a method of and apparatus for controlling data transfer between two stations comprises a link manager for controlling allocation of available channels in a plurality of communications links . in each of the communications links data is transferred between two stations in at least one channel . data for transfer from a data source is buffered in a data buffer . a controller determines latency in the buffer from the amount of data in the buffer and the rate at which data is being output from the buffer . the controller generates a request for a change in the allocation of channels in a communications link between two stations depending on the latency in the buffer and preset threshold values . the link manager is responsive to a request generated by the controller either to allocate a different number of channels to the communications link or to generate a refusal of the request .