The explosive growth of the Internet, which has doubled in size in the past year, and today has more than seven times as many computers connected to it than in 1993, is leading to blocked local telephone exchanges in parts of the US.
Calls to access the Internet are typically much longer than voice calls - an average of 20 minutes rather than three, though some Internet sessions can last hours. And the rapid growth in Internet use has overwhelmed the ability of the local telephone companies to upgrade exchange capacity.
The result is engaged signals or long silences before the dial tone is available, a phenomenon which technicians call "contention". Bellcore, the research arm of the US local telephone companies, says that the growth of Internet use "poses an immediate threat to the capacity of the public telephone network".
In California, home to Los Angeles, San Francisco and the high concentration of high-tech industries in the area south of San Francisco known as Silicon Valley, Pacific Bell, the local telephone company, has found that one in 10 "Internet" calls lasts six hours or more. As a result, 1 per cent of callers in California face a delay in getting a line; but at times this year the figure has hit 16 per cent.
However, the problem is unlikely to be repeated in Europe. A spokesman for BT said: "We're not seeing anything like this at the moment. And it's worth noting that the `backbone' telephone network in the US isn't overloaded. It's all at the local level." The problem in California was the result of "a very high concentration of Internet usage in a small area with a network that was designed for voice", he added.