Wired Transmission Media
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| Wired Transmission Media |
Wired transmission media are used in fixed networks physically connecting every
network element.
There are different types of physical media, the most common of
which are copper wires, twisted pair, coaxial cables, and optical fibers.
Copper wires have been traditionally used in communication because of their
low resistance to electrical currents that allows signals to travel even further. But
copper wires suffer interference from electromagnetic energy in the environment,
and because of this, they must always be insulated.
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| Copper wire |
Twisted pair is a pair of wires consisting of insulated copper wire each wrapped
around the other, forming frequent and numerous twists.
Together, the twisted, insulated copper wires act as a full-duplex communication link. The twisting of the wires
reduces the sensitivity of the cable to electromagnetic interference and also reduces
the radiation of radio frequency noises that may interfere with nearby cables and
electronic components.
To increase the capacity of the transmitting medium, more
than one pair of the twisted wires may be bundled together in a protective coating.
Because twisted pairs were far less expensive, easy to install, and had a high quality of voice data, they were widely used in telephone networks. However, because
they are poor in upward scalability in transmission rate, distance, and bandwidth in Data Communication Media Technology 11
LANs, twisted pair technology has been abandoned in favor of other technologies.
Figure 1.8 shows a twisted pair.
Coaxial cables
Coaxial cables are dual-conductor cables with a shared inner conductor in the
core of the cable protected by an insulation layer and the outer conductor surrounding the insulation. These cables are called coaxial because they share the inner
conductor.
- The inner core conductor is usually made of solid copper wire, but at times can also be made up of stranded wire. The outer conductor commonly made of braided wires, but sometimes made of metallic foil or both, forms a protective tube around the inner conductor.
- This outer conductor is also further protected by another outer coating called the sheath. Coaxial cables are commonly used in television transmissions.
- Unlike twisted pairs, coaxial cables can be used over long distances.
- There are two types of coaxial cables: thinnet, a light and flexible cabling medium that is inexpensive and easy to install; and the thickent, which is thicker and harder to break and can carry more signals through a longer distance than thinnet.
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| Coaxial cables |
Optical fiber
Optical fiber is a small medium made up of glass and plastics and conducts
an optical ray. This is the most ideal cable for data transmission because it can
accommodate extremely high bandwidths and has few problems with electromagnetic interference that coaxial cables suffer from.
It can also support cabling for
several kilometers. The two disadvantages of fiber-optic cables, however, are cost
and installation difficulty. A simple optical fiber has a central
core made up of thin fibers of glass or plastics. The fibers are protected by a glass or
plastic coating called a cladding.
The cladding, though made up of the same materials as the core, has different properties that give it the capacity to reflect back the
core rays that tangentially hit on it.
The cladding itself is encased in a plastic jacket.
The jacket protects the inner fiber from external abuses such as bending and abrasions. Optical fiber cables transmit data signals by first converting them into light
signals. The transmitted light is emitted at the source from either a light emitting diode (LED) or an injection laser diode (ILD).
At the receiving end, the emitted rays
are received by a photo detector that converts them back to the original form.
Twisted pair
Twisted pair is a pair of wires consisting of insulated copper wire each wrapped around the other, forming frequent and numerous twists.
Together, the twisted, insulated copper wires act as a full-duplex communication link. The twisting of the wires reduces the sensitivity of the cable to electromagnetic interference and also reduces the radiation of radio frequency noises that may interfere with nearby cables and electronic components.
Wired transmission media is media used to transfer information from a network to another network using transmission cables.
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