The need to exchange data and programs between multiple systems became apparent early in the development of computer systems.Although everybody in the computing community could agree on the need to connect computers — the "How to do it?" was another issue. Computer manufacturers had developed their own rules for connecting their own systems together (communication protocols). Some, such as IBM's BSC and SNA, became defacto standards because of IBM's dominance in the computer market. To compete, some companies provided emulation products of IBM's equipment, while other companies developed radically different schemes that either used modified forms of IBM's protocols or used proprietary solutions. As a result of this unorganized effort, the owners (or users) of the computer equipment ended up with multiple computer networks - one for each type of computer or manufacturer. Even today it is still common to have multiple terminals for a data-entry operator who must access several computers. This proprietary network approach transformed the computer communications problem from "How do I connect computers together?" into "How do I connect my computer networks together?".
During the 1970s, many research institutions addressed the problem of interconnecting computers with a manufacturer independent protocol. Networks that incorporated computers from different manufacturers were built. For researchers, universities, and the government the Arpanet and Internet networks were available. For corporations — Telenet, Tymnet, and other wide area networks (WAN) came into existence. These networks used either network manufacturer supplied proprietary protocols or protocols developed by industrial consortiums. The move from using protocols designed by a manufacturer to protocols designed by the computing community had begun.
During the 1980s the US, Japanese, and European governments became more involved with communications standards. National, international and industrial standards organizations (such as the National Bureau of Standards (NBS), International Standards Organization (ISO), International Telegraph and Telephone Consultative Committee (CCITT), Institute of Electrical and Electronics Engineers (IEEE)) developed system independent approaches to resolve inter-vender computer communications. These standards specified protocols for interconnecting computers-to-computers, computers-to-communications equipment, and communications equipment-to-communications equipment for local and wide area networks. These protocols are now implemented on networks that interconnect computers throughout the world, allowing for system independent exchange of information.
OSI Reference Model
The most significant concept to emerge from the standards process was ISO's Open System Interconnect (OSI) goals statements. The goals were presented what is now known as the OSI References Model. This model segments a computer communications system into seven processing layers. Each layer performs specific functions as part of the overall task of allowing two application programs, on different systems located anywhere in the world, to communicate with each other as if the two programs resided in the same system. (See the "OSI Reference Model" box.)In the early part of the 1980s, research and development centered on the lower protocol layers of the OSI (See the "OSI Reference Model" box). Standards such as IEEE 802.1-5, CCITT X.25 & X.75 (1980, 1984, and 1988), Arpanet/DDN's TCP/IP helped link dissimilar computers together.
In the latter part of the decade, the research focus shifted to the upper layers. The best known products using these protocols are AT&Ts NFS, Sun's RFS, Novell's Netware (SPX/IPX), and Microsoft's Lan Manager (SMB). Typically these products require a Local Area Network (LAN) and provide a network-based file access method. The applications that use these protocols do not need to distinguish the locality of a file (what system/disk the file physically resides on) and the users of such systems are normally only aware of a new hard disk or an additional mounted file system or directory.