Real Distribution of Response Time Instability in Service-Oriented Architecture

This paper reports our practical experience of benchmarking a complex System Biology Web Service, and investigates the instability of its behaviour and the delays induced by the communication medium. We present the results of our statistical data analysis and distributions which fit and predict the response time instability typical of Service-Oriented Architectures (SOAs) built over the Internet. Our experiment has shown that the request processing time of the target e-science Web Service (WS) has a higher instability than the network round trip time. It has been found that by using a particular theoretical distribution, within short time intervals the request processing time can be represented better than the network round trip time. Moreover, certain characteristics of the probability distribution series of the round trip time make it particularly difficult to fit them theoretically. The experimental work reported in the paper supports our claim that dealing with the uncertainty inherent in the very nature of SOA and WSs is one of the main challenges in building dependable service-oriented systems. In particular, this uncertainty exhibits itself through very unstable web service response times and Internet data transfer delays that are hard to predict. Our findings indicate that the more experimental data is considered the less precise distributional approximations become. The paper concludes with a discussion of the lessons learnt about the analysis techniques to be used in such experiments, the validity of the data, the main causes of uncertainty and possible remedial actions.