Distributed denial of service (DoS) attacks on cyber-resources are complex problems that are difficult to completely define, characterize, and mitigate. We recognize the process-nature of DoS attacks and view them from multiple perspectives. Identification of opportunities for mitigation and further research may result from this attempt to characterize the DoS problem space. We examine DoS attacks from the point of view of (1) a high-level that establishes common terminology and a framework for discussing the DoS process, (2) layers of the communication stack, from attack origination to the victim of the attack, (3) specific network and computer elements, and (4) attack manifestations. We also examine DoS issues associated with wireless com...