Using the Ethernet

Thin Ethernet, also referred to as Thinnet or 10 Base-2, is a thin coaxial cable. It is basically the same as thick coaxial cable except that the diameter of the cable is smaller. Thin Ethernet coaxial cable is RG-58. Figure 1.10 shows an example of Thin Thernet.

With Thinnet cable, you use BNC connectors (see Figure 1.11) to attach stations to the network. It is beyond my province to settle the long-standing argument over the meaning of the abbreviation BNC. BNC could mean BayoNet Connector, Bayoner Nut Connector, or British Navel Connector. But it is mot commonly referred to as the Bayonet Neill-Concelman connector. What is relevant is that the BNC connector locks securely with a quarter-twist motion.

The BNC connector can be attached to a cable in two way. the first is with a crimper, which looks like funny pliers and has a die to crimp the connector. Pressing the levers crimps the connector to the cable. Choice number two is a screw-on connector, which is very unreliable. If at all possible, avoid the screw-on connector!

In order to attach the backbone cable run to each station, a passive device, known as T-connector, is used. Picture the uncut backbone cable extending to the back of each device. In order to complete the connection, the cable needs to be cut at the point where the loop is chosest to the interface. The two cut ends then need to be terminated with male BNC connectors and plugged into the two female BNC interfaces of the T-connector, with the third, male connector attaching to the female BNC interface on the device’s NIC card. It is in violation of the standard to have any sort of drop cable extending from the back of the device, unlike 10 Base-5, where such an attachment was customary. This requirement introduces a minimum of two caveats. The first is that any user that gains access to the back of their computer, and that wouldn’t be very hard, could disconnect the connectorized ends of the cut backbone, thus producing two unterminated LAN segments, neither one working properly. The second is that so many interconnections introduce failure points and opportunities for noise introduction.


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