Definitions and fundamental principles

This chapter provides definitions and fundamental principles of communication systems. A communications process requires components that include a source of the information, a transmitter to convert the information into data signals compatible with the communications channel, and a communications channel. For the communications to be successful, the source and destination must use a mutually agreed method of conveying the data. The main factors that must be considered include the form of signaling and the magnitude of the signals to be used, the type of communications link, and the arrangement of signals to form character codes from which the message can be constructed. An interface standard defines electrical and mechanical aspects of the interface to allow the communications equipment from different manufacturers to operate together. A protocol is essential for defining the common message format and procedures for transferring data between all devices on the network. The protocol includes the important features such as initialization, framing and synchronization, and flow control. The signal measurement on communications channel and signal attenuation are also elaborated.