The invention provides a method of controlling transmission of packets from a transmitter to a receiver via a channel, and a corresponding transmitter and receiver. The method comprises: transmitting packets from a queue, each packet having a packet size based on data in the packet; determining a transmission time for each packet, based on a transmission clock; determining a reception time of each packet, based on a reception clock; supplying to an estimation function successive sets of observations including in each set transmission time, reception time and packet size, the estimate function being arranged to provide an estimate of bandwidth for the channel using the relationship between the bandwidth, the amount of data in the queue, packet size and the delay between transmitting successive packets from the queue; and using the estimated bandwidth to control transmission of packets.