A scheduler for SCADA-based multi-source fusion systems

摘要

In this article, we report on our experience regarding devising, implementing, and deploying a scheduler for multi-source fusion in the context of SCADA systems (Supervisory Control and Data Acquisition). They are challenging because they commonly rely on low-end boards with very limited computing, memory, and storage capabilities, but have to run hundreds if not thousands of agents that co-ordinate by means of complex multi-way rendezvouses. Our work was carried out in the context of a solar plant in which we could easily confirm that not scheduling the rendez-vouses fairly may easily drive the system into as many as 3 779.10 critical-failure states per hour, whereas a straightforward solution to the problem can reduce the figure to 1 094.76 critical-failure states per hour. Unfortunately, that is far from zero, which is the ideal number. In the literature, there are several proposals to deal with this problem, but most of them could not be adapted to our context, namely: some of them can deal with two-way rendez-vouses only, whereas ours involve an average of 12.89 agents; others require to instrument the agents, but many of them are hardware devices that cannot be modified; a few others cannot work with rendez-vouses that can get intermittently enabled and disabled along an execution, which makes them of little interest in our context; and some require to use shared memory, which is an advanced hardware feature that is not supported by our low-end computing boards. The two proposals that we managed to adapt were not efficient enough in our context since they led to an average of 1 102.77 and 1 458.65 critical-failure states per hour, respectively. That motivated us to work on a new proposal that does not have any of the previous problems. It relies on a incremental approach that was implemented very efficiently using bounded counters and queues. Furthermore, the experimental results and the corresponding statistical analysis confirm that it works very well in practice.