Elementary Information Security, 3rd Edition

▶ 10.2 Transmitting Data

Humanity has carried written messages for as long as it has had written words. Data networks eliminate the physical messages: they carry the text using a common alphabet or other set of symbols, often at the speed of light. Signal fires were perhaps the earliest such technique, though telegraphs were the first data networks to cover the globe.

The first true telegraph sent messages a letter at a time via sets of flags; the electrical telegraph coded letters as a series of clicks. The telegraph required skilled operators. To send or receive a message, the operator had to convert it between written text and telegraph code. Speed and reliability depended on operator skill, and good operators were hard to find.

This posed ...