ARPANET stands for Advanced Research Projects Agency Network. This was created by ARPA of the United States Department of Defense during the Cold War. The ARPANET was the world’s first operational packet switching network, and the predecessor of the global Internet.
Packet switching is currently the leading foundation for both voice and data communication worldwide this was a new and significant concept in data communications. Formally, data communication was based on the concept of circuit switching, as was prominent in the old typical telephone circuit, where a dedicated circuit is tied up for the duration of the call and communication is only possible with the single party on the other end of the circuit.
A system could use one communication link to communicate with more than one machine with packet switching. This is done by disassembling data into datagrams then collect these as packets. The link could be shared and each packet could be routed independently of other packets.
J.C.R. Licklider of Bolt, Beranek and Newman (BBN) devised the concepts of a computer network that allowed general communication between users of various computers in August 1962, in a series of memos discussing his “Intergalactic Computer Network” concept. These ideas contained almost everything that the Internet is today.
Licklider was appointed head of the Behavioral Sciences and Command and Control programs at ARPA the United States Department of Defense Advanced Research Projects Agency in October 1963. Before any actual work on his vision was performed Licklider left ARPANET even though he then convinced Ivan Sutherland and Bob Taylor that this was a very important concept.
ARPA and Taylor continued to be interested in creating a computer communication network, in part to allow ARPA-sponsored researchers in various locations to use various computers which ARPA was providing, and in part to make new software and other results widely available quickly.
The starting point for host-to-host communication on the ARPANET was the 1822 protocol which defined the way that a host sent messages to an ARPANET IMP. The message format was designed to work unambiguously with a broad range of computer architectures. Essentially, an 1822 message consisted of a numeric host address, a message type, and a data field.
In order to send a data message to another host, the sending host would structure a data message which includes the destination host’s address as well as the data to be sent, and transmit the message through the 1822 hardware interface. The IMP would see that the message was delivered to its destination, either by delivering it to a locally connected host or by delivering it to another IMP. When the message was ultimately delivered to the destination host, the IMP would send an acknowledgment message to the sending host indicating receipt.