The following is a short history of Study Group 17 and the related X-series and Z-series of Recommendations. As many of you know SG 17 was formed by the merger of Study Groups 7 and 10 in 2001.

Study Group 7 had its roots back to the Joint Working Party on New Data Networks, which was created by the IVth Plenary Assembly of the CCITT in 1968. Table 1 below shows the evolution over the various study periods and the study group leadership until the merger with SG 10 in 2001. The work program evolved significantly over this time. In the late 60s and early 70s, the work focused on digital leased lines and digital circuit switched data networks with the first X-series Recommendations approved at the December 1972 Vth CCITT Plenary Assembly. Packet switched networks was the hot topic of the 70s and 80s with the first edition of the famous X.25 Recommendation approved in 1976. An ever increasing number of packet data network Recommendations were developed and approved in 1980, 1984 and 1988. Work on Open Systems Interconnection (OSI) in conjunction with ISO and IEC began in the early 80s and was very intense through the 80s and 90s. By 2000, this work had reached maturity and SG VII began to build its efforts on security.

Study Group 10 had its roots as part of the work of CCITT Study Group XI with three Questions on languages for stored program control telephone exchanges adopted by the Vth CCITT Plenary Assembly in 1972. Table 2 below shows the evolution over the various study periods and the study group leadership until the merger with SG 7. In 1976, skeleton Recommendations on Specification and Description Language (SDL) and Man-Machine Language (MML) were adopted as the first Z-series Recommendations. These were further developed in the next 8 years along with CHILL with approvals in 1980 and 1984. The VIIIth CCITT Plenary Assembly in October 1984 established Study Group 10. By 2000, a suite of Z-series Recommendations was in place with MSC (Message Sequence Chart) as the major addition in the 1990s. Focus in the later years moved to aligning ITU-T languages, such as SDL and MSC, to OMG’s UML (Unified Modeling Language).

In 2001, TSAG agreed to merge Study Groups 7 and 10 to form Study Group 17 (7 + 10 = 17). The chairman of the two study groups became co-chairmen of the new Study Group 17 and all the vice chairmen of the two study groups became vice chairman of the new Study Group 17. Table 3 below shows the evolution of Study Group 17 over the three study periods and the study group leadership. A major change was made at WTSA-04 when the remaining data network work was transferred to Study Group 13 and the major focus of Study Group 17 was shifted to security while also continuing its work on languages. By WTSA-08, a substantial set of security Recommendations had been approved and WTSA-08 changed the title of Study Group 17 to Security. the role of Study Group 17 was continued essentially unchanged by WTSA-12. Study Group 17 has lead study group responsibilities for:

• Security
• Identity management (IdM) 
• Languages and description techniques

Table 4 shows the history of X and Z series Recommendations approved by the various CCITT Plenary Assemblies. After 1988, Recommendations were developed, approved and published individually, rather than in the sequence of color books published every four years. The X-series expanded in scope over the years from “New data networks” to “Data communication networks” to “Data networks and open system communications” to “Data networks, open system communications and security”. In a similar manner, the Z-series expanded over the years from “Programming languages for SPC exchanges" to "Programming languages”, to “Languages and general software aspects for telecommunication systems”. Tables 5, 6, 7 and 8 show the set of 315 approved Recommendations and 18 approved Supplements under the responsibility of Study Group 17 as of 15 June 2013.