DTJ Number 3 September 1987 - Digital Technical Journals

john Forecastjames L. jacksonjeffrey A. SchriesheimIThe DECnet- ULTRIXSoftwareThe UL TRIX system is the second operating system approved by Digitalfor its VAX processors. Incorporating the Digital Networking Architecture(DNA) capabilities into this software was important to support distributedapplications. A key constraint was that no changes should berequired to existing DNA protocols or DECnet implementations. The4.2BSD socket interface was expanded to support the DECnet protocolsand a unique object spawner was created to simplify writing new servers.A network management structure incorporating DECnet's database conceptalso had to be built. The DECnet-UL TRIX software is the first productimplementing the DNA strategy on any variant of the UNIX software.Project GoalsThe DECnet-ULTRIX software is Digital's firstproduct to be layered on the ULTRIX-32 softwareand is a key part of our ULTRIX strategy. Onemajor reason for developing DECnet-ULTRIX wasto bring the ULTRIX system into Digital's computingenvironment. We believe that our customerswill better meet their computing needsby being able to use the VMS and ULTRIX operatingsystems together. Such a mixture of systemsrequires communications mechanisms thatare easy to use and manage, yet provide highthroughput. These mechanisms make possiblethe transportation of existing applications fromVMS systems to ULTRIX systems. Thus new distributedapplications can be built by takingadvantage of the strengths of each system.DECnet-ULTRIX Version 1.0 provides filetransfer, remote terminal access, mail, networkmanagement, and user programming interfaces.All these functions are completely compatiblewith all current implementations of the DigitalNetwork Architecture (DNA) . The DECnet­ULTRIX software also makes possible a largenumber of other options, such as support for terminalservers, protocol gateways developed byDigital, layered applications, and managementtools. As we migrate the DECnet protocolstoward the Open Systems Interconnect (OSI)protocols, the DECnet-ULTRIX software willprovide the means for ULTRIX systems to communicatewith those of other vendors.Project ConstraintsIn planning the DECnet-ULTRIX design, wewanted to clearly identify our constraints at theoutset of the project. Thus we would have a consistentand well conceived framework for makingdesign decisions.We decided that the software should requireno changes to the currently available DNA protocolsand DECnet implementations. If problemswith other DECnet products were uncovered bythe DECnet-ULTRIX software, those problemswould be solved. This decision was made so thatthe software could be completely compatiblewith the large base of existing DECnet networkswithout requiring the upgrading or patching ofsoftware for any system. Our goal was to haveULTRIX systems simply "plug" into existingnetworks, thus adding new capabilities for ourcustomers.All features of the DECnet programming interfacehad to be provided even though some wouldnever be used by many customers. A DECnet­ULTRIX user should be able to write programs tocommunicate with any existing DECnet applicationprogram on any type of DECnet system.These features include passing optional datawith connection establishment and dissolution,passing access control information on a connectrequest, and rejecting a requested connectionwhile supplying a reason code.We decided that the DECnet-ULTRIX softwareshould be culturally compatible with the UNIX100Digital TecbnlcalJournalNo. 3 September 1986