Lack of redundancy

With the current separation of the Internet and the PSTN, a certain amount of redundancy is provided. An Internet outage does not necessarily mean that a voice communication outage will occur simultaneously, allowing individuals to call for emergency services and many businesses to continue to operate normally. In situations where telephone services become completely reliant on the Internet infrastructure, a single-point failure can isolate communities from all communication, including Enhanced 911 and equivalent services in other locales.^{[original research?]} However, the internet as designed by DARPA in the early 1980s was specifically designed to be fault tolerant under adverse conditions. Even during the 9/11 attacks on the World Trade Centers the internet routed data around the failed nodes that were housed in or near the towers. So single point failures while possible in some geographic areas are not the norm for the internet as a whole.