In a telecommunication system, Service Data Units (SDUs) are received and copies are stored in an SDU management buffer 101. The SDUs are concatenated and segmented 105 to generate Protocol Data Units (PDUs), which are stored in a transmission buffer 111 for transmission to a mobile communication device. A feedback message 113 is sent to the SDU management buffer identifying an SDU that may be removed when, for Unacknowledge Mode (UM) data, the PDUs corresponding to that SDU have been forwarded from the transmission buffer or when, for Acknowledge Mode (AM) data, receipt of the PDUs corresponding to the SDU has been acknowledged by the mobile communication device. In response to receipt of the feedback message, the identified SDU is removed from the SDU management buffer. A system is also proposed to provide handover in which a source base station stops downlink traffic on detecting a handover in progress whereas the uplink traffic is separately stopped by the user equipment on receiving a handover command. A new buffer management entity is provided in the outer ARQ entities for controlling the storage of data packets that are to be forwarded to a target base station in order to prevent or minimise packet loss.