The v.90 signalling protocol is the product of a rare cooperation between archrivals. The fact that it even works is even more amusing (You might want to read about Shannon's Law).

'The standard' is an ITU-ratified standard that was apporoved on February 6th, 1998 in Geneva, Switzerland. Before that time there were two warring (and mutually incompatible) factions, the X2 camp and the k56flex camp, but on this day a rare compromise was reached and the users of analogue modems did rejoice. According to the rhetoric, the v.90 standard is supposed to be the final analogue signaling standard. This is in part because it's not really analogue after all...

In v.90 technology an assumption is made: that one end of the modem session has a pure-digital connection to the phone network -- in this case it is usually the ISP that is connected digitally.

By looking at the public switched telephone network like a digital network, v.90 technology is able to accelerate data downstream from the Internet to your computer at speeds of up to a theoretical 56Kbps. However, in the United States, the FCC limitations on voltages capped the effective speed to about 53kbps.

However, the returning stream (from user to ISP) begins its journey on an analogue circuit, and so this arrangment cannot usually work in reverse so upstream from user conections are usually limited at 33.6kbps.

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