5 – Data Communication Concepts

This chapter introduces to data networking, it discusses fundamental concepts and architecture of data communication and networking, advantages of digital transmission. Transmission is the communication of data that is propagated and processed from one point in a network to another point in the network by means of electrical, electromagnetic, or optical signals. There are four possible combinations of data and signals: (1) digital data and analog signal, (2) analog data and digital signal, (3) digital data and digital signal, and (4) analog data and analog signal. Advantages of digital transmission are also highlighted in the chapter. In addition, there are two types of transmission techniques asynchronous and synchronous. In asynchronous transmission each character is enclosed with a start bit, 7 or 8 data bits, an optional parity bit, and stop bits. The gap between character transmission is not necessarily fixed in length of time. It is cheaper but is less efficient. In synchronous transmission all characters are blocked together and transmitted without a gap between two characters being transmitted. It requires more complicated hardware to handle buffering and blocking, but this hardware more efficient. The signal received may differ from the signal transmitted. The effect degrades the signal quality for analog signals and introduces bit errors for digital signals. There are three types of transmission impairments: attenuation, delay distortion, and noise. Due to the transmission impairments, a message arriving at the receiving station might be in error.