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Reliable, reusable Ada components for constructing large, distributed multi-task networks: networks architecture services (NAS)

This paper will introduce the key concepts of TRW's Reusable Message Based Design Software (Network Architecture Services- NAS) which has proven to be key to the CCPDS-R project's progress to date. The NAS software and supporting tools have provided the CCPDS-R Project team with reliable, powerful building blocks that have been integrated into extensive demonstrations to validate the critical design approaches. The CCPDS-R PDR Demonstration consisted of 130 Ada tasks interconnected via 450 different task to task interfaces, executing in a network of 3 VAX nodes. The extensive reuse of NAS software building blocks and Ada generics resulted in the translation of 120,000 Ada Source lines into over 2 million lines of executable machine language instructions. The NAS software (about 20,000 Ada source lines) was conceived in a TRW Independent Research and Development project in 1985, and has since been refined and evolved into a truly reusable state. Although NAS reuse is limited currently to Digital Equipment Corporation VAX VMS networks, efforts are underway to provide heterogeneous NAS capabilities.
The advantages of NAS usage are twofold:Value added operational software through reuse of mission independent, performance tunable components which support open architectures, and
Overall project productivity enhancement as a result of NAS support for rapid prototyping, runtime instrumentation toolsuite, and encapsulation of the difficult capabilities required in any distributed real-time system into a standard set of building blocks with simple applications interfaces. This isolation of the “hard parts” into an easily used standard software chipset, results in a large net reduction in applications software complexity, less reliance on scarce real-time programming experts, and a substantial reduction in overall project risk.

This paper describes the message based design techniques which drove us to the development of NAS, the capabilities and components inherent in the NAS product, and the CCPDS-R experience in using NAS in a stringent real time command and control environment.