Data transmission system

A data-transmission system in which forward signals including synchronization codes and data blocks are transmitted from a transmitter to a receiver and backward signals including a synchronization code detection signal is transmittted from said receiver to said transmitter through a transmission channel subject to variations in transmission delay, the improvement comprising:

• means for transmitting synchronization codes repeatedly at a constant time interval from said transmitter to said receiver until said transmitter detects a synchronization code detection signal from said receiver;
• means for transmitting a plurality of test data blocks each including a test data and error check bits during the time interval between two adjacent synchronization codes from said transmitter to said receiver;
• means responsive to detection of an error-free synchronization code at said receiver for transmitting a synchronization code detection signal from said receiver to said transmitter;
• means responsive to detection of said synchronization code detection signal at said transmitter for transmitting data blocks from said transmitter to said receiver, starting with the point of time at which said transmitter transmits the succeeding synchronization code;
• error rate-detecting means for detecting an error rate concerning test data blocks received by said receiver;
• means responsive to said error rate-detecting means for transmitting a data-rate specifying signal from said receiver to said transmitter;
• and
• means responsive to detection of said data-rate specifying signal at said transmitter for controlling the rate at which data are transmitted from said transmitter to said receiver.