The introduction is brief, and we don't attempt to cover these topics completely.
The Internet had its beginnings in the late 1960s with the development of ARPAnet. A primary goal of ARPAnet was to provide a decentralized network of computing resources that did not rely on any one machine or system to operate; that is, no single point of failure could bring the network down. For a network to achieve this, the topology has to provide multiple paths between the computers connected to the network. Such a topology is shown in Figure B-1. Computers are connected to nodes in the network-or form nodes themselves-and so long as a path can be followed through the links between nodes, the computers can communicate.
Figure B-1. A network topology that provides multiple communication paths
Another feature of ARPAnet was the use of packet switching. Unlike telephone networks, where a dedicated circuit is established to carry the conversation between two parties, ARPAnet carried data between two communicating systems as a stream of packets, each sent as an individual transmission over the network. Sending a message as a stream of packets allows valuable network bandwidth-the amount of data that can be transmitted for a given period of time-to be shared between different communications.
Packet switching adds complexity. The process of breaking a message into small packets, deciding on the path to send packets, and reassembling of the message before presenting the data to the receiving computer system required the development of network protocols. One of the first protocols was the Network Control Protocol (NCP); it was replaced in 1982 by the Transmission Control Protocol (TCP) and the Internet Protocol (IP). The protocol suite is commonly known as TCP/IP.
Other networks using packet technologies were also being developed and, with the introduction of TCP/IP, interconnections between these networks were possible. Small office-based networks could be connected to main backbone networks such as ARPAnet or the CSNET, the university-based Computer Science Network. These backbone networks were connected to similar networks in other countries over satellite links and submarine cables, and the Internet was born. The Internet isn't one single network: it is many interconnected networks.