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Table Of Contents  CertiGuide to A+ (A+ 4 Real)
 9  Chapter 13: Basic Networking Terminology
      9  Cables and Fibers

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Ethernet Cabling Summary
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SingleMode/MultiMode Fiber
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Fiber Optic Cabling

Fiber-optics use light pulses instead of electrons, as in copper-based cabling, to transmit information. This process begins with a transmitter. The transmitter accepts coded electronic information and converts this information into coded light. By using a lens, the information is sent into the fiber-optic cable. The coded light information travels down the fiber-optic carrier/core by a process known as internal reflection. Just as with metal-based communication, for example copper cable, a communications signal typically travels only one direction. The reason for this has nothing to do with the laws of physics. It is more a matter of economics. It is cheaper to connect either type of cable to electronics that are designed to do one job, such as transmit or receive, than to do both. Just as with communications with copper wire and unshielded twisted pair, multiple conductors may be hidden inside an outer jacket, making it not visually obvious that more than one conductor is at work. With this understanding, lets look at what makes up a fiber-optic cable.

Five elements are combined to make a fiber-optic cable. They are: the optic core, and optic cladding, a buffer material, other material for strength, with an outer jacket completing the fiber-optic cable.

It is the cladding that creates a reflective surface, allowing the light pulses to reflect off the interface so it remains within the core. The buffer material is used to prevent the core and cladding from being damaged. Surrounding the buffer is a strength material such as Kevlar to prevent stretching when the fiber cable is being installed. The outer jacket is added to protect from contaminants and abrasion.

As with copper cable, the outer jacket of fiber-optic cable must be plenum rated if it is going to be installed in the concealed space above suspended ceilings, or encased in conduit. This has to do with protecting humans and the environment from toxic fumes that are created when plastic burns. Figure 425 depicts the construction of fiber-optic cable.


Figure 425: Construction of a Fiber Optic Cable

 


When the light pulses arrive at the destination they are funneled into an optical receiver. It is the goal of an optical receiver to receive light and convert it to an electrical signal conveying information from the transmitting end. The data is now ready for a computer, TV, or telephone.

In comparison to copper, fiber-optic technology has several advantages. These include: smaller physical size, lighter weight, as well as immunity to EMI, RFI and voltage spikes. EMI (Electromagnetic interference) is generated by the circuits inside PCís and CRT displays, among other things. RFI (Radio Frequency interference) is generated by devices such as cell phones and wireless networking. As you can see, a typical office environment is likely to have its share of both.

Fiber-optics does not produce electrical sparks, preventing a fire hazard. Fiber-optic cable can carry a signal over longer distances than copper or aluminum cable before the signal degrades. Since light waves operate at a higher frequency than electrical/electronic signals, more data is delivered than with metallic conductors.

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Ethernet Cabling Summary
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SingleMode/MultiMode Fiber
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