In a General Packet Radio Service (GPRS) system in which a Serving GPRS Support Node operates a leaky bucket algorithm to control data flow, a packet control unit in the base station is arranged so that on connection of a new mobile, a flow control message in the form of new values of B the maximum bucket capacity and R the leak rate is sent to the Serving GPRS Support Node only when it is known that the new connection is non-bursty. In the Temporary Block Flow queue for the new connection, a threshold is set at a queue length which ensures that at least two Logical Link Layer-Protocol Data Units are received before the threshold is reached. New values of B and R are then sent, the new value of B being related to the maximum data capacity of the newly connected mobile.