Have dial-up modems reached their limit?

It's not likely that users will soon see modems that exceed 56K bit/sec on store shelves, but it is also not impossible.

ISPs are slow to adopt V.92, the International Telecommunications Union's latest modem standard, but technically, modems can go faster.

"It seems that for the time being we have reached a limit, since there is no proposal from the industry for new algorithms," says Pierre-Andre Probst, a senior telecommunications advisor at Swisscom AG and chairman of the International Telecommunications Union's (ITU) study group 16, which works on access standards.

But Probst points out that it is difficult to predict what may develop in the future. "Four years ago the experts were of the opinion that the modem work was almost complete, and they did not expect new standards," he says. Then the ITU was pushed to develop the 56K bit/sec standards.

Although the ITU's V.90 and V.92 standards max out at 56K bit/sec downstream, that doesn't mean modems theoretically cannot go faster.

It's important to note that the limit has nothing to do with the copper lines which make up the public switched telephone network, but instead has to do with the analog-to-digital converters deployed on that network, Probst says.

Each telephone line channel contains 4 KHz of analog bandwidth, which is equivalent to 64K bit/sec of digital bandwidth, he says. With perfect conditions a telephone line could - again, theoretically - support 64K bit/sec.

It's powerful signal processing in V.90 and V.92 modems that allows for 56K bit/sec over this channel today, Probst says. "Further improvements to increase this (throughput) will not only depend on progress in technologies, but also on the priority given by the industry. It seems they are focusing on other products such as DSL."

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