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What is V.90? How does 56K work?
Most of the modems we encounter today are "56K" modems allowing a download speed of up to 56K and an upload speed limited to 33.6kpbs. The three standard protocols for accomplishing these lightning fast speeds are K56Flex, x2, and V.90. Dialing into modem racks that support x2/v90 tends to cause problems for modems that attempt to modulate K56Flex, or fallback to K56Flex after establishing a V.90 connection and vice versa. This will be the one point where you will spend most of your time teching modem problems, and is the primary focus of these modem support pages. This just covers the basics.
The basic requirement for 56K technology is that the connection from the Public Switched Telephone Network (PSTN) to the ISP be a digital connection. (The PSTN is really all digital these days. The only true analog part of the connection is from the user's home to the Central Office (CO). Hence, there is only one analog to digital conversion. If the signal is converted back to analog where the ISP recieves the call, 56K will not work. There are other problems that make 56K connections impossible, like load coils on the line that amplify voice calls and reduce noise on the line (noise that happens to be in the range used by 56K signals). Furthermore, it is required that V.90 be supported on both ends, so make sure you check with your ISP to make sure they support it.
Getting connected at 56Kbps is not impossible but ususally unlikely. When 56k technologiy first came out, the signal strength required for a 56000 bps connection exceeded FCC regulations, so 53,333 bps was the absolute maximum. 54,666 bps and 56,000 bps connections are possible, but usually very unstable due to fluctuations in the local loop quality. Typically V.90 connections are in the 40s and are very sensitive to noise in shoddy phone lines or passing through several connections, like running the phone through a fax machine, an answering machine, a splitter, or even a surge protector. The best setup is to use a quality V.90 modem with updated firmware and/or drivers connected directly to the wall jack with one short phone cord no more than 10 feet in lenght. Then add devices (like the surge protector) until you find the culprit. If this set up still does not allow a V.90 connection, it likely has to do with the quality of the phone lines/local loop and needs to be taken up with the telephone company.
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