This ETS defines the stage one of the Calling Line Identification Presentation (CLIP) 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).