9/11 network impact (posted 2001-09-29)
The terrorist attack on the World Trade Center in New York City resulted in outages for a number of ISPs. Of the destroyed buildings, WTC 1 and 7 housed colocation facilities. The Telehouse America facility on 25 Broadway in Manhattan, not far from the WTC, lost power. The facility was not damaged, but commercial power was lost and after running on generator power for two days, the generators overheated and had to be turned off for several hours. Affected ISPs received many offers for temporary connectivity and assistence rebuilding their networks.
The phone network experienced congestion in many places on the day of the attack. Although individual (news) sites were slow or hard to reach, general Internet connectivity held up very well. While phone traffic was much higher than usual, traffic over the Internet rose shortly after the attack, but then it declined and stayed somewhat lower than normal the rest of the day, with some unusual traffic patterns.
It seems obvious that packet switched network have better graceful degradation than circuit switched networks. A phone call always uses the same amount of bandwidth, so either you are lucky and it works, or you are unlucky and you get nothing. Packet networks on the other hand, slow down but generally don't cut off users completely until things get really, really bad. And while the current Internet holds its own in many-to-many communication, it can't really cope with massive one-to-many traffic.