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Table Of Contents  CertiGuide to Network+
 9  Chapter 0001:  LAN Cabling
      9  IV  Coaxial Cable (Coax)

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5-4-3 Rule for Coax
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Coax Termination
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Connecting Computers to a LAN Using Coax

Multiple computers are attached to a single segment in different ways, depending on whether the network is wired with 10Base2 or 10Base5 cable. The process of attaching a computer to a 10Base5 cable is called tapping. The tapping device is called a vampire tap, because it works by puncturing the outside of the 10Base5 cable to create a connection between the 10Base5 cable and a drop cable leading to the workstation.

Connections to 10Base2 networks are normally accomplished by daisy-chaining lengths of coax between individual stations on the network via a three-connector adapter called a T-connector. When seeing a 10Base2 network cable for the first time, one is tempted to plug it straight into the matching BNC connector on a computer’s network interface card, like one would plug a cable TV wire into a television.

Instead, the proper way to connect a workstation to a 10Base2 network is to attach the two sides of the bus network’s backbone to the two opposite-pointing connectors on the BNC tee connector, and attach the center connector in the Tee to the PC’s NIC directly. The name of the tee connector, or T-connector, comes from its T-shaped resemblance to a pipe tee, which allows the ends of three cables to be connected together.

The NIC is the host hardware component, usually in the form of a plug-in hardware card, which includes a matching connector for the specified type of network cabling (be it BNC, RJ-45, or something else), and which takes care of sending and receiving data to and from the network, for the host.

Why indirectly connect via a T-connector, instead of plugging the cable directly in? Remember, 10Base2 networks implement a bus topology. The cable shouldn’t end at any host. If it did, there would be no way to connect additional computers to the bus on either side of that host. Rather, the cable should function as a long, continuous “bus” which periodically includes connections to devices such as computers.

Since normally cable continues on both sides of each computer plugged in to a bus network, to keep the signal flowing along the cable, you might wonder what happens to the computers that are at the two ends of the bus. The answer is that they are connected in the same way as other devices on the network, with the two ends of a bus network treated as a special case, requiring termination. In that case, instead of cables being attached to both sides of the T, a cable will be attached to one side, and a terminator (or terminating resistor) will be attached to the other side.

Table 1: Legacy Coax Cable Tolerances and Specifications


Popular Name



5-4-3 RuleType



500 meters





185 meters



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