A Reliability Evaluation Of Time-Constrained Distributed Software

The reliability of distributed computing system depends not only on the reliability of communication links and nodes, but also on the resources distribution, including programs and data files.Reliability models so far proposed for distributed software reliability evaluation can't capture the effect of real-time constraints. This proposal presents an approach for the reliability performance analysis of distributed software addressed on the real-time constraint issue. With time-constraint information and the execution time of each File Spanning Tree (FST), the corresponding Markov state space can be defined for reliability computation. To speed up the evaluation process and reduce the size of the Markov state space, several dynamic reliability-preserving reduction techniques are developed. A realizable recursive algorism is proposed to search all the File Spanning Trees for a given program in the distributed system. To search all the File Transmission Paths (FTP) for each FST, we make use of the node-add method used in Minimum File Spanning Tree (MFST) and check if the FTP set includes the same tree before an FTP added. In the evaluation of file transmission time, based on the algorism for linear transmission path, we take the branched path into account to make the algorism perfect. We also present how to compute the reliability of a program based on factoring method and Markov model.The Time-Constrained Distributed Software Reliability (TCDSR) evaluation system is composed of Node Emulator (NE), Distributed System Emulator (DSE) and Reliability Evaluator (RE). The NE and DSE, which dispatch the programs and files randomly, together emulate the distributed software. The RE gets the information of all the nodes to work out the metrics. The test result illuminates that the TCDSR system can be applied to distributed system with any topology, such as line, star, ring and net topology. By changing the parameters, such as time-constrainat and the reliability of the links, the test result can help the distributed system engineer to optimize the performance of the system and software.