The ITU-T is a sector of the International Telecommunication Union (ITU) responsible for international recommendations and standardization in telecommunications. The proposals for standardization topics come from the World Telecommunication Standardization Assembly (WTSA), which is also responsible for releasing the recommendations.
In the ITU-T, the international advisory committee for telegraph, telephone and telecommunications services, the telecommunications administrations and manufacturers draw up the ITU-T recommendations. They serve as guidelines for the procurement of equipment, for telecommunications services and for the approval of terminal equipment that wishes to use these services. Commonly known are the V. and X. series recommendations for interfaces, the I. series and Q. series for ISDN and B-ISDN, and the G. series for Synchronous Digital Hierarchy( SDH) and ATM.