DECnet

DECnet is a suite of network protocols created by Digital Equipment Corporation. Originally released in 1975 in order to connect two PDP-11 minicomputers, it evolved into one of the first peer-to-peer network architectures, thus transforming DEC into a networking powerhouse in the 1980s. Initially built with three layers, it later (1982) evolved into a seven-layer OSI-compliant networking protocol. DECnet was built right into the DEC flagship operating system VMS since its inception. Later Digital ported it to Ultrix, as well as Apple Macintosh and IBM PC running variants of DOS and Microsoft Windows under the name DEC Pathworks, allowing these systems to connect to DECnet networks of VAX machines as terminal nodes. While the DECnet protocols were designed entirely by Digital Equipment Corporation, DECnet Phase II (and later) were open standards with published specifications, and several implementations were developed outside DEC, including ones for FreeBSD and Linux. DECnet code in the Linux kernel was marked as orphaned on February 18, 2010. DECnet refers to a specific set of hardware and software networking products which implement the DIGITAL Network Architecture (DNA). The DIGITAL Network Architecture has a set of documents which define the network architecture in general, state the specifications for each layer of the architecture, and describe the protocols which operate within each layer. Although network protocol analyzer tools tend to categorize all protocols from DIGITAL as 'DECnet', strictly speaking, non-routed DIGITAL protocols such as LAT, SCS, AMDS, LAST/LAD are not DECnet protocols and are not part of the DIGITAL Network Architecture. To trace the evolution of DECnet is to trace the development of DNA. The beginnings of DNA were in the early 1970s. DIGITAL published its first DNA specification at about the same time that IBM announced its Systems Network Architecture (SNA). Since that time, development of DNA has evolved through the following phases: Phase I (1974)Support limited to two PDP-11s running the RSX-11 operating system only, with communication over point-to-point (DDCMP) links between nodes. Phase II (1975)Support for networks of up to 32 nodes with multiple, different implementations which could inter-operate with each other. Implementations expanded to include RSTS, TOPS-10 and TOPS-20 with communications between processors still limited to point-to-point links only. Introduction of downline loading (MOP), and file transfer using File Access Listener (FAL), remote file access using Data Access Protocol (DAP), task-to-task programming interfaces and network management features. Phase III (1980).Support for networks of up to 255 nodes over point-to point and multi-drop links. Introduction of adaptive routing capability, record access, a network management architecture, and gateways to other types of networks including IBM’s SNA and CCITT Recommendation X.25.