A buffer is disclosed for storing data being transferred using a plurality of control channels, a data item of said data being transferred between a data source and a data destination using one of said plurality of control channels, said buffer comprising: a data input port operable to receive said data being transferred using said plurality of control channels; a data output port operable to output data to be transferred using said plurality of control channels; and a data store operable to store data received from said data input port prior to it being output by said data output port, said data store comprising a plurality of storage locations each operable to store a data item, said storage locations being arranged in groups, a storage location being allocated to a group in dependence on the control channel that a data item that it stores is received from, such that each group comprises storage locations storing data items received from a same one of said plurality of control channels. Free storage locations are not allocated to any of the plurality of groups, so that new data items received can be stored in any of the free storage locations, these locations then being allocated to the group corresponding to the channel being used.