X2A technology developed by U.S. Robotics (now 3COM) for delivering data rates up to 56 Kbps over plain old telephone service (POTS). It was long believed that the maximum data transmission rate over copper telephone wires was 33.6 Kbps, but X2 achieves higher rates by taking advantage of the fact that most phone switching stations are connected by high-speed digital lines. X2 bypasses the normal digital-to-analog conversion and sends the digital data over the telephone wires directly to your modem where it is decoded.
While X2 offers faster Internet access than normal modems, there are several caveats to using an X2 modem:
1. The high speeds are available only with downstream traffic (e.g., data sent to your computer). Upstream traffic is delivered using normal techniques, with a maximum speed of 40 Kbps.
2. To connect to the Internet at X2 speeds, your Internet Service Provider (ISP) must have a modem at the other end that supports V.90.
3. Even if your ISP supports V.90, you might not achieve maximum transmission rates due to noisy lines.