Integrated Services Digital Network (ISDN) - Completion of Calls to Busy Subscriber (CCBS) supplementary service; Digital Subscriber Signalling System No. one (DSS1) protocol - Part 5: Test Suite Structure and Test Purposes (TSS&TP) specification for the network (Endorsement of the English version EN 300359-5 V 1.2.4 (1998-06) as German standard)