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As the digital signals cannot be transmitted along the telephone lines, therefore, the modem 1 at the transmitting station 1 converts the digital data from the machine into the analog form, modulates a suitable carrier wave with this analog form of the audio signal, and finally transmits the modulated wave along the telephone line.
Modem - types of modem.
Introduction:
The modem, a remarkable device (from MOdulator—DEModulator) heralded a new age of communications and played a big role in the the internet explosion .
The first PC modem (80-103A) was created in the year 1977, by Dale Heatherington and Dennis Hayes. Dennis Hayes was born in 1950 and Dale Heatherington was born in 1948. Dennis Hayes met Dale Heartherington at National Data Corporation, when he worked after completing his studies at Georgia Institute of Technology.
Modem-types of modem
A modem is a device that can connect one computer to another across ordinary telephone lines.
The name modem is actually the short form of the terms modulator and demodulator I. e., It is a device which performs the function of both, the modulator and the demodulator. In fact, a modem acts as a modulator in the transmitting mode and acts as a demodulator in the receiving mode.
Figure, shows the communication circuit of a modem.
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| Modem |
Modem 2 at the receiving station 2 demodulates the modulated carrier to retrieve the data on the 2 computer in the digital form.
In the same way, for sending the data from station 2-1 , modulator section of modem 2 and demodulator section of modem 1 perform the function.
This work is performed by modems in a variety of speeds, as it depends on the availability of access line and the technology.
Some important features of modems are :
1. Bits per second (bps) :-
This is the rate of transmitting and receiving data by a modem. Data 14.4 kbps are often used by a modem for sending and receiving electronic male or faxes.
To denote high data speeds, large units are sometimes used . One kilobit per second which is abbreviated as bps in the U.S and kbps in other countries is equal to 1,000 bps. One megabit per second (Mbps) is equal to 1,000,000 bps or 1,000 Kbps.
2. Voice /data mode :-
In voice mode, the modem acts like a regular telephone and in data mode, the modem acts like a regular modem .
When a modem with voice capability is in "voice data "mode, any data sent to the modem is interpreted as an audio data and is then played over the phone line, rather than character bytes which are transmitted digitally to the other party.
3. Auto answer :-
An auto answer modem enables our computer to receive calls in our absence. These are suitably recorded and can be reproduced.
Types of modems :
Three types of modems are in use which are named as internal modems, external modems and PCMCIA modems.
I) Internal modems :-
These type of modems are generally less expensive and are the modems which are easy to install. Internal modems come on a card that plugs into our PC bus.
II) External modems :-
These type of modems are having their own power supply and are the modems which are connected to PC through a cable. They can be moved easily and are having many independent controls.
iii) PCMCIA modems:-
These type of modems are popular for laptops being used by the people on the move.
The modems can be used to transmit and retrieve the data in the following three modes:
1. Simplex mode :
In this mode , the data signals can be transmitted between the two stations in only One Direction.
2. Half duplex mode :
In this mode , the data signals can be transmitted between the two stations in both the directions, with the restriction that only One Direction can be used at a time.
3. Full duplex mode :
In this mode, data signals can be transmitted between the two stations in both the directions at the same time. This is one of most efficient mode.
Conclusion:
This article has discussed about the concept of modem and the types of modem. This article also provides you information about how the modem helps in transmitting data. By the end, the concept of modem and it's types is clear.
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