Abstract: A flow control system for packet transmission networks is centered in the user applications supplying data to the network. Changes in control are responsive to changes in the transmission parameters of the network, measured in the network and transmitted to the user application. The user application specifies desired ranges of Quality of Service parameters and, when the measured network parameters fall outside of the desired range, the user application modifies the transmission strategy to match the available transmission parameters. Measurements of network parameters are made over a pre-selected observation period to average the values of the transmission parameters.