A computer data transmission system is provided with proportional-integral-derivative (PID) control over a data transmission rate so as to maximize use of available bandwidth of a datagram-based network. A data channel and a separate feedback channel are established between the sender and receiver units of the system. The sender unit coupled to the data and feedback channels sends datagrams over the data channel to the receiver continuously until a source of data is exhausted or paused by the receiver unit. The receiver unit sends acknowledgment messages over the feedback channel to the sender unit at predetermined intervals. A PID controller in the sender unit uses the information provided in the acknowledgment messages to track unsuccessfully transmitted datagrams and to adapt the data transmission rate to any changing network transfer conditions. In particular, the rate of datagram loss may be used as a PID process variable to control an inter-datagram delay of the sender. There may also be absolute speed and transmission rate acceleration/deceleration limits constraining the PID control. PID control may also be adapted for data compression control, datagram block sizes, and degree of redundancy in the datagrams sent.