Get wired

Like it or not, life is becoming increasingly digitised. The networking tentacles have reached outside the spare bedroom and are strongly entwined around the lounge, kitchen and bedroom. In short, you really need to consider installing network cabling around your house.

"Wait a minute," I hear you say, "what's the point? Surely with 802.11n just around the corner, we'll soon be awash with Wi-Fi bandwidth with none of this wiring hassle and expense?" Well, wireless may be getting better, but it still isn't good enough to satisfy the digital-media demands of a home network. As Wi-Fi becomes more popular, the airwaves in the 2.4GHz spectrum are going to get ever more crowded, causing local interference problems and reducing bandwidth.

It really isn't that hard to run network cabling in the house. If you've ever had to put in some extra mains or phone sockets then you're up to the task of installing network points, too. It's a simple matter of fitting socket boxes to the wall, running the cable to each socket box and connecting the cable to the network sockets using a punch-down tool.

Cabling tales

100 Base-T Ethernet cabling calls for two transmission lines. Each consists of a pair of twisted wires, one to receive and the other to transmit data signals. Category 5E (otherwise known as CAT5e) unshielded twisted pair cabling is commonly used for networking. It can safely handle bandwidths of up to one gigabit per second (Gbps), so it's fairly future-proof, particularly if you have visions of streaming HDTV (high-definition television) signals down the wire - try handling that with your wireless setup!

Open up a CAT5e cable and you'll find it has four twisted pairs - a total of eight individually insulated wires. Each pair is colour coded, with one wire having a solid colour - blue, orange, green or brown - twisted around a second wire with a white background and a stripe of the same colour. The solid colours may have a white stripe in some cables. Cable colours are commonly described using the background colour followed by the colour of the stripe. White-orange is a cable with a white background and orange stripe.

There are two types of cable wiring configurations. These are straight through, for when you connect a PC to a hub, and cross­over, which is when two PCs are directly linked by a CAT5e cable. Figure 1 shows how the pins in each plug should be connected.

Note that the Tx (transmitter) pins are connected to corresponding Rx (receiver) pins, plus to plus and minus to minus. Pins four, five, seven and eight, the blue and brown pairs, aren't used in either configuration. The orange wires aren't adjacent and the order of the blue pair is reversed.

Things get more complicated when it comes to patch-connector sockets. There are two wiring schemes available, called EIA/TIA 568A and EIA/TIA 568B. Each has subtly different pin assignments.

The pin assignments of the orange and green pairs are swapped. If you look at Figure 2, it uses 568A at one end and 568B at the other, while the straight-through cable uses 568A at both ends. RJ-45 plugs are easy to tell apart: straight-through cable has identical ends, but crossover wire ends differ.

There's no difference in con­nectivity or performance, but if you want to run phone cabling as well, it makes sense to use the 568B scheme because it's consistent with most installed phone cabling.

It all boils down to convenience - if you're linking socket to socket it makes no odds, but if you're making a plug-to-socket connection, 568A has a more logical pin assignment. Choose one of the two standards and stick to it at both ends; otherwise your cable won't work, unless you want a crossover, that is.

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Roger Gann

PC Advisor (UK)
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