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Introduction to Networking: Difference between revisions
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== Cables and wires ==
A network can connect using cables, coax, fibre, or radio, but we will concentrate on cables. Generally, the way a network operates once connected is the same whatever method you use. The speed may change, but it is still effectively an ethernet network we are talking about.
The cables you will have heard of are "cat 5" or "category 5" or "cat 5e". Cat 5 is basically a system of structure cabling, and a cat5 lead or patch lead is just part of that. A patch lead is just a lead with a plug each end that connects things together. Cat5 cabling does not generally have any cables over 100m long, and some types of network need shorter lengths to work at full speed.
The cable itself has 8 wires arranged as 4 pairs. The fact that they are pairs is important to the way the electrical signals are carried. Each pair has a colour: blue, orange, green and brown. Each pair is two wires twisted together (see picture on right). One is coloured (with maybe thin white stripes) and the other is white with thin coloured stripes.
The colours themselves don't matter - the electrical signals don't matter, but there are conventions which you should follow, and it is important that the pairs are not split.
▲[[Image:plug.gif|RJ45 plug]]If you look at the plugs on the end of the cable they are 8 way square, usually clear plastic and you can see the wires in the plug.
The colours normally used, are...
*One pair is ''transmit''
*and one is ''receive''.
Normally a cable is straight, i.e. the same wiring at each end - pin 1 to pin 1, pin 2 to pin 2, etc. To make this work there are two types of sockets - the ones you find on a computer and the ones you find on a hub. The two types of sockets are wired differently so that a straight cable can be used to connect between them correctly. This means that at one end pins 1 and 2 are transmit and at the other end they are receive, so it works.
In some cases you need to connect a computer port to a computer port or a hub to a hub. Some hubs have an alternative or switched port to allow hub to hub connections with a straight lead, but if this is not the case, or it is in use, you need a crossover lead. A crossover lead has transmit connected to receive. i.e. 1 to 3, 2 to 6, 3 to 1, and 6 to 2. You can tell a crossover lead as the colours of the cables are different at each end, e.g. one end normally starts White then Green rather than White then Orange as normal.
== Hubs and switches ==
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