services in the network) that are available to the system to ensure that the provided service is not impaired. It also provides further feedback to the challenge analysis on the remedy to the challenge, which is incorporated into future evolution strategies. Reactive Evolution to Sudden Changes A key aspect of network resilience is one of the axioms expressed by the ResiliNets framework: the ability to address the requirements placed on the network satisfactorily under all conditions initiated by establishing an understanding of the expectations of acceptable levels of service from the network. This should be followed by a thorough study of past challenges faced by the network in providing resilience. The outputs of such a study will illustrate the challenges and their impacts on resilience, including actions taken at those times and their impact on recovering the resilience characteristics of the network. The following quote further explains the axioms mentioned previously: We define an adverse event or ongoing condition as challenging (Section 3) the normal operation of the network. We can further classify adverse events and conditions by severity as mild, moderate, or severe, and categorise them into two types: (1) Anticipated adverse events and conditions are ones that we can predict based either on past events (such as natural disasters), and attacks (e.g. viruses, worms, DDoS) or that a reasoned threat analysis would predict might occur. (2) Unanticipated adverse events and conditions are those that we cannot predict with any specificity, but for which we can still be prepared in a general sense. For example, there will be new classes of attacks for which we should be prepared. Resilience and Survivability in Communication Networks: Strategies, Principles, and Survey of Disciplines -J.P.G. Sterbenz et al. (2010) To clarify further, this section will explain how to formulate a cogent set of steps to address those challenges that can be anticipated, their effect on the network resilience as studied and unders