ISODE The ISODE software , originally perhaps intended to be an ISO Development Environment , was an implementation of the OSI upper layer protocols , from transport layer to application layer , which was widely used in the Internet research community to experiment with implementation and deployment of OSI during the late 1980s and early 1990s . While the ISODE implementation could be configured to use one of several X.25 ( CONS ) or connectionless lower layer protocols , many ISODE deployments were based on [ RFC 1006 ] , the implementation of OSI transport protocol TP0 as a layer atop TCP , in order to use IP-based networks which were becoming increasingly common . ISODE formed the basis for popular implementations of X.400 ( PP ) and X.500 ( QUIPU ) , and the approaches for providing a simplified directory lookup protocol that was easier to implement in a client than X.500 's Directory Access Protocol led to the development of the Lightweight Directory Access Protocol . Implementations of FTAM and VT were included in ISODE , and implementations of X.400 P7 ( PPMS ) , TMN ( OSIMIS ) and other OSI protocols were also made atop ISODE . Isode is also the name of the company founded by Steve Kille , one of the LDAP protocol authors to produce and market LDAP/X.500 directory servers and messaging systems based on the X.400 protocol . Categories : System software 