Method and controlling network node (140) for transmitting data to a user equipment (130) over a set of radio links (115, 125), when a radio link (115, 125) is added, or removed. The controlling network node (140) is configured to communicate data to the respective radio network node (110, 120) over a respective backhaul link (118, 128), of which at least one backhaul link (118) is connected over an Internet Protocol, IP, network (150). The method (500) comprises measuring (501) the time delay over the corresponding backhaul link (118, 128) for each radio link (115, 125), determining (502) time difference between them, calculating (503) a buffer time for each radio link (115, 125), and buffering (507) data in a buffer (625) for the calculated period of time before forwarding the data to the radio network node (110, 120), for transmission to the user equipment (130).