When the whole world heard New York and Washington, D.C., had been attacked, the whole world called New York and Washington to ask, "Are you OK?"
And the nations public switched telephone network answered exactly as it was supposed to, blocking incoming calls to make room for critical emergency communications and outgoing calls.
When the wireline network got clogged, users turned to their cell phones, wireless e-mail and voice-over-Internet services to get their messages through, with varying success.
By late last week, however, it was clear that the destruction of switching offices near the World Trade Center will cause long-term problems. Verizon Communications said all phone lines to the New York Stock Exchange were damaged. Telecommunications services could be further affected by power outages that continued through the end of the week.
In the hours following the suicide airplane crashes into the twin World Trade Center towers and the Pentagon, when call volume more than doubled the norm in New York and Washington, the wireline network remained operational.
"The traditional public switched telephone network is pretty darn amazing," said David Frankel, chief technology officer and founder of IP and DSL gear maker Jetstream Communications.
"While it was congested, and some calls were blocked, the network stayed up and handled a record number of calls. Any frustration you experienced, like you couldnt make calls into New York, that was absolutely by design."
When traditional forms of voice communications were sluggish, many turned to tools that use next-generation technology, such as Voice-over-IP (VoIP) and wireless messaging, to make their calls.
"Our network was definitely in overdrive," said Bart Bartolozzi, a Net2Phone spokesman.
Net2Phone is a communications provider that lets people make phone calls using their PCs.
Bartolozzi said the peak last week came right after the attack, especially in international calls coming directly into New York. While the city is traditionally one of the largest destinations for international calls on Net2Phones network, during the period following the attack, 95 percent of all international calls coming into the U.S. were to New York.
Bartolozzi said those from abroad who have family living in the city typically have no idea if their loved ones live near the Twin Towers or Bensonhurst, Brooklyn, so after seeing the damage on television, there were plenty of panicked calls being made.
"According to our network guys, we never got to a point of congestion," Bartolozzi said. "I think, luckily for us, service was maintained and, luckily for those using it, they were able to get in touch with friends and family."
David Gilcreast, a spokesman of VoIP communications provider Dialpad Communications, said that after the incident, the network saw a 25 percent to 30 percent overall jump in traffic, which the company was able to handle. The most successful calls were those coming directly from PCs with broadband connections, since they were able to bypass the congested local telephone network altogether.
Some wireless users with data-capable phones found that though they couldnt make voice calls, they could send and receive text messages. Thats because when a user sends a text message, the network holds it until capacity is available and then sends it. With a voice call, if capacity is full, users cant connect - period.
Verizon owns most of the last-mile pipes in the area and sustained the worst damage. Several of its central offices, the telephone substations that switch phone calls, were damaged or destroyed. The company said its outages will have a direct impact on telephone connections not only to the stock exchange but also to companies working in lower Manhattan.
The wall of one central office was breached when Building 7 at the World Trade Center collapsed. The CO, about five stories below ground, was flooded, covered with debris and without power. A second CO, on Broad Street, was also experiencing power problems late last week.
Verizons troubles were affecting network operators, which were beginning to see their high-speed data lines go down. Ordinarily, such lines would be tested and restarted, but Verizon was in disaster mode and was not performing such services.
AT&T, which moves about 60 percent of all long-distance traffic in the U.S., reported that call volume at midday Tuesday was double normal, with big spikes in New York and Washington.
"Thats fairly typical of any disaster, natural or man-made," spokesman Dan Lawler said.
AT&T had one local-service node in the basement of one of the World Trade Center towers. "Obviously that is out of commission right now," Lawler said. "But there was no network damage. The systems are running as designed. Theyre just hanging on and running it."
BellSouth, Broadwing, Qwest Communications International, SBC Communications and Telseon said their networks were fully operational even as they received a higher number of calls.
Wireless operators added that their networks were extremely overloaded, though none failed completely.
Cingular Wireless reported a 1,000 percent increase in call attempts Tuesday morning. Cingular Interactive reported that eight cells on its wireless data network went down in Manhattan, but the network remained operational with lower than normal use.
Operators including Verizon Wireless lost cell sites in lower Manhattan, but had enough redundancies built into the network so that users were able to continue to make calls, a spokesman said. Verizon Wireless immediately rolled mobile cell sites to New Jersey, trying to increase capacity and coverage lost due to damaged gear near the World Trade Center.
Verizon Wireless introduced cell sites in the vicinity of the Pentagon and nearby Shenendoah National Park to ensure that rescue workers could rely on the network. Cingular Wireless also introduced cell sites to beef up its network.
Nancy Gohring, Brian Ploskina and Bill Scanlon contributed to this report.