Data transfer in Dial up Modems
The modem is the connection device between your computer and
the telephone line through which you connect to internet. The
word "modem" is a contraction of the words modulator
and demodulator. A modem is used to send and receive data over
a phone line. For an internet user, a modem is device that lets
you connect your computer to a standard telephone line so you
can get connected to internet. It is the key that unlocks the
world of the Internet and its World Wide Web, commercial online
services, electronic mail (E-mail), and bulletin board systems.
The phone lines transmit data in analog form and the data on
internet transmits in digital form. Also, your computer can process
data in digital form, in 0s and 1s. Hence, the main function of
the modem is to make both sides comfortable by providing data
in the form they could process or transmit. The sending modem
modulates the data into a signal that is compatible with the phone
line, and the receiving modem demodulates the signal back into
The modem has two ends one connects to the computer and other
one to the telephone line. When you try to makes a connection,
you can hear screeching sounds coming from the modem. These are
basically, digital signals coming from the computer to modem.
The modem modulates then into audible sounds to transmit over
the phone line. Then the modem sends them over to telephone line.
Modem sends a higher pitched tone to represent the digit 1 and
a lower pitched tone to represent the digit 0.
At the other end of your modem
connection, the computer attached to its modem reverses this
process. The receiving modem demodulates the received tones into
digital signals and sends them to the receiving computer.
This may sound very simple to most people. Actually, the process
is a much more complex than sending and receiving signals in one
direction and then another. Modems simultaneously send and receive
signals in small packets. This is important to gain the speed
in the transmission. For smooth working of a dial up connection
the modem should gain and give data simultaneously.
Another part of the translation process involves transmission
integrity. It is equally important to send and receive data properly
so could be represented in a proper form in front of user. Hence,
the modems also exchange an added mathematical code along the
way. It allows both terminals to know if the data packets are
transmitted in correct order. If the code does not match then
the modems communicate with each other by resending the missing
segments of data.
Modems also have special circuitry that allows them to compress
digital signals before modulating them and then decompressing
them after demodulating the signals. The compression/decompression
processes manage the data in a way that it can travel along telephone
lines more efficiently.
Hence, a modem is just more then a translator. Indeed, it is
the most important device in the dial
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