This International Standard specifies the Additional Network Feature (ANF) Call Identification and Call Linkage (CIDL), which is applicable to various basic services supported by Private Integrated Services Networks (PISN). Basic services are specified in ISO/IEC 11574. ANF-CIDL is an additional network feature which allows the identification and correlation of calls throughout a PISN by assigning unambiguous identifiers to each new call and also, as an option, to transformed and logically linked calls. NOTE 1 - This ANF has been developed to support the use of CSTA (ISO/IEC 18051) in a networked environment, i.e. in a PISN. Use of this ANF for other applications is not precluded. Supplementary service specifications are produced in three stages, according to the method described in ETS 300 387. This International Standard contains the stage 1 and stage 2 specifications of ANF-CIDL. The stage 1 specification (clause 6) specifies the general feature principles and capabilities. The stage 2 specification (clause 7) identifies the Functional Entities involved in the supplementary service and the information flows between them.