Ethernet Video Series

Episode 03, Segment 03 of 04

Ethernet Cables (continued)


The second of two fundamental electrical characteristics has to do with what they call “category.” Higher category numbers indicate greater quality, and a better ability to handle fast information. The quality of these cables has to do with the materials from which they are made, the number of twists per inch, and the way they are put together, and the ability of the cable to carry high-speed data. The little printed notation that says “cat 5” right here indicates that this is a category 5 cable, which by industry standard definition can handle a hundred million bits per second. This is the kind of cable that most small businesses and home networks will be using. Even if your existing network equipment is limited to 10 million bits per second, you really ought to consider getting cat5 or better cable when you wire up your house or small business because it doesn’t cost very much to buy this kind of cable, but it costs a lot to rip out the old stuff, and replace it with faster cables later on.

Let’s talk about the use of regular straight-through patch cables versus cross-over cables. When would you use which one? Well, most people start thinking about an Ethernet after they’ve installed their second computer, and they want to hook the two computers together. So, here’s a picture of two computers.

(Click on any of the small images below for a larger version)

For most people, the best way to connect the two computers to each other is to buy a router, or a switch, or a hub. Generically, I’ve shown that in this diagram with a box labeled “hub.” You place that between those two computers, and then you use regular straight-through Ethernet patch cables to connect each of the two computers to two corresponding Ethernet connections on that hub, switch, or router as shown here. This used for a regular, straight-through ordinary patch cable of the most common type. You can continue adding computers until you use up all of the connectors in your router, hub, or switch. At that point, you’ll have to expand your network connection somehow (for example, by buying a second hub, or a second switch, as illustrated here). You can expand the number of Ethernet connectors in your local Ethernet network almost indefinitely by adding additional hubs or switches, and daisy-chaining them together with a cross-over cable, as illustrated here. This is a case when you would use a cross-over cable.

A cross-over cable is used whenever you are connecting two devices of similar type, such as two network infrastructure devices. By the same reasoning, you might be asking, “Couldn’t I use a cross-over cable to connect two computers together?” and the answer is yes. The very simplest kind of primitive Ethernet with just two computers can be built by connecting those two computers with a single cross-over cable, as you see here. That will allow them to share printers, disk drives, and to use certain types of games or specially prepared applications that know about Ethernet.

There are a couple of little wrinkles in this logic in selection of a cross-over cable versus a straight-through cable. For one of these little wrinkles, take a little look at the connector labeled 4 in this diagram (the one on the left).

Look below it. There’s a little arrow pointing off to the left heading toward a little switch, and the switch has two positions, one of which is labeled “to hub,” and the other labeled, “to PC.” Well, that switch is actually able to reconfigure that connector from a cross-over compatible connector to a straight-through compatible connector. So, if you have the wrong kind of cable plugged into that connector, you can compensate for it by reversing the position of that switch. It’ll compensate for the wrong kind of cable, cross-over versus straight-throughstraight-through were quite popular in 1992-1993, etc. But later on, the . Those switches, reversing a connector from cross-over to logic inside hubs and switches got so smart that it would automatically reconfigure the connectors for you if you connect in the wrong kind of a cable. Therefore, nowadays, most of the time, you’re just going to use straight-through connectors, and the equipment you buy will probably adapt to the appropriate kind of connection – cross-over versus straight-through – as necessary.

Episode 03, Segment 4 of 4