Keywords:
Additional equipment, Circuit networks, Communication networks, Communication service, Communication technology, Computer terminals, Digital, Digital engineering, Digital signals, Electric cables, Electrical engineering, ETSI, Information processing, Integrated services digital network, ISDN, Procedures, Protocols, Radio systems, Safety, Signal transmission, Signalling systems, Subscriber's systems, Telecommunication, Telecommunication networks, Telecommunication systems, Telecommunications, Telephone networks, Testing, Transmission characteristics, Transmission technique, User