A modem that has the ability to adjust its transmission rate downward in the event that the connection quality degrades. For example,V.90 modems also are V.34bis modems. Assuming that the terminating modem is V.34bis, the V.90 modem adjusts its maximum downstream rate of 56 kbps downward to the V.34bis maximum transmission rate of 33.6 kbps. See also downstream, dynamic rate adaption, modem, transmission rate, V.34bis, and V.90.
A modem that dials a connection only when a primary, usually leased, line has failed.