DECnet Phase IV

DECnet Phase IV is commonly considered the traditional DECnet and is still used on many OpenVMS systems, several years after the introduction of DECnet OSI.

DECnet Phase IV is based on the Phase IV Digital Network Architecture (DNA) and is still offered as an alternative to Phase V because a strong, vocal portion of the customer base prefers Phase IV. A system manager might choose Phase IV for his years of familiarity with it or because its routing functions impose a lighter load on the resources of older, slower systems.

Phase IV routing is performed by the proprietary DECnet Routing Protocol (DRP).