Integrated Services Digital Network (ISDN); Call Hold (HOLD) supplementary service; functional capabilities and information flows; english version ETS 300140:1992
Integrated Services Digital Network (ISDN) - Signalling System No.7 (SS7) - ISDN User Part (ISUP) version 4 for the international interface - Part 16: Call Hold (HOLD) supplementary service [ITU-T Recommendation Q.733, clause 2 (1993), modified]
