ETSI TS 101 377-2-4
ETSI TS 101 377-2-4
GEO-Mobile Radio Interface Specifications; Part 2: Service specifications; Sub-part 4: Call Waiting (CW) and Call Hold (HOLD) Supplementary Services - Stage 1; GMR-2 02.083
standard published 03/01/2001 by European Telecommunications Standards Institute