DTJ Number 3 September 1987 - Digital Technical Journals

Paul R. Beckjames A. KryckaThe DECnet- VAX ProductAn Integrated App roachto NetworkingEarly DECnet implementations were completely layered above the servicesof the operating system. This loose bonding of network products tothe operating system resulted from separate development effo rts. From itsinception in 1976, the VMS operating system integrated networkingfunctionsadhering to the Digital Network Architecture (DNA). The DECnet­VAX product is the DECnet implementation most tightly coupled with itsparent operating system. This product provides an unprecedented degreeof transparency fo r network applications while remaining true to theDNA strategy. Transparency is achieved by providing access to networkcapabilities through system services, record management services, andthe standard 1/0 statements of high-level languages.When the first VAX processor and its VMS operatingsystem were designed a decade ago, theDECnet architecture was in its second majorphase . Several of Digital's major operating systemshad already implemented DECnet Phase II.Therefore, a major goal of the VMS DevelopmentGroup was to provide networking capabilitieswith the initial release of that group's product.Both the VAX architecture and the VMS operatingsystem were completely new designs. However,the VMS system shares a common heritagewith the RSX- llM operating system. Some of theutilities in the first few VMS releases were actuallyimages of their RSX- llM equivalents runningin compatibility mode. That was not thecase with the DECnet-VAX product, the networkproduct in the VMS system.Previously, DECnet implementations had beenadd-ons to their host operating systems, whichpredated the development of the DECnet architecture.The VMS system, on the other hand, wasdesigned after the DECnet architecture had beenwell established. The VMS architects recognizedthat including networking capabilities was vitalto their system's success in the future. Thus theydecided to integrate those capabilities smoothlyinto the operating system itself rather than tolayer the architecture on top. Although sold as alayered product, DECnet-VAX was designed andimplemented by the same group that developedthe VMS software. This product was designedfrom the beginning to be a coherent pan of theVMS system . Its components are maintained withthe VMS source code and compiled as part ofeach VMS base level . This decision to integratethe DECnet-VAX development into the overallVMS project was instrumental in achieving thelevels of integration and transparency found intoday's product.In designing DECnet-VAX, a completely integratedapproach to networking was taken toachieve the following goals:• A high degree of transparency at many levels,allowing remote services to function in a waythat appears local to the system• The utilization of unique features in the VAXhardware and VMS software• High performance and efficiency• Ease of implementation of networkapplicationsTo build adequate DECnet capabilities into theVMS system, a model to view network functionshad to be developed. This model had to provideanswers to a number of strategic questions. How88Digital Tecbnical]ournalNo. 3 September 1986