Communication media means sending and receiving data. Media is the general term used to describe the data path that forms the physical channel between the sender and the receiver. Media can be twisted-pair wire, such as that used for telephone installations It can be coaxial cable of various sizes and electrical characteristics. It can be also fiber-optic cables and wireless, supporting either light waves or radio waves.
Note : Wire or fiber-optic media are referred to as bounded media. Wireless media are sometime referred to as unbounded media.
Media differ in the capability to support high data rates and long, distance transmission. the reasons for this are:
Noise absorption is the susceptibility of the media to external electrical noise that can cause distortion of the data signal and thus data errors.
Radiation is the leakage of signal form the media caused by undesirable electrical characteristics of the media.
Attenuation is the decline of the magnitude of signal with distance due to the absorption of energy by the media. Radiation and the physical characteristics of the media contribute to attenuation or the reduction in signal as the signal travels down the wire or through free space.
Bandwidth is similar to the concept of frequency response in a stereo amplifier, the greater the frequency response the higher the bandwidth. According to a fundamental principle of information theory, a higher data transfer rate.
There are several types of physical channels (communication media) through which data can be transmitted of energy can be either guided of unguided. Some of the most common data transmission media are briefly described in the following sections :
Guided media refers to the method of transmission of data over which signal can travel in a network. Examples of guided media include the following :
A twisted-pair wire consists of two insulated copper wires typically 1mm thick. The wires are twisted together in a helical shape. The purpose of twisting the wires is to reduce electrical interference from similar pairs that are close by. In local telephone communication and for digital data transmission over short distances up to 1km. When many twisted pairs run in parallel for a substantial distance such as all the wires coming from a multistory apartment building to the telephone exchange they are bundled together and placed in a protective sheath.
Coaxial cable consists of a stiff copper wire as the core surrounded by an insulating material. The insulator is encased within a cylindrical conductor, often as a closely woven braided mesh. The outer conductor covered in a protective plastic sheath. Two kinds of coaxial cable are widely used. One kind 50-ohm cable, is commonly used for digital transmission. The other kind - 75-ohm cables, is commonly used for analog transmission in cable TV transmission.
Optic fiber is the newest form of bounded media. This media is superior in data handling and security characteristics. The fiber-optic cable transmits light signals rather than electrical signals. It is by far more efficient than other network transmission media. Each fiber has an inner core of glass or plastic that conducts light. There are two types of light sources for which fiber cables are available. These sources are :
Media in which the signals are not guided through a solid medium are known as unguided media. Air is the media through which electromagnetic energy can flow easily. Therefore there are several methods which are in use to send electromagnetic energy through air.
( Learn more about unguided media here: Wireless Communication or Transmission )
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