This Supplementary Service describes the procedures and the signalling protocol for the Call Hold supplementary service in H.323 (Packet Based Multimedia Communications Systems) networks. SS-HOLD enables the Served (Holding) User A to put User B (with whom User A has an active call) into a hold condition (Held User) and subsequently to retrieve that User again. During this hold condition, User B may be provided with music and/or video on hold. The Served (Holding) User A may perform other actions while User B is being held, e. g. consulting with another User C. The call between User A and User B has to be in the active state before SS-HOLD may be invoked. This Recommendation makes use of the Generic functional protocol for the support of supplementary services in H.323 as defined in Recommendation H.450.1.