Keywords:
Call numbers, Circuit networks, Communication networks, Communication procedures, Communication service, Communication technology, Digital, ETSI, Information processing, Integrated services digital network, Interfaces, Interfaces (data processing), ISDN, PIXIT, Radio systems, Signal transmission, Signalling systems, Supplementary services, Telecommunication, Telecommunication networks, Telecommunication systems, Telecommunications, Telephone networks, Test specifications, Testing, Transmission, User