A method and system for communicating digital data particularly adapted for transferring large amounts of bulk data from a first station to a second station over a long propagation delay path, as for example, between first and second earth stations via a satellite repeater. The system implements a procedure or protocol which is characterized by causing the source station to continuously transmit data frames at fixed intervals, each such data frame including an identification number and an information field, generally containing a portion of a user data record. Error checking means at the destination station determines whether the data frames received thereat are error free. The destination station also continuously transmits data frames at fixed intervals substantially synchronized with the source station data frame intervals. Each data frame transmitted by the destination station may include a source station identification number and a positive or negative acknowledgement to indicate whether or not the identified source station data frame was correctly received by the destination station. The source station then interprets the destination station data frame to determine whether it is necessary to retransmit any previously transmitted data frames.