ITU (International Telecommunications Union) standard for 56 Kbps analog modems. An important detail is that 56 Kbps modems can only achieve a transfer rate up to 53 Kbps since this is the maximum transfer speed of the switching circuits used by the phone companies. Also this transfer speed is only achieved downstream (for downloading data). Upstream (for uploading data) the maximum transfer rate is 48 Kbps (on V.90 modems the maximum upload speed is 33,600 bps). You ISP must be V.92 compatible; otherwise your V.92 modem will work as if it was a V.90 one.