For data transmission or transmissions, depending on the distance between devices and transmission media, the data must be converted in a form that can be quickly and correctly transmitted. Mostly the information is transmitted in the form of electrical signals. The conversion of data bits into electrical signals cannot be sufficient; instead, there are soon more transmission requirements.
Some transmission requirements are sufficient to signal transitions in the transmitted signal, bandwidth matching of signal and transmission media and proper differentiation in states of received signals. It can meet these requirements, and the data should be converted in a valid format. This conversion is known as data encoding or signal encoding. The data to be sent can be one of the two types.
Four types of encoding may be required depending on data, transmission media and distance between sender and receiver. They are
Data is sent in the structure of electrical signals. These electrical signals can have an analog signal (analog waveform), which are continuous and non-discrete. They gradually change from high to low and low to high voltage values or a form of the digital signal represented by discrete voltage levels having abrupt changes in high and low voltage states, as shown in the figure.
In both the signals, a high voltage indicates 1, and a low indicates '0'. Digital data has a binary format. While converting them to an electrical signal, a positive voltage can be considered '1' and –ve voltage as '0'.
These signals will be digital, but conversion to electrical signals will not be sufficient but has to convert into analog signals if the data is transmitted through telephone lines or satellite. But analog signals have drawbacks like relaying through amplifiers, and transducers may cause linear distortion noise on the channel is called attenuation.