Telecommunication Media:
The various media over which data is transmitted and received in a telecommunications network are called telecommunication media. The media to interconnect the various components of a telecommunications network are basically classified as guided media and unguided media.
Guided media:
Guided media, also called bounded media, consists of a solid medium called a transmission line through which the waves are guided. This type of media consists of a cabling system. The cabling system guides the signals through a specific path. These include open wires, twisted-pair wires, coaxial cables, and fiber optic cables, which provide physical link to the devices in a network. For guided media, transmission of data depends largely upon the transmission medium used.
Open wires: Open wires (similar to electrical wires hung between poles) do not have protection or shielding from noise or other kinds of interferences.
Twisted-pair wires: Twisted-pair wires are the most commonly used medium for telecommunications today. This transmission medium is mostly used in star and hub networks. A twisted-pair wire consists of copper wires twisted into a pair. The wires are twisted together to reduce noise. Such networks can transmit both voice and data. This transmission medium also enhances the electrical performance and gives out higher bit rates compared to the untwisted-pair wires. The twisted-pair wires are twisted to form cables which are useful for high speed communication. Twisted-pair wires are more flexible than coaxial cables and optical fibers and it is very easy to install them.
Optical fibers: Optical fibers use cables consisting of one or more hair-thin filaments of glass fiber wrapped in a protective jacket. They can conduct light pulses generated by lasers at transmission rates of as high as 30 billion bits per second. Optical fibers have the highest bit rates among all the telecommunications media. These cables reduce the size and weight of the network substantially, work at a greater speed, and have greater carrying capacity. The disadvantage with them is that there is difficulty in slicing them to make connections. This, however, can be a security advantage as it limits line tapping.
Unguided media:
Unguided media, also called unbound media or wireless media, are media through which transmission and reception takes place through an antenna. This type of a medium has a means for the signals to travel. However, the signals are not guided through a specific path. In other words, the data signals are not bound by a cabling system as in guided media. These include terrestrial microwaves, communication satellites, cellular phone systems, and wireless LANs, which use microwave and other radio waves. In addition, there are infrared systems. For unguided media, transmission of data depends largely upon the bandwidth produced by the antenna.
Terrestrial microwaves: Terrestrial microwave involves earthbound microwave systems that transmit high-speed radio signals between the relay stations spaced approximately at 30 mile intervals. Microwaves are similar to radio waves or light and can cover long distances. Microwave antennas, placed on top of buildings, towers, hills, and mountain peaks, carry out the transmission from one station to another. Systems equipped with microwaves have enough bandwidth to support numerous voice channels and about two television channels. This medium can be widely used in locations where cabling is very expensive. The major disadvantage with this system is that the microwave antennas are required to be placed in line of sight or in a place where they are visible from each other. Geographical constraints could make this a difficult proposition in some areas.
Communication satellites: Communication satellites are special applications of microwaves. Satellites use microwave radio as a telecommunication medium but are placed in stationary geosynchronous orbits. They are powered by solar panels and transmit microwave signals at the rate of several hundred million bits per second. Communication satellites are mainly used for voice and video transmission where high-speed transmission of large volumes of data is required. Many large corporations and other users have developed satellite networks, using satellite dish antennas known as VSAT (Very Small Aperture Terminal) to connect their distant work areas. The disadvantage with using satellites as a telecommunication medium is the high cost involved in manufacturing and installing them.
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