When signals are transmitted from one modem to another, each modem interfaces at a specific speed. If one modem communicates at a faster rate than the modem at the other end, then the faster modem falls back to a slower modulation. For example, if a user connects to the Internet using a 14000-bps modem and attempts to download a file from a user who is connected to the Internet at 2400-bps, modulation fallback occurs and the two modems will only be able to communicate at the slower speed because that is the highest speed they have in common.
