AUTOMATIC DATA RESTORAL FOR MODEMS
This invention relates to the automatic restoral of data transmission by monitoring line degradation and switching to new lines (36, 38) when line quality falls below a prescribed standard. Data transmission is maintained on the leased lines (8, 10) while communication is being established on the dial lines (36, 38) so as not to disrupt data transmission. Energy is maintained on the dial lines (36, 38) at times when data is not being transmitted to prevent a change of channel on the dial lines (36, 38). A signal processor (30), associated memory (32), and analog interface circuitry (80) provide the data restoral functions. Control of the restoral procedure is handled by one modem (e.g., the calling modem (2)), and commands are sent to the other modem over either the leased lines (8, 10) or dial lines (36, 38). Communication is established across two leased lines (8, 10) and two dial lines (36, 38) in the dual line modulation mode and across one leased line (8) and one dial line (36) in the single line modulation mode.