This European Telecommunication Standard (ETS) defines the stage one of the Calling Line Identification Restriction (CLIR) supplementary service for the Public Switched Telephone Network (PSTN) as provided by European public network operators. Stage one is an overall service description from the user's point of view (see CCITT Recommendation I.130 [3])@ but does not deal with the details of the human interface itself. This ETS defines the interworking requirements between PSTNs and private networks@ PSTNs and Integrated Services Digital Networks (ISDNs)@ and Public Land Mobile Networks (PLMNs). Interactions with supplementary services not listed in clause 8 are outside the scope of this ETS. Charging principles are outside the scope of this ETS. The CLIR supplementary service enables the calling party to prevent presentation of its calling line identity to the called party. This ETS is applicable to the ETS containing the subscriber line protocol to support the CLIR supplementary service. Where the text indicates the status of a requirement (i.e. as strict command or prohibition@ as authorization leaving freedom@ or as a capability or possibility)@ this shall be reflected in the text of that standard. Furthermore@ conformance to this ETS is met by conforming to the standards containing the subscriber line protocol to support the CLIR supplementary service with the field of application appropriate to the equipment being implemented. Therefore no method of testing is provided for this ETS.