Open systems interconnect

In 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.

IS-IS also survives as a network routing protocol used by larger
telecommunications companies although it has been adapted for use with the
Internet protocol.

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