The information can be transmitted in either analog form or digital form or both with communication network. Computer generated data is digital whereas the telephone lines carry analog signals. On the basis of data transmission capabilities we can classify the data transmission as follows:-
- Analog Data Transmission
- Digital Data Transmission
Analog Data Transmission
Analog signal is another mode of transmission of the data, in which the signal is transmitted as a wave from terminal to other. This wave keeps on distorting as time passes. In needs an amplifier to make it in original wavelength. It is very important to note that these signals distorts with time and needs an external device to make it in original wavelength. For example a voice signal of telephone is analog signal. The analog signal is mostly used for long distance transmission as there is no loss of the data. The analogous signals are continuous. It occurs due to the changes in the sound, light, temperature, pressure and voltage. The change is occurred in the frequency of any of these will result in the change in the analog signal.
In comparison with analog signals, digital signals are non-continuous. It has a pulse or signal with two amplitude node. In this transmission of data, there are two states i.e. the “ON” and “OFF” states of electricity. The data is represented as “PRESENCE” i.e. “ON” and “ABSENCE” i.e. “OFF” of electric pulse. The presence of electric current is represented as 1 for HIGH and absence of current is represented by 0 for LOW (as the computer understands only 0’s and 1’s). Here, the signal cannot have HIGH-HIGH or LOW-LOW, the combination of the signal is always LOW-HIGH or HIGH-LOW. The digital transmission is faster than the analog signal transmission. Mostly telephone lines work on analog data transmission. Therefore, to convert digital signal to analog signal we use MODEMS.
The computer works in the principle of 0s, and 1s. These two digits are only used in the binary language because it is the language of the computer. The data in computer system exists as digital pulses but the telephone lines are made to transmit analog pulses or signals. For long distances the data has to be transmitted through telephone lines between different computers. This conversion is done by a device known as MODEM. This device performs following two types of functions (operations) :-
If we use telephone lines then before data transmission from one computer to another, data has to be converted from digital to analog signal. The process of converting digital data, before transmitting into analog data is known as MODULATION.
After the modulation the receiving computer has to reconvert the analog data receiving into digital form. This process is again done by reconverting analog signal to digital pulses or signals is called DEMODULATION.