An ITU standard (1998) for a modem that communicates at 56 Kbps downstream and 33.6 Kbps upstream. It is intended for use only with ISPs and online services that are digitally attached to the telephone system. Most service providers are typically connected with high-speed digital T1 or T3 circuits.

In practice, the downstream link isn't generally faster than 45 Kbps in these PCM modems, so called because they use pulse code modulation downstream and standard V.34 upstream. Initially, two incompatible technologies competed in this arena: x2 from U.S. Robotics and K56Flex from Rockwell and Lucent. Such modems can be upgraded to V.90 if they contain software-upgradable memory chips. See V.92, V.34 and channel bonding.