While many things went wrong during the aftermath and, the technical issue that sticks out the most is the , a failure which hamstrung rescuers. The storm knocked out 3 million telephone lines, 1,000 cellular sites and 38 emergency-call centers in Louisiana, Mississippi and Alabama, according to the Federal Communications Commission.
So what was the weak link in the chain that caused the supposedly 99.999-percent-reliable telephone network to go down, local television stations throughout the area to go off the air, and cable operators to suspend service? The answer is simple: Flood waters poured into facilities, knocking out commercial electrical power sources as well as back-up generators and batteries.
"It doesn't matter what kind of natural disaster it is," said Mark Marchand, a spokesman for Verizon Communications. "If you don't have power, the network doesn't work."
When disasters such as hurricanes and earthquakes strike, communications networks often prove just how fragile they can be. Phone companies, cellular providers and cable operators rely on electrical power to run the equipment necessary to sustain service.
Many phone companies are already starting to convert parts of their network to IP. While IP technology will eventually find its way into traditional phone networks, that won't solve all the old problems, like access to electrical power.
As part of their disaster relief plans, phone companies, cellular providers and cable operators haveto keep their equipment running. But still, sometimes things fall apart.
Dependence on electrical power and what happens when that power is cut off is best illustrated by BellSouth's problems during Hurricane Katrina. BellSouth, which serves much of the Southeast, including the Gulf Coast and parts of Florida, has been through more natural disasters than any other phone company in the United States. Since 1992, 22 hurricanes have hit the state. And prior to Katrina, BellSouth never lost service in a central office. But this time was different. Massive flooding throughout the region made its way to the company's central office, making its back-up power generators essentially useless.
"BellSouth has a foolproof plan for dealing with loss of power," said Nadine Randall, a spokeswoman for BellSouth. "The problem occurred when flooding caused the central office to go down. We knew the office in New Orleans was in a floodplain, so we actually built the facility on stilts and put all the critical switching gear on the second and third floors and filled them with sandbags before the storm hit. But in the end, Mother Nature wins." The switches may not have gotten wet, but technicians couldn't get any power to them.
The failing of BellSouth's local phone network also had a ripple effect on other communications networks.
"One thing that people don't understand is the relationship between the mobile phone network, local phone companies and commercial power companies," said John Taylor, senior manager of public affairs for Sprint Nextel. "We depend on local phone and power to run our wireless networks."
In a mobile phone network, a cell tower will service a particular region. The tower is usually connected to the local phone network via a T1 data link. If the local phone network is out, the cell tower is unable to transmit the traffic. Cell towers are also vulnerable to power outages because they need electricity to run the radios that transmit signals to customers and the switches that send the traffic to the local phone network. Without power, the cell tower cannot operate.
Many cell towers have backup batteries, but unlike the central offices of the local phone network, not every tower has its own back-up generator. Instead, cell phone operators deploy trucks with generators to a particular region and then work to restore power in affected areas as quickly as they can after a storm or other emergency situation subsides.
Designed for resiliency, the local phone network is among the most reliable utilities in the country. From the facilities that house the critical equipment that switches and routes calls to the network itself, the traditional telephone network boasts a reliability rate of 99.999 percent. If a link on the network is cut, the network usually is able to reroute traffic around the outage. This often happens during ice storms, hurricanes and earthquakes. Phone companies, in particular, have learned to keep their networks decentralized and to build redundancy into links.
But sometimes the network fails, as it did during and after Hurricane Katrina. The first call between stranded officials in New Orleans and President Bush was not carried over the traditional phone network or even the cell phone network. It went over the Internet using a laptop running software from voice over Internet Protocol (VoIP) provider Vonage. Mayor Ray Nagin and his staff were able to use the Vonage service because the New Orleans Hyatt Regency hotel, where they were stationed during the hurricane, had emergency power and a fairly hardy T1 access line. As a result, the broadband connection to the hotel remained up and they were able to receive the call from Bush.
The Internet itself originally was designed to be redundant and hard to bring down, so it stands to reason that during a major disaster, it is one of the most resilient and reliable communications networks. The benefit of the Internet and the underlying technology is that they have been designed in a distributed fashion, with no single points of failure. So if one or two links are destroyed, traffic automatically finds a different path.
The traditional phone network is built on circuit-switched technology, which establishes point-to-point links. One call is routed by connecting directly to a destination on the other side. But an IP network is built like a mesh; when calls are made, it establishes connections as the call is passed from one part of the network to the next until it reaches the final destination.
Many phone companies, including Verizon and BellSouth, are starting to convert parts of their networks to IP. But, although traditional phone networks eventually will adopt IP technology, that won't solve all the old problems, like access to electrical power.
According to media coverage of an industry event in Boston last month, Bill Smith, BellSouth's chief technology officer, cautioned audience members during a keynote speech that IP technology is not a panacea for increasing network reliability during a disaster. You can't count on a lucky break like emergency power returning and a T1 line holding up, he said.
"VoIP is a wonderful thing, but it has to run on something," he said, according to TelephonyOnline. "The biggest problem (in the areas hit by Katrina) was power. Most VoIP equipment runs on power. It does a disservice to the industry to create an impression that VoIP can run under any conditions. It requires some fundamental infrastructure."