The Flexible Time-Triggered (FTT) Paradigm: An Approach to QoS Management in Distributed Real-Time Systems

Real-time distributed systems are becoming pervasive, supporting a broad range of applications such as avionics, automotive, adaptive control, robotics, computer vision and multimedia. In such systems, several activities are executed on different nodes and cooperate via message passing. One increasingly important concept is that of Quality-of-Service (QoS), i.e. a system performance metric from the application point-of-view. Concerning the communication system, the QoS delivered to the application is a function of communication parameters such as the rates of message streams. In previous work, the authors have developed two network protocols, FTT-CAN and FTT-Ethernet, which allow on-line changes to the set of message streams under guaranteed timeliness. In this paper, the specific network protocols are abstracted away leading to a generic communication paradigm named Flexible Time-Triggered (FTT), which supports on-line QoS management, with arbitrary policies, in distributed realtime systems. Two possible QoS management policies are referred, priority-based and another one based on the elastic task model, and their use is illustrated with a case study.