  Traditional power grids are evolving to keep pace with the demands of the
modern age. Smart grids contain integrated IT systems for better management and
efficiency, but in doing so, also inherit a plethora of cyber-security threats
and vulnerabilities. Denial-of-Service (DoS) is one such threat. At the same
time, the smart grid has particular characteristics (e.g. minimal delay
tolerance), which can influence the nature of threats and so require special
consideration. In this paper, we identify a set of possible smart grid-specific
DoS scenarios based on current research, and analyse them in the context of the
grid components they target. Based on this, we propose a novel target-based
classification scheme and further characterise each scenario by qualitatively
exploring it in the context of the underlying grid infrastructure. This
culminates in a smart grid-centric analysis of the threat to reveal the nature
of DoS in this environment.
