What is the Function of a Modem

Modulation is the process of changing the form of the signal carrying the information. The demodulation process does the task of extracting information from the signals that are modulated. Analog signals can be transmitted by using devices such as a radio or a diode. Modems are classified on the basis of two criteria,

• Data sent per unit time
• Change in the state of the signal per unit time

Modems were first used in the '60s decade, for connecting computers over a network of telephone lines. The period is also known as the age of time-share computers, since the computers had to buy time in order to connect to the network by means of a modem which had a speed of 300 bits/second.

How Does a Modem Work?
A computer sends information in the form of digital signals. But the information over the telephone lines needs to be transmitted in the form of analog signals. To solve this problem, the functionality of a modem comes into play. It converts the digital signals into analog signals. These analog signals are carried over the telephone lines. When these signals reach another computer, the analog signals are converted back to the digital form by its modem.

Different Functions of the Modem
In addition to converting digital signals into analog signals, the modems carry out many other tasks. Modems minimize the errors that occur while the transmission of signals. They also have the functionality of compressing the data sent via signals. Modems also do the task of regulating the information sent over a network.

• Error Correction: In this process the modem checks if the information they receive is undamaged. The modems involved in error correction divide the information into packets called frames. Before sending this information, the modems tag each of the frames with checksums. Checksum is a method of checking redundancy in the data present on the computer. The modems that receive the information, verify if the information matches with checksums, sent by the error-correcting modem. If it fails to match with the checksum, the information is sent back.
• Compressing the Data: For compressing the data, it is sent together in many bits. The bits are grouped together by the modem, in order to compress them.
• Flow Control: Different modems vary in their speed of sending signals. Thus, it creates problems in receiving the signals if either one of the modems is slow. In the flow control mechanism, the slower modem signals the faster one to pause, by sending a 'character'. When it is ready to catch up with the faster modem, a different character is sent, which in turn resumes the flow of signals.

Different Types Of Modems
Modems are classified on the basis of different criteria such as the place where they are installed, the manner in which they accept information and the way they transmit signals. Based on these criteria, modems are divided into the following types.

• Internal and External Modems: Internal modems are in the form of circuit boards, fitted in expansion slots of the motherboard. External modems are enclosed in separate cases and not inside the system units. The modem is connected to the computer and telephone line by means of two separate cables.
• Intelligent and Standard Modems: The standard modems accept instructions entered from the keyboard of a microcomputer. The intelligent modems respond to commands and transmit information simultaneously. It is done with the help of microprocessor chips.
• Wireless and Short-Haul Modems: Short-Haul modems transfer data by means of cables. Since they don't need an external power source, they are also called 'modern eliminators'. The wireless modems don't require any kind of cable to transmit the data signals.

Modems have an important role to play in computer networking. Broadband USB modems have proven useful for laptops. With improvement in technology, the modems are becoming advanced and refined in their working. Facilities like satellite internet are provided by the means of satellite modems. In this age of information technology the use of high speed internet access like the broadband and in turn modems, is bound to grow.