DECnet

DECnet is a family of network protocols and architectures developed by Digital Equipment Corporation (DEC) to connect its computer systems across local and wide area networks. Introduced in the 1970s, DECnet was designed to interoperate between DEC hardware such as PDP-11, VAX, and later Alpha systems, providing routing, addressing, and basic application services within a DEC-centric environment.

DECnet evolved through a series of phases, commonly referred to as Phase I through Phase V. Phase I provided basic host-to-host communications and simple addressing. Phase II expanded routing options and management capabilities. Phase III and Phase IV added greater scalability, fault containment, and more robust network management. Phase V, marketed as DECnet-Plus, introduced OSI-compatible features and, in later implementations, interoperability with TCP/IP.

Key characteristics of DECnet include a hierarchical or region-based addressing and a distributed routing approach that allows networks of varying size and media to be interlinked. The protocol suite encompassed elements for name resolution, resource location, and remote login services on supported DEC systems, along with tools for network monitoring and maintenance.

With the growth of the Internet and TCP/IP, DECnet usage declined in favor of IP-based networking. DECnet-Plus and related products, however, maintained ongoing support for existing DEC networks and offered limited interoperability with TCP/IP environments. Some DECnet implementations continue to be used in niche or legacy installations and in software projects that preserve historical networking technology.