Modern communication network

Author: Mao Jingli / et al.
Editor-in-Chief: Sun Weiling / et al.
Publisher:
Publish Date: 2002-07-30
Features: Briefly introduces the basic knowledge of graph theory, queuing theory, and the theoretical foundation of reliability, as well as the basic theories of modern communication networks and their applications in network design. Building on these basic theories, the book focuses on discussions of network structures, communication network planning and design, N-ISDN, B-ISDN, ATM, telecommunication support networks, and access network technologies. This book can be used as a textbook for communication majors in universities and colleges, as well as a reference for scientific research and engineering technicians engaged in communication work.
Excerpt:
> Introduction
With the continuous progress of society and the rapid development of the economy, information transmission has become increasingly important, and communication networks have become closely integrated with people's lives. This chapter provides a brief introduction to communication networks, covering the following aspects:
(1) Defining communication networks based on the composition of communication systems.
(2) The constituent elements of communication networks.
(3) Classification of communication networks.
(4) Several basic structures of communication networks and their characteristics.
(5) The composition and development of modern communication networks.
Section 1. Basic Concepts of Communication Networks
I. Composition of Communication Systems
To introduce the concept of communication networks, let's first briefly discuss communication systems.
1. Definition of Communication Systems
A communication system is a system that transmits information using electrical signals (or optical signals), also known as a telecommunication system.
2. Classification of Communication Systems
Communication systems can be classified from different perspectives:
① Classification by Communication Services
If classified by communication services, communication systems can be divided into telephone, telegraph, fax, broadcast television, data communication systems, etc.
② Classification by Signal Form
If classified by the form of signals transmitted in the channel, communication systems can be divided into analog communication systems and digital communication systems, etc.
3. Composition of Communication Systems
The model of a communication system is shown in Figure 1.1, with its basic components including the source, transformer, channel, noise source, inverse transformer, and sink.
Transformer—Its function is to transform the information emitted by the source into a signal suitable for transmission in the channel. Corresponding to different sources and different communication systems, the transformer has different compositions and transformation functions. For example:
In an analog telephone communication system, the transformer includes a microphone and a carrier machine (mainly composed of amplifiers, filters, modulators, etc.). Among them, the microphone transforms human voice signals into electrical signals; the carrier machine shifts the frequency range of the voice signal output by the microphone (0.3–3.4 kHz) through frequency shifting and frequency division multiplexing, transforming it into a signal suitable for transmission in an analog channel.
For digital telephone communication systems, the transformer includes a microphone and an analog-to-digital converter. The analog-to-digital converter transforms the analog voice signal output by the microphone through analog-to-digital conversion and time division multiplexing, transforming it into a signal suitable for transmission in a digital channel.