Open systems interconnectIn the 1980s, the International Organization for Standardization (ISO) documented a new effort in networking called Open Systems Interconnect or OSI.
Prior to OSI, networking was completely vendor-developed and proprietary, with standards such as SNA. OSI was a new industry effort, attempting to get everyone to agree to common network standards to provide multi-vendor interoperability. The OSI model was the most important advance in teaching network concepts. However, the actual OSI protocols or "stack" that were specified as part of the project were considered by many to be too complicated. Standards like X.400 for e-mail took up several large books, while Internet e-mail (SMTP) took only a few dozen pages at most in RFC-822 and 823. Most protocols and specifications in the OSI stack are long-gone today, such as token-bus media, CLNP packet delivery, FTAM file transfer, and X.400 e-mail. Only one, the X.500 directory service, still survives with significant usage, mainly because the original unwieldy protocol has been stripped away and effectively replaced with LDAP.