A method of transmitting data by a communications device, the method comprising receiving a plurality of service data units including a first service data unit and a second service data unit at a Service Data Adaptation Protocol (SDAP), service access point (SAP) according to one or more quality of service (QoS) flows, each of the QoS flows defining a quality of service for the data received from the service data units, mapping the service data units received according to the one or more QoS flows on to one or more radio bearers, each of the one or more radio bearers being defined by a packet data convergence protocol (PDCP) entity within a PDCP layer, forming the service data units into protocol data units for transmission via the radio bearer to which the corresponding QoS flow has been mapped, and transmitting the protocol data units via the corresponding radio bearer.