I. Introduction
The Internet has become a critical infrastructure of our society, yet few studies have focused on not only how to monitor the Internet as a whole, but also how to quantify the impact that disruptive events (such as [1]–[7]) may have on it. Although events such as security attacks, large-scale power outages, hurricanes, undersea cable cuts, and other types of natural disasters may cause observable disturbances to the normal operation of the Internet, we know little about the kind of impact each event might cause and how big it might be. The lack of such knowledge also makes it difficult to conduct effective network diagnosis, recovery, or other operation tasks. In fact, there is not even an established criterion for observing different kinds of impacts or for quantifying what “big” or “small” means.