ModemPresented by

Ravi Namboori

Index

Introduction to modem

Types of modem

Modem Functions

Modem purpose

Modem security

Introduction

A modem is an electronic device that transforms computer's digital information into analog carrier signals and vice versa. Computers use modems to interconnect with each other over a network. The word modem is derived from "modulator-demodulator" that defines the functions it performs. 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.

Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second (bit/s or bps), or bytes per second (B/s). Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal.

The following characteristics distinguish one modem from another:

Bps : How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 57,600 bps, although they can achieve even higher rates by compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data.

Voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.

Auto-answer: An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.

Data compression: Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.

Flash memory : Some modems come with flash memory rather than conventional ROM, which means that the protocols can be easily updated if necessary.

Fax capability: Most modern modems are fax modems, which means that they can send and receive faxes.

Different types of Modem are as follows:

Types of modem

Internal Modem

External Modem

PC Card Modem

It is the device installed in the desktop or laptop computer to communicate over a network with other connected computers. These are cheaper than external modems as they do not require a power supply or a chassis. There are two types of internal modems: dial-up and Wi-Fi (wireless). Dial up works on the telephone cables and requires a network access phone number and log on credentials to make a connection and Wi-Fi modem comments to the network without filling these credentials.

Internal Modem:

A modem that resides in a self-contained box outside the computer system. Contrast with an internal modem, which resides on a printed circuit board inserted into the computer. External modems are the simplest type of the modem to install this kind of modem you didn’t open the computer. The telephone line plugs into a socket on the rear panel of the modem. As external modems have their own power supply you can turn off the modem quickly to break the connection. The examples of these modems are the DSL modems which are used in the broadband connections. External modems tend to be slightly more expensive than internal modems.  

External Modem:

These modems, designed for portable computers, are the size of a credit card and fit into the PC Card slot on notebook and handheld computers. These modems are removed when the modem is not needed. Except for their size, PC Card modems are like a combination of external and internal modems. These devices are plugged directly into an external slot in the portable computer. So no cable is required other than the telephone line connection. The cards are powered by the computer, which is fine unless the computer is battery-operated. Running a PC Card modem while the portable computer is operating on battery power drastically decreases the life of your batteries.

PC Card Modem:

Functions of Modem Error correction

Flow control

Compressing the data

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