There are various techniques used to convert the analog signal to digital signal. But the other way of obtaining digital data is from the source such as computers.

The information from such a source is inherently discrete in nature.

If such a discrete signal is transmitted over a band limited channel, then the signal gets dispersed. This causes the pulse to overlap and cause distortion.

Such a distortion is called intersymbol interference (ISI).In order to avoid this discrete signal should not be transmitted as it is on the transmission medium. This data is first converted into a PAM suitable format and then transmitted over a communication channel. The various formats used are also called as line codes.

The data formats or line codes are: