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Chapter 1. Introduction

Chapter 1. Introduction

Using a PC at home to finish a little bit of work or to access the Internet has become a common practice. You might use a dial-up connection, a cable modem, or a DSL (Digital Subscriber Line) for your access. A broadband access service, such as a cable modem or a DSL, usually costs twice as much as that of the dial-up service. However, it is a much better option than installing a second phone line to keep the primary line open for in-coming calls, especially during prime hours. Used with a wired or wireless home network, multiple PCs and their users can share broadband access service at home simultaneously without noticeable access time degradation. Because of the popularity of broadband access services, the number of PCs at home, and the affordability of transmission devices, home networks are turning up in a growing number of households. With so many different households having network connections and a wide range of electronic devices, you might wonder at one time what is really going on when a Web page from a remote corner of the Earth is being displayed on your PC screen.

Information such as a text document, picture, or piece of recorded music is encoded as binary digits, or bits, of 1s and 0s. When interacting with a computer or a Web site, your commanding or responding key strokes are also coded into bits. Information and command bits are converted into electrical or light signals when relaying over a copper or optical communication link. To achieve high efficiency and reliability, a different protocol, including the definition of the electrical or optical signal, the encapsulation of information bits, and the set-up procedure, is usually specified for each individual communication link according to its unique throughput requirements and transmission media characteristics. An Internet access from a home PC consists of many communication links, which could include an Ethernet from a PC to a DSL modem at home, a DSL connecting a home to a CO (Central Office), an OC-3 (Optical Carrier 3) from a CO to a regional Internet access point. From the Web site regional Internet access point, there might be another OC-3 to a local CO, and a T3 from a CO to the Web site host location. SONET (Synchronous Optical NETwork) rings might be involved from one Internet access point to another.


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