2. 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
3. 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.
4. 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.
5. 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
8. 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.
9. 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.
10. 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.
11. 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.
.
12. High speed modem :
They are design to transfer the data with signaling
rate up to 19.6kbaud.
PSK modulation techniques are used.
13. 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 .
14. 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.
15. More useful in connecting LAN with the Internet
Speed depends on the cost
modem is probably the most widely used data
communication roadway.
16. 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.
17. Niniejszym NETGEAR, Modem connection ,
Andrew S.Tanenbaum ,Pearson addition
Titles by Behrouz A. Forouzan on Data
Communications and Networking , edition
