There is provided a radio bearer to user equipment on a first component carrier by a first network node and on a second component carrier via a second network node connecting to the first network node. A control plane configuration message is transmitted that indicates an uplink component carrier of a network node that terminates an air-interface protocol linked to the first and/or the second component carrier. The uplink component carrier (it can be more than one) is then used for uplink transmission of data units that include information about reception of data units of the air-interface protocol.