“…The prime motivation for the study of such a system model comes from certain time-sensitive e-service applications, where it is desirable but not mandatory to meet given transaction deadlines, and which increasingly rely on heterogeneous multicluster web-server architectures. Examples of such soft real-time applications include e-commerce (see Bertini et al (2010)), real-time databases, e.g., for online stock trading (see Kao and García-Molina (1996) and Kang et al (2007)), and scientific computing (see Zhu (2001) and Plankensteiner et al (2010)). See also He et al (2006), which considers a similar model to the present one, yet focusing on the pure-routing case, i.e., without admission control.…”