|  | 4.4 | Basics of Encoding Networking Signals
| 4.4.1 | Historical examples of encoding

Whenever you want to send a message over a long distance, there are two problems you must solve. First, how to express the message (encoding or modulation) and second, which method to use to transport the message (carrier). Throughout history there have been a variety of ways in which the problem of carrying a long distance communication has been solved: runners, riders, horses, optical telescopes, carrier pigeons, and smoke signals. Each method of delivery required a form of encoding. For example, smoke signals announcing that good hunting had just been found might be three short puffs of smoke. A carrier pigeon message that someone had reached a destination safely might be a picture of a smiling face. In more modern times, the creation of Morse code revolutionized communications. Two symbols, the dot and the dash, were used to encode the alphabet. For instance, × × × - - - × × × means SOS, the universal distress signal. Modern telephones, FAX, AM, FM, short wave radio, and TV all encode their signals electronically. Typically the modulation of waves from different parts of the electromagnetic spectrum are used.

Encoding means converting binary data into a form that can travel on a physical communications link; modulation means using the binary data to manipulate a wave. Computers use three particular technologies, all of which have their counterparts in history. These technologies are: encoding messages as voltages on various forms of copper wire; encoding messages as pulses of guided light on optical fibers; and encoding messages as modulated, radiated electromagnetic waves.