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DECnet to TCP/IP migration for OpenVMS

OpenVMS and DECnet have provided customers excellent service for over 25 years.

OpenVMS and DECnet will continue to provide a viable platform running on state-of-the-art systems for years more to come. Customers World Wide have been consistently pleased with its reliability, robustness, security, and performance. OpenVMS customers continue to use DECnet to perform demanding tasks at installations in a variety of vertical markets.

While all the above are compelling reasons to stay with DECnet, we see migrating from DECnet to TCP/IP for networked applications as a viable option that should be entertained by our loyal customer base.

We have found many users who have demonstrated success by performing an orderly and cost-effective DECnet phase out, replacing it with TCP/IP, the industry networking standard.

Customers have retained the benefits of OpenVMS while integrating TCP/IP as their primary interconnect strategy.

In general, DECnet and TCP/IP offer the same basic services to applications and the operating system. Both offer a QIO interface that applications may use to communicate across the network. Both offer high-level utilities for file transfer, email, and remote terminal access (among others).

In contrast, TCP/IP provides a stream or byte oriented protocol, while DECnet provides a packet oriented protocol. DECnet is more closely coupled to the file system offering additional file system related services transparently to the application via either file system calls or I/O operations provided by a particular language. TCP/IP is not quite as closely coupled in general, but is fairly transparent when using the C programming language. TCP/IP also provides an additional programming interface that is not available with DECnet.

Learn more about migration

» DECnet over TCP/IP Quick Reference Card [PDF]
» DECnet to TCP/IP Migration Considerations (EDS white paper)   [PDF]
» DECnet to TCP/IP Migration for OpenVMS Users (ArrAy, Inc. white paper) [PDF]
» benefits of moving to IP
» alternative migration scenarios
» recommendation
» DECnet migration services from ArrAy and EDS

Benefits of moving to IP

So why is there a need for change? While the maturity of DECnet provides many benefits such as high reliability and stability there are compelling reasons to migrate to IP:

  • DECnet applications can only communicate with other DECnet applications. They cannot communicate and interoperate with TCP/IP applications on the same or other systems.
  • There is a large installed base of third party and open source applications that run IP and it gets larger with each day.
  • Enterprises can save money and simplify their networks by mandating that only IP will be supported. Why support multiprotocols?
  • Personnel with IP management, administrative, and development skills are more available today because it is an industry standard.
  • TCP/IP, with all its services, programming interfaces, etc., provides the industry standard for networking, and many users are choosing IP to replace proprietary protocols.
  • While routers may handle both DECnet and IP, it will be possible in some environments to eliminate duplicate circuits, wiring, and networking equipment, and administrative costs can be reduced, as DECnet routing requirements are eliminated.
  • HP TCP/IP for OpenVMS has been engineered by OpenVMS engineering. The very same engineering expertise that brought you DECnet providing you a migration alternative that has been extensively qualified and tested with the OpenVMS operating system.

Alternative migration scenarios

We see three primary scenarios available to our users of DECnet:

DECnet Islands This is a passive strategy to allow OpenVMS and DECnet applications to continue in operation without significant upgrades and to use TCP/IP for new systems and applications. This approach will, over time create smaller and smaller DECnet island LAN's.
DECnet over TCP/IP Coexistence with DECnet over TCP/IP Switch to DECnet over TCP/IP, allowing wide area operation in the WAN's IP environment. Running DECnet over IP means that DECnet uses the TCP/IP transport stack. This switch away from native DECnet does not require application changes and will allow DECnet applications to continue to operate in the enterprise, but it will not allow them to interoperate with other TCP/IP applications.
Full TCP/IP Migration This is a proactive strategy to eliminate all DECnet usage, even within LANs, and is the most complex of the alternatives. The most significant tasks are upgrading or replacing all of the custom and third party applications in the application portfolio that use DECnet QIO System Services, replacing QIO System Services usage with sockets. This can require reprogramming as well as development costs. The reprogramming task is complex, using a stream-oriented programming model rather than DECnet packets.

It is also not uncommon for the migration path to go from DECnet to DECnet over IP to full TCP/IP implementation and can be recommended.


Each customer is unique and will have unique migration requirements. Some customers will not want to make intrusive changes to their applications, thus eliminating the "Complete Migration" option. Some customers may be willing to make application changes, but will compare the cost of those changes against the cost associated with migrating to an entirely different application that doesn't have the same migration issues.

Because each application is unique, it's difficult to create a step-by-step procedure for application modification that will apply to every application.

We have provided IP migration white papers from ArrAy and EDS to help you better appraise the implementation issues that you may face in your quest of moving to IP. Of note are the migration services that can be provided to your business by both ArrAy and EDS to help you in your implementation journey. Good luck in you migration efforts!

DECnet Migration Services from ArrAy and EDS

Workshops Provide information to OpenVMS users about DECnet to TCP/IP migration
Assessment Work with the customer to determine goals, requirements, and objectives and to understand current and future operations
Project Planning Create a phased migration schedule, plan resource usage and costs, specify any hardware and software purchases, training requirements, and acceptance criteria
Technical Specifications Define service mapping, application migration techniques, etc.
Tools Assist in migration and for ongoing use onece the migration is complete
Project Execution and Management Perform the migration as specified during planning
Testing and Acceptance Assure that all customer requirements are satisfied