The Internet Book

Chapter 5

3 The World Was Once Digital 150 years ago, telegraph messages were sent from one town to another. –Using audible clicks to encode messages –Switching a light “on” and “off” is a similar principle

4 A Telegraph Is Digital A telegraph is digital technology because data is: –Transferred by discrete clicks –Not transferred as a continuous varying signal

5 Morse Code Telegraph operators used this code because it: –Represented letters and words –Used short and long clicks (dots and dashes)

6 Letters And Digits In Morse Code Figure 5.1: Example of Morse code

7 Users Did Not Encounter Morse Code The relevance of the telegraph to the Internet is because it: –Encoded all letters and digits using only 2 values –Used a code to transmit a message –Used an encoding scheme not encountered by customer

8 Virtually Instant Communication Sending messages to far away locations was: –Accomplished without using a human courier –Allowed people to learn about events as they occurred

9 Speed Is Relative The telegraph changed the world because it was so fast compared to a courier. By today’s standards communication by telegraph is slow.

10 Conclusion Is it necessary to understand the binary encoding of Internet messages in order to use the Internet?

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12 Glossary Binary – Any number system that uses two values. Binary digit (bit) –Either a 0 or 1. Digital – Any technology that uses numbers to represent information.