V.90 - 56Kbps Modems
This allows up to 56 Kbps from the Server/ISP end to the user, and up to 28.8 Kbps from the user to the ISP.
Actually, there is a 20-year old FCC rule that prevents these modems from operating at speeds higher than 53 Kbps. The rules were designed to prevent interference to people's telephone conversations. But technological improvements have made the modern-day phone system less susceptible to signal interference. So, the current power limits on modems are no longer needed, FCC officials said in September of 1998.
It is primarily the quantization noise produced by the analog-to-digital conversion at the CO that ultimately restricts upstream network speed to the V.34 speed of 33.6 Kbps. If the server end has a digital connection, this noisy conversion for is not needed when data is sent from the server to the client. This is the premise upon which V.90 rests.
There were two protocols in contention for becoming the ITU-T V.90 standard, which drew upon parts of both: One technology, called K56Flex(TM), is from Lucent Technologies and Rockwell Semiconductor. The other, called x2 is from US Robotics and 3COM.