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Introduction to Signal Transmission and the Basic Line Circuit To make it suitable for carriage over most telecommunications networks, information must first be encoded in an electrical manner, as anelectrical signal. Only such signalscan be conveyed over the wires and exchanges that comprise ‘transport the mechanism’ of telecommunications been developed forencoding different types of information. | Networks and Telecommunications Design and Operation Second Edition. Martin P. Clark Copyright 1991 1997 John Wiley Sons Ltd ISBNs 0-471-97346-7 Hardback 0-470-84158-3 Electronic 2 Introduction to Signal Transmission and the Basic Line Circuit To make it suitable for carriage over most telecommunications networks information must first be encoded in an electrical manner as an electrical signal. Only such signals can be conveyed over the wires and exchanges that comprise the transport mechanism of telecommunications networks. Over the years a variety of different methods have been developed for encoding different types of information. This chapter categorizes all methods of information transmission into one of two basic types analogue transmission and digital transmission describing the principles of both types but concentrating on the technique of analogue transmission. Chapter 3 continues the subject of analogue transmission explaining its use for information conveyance over long distances and Chapters 4 and 5 expand the details of digital transmission. ANALOGUE AND DIGITAL TRANSMISSION The simplest type of physical medium transport mechanism used in telecommunications networks is a pair of electrical wires. These allow the conveyance of an electrical current or signal from a transmitter at one end of the wires to the receiver at the other end. There are two basic methods for information encoding which may be applied by the transmitter and decoded by the receiver. These are analogue signal encoding and transmission and digital encoding and transmission. As the name suggests analogue signal encoding involves the creation of an electrical signal waveform which is analogous to the waveform of the original information . a speech wave pattern . In this way the electrical signal is similar in shape to the speech or other information waveform that it represents. Analogue transmission lines are used to convey analogue encoded signals and until the early 1980s .