Texas Instruments Corporation

Sharmila Kannangara

Thomas Anton Leyrer

Umashankar S Iyer

A method of resynchronizing data transfer between a first modem assigned to a central office and connected by a dedicated line a second modem assigned to a remote subscriber following a fault caused by a ringing signal. A ringing ID is set up in the central office modem as soon as a ringing signal is to be sent to the subscriber modem, and a ringing alert is transferred to the connected subscriber modem. Transmission of the pilot tone accompanying the data transfer set by the central office modem is interrupted as is the clock frequency synchronization implemented during data transfer in the subscriber modem with the pilot tone as reference. The two modems are put on hold to save the characteristic parameters for the momentary data transfer followed by transfer of the ringing signal via the dedicated line to the subscriber modem. The ringing ID is reset in the central office modem, the pilot tone is resent via the central office modem and reinstating synchronization of the clock frequency reinstated in making use of the pilot tone as reference. The prior data transfer mode of using the saved characteristic parameters and the subscriber modem is synchronized to the data stream coming from the central office modem by searching for and detecting specific code groups occurring regularly in the transferred data stream.

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Reston, VA, United States of America

Sharmila Kannangara