A two level strategy for software fault tolerance of service control point

Fault tolerance (FT) is a feature of top importance in the long-life real-time systems. The Service Control Point (SCP) in the Intelligent Network (IN) is just one of this kind of systems. Its dependability affects directly the Quality of Service (QoS) of the whole network. In the paper, we give a overview on the software fault tolerance (SFT) at first, and decide to adopt the Time-Redundancy approach to implemant the SFT of SCP according to the special features of the IN application. Based on the processing mechanism of IN calls and under the consideration of load-balance, software fault-tolerance and software upgrading on-line, we present a Two-Level Concurrence Model of SCP software, and give our implemen-tation of this model in the multi-task environment. Furthermore, we discuss in detail the issuses of SFT based on this model, and give the corresponding strategies and algorithms to achieve the specified whole FT targets. At last, we have a further discuss on the system effectiveness of the SCP software, and provide a computing method of the effectiveness of the SCP software based on the Markov model.