MODEM

Prepared by:

Kishan N. Patel

INTRODUCTION HISTORY TYPES OF MODEM FUNCTION OF MODEM WHY USE MODEM? TYPES OF MODEM BASED ON SPEED OF DATA

TRANSMISION ROLE OF MODEM MODULATION TECHNIQUES ADVANTAGES AND DISADVANTAGES OF MODEM CONCLUSION

INDEX:

Modem is a communication device that converts binary signal into analog signals for transmission over telephone lines and converts these analog signals back into binary form at the receiving end.

Conversion to analog signal is known as modulation. conversion back to binary signal is known as demodulation.

INTRODUCTION

Modems developed from the need to transmit data for North American air defence during the 1950s.

Robert Lucky invented the automatic adaptive equalizer in 1965 at Bell Laboratories.

In 1962, the first commercial modem was manufactured - the Bell 103 by AT&T.

The 56K modem was invented by Dr. Brent Townshend in 1996.

HISTORY

Modem can be a several types and they are categorized in a number of ways:

1. Directional capability : Half and full duplex modem

2. Connection to the telephone Line:2 or 4 wire modem

3. Transmission mode: Asynchronous or synchronous modem

TYPES OF MODEM:

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Data Compression Error Correction Flow Control

Internal Function of Modem

Function to be perform at transmitting end:

1. Take the data from RS-232 interface.2. Convert the data (0s and 1s) into

appropriate analog signal.3. Perform the line control and signaling to

other end of phone line.4. Send the dialing signal if modem is design

to dial without presence of user.5. Have protection against the line overload

and other problem.

FUNCTION OF MODEM:

Function to be perform at receiving end:

1. Receiving the analog signal and demodulate them into 1s and 0s form.

2. Put the demodulate into RS-232 format connect to RS-232 interface.

3. Perform the line signaling and control. 4. Have protection against the overload

problem.

5. Recover the data with minimum numbers of errors from the receiving signal corrupted by noise.

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A MO(dulator) DEM(odultor) is a device that translates an analog signal to digital and back. We use them to take patters of zeros and ones and turn them in to analog electrical signals so they can be sent along a wire, and then translated back to zeros and ones on the other end.

WHY USE MODEM?

Low speed modem : They are design to transfer the data with

signaling rate up to 300 or 600 bauds. Fsk modulation techniques is used.

Medium speed modem : They are design to transfer the data with

signaling rate up to 1200 to 4800 baud. BPSK,DPSK techniques is used. .

TYPES OF MODEM BASED ON SPEED OF DATA TRANSMISSION:

High speed modem : They are design to transfer the data with

signaling rate up to 19.6kbaud. PSK modulation techniques are used.

The normal digital signal cannot be put directly on the telephone line.

The role of modem is to convert the analog signal to digital signal and digital signal to analog signal.

A modem contains a modulator as well as a demodulator.

Modulator will convert digital signal to analog signal and Demodulator will convert the analog signal to digital signal .

ROLE OF MODEM

The basic modulation techniques used by modem to convert digital data to analog signal :

1. Amplitude shift key (ASK)2. Frequency shift key (FSK)3. Phase shift key (PSK) Modem is always used in pairs. Any system

whether half or full duplex require a modem at transmitting as well as receiving end.

MODULATION TECHNIQUES USED FOR MODEM

More useful in connecting LAN with the Internet

Speed depends on the cost modem is probably the most widely used

data communication roadway.

ADVANTAGES OF MODEM

Slow speed when compared to hub. Acts just as a interface between LAN and

Internet No traffic maintenance is present main disadvantage of modem is speed. if

although if you spend more money you get more speed. but that shouldn't be expectable.

DISADVANTAGE OF MODEM

Niniejszym NETGEAR, Modem connection , Andrew S.Tanenbaum ,Pearson addition   Titles by Behrouz A. Forouzan on Data

Communications and Networking , edition

REFERENCES