This European Telecommunication Standard (ETS) fits into the series of standards about audiovisual communication over the Integrated Services Digital Network (ISDN)@ which is introduced in the ITU-T H.200 series of Recommendations. In ITU-T Recommendations H.233 [1] and H.234 [2]@ the basic mechanisms for confidentiality and key exchange are specified. On top of these@ this ETS specifies the confidentiality related protocol extensions needed for the establishment@ modification and termination of audiovisual conferences using one or more Multipoint Control Units (MCUs).