Open systems interconnect

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 OSI protocols or "stack" that were specified as part of the project were a bloated mess. Standards like X.400[?] for e-mail took up several large books, while Internet e-mail 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.