The nation's wired and wireless communications networks last week managed to handle sharply increased traffic, which spiked 400 percent above normal on some networks immediately after the terrorist attacks on New York and Washington. This was the case despite the fact that the collapse of the World Trade Center knocked out switches and fiber circuits in the building's basement and destroyed cellular telephone towers in lower Manhattan.
The Pentagon's global command and control network, the Defense Information Systems Network (DISN), provides voice, data and video services over separate classified and unclassified Synchronous Optical Networks (Sonet), which are provided by WorldCom Inc. Both operated without outages, according to Betsy Flood, a spokeswoman for the Arlington, Va.-based Defense Information Systems Agency, which operates the network.
"We've had no problems with the DISN," said Flood. DISN is the successor to Arpanet, the original Internet designed to route traffic around network nodes destroyed in an attack.
WorldCom Inc. lost service on 200 high-speed DS-3 circuits carrying commercial traffic through the World Trade Center's basement, but the self-healing Sonet rings that WorldCom uses helped to quickly restore service, said Diana Gwen, vice president of the company's government markets division.
Verizon Communications Inc. in New York, the local carrier that serves New York and Washington, as well as Sprint Corp. and AT&T Corp., also had switches in the basement of the World Trade Center. The collapse of the building initially caused traffic disruptions, but by the end of the week, all reported that rerouting had restored network operations to normal.
Cellular carriers reported unprecedented calling volumes in the hours after the attacks. Peter Nilsson, a spokesman for Cingular Wireless in Atlanta, reported that usage on the company's network surged some 400 percent above normal in the first few hours after the attack. The day after the attack, volumes had dropped to 20 percent above normal, Nilsson said.
The major cellular carriers, including Redmond, Wash.-based AT&T Wireless, Verizon Wireless and Cingular, all deployed temporary Cellular on Wheels Systems (COWS) to New York and Washington to replace downed cell towers and provide communications to emergency personnel.
Andrea Linsky, a spokeswoman for Verizon Wireless, said COWS are housed on trailers, which incorporate base-station electronics and telescoping antenna masts that can go as high as 60 feet. Linsky said Verizon has three COWS in service in the New York/New Jersey area, two in Washington and one in Pennsylvania, near the crash site of one of the hijacked aircraft.
Cingular Wireless has three COWS in operation in Washington, and AT&T Wireless has six in the New York area.
Spokesmen for both wired and wireless communications companies emphasized that although their networks handled a surge in traffic after initial disruptions, the public could help by limiting their calls.