The International Network Working Group agreed on a connectionless datagram standard which was presented to the CCITT in 1975 but was not adopted by the CCITT nor by the ARPANET.[19] Separate international research, particularly the work of Rmi Desprs, contributed to the development of the X.25 standard, based on virtual circuits, which was adopted by the CCITT in 1976.[20][21] Computer manufacturers developed proprietary protocols such as IBM's Systems Network Architecture (SNA), Digital Equipment Corporation's DECnet and Xerox Network Systems.[22]