Wikipedia

DECnet

DECnetis a suite ofnetwork protocolscreated byDigital Equipment Corporation.Originally released in 1975 in order to connect twoPDP-11minicomputers,it evolved into one of the firstpeer-to-peernetwork architectures, thus transforming DEC into a networking powerhouse in the 1980s. Initially built with threelayers,it later (1982) evolved into a seven-layerOSI-compliant networking protocol.

DECnet[1]was built right into the DEC flagship operating systemOpenVMSsince its inception. Later Digital ported it toUltrix,OSF/1 (laterTru64) as well asApple MacintoshandIBM PCrunning variants ofDOS,OS/2andMicrosoft Windowsunder the namePATHWORKS,allowing these systems to connect to DECnet networks ofVAXmachines as terminal nodes.[2]

While the DECnet protocols were designed entirely by Digital Equipment Corporation, DECnet Phase II (and later) wereopen standardswith published specifications, and several implementations were developed outside DEC, including ones forFreeBSDandLinux.[3]DECnet code in the Linux kernel was marked as orphaned on February 18, 2010[4][5]and removed August 22, 2022.[6]

Evolution

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DECnet refers to a specific set of hardware and software networking products which implement theDIGITAL 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 theprotocolswhich operate within each layer. Althoughnetwork protocol analyzer toolstend to categorize all protocols from DIGITAL as "DECnet", strictly speaking, non-routed DIGITAL protocols such asLAT,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 thatIBMannounced itsSystems Network Architecture(SNA). Since that time, development of DNA has evolved through the following phases:

1970–1980

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Phase I(1974) Support limited to twoPDP-11srunning theRSX-11operating system, or a small number ofPDP-8srunning theRTS-8operating system, with communication over point-to-point (DDCMP) links between nodes.

Phase II(1975)[7] Support for networks of up to 32 nodes with multiple, different implementations which could inter-operate with each other. Implementations expanded to includeRSTS,TOPS-10,TOPS-20andVAX/VMS[8]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).[9]Support for networks of up to 255 nodes with 8-bit addresses, 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 andCCITTRecommendationX.25.

DECnet Phase IV protocol suite
Application DAP: Data Access Protocol

CTERM: Command Terminal

Network Management NICE: Network Information (and) Control Exchange

MOP:Maintenance Operations Protocol

Session SCP: Session Control Protocol
Transport NSP: Network Service Protocol
Network DRP: DECnet Routing Protocol
Data link DDCMP: Digital Data Communications Message Protocol
Ethernet,Token Ring,HDLC,FDDI,...
Physical Ethernet,Token Ring,FDDI,...

1981–1986

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Phase IV[10][11]andPhase IV+(1982). Phase IV was released initially toRSX-11andVMSsystems, laterTOPS-20,TOPS-10,ULTRIX,VAXELN,andRSTS/Egained support. Support for networks of up to 64,449 nodes (63 areas of 1023 nodes) with 16-bit addresses, datalink capabilities expanded beyond DDCMP to includeEthernetlocal area networksupport as the datalink of choice, expanded adaptive routing capability to include hierarchical routing (areas, level 1 and level 2 routers),VMSclustersupport (cluster alias) and host services (CTERM). CTERM allowed a user on one computer to log into another computer remotely, performing the same function thatTelnetdoes in theTCP/IPprotocol stack. Digital also released a product called the PATHWORKS client, and more commonly known as the PATHWORKS 32 client, that implemented much of DECnet Phase IV for DOS, and 16 and 32 bit Microsoft Windows platforms (all the way through to Windows Server 2003).

Phase IV implemented an 8 layer architecture similar to theOSI(7 layer) model especially at the lower levels. Since the OSI standards were not yet fully developed at the time, many of the Phase IV protocols remained proprietary.

The Ethernet implementation was unusual in that the software changed the physical address of the Ethernet interface on the network to AA-00-04-00-xx-yy where xx-yy reflected the DECnetnetwork addressof the host. This allowed ARP-less LAN operation because the LAN address could be deduced from the DECnet address. This precluded connecting twoNICsfrom the same DECnet node onto the same LAN segment, however.

The initial implementations released were for VAX/VMS and RSX-11, later this expanded to virtually everyoperating systemDIGITAL ever shipped with the notable exception ofRT-11.DECnet stacks are found on Linux, SunOS and other platforms, and Cisco and other network vendors offer products that can cooperate with and operate within DECnet networks. Full DECnet Phase IV specifications are available.

At the same time that DECnet Phase IV was released, the company also released a proprietary protocol calledLATfor serial terminal access viaTerminal servers.LAT shared the OSI physical and datalink layers with DECnet and LAT terminal servers used MOP for the server image download and related bootstrap processing.

Enhancements made to DECnet Phase IV eventually became known as DECnet Phase IV+, although systems running this protocol remained completely interoperable with DECnet Phase IV systems.

