This specifies the default 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, and an explicit Phase IV prefix is not specified. PHASEIV_PREFIX addr-prefix For example: SET DEFAULT PHASEIV_PREFIX 39:840:800AB738 See the PHASE_IV_PREFIXES topic for details about Phase IV prefix values.