Early Networks
ARPANET and SITA HLN became operational in 1969. Before the introduction of X.25 in 1973, about twenty different network technologies were developed. There was a debate about the merits of two drastically different views as to proper division of labor between the hosts and the network. In the datagram system the host must detect loss or duplication of packets. Transmission Control Protocol /Internet Protocol (TCP/IP) is the best known example of a host to datagram protocol. In the virtual call system, the network guarantees sequenced delivery of data to the host. This results in a simpler host interface with less functionality than in the datagram model. X.25 is the best known virtual call protocol.
Inexpensive minicomputers were an important component in the early networks. In some cases custom I/O devices were added to allow inexpensive or exotic attachments to communication lines.
Read more about this topic: Packet-switched Network
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