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 and invocation of MultiParty supplementary s ervices. 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 the GSM 02.8x and 02.9x-series. GSM 02.84 is related specially to MultiParty supplementary services. Technical realization of supplementary services is described in GSM 03 .11 and the GSM 03.8x and 03.9x-series. GSM 03.84 is related specially to MultiParty supplementary services. The procedures for Call Control, Mobility Management and Radio Resourc e management at the layer 3 radio interface are defined in GSM 04.07 a nd GSM 04.08. The following supplementary service belongs to the MultiParty suppleme ntary services and is described in this ETS: - MultiParty service (MPTY) (clause 1).