The CCITT (later ITU-T) Study Group VII began developing a standard for packet-switched data communication in the mid-1970s based upon a number of emerging data network projects. Participants in the design of X.25 included engineers from Canada, France, Japan, the UK, and the USA representing a mix of national PTTs (France, Japan, UK) and private operators (Canada, USA). In particular, the work of Rémi Després, contributed significantly to the standard. A few minor changes, which complemented the proposed specification, were accommodated to enable Larry Roberts to join the agreement. Various updates and additions were worked into the standard, eventually recorded in the ITU series of technical books describing the telecommunication systems. These books were published every fourth year with different-colored covers. The X.25 specification is only part of the larger set of X-Series.