Note

Purpose and Origin

OSF provides a reference implementation (source code) on which all DCE products are based [OSF 96a].The DCE is portable and flexible- the reference implementation is independent of both networks and operating systems and provides an architecture in which new technologies can be included, thus allowing for future enhancements. The intent of the DCE is that the reference implementation will include mature, proven technology that can be used in parts- individual services- or as a complete integrated infrastructure.

The DCE infrastructure supports the construction and integration of client/server applications while attempting to hide the inherent complexity of the distributed processing from the user [Schill 93]. The OSF DCE is intended to form a comprehensive software platform on which distributed applications can be built, executed, and maintained.

Technical Detail

Figure 10: Distributed Computing Environment Architecture

DCE services are organized into two categories:

1. Fundamental distributed services provide tools for software developers to create the end-user services needed for distributed computing. They include
   • Remote Procedure Call, which provides portability, network independence, and secure distributed applications.
   • Directory services, which provide full X.500 support and a single naming model to allow programmers and maintainers to identify and access distributed resources more easily.
   • Time service, which provides a mechanism to monitor and track clocks in a distributed environment and accurate time stamps to reduce the load on system administrator.
   • Security service, which provides the network with authentication, authorization, and user account management services to maintain the integrity, privacy, and authenticity of the distributed system.
   • Thread service, which provides a simple, portable, programming model for building concurrent applications.
2. Data-sharing services provide end users with capabilities built upon the fundamental distributed services. These services require no programming on the part of the end user and facilitate better use of information. They include
   • Distributed file system, which interoperates with the network file system to provide a high-performance, scalable, and secure file access system.
   • Diskless support, which allows low-cost workstations to use disks on servers, possibly reducing the need/cost for local disks, and provides performance enhancements to reduce network overhead.

Usage Considerations

DCE works internally with the client/server model and is well-suited for development of applications that are structured according to this model. Most DCE services are especially optimized for a structuring of distributed computing systems into a "cell" (a set of nodes/platforms) that is managed together by one authority.

For DCE, intra-cell communication is optimized and relatively secure and transparent. Inter-cell communication, however, requires more specialized processing and more complexity than its intra-cell counterpart, and requires a greater degree of programming expertise.

When using the thread services provided by DCE, the application programmer must be aware of thread synchronization and shared data across threads. While different threads are mutually asynchronous up to a static number defined at initialization, an individual thread is synchronous. The complexity of thread programming should be considered if these services are to be used.

DCE is being used or is planned for use on a wide variety of applications, including the following:

• The Common Operating Environment. DCE has been approved by DISA (Defense Information Systems Agency) as the distributed computing technology for the Common Operating Environment (COE) (see Defense Information Infrastructure Common Operating Environment).
• The Advanced Photon Source (APS) system. This is a synchrotron radiation facility under construction at Argonne National Laboratory.
• The Alaska Synthetic Aperture Radar Facility (ASF). This is the ground station for a set of earth-observing radar spacecraft, and is one of the first NASA projects to use DCE in an operational system.
• The Deep Space Network's Communications Complexes Monitor and Control Subsystem. This project is deploying DCE for subsystem internal communications, with the expectation that DCE will eventually form the infrastructure of the entire information system.
• The Multimission Ground Data System Prototype. This project evaluated the applicability of DCE technology to ground data systems for support of JPL flight projects (Voyager, Cassini, Mars Global Surveyor, Mars Pathfinder).
• Earth Observing Systems Data Information System. This NASA system is one of the largest information systems ever implemented. The system is comprised of legacy systems and data, computers of many varieties, networks, and satellites in space.
• Command and control prototypes. MITRE has prototyped command and control (C2) applications using DCE technology. These applications provide critical data such as unit strength, supplies, and equipment, and allow staff officers to view maps of areas of operation [OSF 96b].

Maturity

The DCE continues to evolve, but many large organizations have committed to basing their next generation systems on the DCE- over 14 major vendors provided DCE implementations by late 1994, when DCE 1.1 was released.

DCE 1.2.1, released in March 1996, provided the following new features:

• Interface definition language (IDL) support for C++ to include features such as inheritance and object references in support of object-oriented applications. This feature supports adoption of any object model or class hierarchy, thus providing developers with additional flexibility.
• Features to provide for coexistence with other application environments.
• Improvements over DCE 1.1 including enhancements to achieve greater reliability and better performance [OSF 96a].

1. Installing a CORBA-based product over DCE to provide additional support for distributed object technologies and a wide range of standardized service interfaces.
2. Integrating Network COM/DCOM (see Component Object Model (COM), DCOM, and Related Capabilities) into the DCE infrastructure.

Costs and Limitations

Object-oriented extensions of the DCE have been developed by industry, but an agreed to vendor-neutral standard was still being worked in 1996.

Dependencies

Alternatives

Complementary Technologies

Index Categories

Name of technology	Distributed Computing Environment
Application category	Distributed Computing (AP.2.1.2)
Quality measures category	Interoperability (QM.4.1) Portability (QM.4.2) Scalability (QM.4.3) Security (QM.2.1.5) Maintainability (QM.3.1) Complexity (QM.3.2.1) Throughput (QM.2.2.3)
Computing reviews category	Distributed Systems (C.2.4)

References and Information Sources

Current Author/Maintainer

Modifications