Moreover with the isdn no modem is necessary because

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Unformatted text preview: purpose of & repeater is to strengthen a weak digital signal over long distances. Digital transmission of digital data is preferred to analog transmission of digital data due to the following reasons: 1. Lower cost, 2. No modems required, 3. Higher transmission speeds possible, and 4. Lower error rate (higher reliability). DATA TRANSMISSION SERVICES We saw that there are many different types of data transmission media that may be used for transmission of from one point to another. In practice, transmission of data from one computer system to another often involves several data transmission media, which together constitute the data transmission path between the sender and receiver computers. For example, the data transmission path between two computers located far apart might be constituted of copper wire, fiber optic cable and communication satellite. Organizations may afford to lay their own communication channels in a smaller geographical area such as within a building or a campus. However, it becomes impractical for organizations to do so in a larger geographical area such as between two cities or two countries. It is also impractical for them to set their own satellites in orbit. Therefore, organizations hire the services of data transmission service providers (popularly known as common carriers) for their data communications needs. VSNL (Videsh Sanchar Nigam Limited), BSNL (Bharat Sanchar Nigam Limited) and MTNL (Mahanagar Telephone Nigam Limited) are a few such common carriers in India, whereas AT&T, MCI, Western Union and GTE are a few such common carriers in the USA. The various types of services offered by the common carriers are: 1. Dial-up line. Dial-up line (also known as switched line) is a service that operates in a manner similar to a telephone call. That is, a user of a computer willing to communicate with a remote computer, first makes a connection request by dialing up the remote computer. A circuit is then established between the two computers via the telep...
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This document was uploaded on 04/07/2014.

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