is better than Cat 5e for Gigabit Ethernet.

Cat 7 – Also called Class F, this is fully-shielded cabling and supports up to 600Mhz. This is a relatively new type of cabling and isn't used much.

Most companies today are still using and even installing Category 5e as it works for the 100Mb Fast-Ethernet in use on almost every desktop PC. Plus, it is economical compared to the higher categories of cabling. If you go to a computer store and buy an Ethernet cable, 99 percent of the time it will be a Cat 5e cable.

Normal Ethernet Cables

You should be familiar with the different types of plugs that are at each end of the cable. When you go to a computer store and buy a 'regular' Ethernet cable, what you are really buying is a straight-through cable. This means that if you hold both ends side by side, the colors of each of the different ---smaller cables inside an Ethernet cable, will be in the same order, from left to right. Take a look at the picture below to see what I am talking about:

Ethernet cabling standard T-568A

Ethernet cabling standard T-568A (Image: Internet Centre)

This type of cable is a "regular" or straight-through cable. You use this type of cable to connect a PC to a hub/switch or a router to a switch.

You should also know that there are two standards for how the colors are arranged on this cable. However, these coloring standards don't affect the performance or function of the cable. The standard above was called the T-568A. The standard in the picture below is called the T-568B.

Ethernet cabling standard T-568B

Ethernet cabling standard T-568B (Image: Internet Centre)


Crossover Cables

Now that you're knowledgeable about standard Ethernet cables, let's learn about crossover Ethernet cables. These cables have a different pin on one side. The purpose of a crossover cable is to connect one device, directly, to another device, without a hub or switch in the middle. Usually, the hub/switch performs the crossover for you. So, you can use a crossover cable to connect a PC to a PC, directly, without any hub or switch. You can also use a crossover cable to connect two switches together. Here are the pinouts for a crossover cable:

A crossover cable

A crossover cable (Image: Internet Centre)

As you can see, the cross over cables sends pins 1 & 2 to 3 & 6 and 3 & 6 to 1 & 2. You can buy one of these special cables in a store or make one yourself.

What are Rolled Cables?

In the Cisco world, a rolled cable is a cable used to manage a router or switch from the console port of that device. This cable is usually used when configuring one of these devices for the first time. A rolled cable connects the PC’s serial port (using a DB9 to RJ45 adaptor) to the router or switch’s console port.  A rolled cable looks just like an Ethernet cable. The funny thing is that a rolled cable isn’t an Ethernet cable at all. In fact, it is a serial cable. In a rolled cable, Pin 1 connects to Pin 8 on the other side. Here is the pinout for a rolled cable:

Male                    Male

RJ-45                   RJ-45

1            BLU        8

2            ORN       7

3            BLK        6

4            GRN        5

5            RED        4

6            YEL        3

7            BRN        2

8            GRY        1

You cannot use a rolled cable for an Ethernet cable, nor can you use an Ethernet cable for a rolled cable. What you can do is take a straight-through Ethernet cable, cut off one end, flip over the wires, and recrimp it to make your own rolled cable.

In summary, what you need to take home from this article is:

  • Category 5e cables are the most common type of Ethernet cabling today
  • A straight-through cable is what you normally use to connect a PC to a hub or switch
  • A crossover cable is a special type of Ethernet cable used to connect a PC to a PC or a switch to a switch
  • A rolled cable isn’t an Ethernet cable at all but looks like one. It is used to connect a PC to a Cisco router or switch’s console port, for management.

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