A terminal comprising: a radio-frequency transmitter for transmitting packets on an uplink to a wireless cellular network; and processing apparatus comprising an upper protocol stack and a lower protocol stack, the upper stack being arranged to process data according to one or more transport protocols and form the data into packets of a plurality of different types for transmission over a packet-based network, and the lower stack being arranged to receive the packets from the upper stack and process them for transmission via the wireless cellular network. The lower stack comprises a plurality of packet queues each corresponding to a different respective priority level, and a packet decoder configured to supply each packet in dependence on its type to a packet queue of a corresponding priority level. The lower stack further comprises a dequeuing mechanism configured to dequeue packets for transmission from said queues in dependence on the priority levels.