Network Cabling and Components

By Stephen Bucaro

Although the power and sophistication of networking protocols and software is impressive, a network could not operate without physical cable and components. Even a wireless network needs physical components such as access points. And because wireless networks are subject to problems like interference and lower security, cable will be the media of choice for many networks for a long time to come.

Coaxial Cable

Coaxial Cable (coax) uses a solid wire in its core that is surrounded by a braided metal shield. Insulating material separates the wire core and metal shield. The central wire carries the electrical signal of the network data. The metal shield protects the data from electrical interference. Early Ethernet networks used thick RG-8 coaxial cable. This cable is referred to as Thicknet.

The IEEE created a system to specify network cabling. Thicknet is designated 10base5. The 10 specifies the maximum speed in megabits per second at which the cable can transfer data. “Base“ stands for baseband signal type. Baseband means it uses a digital signal. The 5 specifies that 500 meters the maximum length of a cable segment.

Thicknet cable is very rigid, so the network computers and peripherals do not connect directly to the cable. Each computer or other device, referred to as a node, connects to the coax using a thinner drop cable. The Thicknet backbone may run in the ceiling, with drop cables used to attach the individual computers. Each drop cable is connected to the Thicknet backbone using a transceiver.

To attach a transceiver to the Thicknet cable requires a technician to cut a hole through the cable shield and attach a “vampire tap“ which pierces the wire core of the coaxial cable. The transceiver is then connected to the network interface card of the computer using a cable with a DB-15 connecter called a DIX (Digital Intel Xerox) or AUI (Attachment Unit Interface).

Transceivers may be placed no closer together than 2.5 meters and the transceiver drop cable may be no longer than 50 meters. No more than 100 nodes may be connected to the Thicknet segment.

Because of the high cost and difficulty of installation, Thicknet is rarely used today. If it is already installed, or if there is high electrical interference in the environment, it may still be used. Large networks may use Thicknet as a main backbone cable to connect branch network segments.

10Base2

There are two types of coaxial cable. Besides the Thicknet just discussed, there is Thinnet. The IEEE designation for Thinnet is 10Base2. You might think the "2" in 10Base2 means that the maximum length of a cable segment is 200 meters, but in actuality the maximum length is only 185 meters.

The Thinnet network cable does not use a drop cable, but instead connects directly to a computer's NIC using a BNC "T" Connector.

The electronic signal travels through the BNC T connectors to each node on the bus and to the ends of the cable. A BNC terminator is connected to each end of the cable to absorb the signal and prevent it from bouncing back.

If a coax cable needs to be extended, two pieces of cable can be connected together using a barrel connector. But if the entire length of the cable segment is longer than 185 meters, the signal will attenuate (weaken) to the point of becoming unreliable.

The signal is also attenuated slightly anytime it encounters a T connector or barrel connector. For this reason a 10Base2 network may have a maximum of only 30 nodes on a segment.

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