Data flow control method and system

A quality greedy control method for managing the flow of media data from a sending node to a receiving node over a communication network, the receiving node being capable of playing said media data, the data transmitted to the receiving node being a sequence of data segments encoded at a plurality of sequential data rates, and wherein the quality control method is implemented by the receiving node for controlling the data rate of said media data transmitted from the sending node, the method comprising determining the available bandwidth between the sending and receiving nodes; determining a data buffer level at the receiving node from the amount of data present in the data buffer of the receiving node; and if the data buffer level satisfies a criterion: requesting the next data segment in the sequence at a sequentially higher data rate than the current data rate if the available bandwidth exceeds a first bandwidth threshold; and requesting the next data segment in the sequence at the current data rate if the available bandwidth exceeds a second bandwidth threshold.