Decnet

DECnet refers to a specific set of hardware and software network products that implement a digital network architecture (DNA). Digital Network Architecture (DNA) is a set of documents that define the overall architecture of the network as a whole, the provisions of the technical requirements for all levels of architecture and the description of protocols that work at each level.

DECnet evolution tracking means DNA development tracking. The creation of DNA was in the early 1970s. Digital published its first DNA specification at about the same time that IBM announced its Systems Network Architecture (SNA). Since then, the development of DNA has been in the following phases:

Phase I (1974) Support is limited to two PDP-11 mini-computers running the RSX-11 operating system, only with point-to-point communication protocol (DDCMP) between nodes.

Phase II (1975) ^[1] Support for networks of up to 32 nodes with several, different implementations that can interact with each other. Implementations are expanded to include RSTS , TOPS-10 and TOPS-20. Communication between processors is still limited only by a point-to-point protocol. Downstream loading (MOP), and file transfer using the File Access Listener (FAL), remote file access using the Data Access Protocol (DAP) , task-to-task programming interfaces and network management functions.

Phase III (1980). Support for networks of up to 255 nodes through point-to-point and multipoint connections. Implement adaptive routing capabilities, access recording, network management architecture, and gateways to other types of networks, including IBM's SNA and CCITT Recommendation X.25

Phase IV and Phase IV + (1982). Phase IV was originally released for RSX-11 and VMS systems, later TOPS-20 , TOPS-10 , Ultrix , VAXELN , and RSTS / E also received support. Support for networks up to 64,449 nodes (63 areas 1023 nodes), the ability to expand the data channel beyond DDCMP including support for the local Ethernet network as the choice of the data channel, the extension of adaptive routing, the ability to include hierarchical routing (areas, levels 1 and 2 of routers ), support for VMScluster and host services (CTERM). CTERM allowed the user from one computer to gain remote access to another computer, performing the same function as Telnet in the TCP / IP protocol stack . Digital has released a product called the Pathworks client, also commonly known as the Pathworks 32 client, which has implemented most of DECnet's Phase IV for DOS and 16, 32-bit Microsoft Windows platforms (all versions prior to Windows Server 2003)

Phase IV implements an eight-tier architecture that is similar to the (7-tier) OSI model especially at the lower tiers. Since OSI standards, at that time, were not yet fully developed, many protocols from phase IV remained privately owned.

The Ethernet implementation was unusual in that the software changed the physical address of the Ethernet interface on the network from AA-00-04-00-xx-yy, where xx-yy is the reflected network address of the DECnet host. This allowed the Address Resolution Protocol (ARP) to be controlled by the local area network (LAN) because the LAN address could be inferred from the DECnet address. However, this eliminates the connection of two network cards from the same DECnet node on the same LAN segment.

It was originally released for VMS and RSX-11, later expanded for almost all Digital operating systems , it only came with significant exceptions, unlike RT-11 . DECnet stacks are used on Linux, SunOS, and other platforms, and CISCO and other network product providers offer something that can communicate and work on DECnet networks.

At the same time that DECnet Phase IV was released, the company also released its own protocol called LAT for serial terminal access through a terminal server . The LAT separates the physical and link OSI layers from DECnet, the LAT terminal servers used for MOP server image downloads and communication with bootstrap processing.

Modifications made to DECnet Phase IV eventually became known as DECnet Phase IV +, although systems running on this protocol remained fully compatible with DECnet Phase IV systems.

Phase V and Phase V + (1987). Support for very large (architecturally unlimited) networks, a new network management model, a local or distributed name service, and improved performance over phase IV. Moving from a proprietary network to open systems interconnection (OSI) by integrating ISO standards to enable connectivity between different vendors, and compatible with DNA Phase IV, the last two features have led to a hybrid network architecture (DNA and OSI) with separate towers for a joint integrated transport level. Transport layer links in TCP / IP are added through the IETF RFC 1006 (OSI instead of IP) and RFC 1859 (NSP instead of IP) standards (see diagram) .

Later it was renamed to DECnet / OSI to emphasize its connectivity with OSI, and then renamed to DECnet-Plus , it was included as TCP / IP protocols.

DECnet protocols were fully developed by Digital Equipment Corporation. However, DECnet Phase II (and later phases) were open standards with feature publication, and several implementations were developed outside of DEC, including for FreeBSD and Linux .

• Carl Malamud , Analyzing DECnet / OSI Phase V. Van Hostrand Reinhold, 1991. ISBN 0-442-00375-7 .
• James Martin, Joe Leben, DECnet Phase V: An OSI Implementation . Digital Press, 1992. ISBN 1-55580-769-0 .
• DECnet-Plus manuals for OpenVMS are available at http://www.hp.com/go/openvms/doc/ (inaccessible link)
• DECnet Phase IV OpenVMS manuals for DECnet Phase IV; these Phase IV manuals are archived on OpenVMS Freeware V5.0 distribution, at http://arquivo.pt/wayback/20131107100544/http://www.hp.com/go/openvms/freeware/ and other sites.
• DECnet Phase IV architecture manuals (including DDCMP, MOP, NICE, NSP, DAP, CTERM, routing); at https://web.archive.org/web/20140221225835/http://h71000.www7.hp.com/wizard/decnet/ (the originals are mirrored at DECnet for Linux ).

• CCNET (Computer Center Network, 1980s; more info here )
• Hecnet
• Italian Retro DECnet