Twisted Pair Cabling
Twisted-pair (also known as 10BaseT) is ideal for small, medium, or large networks that need flexibility and the capacity to expand as the number of network users grows. 10BaseT cabling looks very similar to that of common telephone cable, although instead of four (4) wires, there are eight (8). In the picture immediately below, you will see an RJ-11 connector or plug, as well as an RJ-45 connector. The RJ-11 connector is common to normal in-door telephone wiring, while the RJ-45 is for 10BaseT network cable.
In most circumstances we recommend using 10BaseT cabling for its flexibility and reliability, however if a single cable must be 325 feet or longer you will need to install a repeater to amplify the signal through the cable. This is where thin coax (10Base2) is sometimes preferred as it can be as long as 600 feet.
In a twisted-pair network, computers are arranged in a star pattern as mentioned earlier. Each computer has a twisted-pair cable that runs to a centralized hub. Twisted-pair is generally more reliable than thin coax networks because the hub is capable of correcting data errors and improving the network's overall transmission speed and reliability. Also known as up-linking, hubs can be chained together for even greater expansion. Until recently it was more expensive to implement a network that included both 10Base2 as well as 10BaseT, as you needed to purchase hubs that accommodated both types of cabling and connectors. With the development of the Balun, (see picture below) it is easy to add a thin coax based (10Base2) computer to a twisted pair (10BaseT) network, and likewise, a 10BaseT based computer to a 10Base2 network.
Immediately below you will see (in a clockwise rotation) a combined network that uses a computer with a 10BaseT network card, a laptop with a PCMCIA network card and a computer with a 10Base2 network card. For clarity purposes, the Balun would be attached to the "T connector on the 10Base2 network card and the RJ-45 plug. A termination plug would then be added to the opposite side of the "T" connector.
There are different grades, or categories, of twisted-pair cabling. Category 5 is the most reliable and widely compatible, and is recommended by most network designers. It runs easily with 10Mbps networks, and is required for Fast Ethernet. You can purchase Category 5 cabling that is in pre-cut lengths, or you can purchase it on bulk spools and cut and crimp to your own specific lengths.
Category 5 cables can be purchased or crimped as either straight-through or crossed. A Category 5 cable has 8 thin, color-coded wires. Although only wires 1, 2, 3, and 6 of the total 8 wires are used by Ethernet networks for communication, all the wires have to be connected in both jacks.
Straight-through cables are used for connecting computers to a hub.
Crossed cables are used for connecting a hub to another hub (the exception to this is when some hubs have the built-in uplink port that is crossed internally, which allows you to uplink hubs together using a straight cable).
In a straight-through cable, wires 1, 2, 3, and 6 at one end of the cable are also wires 1, 2, 3, and 6 at the other end.
In a crossed cable, the order of the wires change from one end to the other: wire 1 becomes 3, and 2 becomes 6.
To figure out which wire is wire number 1, hold the cable so that the end of the plastic RJ-45 tip (the part that goes into a wall jack first) is facing away from you. Flip the clip so that the copper side faces up (the spring lock clip will now be parallel to the floor). When looking down on the coppers, wire 1 will be on the far left. The following examples will show you graphically what this looks like.
Thin coax (also known as 10Base2) is great for small home or office networks with two or three computers. Similar to the cabling used to connect a VCR to a TV set, coax cabling is inexpensive and easy to set up and does not require a hub.
In a thin coax network, which is sometimes called a backbone, computers are arranged in a "chain" with a beginning and an end. Each computer in a backbone requires a network card, a T-connector, and at least one incoming or outgoing coax cable.
The computer at each end of the network will also require a 50-ohm terminator plug.
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