ISO/IEC 15053:2003 specifies Additional Network Feature Call Interception (ANF-CINT), which is applicable to various basic services supported by Private Integrated Services Networks (PISN). Basic services are specified in ISO/IEC 11574.
ANF-CINT is an additional network feature which enables calls that cannot be completed due to certain conditions to be redirected to a pre-defined intercepted-to user.
ANF specifications are produced in three stages, according to the method described in ETS 300 387. ISO/IEC 15053:2003 contains the stage 1 and stage 2 specifications of ANF-CINT. The stage 1 specification (clause 6) specifies the feature as seen by users of PISNs. The stage 2 specification (clause 7) identifies the functional entities involved in the feature and the information flows between them.