The critical infrastructures of transportation and telecommunication networks, as well as energy networks and even financial networks are highly interconnected and interdependent in many ways. The features of interconnectedness and interdependence have been vividly illustrated in numerous ways in recent years through incidents known as single point failures, that is, those in which a single node or link in a network fails, causing major disruptions in related networks and services. Below we highlight several recent examples of such failures.

A Baltimore Train Fire Disrupts Internet Service in the Northeast and Even E-Mail in Africa

A CSX Corp. freight train traveling through Baltimore in July 2001 with 60 cars carrying paper, wood, as well as hazardous materials derailed and caught fire. The fire spread to a tunnel, destroying also the fiber optic cable which ran through it, since temperatures reached 1,500 degrees. In addition, the fire damaged one of UUNet's nearby telecomm routers, which, in turn, further disabled telecommunications traffic. UUNet provides Internet services to business customers worldwide.

Consequently, a train derailment in a tunnel in Baltimore resulted in not only Internet service in the Northeast being disrupted, but also cell phone outages in Maryland and e-mail problems in Africa. For more information, see  http://www.computerworld.com/cwi/stories/0,1199,NAV47-68-84-88-93_STO62375,00.html

A Galaxy IV Satellite Failure Leads to an Outage of Nearly 90% of all Pagers in the US and Disrupts Banking and Financial Services

In the Spring of 1998, the failure of a single satellite, the Galaxy IV satellite, affected nearly 90% of the 40 million pagers in the United States. In addition, Internet acess via satellite was disrupted as were television studio feeds and wire service news transmissions. Many paging customers were surprised that the service was so dependent on a single satellite. From the perspective of interdependencies of networks, this single point failure also disrupted a variety of banking and financial services, including credit card purchases and automated teller transactions. In addition, communications between doctors and emergency workers were disrupted, threatening the human services network.

For further information see: http://news.cnet.com/news/0-1003-200-329483.html?tag=prntfr and the article, "Identifying, Understanding, and Analyzing Critical Infrastructure Interdependencies," by S. M. Rinaldi, J. P. Peerenboom, and T. K. Kelly, in IEEE Control Systems Magazine, December 2001, pages 11-25.