Dependability Modeling and Assessment of Complex Adaptive Networked Systems

The dependability of a networked software system S is a measure of how good S meets its service-level objectives in the presence of uncontrolled external environment conditions incident on S. The dependability attribute is hard to determine due to the inherent complexity of S, i.e., how the behavior of S is affected by the external environment conditions and the network resource availability is difficult to be accurately captured with mathematical models. The complexity arises from the large dimensionality of input parameter space and the interactions between various components in S. This leads to the employment of model-based control techniques that adapt the operations of S over multiple "observe-actuate" rounds and steer S towards a reference input QoS. How close is the actual QoS so achieved to the reference QoS is a measure of the dependability of S. Our paper studies model-based engineering methods to quantify the notion of dependability, and therein enhance the dependability of S. The paper provides a management architecture to dynamically evaluate the dependability of S, and adjust the plant and algorithm parameters to control the dependability.