“First we’ll build an example system that will allow two people to send messages back and forth using plastic tubing and marbles instead of wires and electrical signals.”
Most networking books open with the seven-layer OSI model and lose the reader by page ten. This one starts with marbles in a tube and works up to the early 1960s before touching the modern internet. Only three chapters are done, and the web version stays free. Teaching from first principles beats memorizing acronyms for a certification exam.