V.90 is a serial transmission standard for high-speed communication using modems. V.90, which is part of the V series standards developed by the International Telecommunication Union (ITU), evolved from the earlier x2 modem technology developed by U.S. Robotics (later bought by 3Com) and the K56flex modem technology developed by Rockwell.
V.90 claims to support modem communication at a speed of 56 Kbps, but this is limited by several factors:
Graphic V-2. V.90. Digital and analog segments with V.90 modems and earlier modems.