Integrated Services Digital Network (ISDN) - Call Waiting (CW) supplementary service; Digital Subscriber Signalling System No. one (DSS1) protocol - Part 6: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma specification for the network; (Endorsement of the Englisch version EN 300058-6 V 1.3.3 (1999-11) as German standard)