Before attempting to organize our thoughts on Internet architecture, let’s look for a
human analogy. Actually, we deal with complex systems all the time in our everyday
life. Imagine if someone asked you to describe, for example, the airline system.
How would you find the structure to describe this complex system that has ticketing
agents, baggage checkers, gate personnel, pilots, airplanes, air traffic control, and a
worldwide system for routing airplanes? One way to describe this system might be
to describe the series of actions you take (or others take for you) when you fly on an
airline. You purchase your ticket, check your bags, go to the gate, and eventually get
loaded onto the plane. The plane takes off and is routed to its destination. After your
plane lands, you deplane at the gate and claim your bags. If the trip was bad, you
complain about the flight to the ticket agent (getting nothing for your effort). This
scenario is shown in Figure 1.21.