1.5 MODEM

 In this section we will discuss several issues related to a Modem.

1.5.1 What is Modem?

Modem is an acronym for modulator demodulator. The meaning of the word modulator is to change and the meaning of the word demodulator is to unchange or restore to an original condition. A modem is a communication device that converts (i.e., modulate) binary signal into analog signals for transmission over telephone lines and converts (i.e., demodulate) these acoustics analog signals back into binary form at the receiving end.

The process of converting binary signal to analog signal is known as modulation and the process of converting analog signal back to binary signal is known as demodulation.

The Figure 6 shows the data transmission through modem


1.5.2 Use of Modems

Modems let you link your computer to the outside world i.e., Internet. You can use a modem to send data and files to anyone. You can also access information and download it for use on your PC.

Using a modem, you can connect directly to another computer that is also equipped with a modem, to an online service provider, or to the Internet and World Wide Web.  When you're connected, you can send and receive files or communicate in real timewhich means you communicate with little or no delay, as if you were facetoface with the person at the other computer.

Modems let you communicate over standard telephone lines with other computer users. You can transfer data, exchange electronic files, and even carry on a typed conversation in real time.

These days, a modem is a vital part of a PC; without one, you'll miss out on a wide range of opportunities. Here's a small things you can do with a modem:

  • · Exchange data directly with other computer users
  • · Access an online service or the Internet to gather information or to distribute information about anything, anywhere
  • · Exchange electronic mail
  • · Play interactive online games
  • · Make hotel or airline reservations
  • · Check stock prices
  • · Online Shopping
  • · Online enrollment with the course, the list is exhaustive.

1.5.3 Types of Modems

There are two basic types of modems:

1) Internal Modem

2) External Modem

 Internal Modem: These hardware boards you plug into an expansion slot in your PC's system unit. Internal modems are convenient because they don't take up desk space, and they use the computer's power supply so they are on whenever the computer is on.

An internal modem plugs into an expansion slot inside your PC. The phone jacks are accessed through a port on the back of the system unit.

External Modem: These are connected to the PC by plugging a cable into a port on the system unit. External modems also have their own power cords. You must turn on the modem when you want to make a connection. One benefit of an external modem is that you can move it to another computer if necessary. 

An external modem has controls and status lights on the front that you can use to monitor transmissions. 

Apart from choosing an internal or external modem, some main factors that one should consider are:

  • · Speed: A modem's speed, called the baud rate, is measured in bits per second (bps). Currently, speeds range from 56Kbps onwards, but the development of faster modems is going on.
  • · Cost. The faster the modem, the higher the cost. External modems generally cost higher than internal modems.
  • · Compression Standard: This allows modems to compress data before transmitting it, effectively increasing transmission speeds.

If you only use your modem to send and receive email messages, you may be able to do it with a modem as slow as 14.4Kbps. But if you use your modem to transmit and download heavy files (having images, sound, and animation) you should go for the fastest modem available.

1.5.4 Working of a Modem

A fullduplex modem consists of two sections: the transmitter and the receiver. These two sections are functionally separate from each other.

In order to make a connection using a modem you need the following:

Access to a telephone line: Modems have two jacks where you plug in standard telephone cables. You use one jack to connect the modem to the telephone line, and the other jack to connect the modem to a computer.

Data communications software: You need software to control the modem. Data communications software issues commands such as telling your computer when to dial and when to hang up. It also lets you set communications parameters such as the data transfer rate. The software must be compatible with both the modem and your PC.

Software drivers: You must have the necessary drivers (i.e. program) for the modem to work with your operating system. Windows XP comes with drivers for most of the latest modems.

1.5.5 Connecting a Modem Communication

Connecting a modem involves attaching the modem device to your PC and to the telephone line. The modem should come with the necessary equipment, including a standard RJ11 telephone cord as show in Figure 8. The steps you take depend on whether you have an internal modem or an external modem.

If you have an internal modem, you must install it by removing the cover of the system unit and plugging the modem card into a vacant expansion slot. Unless you are extremely confident about working inside your computer, you should have the modem installed by a professional computer technician.



If you have an external modem, however, you can easily connect it yourself.

To connect an external modem to your PC, follow these steps:

1) Locate the serial cable that comes with a modem. It should have a 25pin male connector at one end and a 25hole female connector at the other end.

2) Plug the female connector into an open 25pin serial port on the PC's system unit, and plug the male connector into the modem device.

3) Secure the connectors using the screws on either side.

4) Locate the power cord for the modem device and plug it into an electrical wall socket, power strip, or uninterruptible power supply. After the modem is connected to your PC, you must connect it to the phone line. This procedure is the same for both external and internal devices.

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