Tip

Networking cable

There are many types of cable used in networking. Some are preferable to others by the simple fact that they can perform better, have met certain specifications, and have less "skew" factor (a measure of signal degradation). Whether cabling a new network or replacing an existing network's cables, some thought should be given as to which type of cable will do the best job. There are several cabling guides that offer useful general-purpose hints and guidelines for selecting and installing cable. A brief search on the Internet should retrieve local vendors, as well as guides.

For example, see any of the following:

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The main trunk of the network is often referred to as the backbone cable. Most often, this connects to an Ethernet hub or switch. Individual nodes and other devices may be connected to this cable using special adapters, transceivers, and separate stretches of cable called drop cable, which connects to the node. Backbone cable typically runs behind walls, in shafts, or under the ground, as opposed to horizontal cable, which runs from a wiring closet or distribution frame.

Backbone cable can be unshielded twisted pair (UTP), which is 100-ohm, multi-pair cable. Older versions are used for voice-grade communications only. Category 5 (Cat-5) UTP can be used for 100Mbps data transmission, but is usually employed in drop cables, not backbones. Shielded twisted pair (STP), 150-ohm cable is sometimes used as in the IBM Cable System. The two most popular types of cable for backbone in use today are Coaxial, and Optical fiber cable. Coaxial cable is often used in Ethernets with 50 ohms impedance, and for CATV cable, which is 75-ohm broadband. Some of the advantages are that broadband coaxial can be used to transmit voice, data, and video. It is very easy to install and is reasonably priced when compared to other types of cable. The downside to coaxial is that it is easily damaged, and the thicker types can be stiff and difficult to work with. It cannot be used with Token Ring networks. Connectors can be expensive.

Optical fiber cable is popular because it is harder to tap, thereby offering more security; has a much higher bandwidth, or data-transfer rate; is safer because there is no electricity to produce shock; and is thinner and lighter than electrical cable. Installation has recently become relatively easy. It is, however, more expensive than other types of cable, and its partner NICs are very expensive. Couplers are often subject to cross talk. Fiber connectors are not as efficient as they could be, and, as a result, signal loss can be high. There are many more parts that can break in a fiber-optic connection. Care must be taken to preserve its shape so that signal loss is kept to a minimum. The cable should not be placed under any heavy weight or bent into unnatural shapes or signals can be distorted. Depending upon what type of network you will be cabling, the size of the network, and what type of transmission is required, either of these cables might be the right choice. A good quality of cable, that meets the appropriate standards, should give you the type of performance needed to ensure a quality networking experience.


Barrie Sosinsky (barries@killerapps.com)is president of consulting company Sosinsky and Associates (Medfield MA). He has written extensively on a variety of computer topics. His company specializes in custom software (database and Web related), training and technical documentation.

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Related Book

Understanding Optical Fiber Communications
Author : Alan J. Rogers
Publisher : Artech House
Published : Mar 2001
Summary :
Here is a book which makes modern optical-fiber communication systems easy to understand. It gives you an up-to-date, comprehensive overview of the principles and operation of present-day optical-fiber communications, without the use of advanced mathematics.


This was first published in April 2001

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