1987 & beyond

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Phase V[12]andPhase V+(1987). Support for very large (architecturally unlimited) networks, a new network management model, local or distributed name service, improved performance over Phase IV. Move from a proprietary network to anOpen Systems Interconnection(OSI) by integration of ISO standards to provide multi-vendor connectivity and compatibility with DNA Phase IV, the last two features resulted in a hybrid network architecture (DNA and OSI) with separate "towers" sharing an integrated transport layer. Transparent transport level links toTCP/IPwere added via theIETFRFC1006 (OSI over IP) and RFC 1859 (NSP over IP) standards(see diagram).

It was later renamedDECnet/OSIto emphasize its OSI interconnectability, and subsequentlyDECnet-Plusas TCP/IP protocols were incorporated.

Notable installations

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DEC Easynet

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Not to be confused withEasynet,anISP.

DEC's internal corporate network was a DECnet network called Easynet, which had evolved from DEC's Engineering Net (E-NET). It included over 2,000 nodes as of 1984,[13]15,000 nodes (in 39 countries) as of 1987,[14]and 54,000 nodes as of 1990.[15]

The DECnet Internet

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DECnet was used at various scientific research centers which linked their networks to form an international network called the DECnet Internet. This included theU.S. Space Physics Analysis Network(US-SPAN), theEuropean Space Physics Analysis Network(E-SPAN),Energy Sciences Network,and other research and education networks.[16][17]The network consisted of over 17,000 nodes as of 1989.[18]Routing between networks with different address spaces involved the use of either "poor man's routing" (PMR) or address translation gateways.[16]In December 1988, VAX/VMS hosts on the DECnet Internet were attacked by theFather Christmas worm.

CCNET

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CCNET (Computer Center Network) was a DECnet network that connected the campuses of various universities in the eastern regions of the United States during the 1980s. A key benefit was the sharing of systems software developed by the operations staff at the various sites, all of which were using a variety of DEC computers.[19]As of March 1983, it includedColumbia University,Carnegie Mellon University,andCase Western Reserve University.By May 1986,New York University,Stevens Institute of Technology,Vassar CollegeandOberlin Collegehad been added. Several other universities joined later.[20]

Hobbyist DECnet networks

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Hobbyist DECnet networks have been in use during the 21st century. These include:

See also

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References

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  1. ^James M. Moran; Brian J. Edwards (February 1984). "Giving DECnet a LAN".Hardcopy.pp. 62–65.
  2. ^"SYSTEMS STRATEGIES".The New York Times.May 13, 1992.DECnet/SNA gateway solution
  3. ^"DECnet for Linux".SourceForge.Archived fromthe originalon October 4, 2009.RetrievedJune 26,2018.
  4. ^Caulfield, Christine (February 18, 2010)."Orphan DECnet".Linux Kernel ChangeLog 2.6.33.Archived fromthe originalon August 11, 2011.RetrievedJune 26,2018.
  5. ^"kernel/git/torvalds/linux.git - Linux kernel source tree".git.kernel.org.RetrievedAugust 3,2022.
  6. ^"kernel/git/torvalds/linux.git - Linux kernel source tree".git.kernel.org.RetrievedOctober 6,2023.
  7. ^Digital Equipment Corporation (1978)."Nineteen Fifty-Seven to the Present"(PDF).Computer History Museum.p. 53. Archived fromthe original(PDF)on December 21, 2013.RetrievedJune 26,2018.
  8. ^"Software Product Description: DECnet-VAX, Version 1"(PDF).DEC. September 1978.RetrievedMay 23,2023.
  9. ^"Introduction to DECnet (Phase III)"(PDF).May 22, 1982.
  10. ^"Overview of DECnet"(PDF).
  11. ^"The DECnet Phase IV Specifications".
  12. ^James Martin;Joel Leben (1992).DECnet Phase V: An OSI Implementation Network.Digital Press.ISBN978-0-1320-2987-2.
  13. ^Erik E. Fair (January 5, 1984).Re: The Plethora of Networks.Usenet fa.human-nets.Retrieved August 19, 2018.ArchivedMarch 14, 2016, at theWayback Machine
  14. ^Network World (September 7, 1987), p.4.DECworld network links hotels, ocean liners.Retrieved August 19, 2018.
  15. ^Network World (August 6, 1990), p.1.DEC shares early lessons on DECnet V.Retrieved August 19, 2018.
  16. ^abL. Stuart Vance (1990).The User's Directory of Computer Networks, The DECnet Internet.Retrieved August 19, 2018.
  17. ^L. Stuart Vance (1990).The User's Directory of Computer Networks, The DECnet Internet (Publisher Summary).Retrieved August 19, 2018.
  18. ^NASA Technical Reports Server (August 1, 1989).Space physics analysis network node directory (The Yellow Pages): Fourth edition.Retrieved August 19, 2018.ArchivedMarch 8, 2021, at theWayback Machine
  19. ^"The DECSYSTEM-20 at Columbia University 1977-1988".Archivedfrom the original on July 7, 2022.RetrievedJuly 1,2024.
  20. ^"Computing at Columbia Timeline".Archivedfrom the original on July 6, 2022.RetrievedJuly 1,2024.
  21. ^HECnet - The hobbyist DECnet.Retrieved January 24, 2022.
  22. ^Retro DECnet.Retrieved August 19, 2018.

General references

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