1.2 DATA AND SIGNAL

 Communication is the need of the day and not having the basic knowledge of the communication system could easily imply to your being uneducated. In the connected world, a computer does not work as a stand alone system but as a part of a communication system. Besides computers the ships, the aircraft’s, the rockets, the satellites etc. rely on the communication system for their successful operation. And thus, communication can be said to be the one of the major factors for the rapid modernization of the world.

In the most fundamental sense, communication involves implicitly the transmission of information from one point to another through a succession of processes. Information being sent is also referred to as data. Data and signals are the two basic building blocks of computer networks. Data transmitted over any communications medium is either digital data or analog data. Analog data (Figure 1 (a)) refer to continuous nature (or states) whereas digital data (Figure 1(b)) refer to discrete states. For example analog watch continuously gives you information in term of hour, minutes and second. Digital data, on the other hand moves suddenly from one to another i.e. 8:30 p.m. to 8:31 p.m. Data is transmitted with a signal and it can take any form either digital signal or analog signal. Analog signals are continuous where digital signals are discrete. Analog signals have very large number of values in a range; digital signals can have only a limited number of value.


The two most important factors affecting the transfer of a signal over a medium are noise and attenuation. Attenuation is defined as degeneration of the signal. In data communications, we shall be studying different ways to overcome these two factors.

Since both data and signals can be either digital or analog, four basic combinations of data and signals can be produced:

1) Digital data converted to a digital signal

2) Digital data converted to an analog signal

3) Analog data converted to an analog signal

4) Analog data converted to a digital signal Communication

Each of these combinations has different mechanism to representation internally. 

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