Section 4.1. Data Links


4.1. Data Links

A data link is the physical path between a data transmitter and data receiver. Figure 4.1 shows the range of electromagnetic-spectrum frequencies for various applications in data communications.

Figure 4.1. Frequency range for various data communications applications

  • The low-frequency subspectrum covers all the frequencies in the range 0 to approximately 15,000 Hz, which is the range of human-voice frequencies generally used in telephone systems .

  • The radio frequency (RF) subspectrum covers frequencies from several KHz to several GHz. RF applications in telecommunications includes radio systems , television systems , Bluetooth communications , and cell phones .

  • The microwave frequency subspectrum ranges from several GHz up to more than 10 11 Hz and is used for such applications as microwave systems , radar , and satellite communications .

  • The infrared frequency subspectrum ranges from more than 10 11 Hz to less than 10 14 Hz. The infrared signal can be used for remote controls , lasers , and guided missiles .

  • The light frequency subspectrum covers all the visible-light components and is used mainly for fiber- optic communications .

Data transmission may use either wired links or wireless links , depending on the application and the available bandwidth of links. Transmission links can also be classified as guided , or directional, and unguided . A wired link is normally considered a guided medium for the propagation of data. A wireless medium can be designed to propagate signals in more than one direction, causing the medium to become unguided. Signals travel on the link in the form of electromagnetic waves. Let c be the speed of electro-magnetic waves, f be the frequency of the traveling signal, and » be the wavelength of the signal. Then:

Equation 4.1


A guided link, whether wired or wireless, can be full-duplex , whereby two bitstreams in opposite directions can be transmitted, or half-duplex , whereby only one bitstream in one direction can be carried at any time. The following section explores the most commonly used data links.



Computer and Communication Networks
Computer and Communication Networks (paperback)
ISBN: 0131389106
EAN: 2147483647
Year: 2007
Pages: 211
Authors: Nader F. Mir

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