s taken in the WRCs, the ITU-R study groups develop global standards, re- ports, and guidelines on radiocommunication matters. The ITU-R study groups mainly focus on Efficient management and use of spectrum by terrestrial services Efficient management and use of orbital resources by space services Characteristics and performance specifications of radio systems Radio station operations Safety aspects of radiocommunications There are six study groups that work on questions assigned to these specialist areas: SG 1: Spectrum management (www.itu.int/ITU-R/go/rsg1) SG 3: Radiowave propagation (www.itu.int/ITU-R/go/rsg3) SG 4: Satellite services (www.itu.int/ITU-R/go/rsg4) SG 5: Terrestrial services (www.itu.int/ITU-R/go/rsg5) SG 6: Broadcasting service (www.itu.int/ITU-R/go/rsg6) SG 7: Science services (www.itu.int/ITU-R/go/rsg7) The ITU-R has been instrumental in terms of providing and defining the basic specifications for In- ternational Mobile Telecommunications: IMT-2000 (3G radio technology), IMT-Advanced (4G ra- dio technology), and IMT-2020 (5G radio technology). ITU-R also publishes specifications for di- gital television and sound, including digital audio broadcasting (DAB), high definition television (HDTV), ultra-high definition television (UHDTV), and the high dynamic range (HDR) enhancement. 4.1.1 ITU-T The ITU Telecommunication Standardization Sector is responsible for defining international recom- mendations (standards) for telecommunication network operations and interworking. There are over 4000 recommendations in force defining services, technical specifications, network architectures and security requirements for many network systems, including broadband, digital subscriber line (DSL), passive optical network (PON) systems, optical transport networks (OTN), next-generation networks, as well as Internet protocol (IP). The framework for the work of the ITU-T is decided by the following two organizations: World Telecommunication Standardization Assembly (WTSA): Provides overall direction and defines pol