Twisted-pair cable comes in various grades called Categories. These Categories are specified by the ANSI/EIA standard 568. (ANSI stands for American National Standards Institute; EIA stands for Electronic Industries Association.) The standards indicate the data capacity, also known as the bandwidth, of the cable.
Although higher-Category cables are more expensive than lower-Category cables, the real cost of installing Ethernet cabling is the labor required to actually pull the cables through the walls. You should never install anything less than Category 5 cable. And if at all possible, you should invest in Category 5e (the e stands for enhanced) or even Category 6 cable to allow for future upgrades to your network.
If you want to sound like you know what you’re talking about, say “Cat 5” instead of “Category 5.”
| Category | Maximum Data Rate | Intended Use |
|---|---|---|
| 1 | 1 Mbps | Voice only |
| 2 | 4 Mbps | 4 Mbps Token Ring |
| 3 | 16 Mbps | 10BaseT Ethernet |
| 4 | 20 Mbps | 16 Mbps Token Ring |
| 5 | 100 Mbps (2 pair) | 100BaseT Ethernet |
| 1,000 Mbps (4 pair) | Gigabit Ethernet | |
| 5e | 1,000 Mbps (2 pair) | Gigabit Ethernet |
| 6 | 1,000 Mbps (2 pair) | Gigabit Ethernet |
| 6a | 10,000 Mbps | 10 gigabit (experimental) |
| 7 | 10,000 Mbps | 10 gigabit (experimental) |
Most twisted-pair cable has four pairs of wires, for a total of eight wires. Standard Ethernet actually uses only two of the pairs, so the other two pairs are unused. You may be tempted to save money by purchasing cable with just two pairs of wires, but that’s a bad idea.
If a network cable develops a problem, you can sometimes fix it by switching over to one of the extra pairs. But if you try to carry a separate connection over the extra pairs, electrical interference will prevent the signals from getting through.
You may also be tempted to use the extra pairs for some other purpose, such as for a voice line. Don’t. The electrical noise generated by voice signals in the extra wires can interfere with your network.
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Source:http://www.dummies.com/how-to/content/network-building-twistedpair-cable-categories.html
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