From the 56k standards web site...

To understand 56K, it's necessary to take a brief look at how traditional analog modems work. Information inside your computer is in digital format all of the data is stored as 1s and 0s. Normal phone lines are analog they transmit data as a series of peaks and valleys. Your "modem" is a MOdulator/DEModulator it modulates outgoing data from digital to analog, and demodulates incoming data from analog to digital.

Above a certain threshold (called Shannon's Limit) the signal-to-noise ratio of any medium becomes too low to reliably transfer data. The analog phone line is the limiting factor in the speed of data transmission because of the inherent noise it contributes. Today's telephone network is increasingly digital. In particular, the portion of the phone connection between the phone company and the Internet Service Provider (ISP) is often digital. Digital lines still have noise, and are still subject to Shannon's limit, but they have less noise and a higher ceiling.

Several companies have created techniques that take advantage of the digital portion of the phone network to achieve higher speeds than were possible with a purely analog pathway. These new techniques treat the phone system as a mostly digital network that just happens to have an analog portion.

There are several consequences to the reliance on a half-digital connection. Your Internet service provider (ISP) must have digitalphone lines to the public switched telephone network (PSTN). That's the easy part if your ISP offers 56K, they've got the digital lines.


3Com V.90 Technology White Paper


Lucent Technologies K56flex FAQ



You need three things to take advantage of 56K technology

1.a 56K modem Internet service provider that supports 56K

3.a phone line that supports 56K

#1 The first one is easy. There are plenty of 56K modems on the market, with more arriving every day.

#2 Once you have your 56K modem, you need a place to call. Nearly a thousand Internet service providers have pledged support for one of the 56K technologies, but only a small percentage of them actually offer 56K access at this time. America Online - with 8 million members - has test modems in only a handful of U.S. cities. (Use AOL keyword "x2" for details.) This situation should improve dramatically.

#3 The third requirement is the one that will prevent some people from using 56K. For 56K to work, you can only have one analog-to-digital conversion between your home or office and the Internet service provider (ISP). If there's more than one, you can't use 56K, and your connection will be limited to V.34 speeds (a maxumim of 28.8 or 33.6K).

3Com/U.S. Robotics has a test line that allows you to dial in with your existing V.34 modem and find out if your phone line supports x2. The phone number to call and other details can be found at the page below. 3Com strongly recommends calling the test line multiple times to get an accurate reading.

If your phone line passes that test, you can probably use a 56K modem. It isn't guaranteed, though. The long distance call to the U.S. Robotics test line may be routed through different circuits than a call to your local ISP. The only 100% guaranteed test is to borrow a 56K modem and dial into your local ISP from your home or office.

If you haven't tested the connection with a 56K modem, you should buy your modem from a dealer with a generous return policy such as AE Systems.

U.S. Robotics x2, 56K Compatibility Test Page is http//

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