This document discusses the components of telecommunications systems including different types of signals, methods of conversion between analog and digital signals, communication channels, network processors and topologies, local and wide area networks, broadband technologies, and electronic commerce services. Analog signals are continuous waveforms that pass through media for video, audio and voice, while digital signals use discrete values of 1s and 0s for data transmission. Communication occurs through wired or wireless channels and is processed by front-end processors, concentrators, controllers and multiplexers within star, bus or ring network topologies. Local and wide area networks provide connectivity along with value-added networks and other services to enable electronic mail, conferencing, commerce and distance learning.