DIN EN 300138-1:2000-01
Действует
Integrated Services Digital Network (ISDN) - Closed User Group (CUG) supplementary service; Digital Subscriber Signalling System No. one (DSS1) protocol - Part 1: Protocol specification (Endorsement of the English version EN 300138-1 V 1.3.4 (1998-06) as German standard)
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