Another classification can be depicted according to the number of receivers addressed by a transmitter. A point-to-point transmission generally refers to a connection restricted to two endpoints, which are usually host computers. In their simplest form, point-to-point communications refer to a direct data transfer without any data or packet formatting. The Input Transmitted Received Output Signal Signal Signal Signal Transmitter Receiver Processing Signal Transmission Channel Adaption Processing Channel Information Source Subsystem to Channel Subsystem Extraction Destination Noise, Interference, and Distortion Fig. 2.1 Data transmission system. Data Transmission Basics end nodes are responsible for data formatting, synchronization, and SO on. In such cases the connection is typically established through a serial protocol like RS-232, which cannot be extended over very long distances. However, for longer-range communications, a point-to- point connection is established through a public network, which is generally packet switched (for example, peer-to-peer file-sharing networks). Point-to-multipoint communications (also known as broadcast), on the other hand, refer to the case where a transmitter sends data for multiple receivers, which can save a consider- able amount of network resources. The efficiency of the transmission is mainly affected by the quality of the media and the characteristics of the sources and receivers that generate and retrieve the signal. There- fore, an understanding of channel characteristics and different types of transmission signals plays a significant role in optimal transmission system design. Analogue and Digital Signals Any transmission signal can be represented as an electromagnetic signal that can vary in time as well as in frequency; therefore, two domains will exist to analyze the signal: time and frequency. Within these two domains, two types of signal are possible: analogue and digital. Analogue signals take a level that can vary continuously in time without any disruption, whe