What do we mean by Network Denial of Service?

Recent network denial-of-service attacks have brought about awareness of the vulnerability of increasingly important network services. While denial of service is not a new problem, and some of the network aspects of denial of service have been addressed, there is currently no unifying definition of what constitutes network denial of service. The goal of this paper is to propose a definition of network denial of service, and to demonstrate a simple network model that can be used to construct a taxonomy of network denial-of-service attacks. This taxonomy provides a means of categorizing existing attacks and demonstrating how future attacks might be constructed, as well as providing a simple a precise way of describing attacks.