This specifies the AFI, IDI, and preDSP to use when constructing an NSAP from a Phase IV address. This is used when a Phase IV address is specified in an address tower. PHASEIV_PREFIX addr-prefix For example: PHASEIV_PREFIX 39:840:800AB738 If not specified, the Phase IV prefix defined in the export file is used. If the export file does not contain a Phase IV prefix definition, then the Phase IV prefix set using the SET DEFAULT command is used. See the PHASE_IV_PREFIXES topic for details about Phase IV prefix values. See the EXPORT_FILE topic for a description of the Phase IV prefix control line.