Tip

Network cable, lesson 3: CAT5 UTP x-over cable

Introduction

The cross-over (x-over) CAT5 UTP cable has to be one of the most used cables after the classic straight-thru cable. The x-over cable allows us to connect two computers without needing a hub or switch. If you recall, the hub does the x-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 x-over.

Why do we need an x-over?

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 an x-over 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 X-over

There is only one way to make a CAT5 x-over cable and it's pretty simple. Those who read the "wiring utp" section know an x-over cable is a a 568A on one end and a 568B on the other. If you haven't read the wiring section, don't worry because I'll be giving you enough information to understand what we are talking about.

As mentioned previously, an x-over cable is as simple as connecting the TX from one end to the RX of the other and vice versa.

Let's now have a

    Requires Free Membership to View

look at the pinouts of a typical x-over CAT5 cable:


As you can see, only 4 pins are needed for a x-over cable. When you buy an x-over cable, you might find that all 8 pins are used, these cables aren't any different from the above, it's just that there are cables running to the unused pins. This won't make any difference in performance, but is just a habit some people follow.

Here are the pinouts for a x-over cable which has all 8 pins connected:


Where else can I use an x-over?

X-over cables are not just used to connect computers, but a variety of other devices. Prime example are switches and hubs. If you have two hubs and you need to connect them, you would usually use the special uplink port which, when activated through a little switch (in most cases), makes that particular port not cross the tx and rx, but leave them as if they where straight through.

What happens though if you haven't got any uplink ports or they are already used? The X-over cable will allow you to connect them and solve your problem. The diagram below shows a few examples to make it simpler:


As you can see in the above diagram, thanks to the uplink port, there is no need for a x-over cable.

Let's now have a look at how to cope when we don't have an uplink to spare, in which case we must make a x-over cable to connect the two hubs:


Network cable, lesson 1, Introduction
Network cable, lesson 2: Straight-through UTP cables
Network cable, lesson 3: CAT5 UTP x-over cable
Network cable, lesson 4: 10Base-T/2/5/F/35 - Ethernet
Network cable, lesson 5: 100Base-(T) TX/T4/FX - Ethernet
Network cable, lesson 6: Fiber
Network cable, lesson 7: Direct Cable Connection
Network cable, lesson 8: Serial Direct Cable Connection
Network cable, lesson 9: Parallel Direct Cable Connection
Network cable, lesson 10: USB Direct Cable Connection
Testing network cable





Click over to Firewall.cx for more articles like this one. You don't have to register or jump through any hoops. All you do is get the networking information you want. Copyright 2004 Firewall.cx.


This was first published in July 2004

There are Comments. Add yours.

 
TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

Disclaimer: Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.