Evaluating policies and mechanisms to support distributed real-time applications with CORBA

To be an effective platform for performance-sensitive realtime systems, commodity-off-the-shelf (COTS) distributed object computing (DOC) middleware must support application quality of service (QoS) requirements end-to-end. However, conventional COTS DOC middleware does not provide this support, which makes it unsuited for applications with stringent latency, determinism, and priority preservation requirements. It is essential, therefore, to develop standards-based, COTS DOC middleware that permits the specification, allocation, and enforcement of application QoS requirements endto-end. The Real-time CORBA and Messaging specifications in the CORBA 2.4 standard are important steps towards defining standards-based, COTS DOC middleware that can deliver end-to-end QoS support at multiple levels in distributed and embedded real-time systems. These specifications still lack sufficient detail, however, to portably configure and control processor, communication, and memory resources for applications with stringent QoS requirements. This paper provides four contributions to research on realtime DOC middleware. First, we illustrate how the CORBA 2.4 Real-time and Messaging specifications provide a starting point to address the needs of an important class of applications with stringent real-time requirements. Second, we illustrate how the CORBA 2.4 specifications are not sufficient to solve all the issues within this application domain. Third, we describe how we have implemented portions of these specifications, as well as several enhancements, using TAO, which is our open-source real-time CORBA ORB. Finally, we evaluate the performance of TAO empirically to illustrate how its features address the QoS requirements for certain classes of real-time applications. This work was funded in part by Boeing, NSF grant NCR-9628218, DARPA contract 9701516, Motorola, Nortel, SAIC, Siemens, and Sprint. Subject Areas: Real-time CORBA; Patterns and Frameworks; Distributed and Real-Time Middleware