This European Telecommunication Standard (ETS) specifies the procedure s used at the radio interface (Reference point Um as defined in GSM 04 .02) for normal operation, registration, erasure, activation, deactiva tion, invocation and interrogation of call completion supplementary se rvices. Provision and withdrawal of supplementary services is an admin istrative matter between the mobile subscriber and the service provide r and cause no signalling on the radio interface. In GSM 04.10 the general aspects of the specification of supplementary services at the layer 3 radio interface are given. GSM 04.80 specifies the formats and coding for the supplementary servi ces. Definitions and descriptions of supplementary services are given in GS M 02.04 and GSM 02.8x and 02.9x-series. GSM 02.83 is related specially to call completion supplementary services. Technical realization of supplementary services is described in GSM 03 .11 and GSM 03.8x and 03.9x-series. GSM 03.83 is related specially to call completion supplementary servic es. The procedures for Call Control, Mobility Management and Radio Resourc e management at the layer 3 radio interface are defined in technical s pecifications GSM 04.07 and GSM 04.08. The following supplementary services belong to the call completion sup plementary services and are described in this ETS: - Call waiting (CW) (clause 1); - Call hold (HOLD) (clause 2).