QoS negotiation in real-time systems and its application to automated flight control

Real-time middleware services must guarantee predictable performance under specified load and failure conditions, and ensure graceful degradation when these conditions are violated. Guaranteed predictable performance typicall y entails reservation of resources and use of admission control. Graceful d egradation, on the other hand, requires dynamic reallocation of resources t o maximize the application-perceived system utility while coping with unant icipated overload and failures. We propose a model for quality-of-service ( QoS) negotiation in building real-time services to meet both of the above r equirements. QoS negotiation is shown to 1) outperform "binary" admission c ontrol schemes (either guaranteeing the required QoS or rejecting the servi ce request), 2) achieve higher application-perceived system utility, and 3) deal with violations of the load and failure hypotheses. We incorporated t he proposed QoS-negotiation model into an example real-time middleware serv ice, called RTPOOL, which manages a distributed pool of shared computing re sources (processors) to guarantee timeliness QoS for real-time applications . In order to guarantee timeliness QoS, the resource pool is encapsulated w ith its own schedulability analysis, admission control, and load-sharing su pport. This support differs from others in that it adheres to the proposed QoS-negotiation model. The efficacy and power of QoS negotiation are demons trated for an automated flight control system implemented on a network of P Cs running RTPOOL. This system is used to fly an F-16 fighter aircraft mode led using the Aerial Combat (ACM) F-16 Flight Simulator. Experimental resul ts indicate that QoS negotiation, while maintaining real-time guarantees, e nables graceful QoS degradation under conditions in which traditional sched ulability analysis and admission control schemes fail.