Modem

A modem is basically a computer peripheral that allows you to connect and communicate with other computers via telephone lines.

Modems allows you to combine the power of your computer with the global reach of the telephone system.

As you know that ordinary telephone lines cannot carry the digital information, a modem changes the digital data from your computer into analog data, a format that can be carried by telephone lines.

In a similar manner, the mode receiving the call then changes the analog signal back into digital data that the computer can digest. This shift of digital data into analog data and back again, allows two computers to speak with one another, called modulation/demodulation, this information of signals is how the modem received its name.

Modulation is the process of sending the data on a wave. There are basically three types of modulation techniques are used, given here:

• AM
• FM
• PM

Here, AM stands for amplitude modulation, FM stands for frequency modulation, and PM stands for phase modulation.

With a modem and a standard telephone line, you can send faxes to the offices or important customers without leaving your computer.

With an online or internet connection, you can also share recipes with fellow gournets catch up on the latest news, views a weather map, keep in touch from friends who are living far away from you just by using electronic mail, the worldwide web and much more.

Working of Modem

Modem converts digital signal to A/F (stands for Audio frequency) tones which are in the frequency range that the telephone lines can transmit and also it can convert transmitted tones back to digital information.

When the power is turned on in Data Terminal Equipment (DTE) and Data Communication Equipment (DCE), the terminal runs for self check, it asserts the Data Terminal ready (DTR) signal to tell the modem that it is ready.

When modem is powered up and ready to transmit the data, then the modem will assert the Data Set Ready (DSR) signal to the terminal.

Under the manual or terminal control the modem dials up the computer on the other end. If the computer is available, then it will send back a specified tone.

Now when the terminal has a character ready to sent, it will assert the Request To Send (RTS) signal to the modem.

Then the modem assert its Carrier Detect (CD) signal to the terminal to indicate that it has established contact with the computer. When the Modem is fully ready to transmit the data, then it asserts Clear-To-Send (CTS) signal back to the terminal. The terminal then sends the serial data characters to the modem.

When the terminal has sent all the characters, then it needs to make its RTS signal high. And this causes the MODEM to unassert its CTS signal and stop transmitting. Similar handshakes occur between Modem and computers on other side also.

Types of Modem

Modems come into the following two varieties:

• Internal Modems
• External Modems

Internal Modems

Internal modems are the modems that are fixed within the computer.

External Modems

External modems are the modems that are connected externally to a computer as other peripherals are connected.

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