This preview shows page 1. Sign up to view the full content.
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...
View Full Document
This document was uploaded on 04/07/2014.
- Spring '14