56 kbit/s

56 kbit/s (56 kilobits per second) is the data rate of a normal single channel digital telephone line in North America. The figure is derived from the bandwidth of 4 kHz allocated for such a channel and the 16-bit encoding (4000 times 16 = 64000) used to change analogue signals to digital, minus the 8000 bit/s used for signalling and supervision. See ISDN and T-channel. Note: due to FCC power limits, the limit over public telephone lines is 53.3 kbit/s. Due to noise, the actual speed may be lower.

For analog modems using the techniques common to k56flex, X2 and V.90 standards see 56K.