British Telecom reported US-bound call volume was 60 times higher than normal, while Verizon says its land-line and cellular systems handled twice their normal call volumes.
"Attempted call traffic hit 60 times the normal peak levels around 5 p.m. yesterday, but quieted down around midnight (London time)," said a British Telecom official.
Because of the tidal wave of people attempting to call the US, British Telecom implemented its call-gapping system on US-bound traffic.
Call-gapping involves intercepting call traffic at the local switch, usually before the full number has been dialed. By quickly returning a busy tone to such calls, they are prevented from leaving the local switch and overloading the national and international network.
The British Telecom official said that, although the carrier was able to bring extra Europe-to-US circuits to handle some of the extra calls, there was still a significant bottleneck on the eastern seaboard of the US.
"Basically, there were only so many circuits in the New York area available after the attacks, so we had to balance our call traffic loading into the area very carefully," he said.
At Verizon, the carrier said that its cellular and land-line networks handled roughly twice their normal peak time volumes of 115 million calls each weekday in New York and 35 million calls each weekday to Washington, DC.
Verizon said in its overnight press statement that its cellular network, "while operating well, is experiencing congestion due to heavy calling."
"Phone lines were extremely busy much of Tuesday, and many people who tried to call into or out of New York City and Washington, DC experienced a ‘fast busy’ signal and had to redial," the carrier added.
Despite having two facilities in the World Trade Center attended to by 488 employees, Verizon says it has accounted for most of its workers. – Newsbytes