A method of estimating available bandwidth for a network comprising a transmitting device and a receiving device, the method comprising: transmitting a media packet stream over the network to the receiving device, the media packets comprising media data for streaming media at the receiving device; transmitting one or more probe packets over the network so as to test the available bandwidth of the network, wherein the probe packets comprise duplicate data of the media packet stream; and determining, during transmission of the probe packets, a measure of network bandwidth availability in dependence on one or more metrics associated with receiving the media packet stream at the receiving device.