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It's Not Your Modem—It's Your Phone Line

As you learned in the previous section, using the wrong dial-up number for your modem will slow down your connection. But what if you say, "Mark, I've already got a V.90 56Kbps modem and I've already installed the latest firmware and drivers. I've called my ISP to confirm that I'm using the right 56K dial-up number. I know about the 53Kbps limitation, but I'm only getting 31.2Kbps maximum speeds! My brother-in-law lives two blocks away and he's getting 53Kbps every time he connects! What's going on?"

I don't know your brother-in-law, but I don't blame you for being upset. The problem isn't with you—or your modem—or even your brother-in-law. It's your phone line. Why?

Basically, the whole 56Kbps modem business is based on playing a sort of technological trick on the phone system, which is, as you learned in Chapter 2, based on analog signals. Originally, the entire phone system used analog signaling, but in recent years, parts of the phone system started using digital signaling. 56Kbps modems are designed to take advantage of the partly digital nature of the telephone system today. A 56Kbps modem can break the 33.6Kbps speed limit only if it can create an unbroken digital connection between your computer and the telephone company's central office, where your call is connected to the rest of the telephone system.

For the Skinny on How 56K Modems Work

If you want more technical background on how 56Kbps modems work (and why they don't always work!), see the 56K Web site, located at http://www.56k.com/basics/

Because of the explosion in demand for telephone and telephone-based services such as fax machines, credit card approval terminals, and so on, telephone systems in some places perform multiple analog-to-digital conversions, making speeds above 33.6Kbps impossible.

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