Centralized, Decentralized, Distributed
Beginning of 60's: Paul from RAND (Research and Development) Corporation had an offer from US Air force to look for the possibilities for the better defense and control of Airways. At 1964 he presented a work called "On Distributed Communications Networks" and in it he developed a packets orientated network (information reduced to small packets).
All elements in network send and retrieve the same kind of information.
They all are equal, no center --> even in a nuclear war the “living” parts could still communicate (e.G. per Satellite).
Information spitted in small parts, every has a number (were from + where to).
Routed with the hot potato principle (send as fast as you can through the next free connection) "and the node is not wearing gloves" [Baran, 1964].
The way was unimportant, only reaching the destination counts. The missing parts were send again every time because that makes sure, that the message arrive its destination.
The first Protocol: 1967 Spec. for Interface Message Processor (IMP): all hosts should be connected to this host and change information with other computers by this way.