 For this same reason, while 56k did permit 56kbit/s "downstream" (from ISP to subscriber), the same speed was never achieved in the "upstream" (from the subscriber to the ISP) direction, because that required going through an analog-to-digital conversion.The first 56k option was a proprietary design from USRobotics, which they called "X2," because 56k was twice the speed (x2) of 28k modems.At that time, USRobotics held a 40-percent share of the retail modem market, while Rockwell International held an 80-percent share of the modem chipset market.