Introduction to Digital and Data Communications provides general overview of data communications and deals with telephone system from the stand point of data transfer usage to electrical specifications and impairments. Details are provided on some common error-detection and error-correction methods used in data digital and network communication system. Elaboration on hardware of low speed data communications as interfaced through the telephone system is discussed adequately and phase shifts and quadrature amplitude modulation schemes have been covered as an extension of the basics of the data communication system.