Introduces underlying theory and practice that enables digital transmission. Starting with theory of signal in communication systems based on sinusoidal signal with Fourier series and Fourier Transform that are the most important fundamental theory for data transmission. To simplify and better understanding of signal transmission requirements the significance of linear system approach are discussed. In transmission the effect of impairments on signals must be considered carefully. The impairments are usually considered as noise. Next step concerns transmission capacity which need understanding of the more complex concept of spectrum and bandwidth. This two factors have important role in preserving signal format during transmissions. There are distinct methods of transmitting digital data. Each method has its own advantages and disadvantages that in practice could change due to technology development. Due to distance requirements, data signals must be carried or converted in order to cover the required distance. The techniques how to carry data signal or convert it to fulfill the distance requirement is called modulation. Data transmission depends on conventional carrier based modulation such as amplitude modulation and angle modulation to cover the desired distance and digital modulation is more reliable and noise resistant. This course introduces line coding and the widely accepted Pulse Code Modulation as digital modulation techniques.