 2 Data Transmission Stuart D. Walker Emilio Hugues-Salas Rouzbeh Razavi Tahmina Ajmal University of Essex Introduction Data transmission is the transfer of information from one entity (transmitter) to another (receiver) via a communication path. The data transfer can be local or remote. For example, it can be a simple file transfer within a computer or it can be Internet browsing where the information is exchanged with the Web over more than one communication medium. Other forms of data communication include e-mail, data storage, database queries and updates, and home shopping. Three types of digital signal can be differentiated on the basis of bit error rate per- formance, bandwidth utilization, and delay requirements. They are data, voice, and video. For data transmission, the bit error rate requirements are more severe in comparison to voice and video applications, but there is a higher tolerance against delay constraints. Utilized bandwidth is an important parameter in the design of a transmission link. For a voice communication, typical bitrates extend from 4.8 kbit/s to 64 kbit/s (see Chapter 1). The bandwidth requirement for a video application depends on a number of factors, such as the type of video codec in use, picture size, frame rate, and SO on (see Chapter 3). Given their natures, both voice and video communications can stand a certain level of bit error rate compared to data transmission, but they are more sensitive to delay. Another major difference between the data and voice/video traffic is that in the latter case, not all the digits in a byte have the same level of importance. Therefore, the end-to-end perfor- mance of video and voice applications can be considerably improved by unequal protec- tion of bits. Chapter 2 Data Transmission Data transmission in its simplest form (binary digital transmission) is related to the transfer of information between terminals, computers, and other equipment for data pro- cessing. This binary data is converted to two-level pulses for transmission through the