SPECIAL REPORT: REBUILDING THE FUTURE
Of All Systems Struck September 11, The Phone Network Fared The Worst. Here's Why.
Telephone networks are designed with one premise in mind: Not every customer will try to make a call at the same time. Like so much else, that assumption failed on the day of the World Trade Center attacks. September 11 call volume far exceeded that of telcos' otherwise peak period - Mother's Day - leaving millions of anxious callers without a dial tone. Which is why Doug Sicker, the Level 3 executive who heads the steering group of the US government's Network Reliability and Interoperability Council, refers to the situation as "an unexpected Mother's Day event."
The problem is that the telephone network requires a dedicated 64-Kbps connection for the duration of each call, and the cost of a switching system that could handle everyone at once would be astronomical. So phone companies rely on statistical averaging to figure out what they'll need under ordinary circumstances.
When disaster strikes, that assumption no longer applies. Instead, the Telecommunications Service Priority system - a federal program designed to guarantee government communications in an emergency - kicks in. Administered by the National Communications System, a little-known agency set up after the Cuban Missile Crisis, TSP calls for circuits to be held in reserve for certain key customers - police, firefighters, hospitals, government agencies, the military. Everyone else gets potluck.
As the World Trade Center collapsed, it took with it some 300,000 voice lines and more than 3 million data lines at a Verizon central office across the street. But despite the sudden loss of capacity, the real problem for most customers was the network itself. Even as Verizon crews in hard hats and respirators rushed downtown to reroute cables, network managers started implementing load-control mechanisms that drastically reduced the chances of any ordinary customer getting a dial tone. Long-distance carriers set up random roadblocks, holding back an avalanche of Manhattan-bound calls so Verizon could keep circuits open for outgoing calls. For days, people trying to call in, especially from overseas, got busy signals, all-circuits-are-busy recordings, or dead air.
"The system degraded properly," says David Farber, professor of telecommunications systems at the University of Pennsylvania. "But the endgame is that some people can't be serviced. You don't want critical facilities to be jammed up by people wondering what happened."
But if this is the plan, you have to ask: Is it really the best one? Little can be done to improve the existing phone network - you can't just drop calls to a lower bandwidth, for example, because you still wouldn't have the switches you'd need to make more connections. The Internet offers another approach. Those who made it online after the attacks had no trouble with email or instant messaging, because traffic on the Net is broken into discrete packets, each one bearing a destination address that routes it through the system and reassembles the message at the other end. In a future disaster, could an Internet-type telephone network handle more calls than the existing circuit-switched network? That's the 64K question.