Abstract: An apparatus for controlling the transfer of communication traffic to an interface having a group of links comprises a detector for detecting the sizes of data units to be transferred to the interface, and a controller for causing data units to be transferred to the interface, wherein the controller is operative to select the link to which to transfer a data unit based on the detected size. The group of links includes a reference link that is used as an overflow to receive data units when other member links are full, and when the reference link is not used in its overflow capacity, the controller is operative to bias selection of the links to which to transfer data units towards the other links relative to the reference link.