This technical report defines rules for usage of the TASE.1 Application Programming Interface (TAPI), i.e. parameter usage and service primitive sequencing. The rules which are set forth by this technical report are to be considered as an extension to the rules enforced by the Telecontrol Application Service Element 1 (TASE.1) itself, and will typically constitute further restrictions on parameter values, etc. The TASE.1 own restrictions and rules apply throughout. They are not explicitly restated in this technical report1). Whenever the present report allows simultaneous Functional Unit invocations on one association, adherence to the TASE.1 primitive sequencing rules2) are implicitly assumed. Internal Functional Unit structures, Coordinating Function structure (see clause 4) and structural relationships between these are not within the scope of this technical report, as these are only conceptual entities, serving as a convenient means for describing TASE.1 service primitive sequences. Also not within scope are all non-communicational aspects of application processes, such as local database design/access, and possible data consistency considerations across different local data access modes. The main object of this technical report is to present the underlying conceptual model of the Telecontrol User Element and to identify the functional units (clause 4). The functional units are described in minute detail, grouped into one function group per clause (clauses 5 to 8).