A method of queuing data packets, said data packets comprising data packets of a first packet type and data packets of a second packet type. The method comprises grouping received packets of said first and second packet types into an ordered series of groups, each group comprising at least one packet, maintaining a group counter indicating the number of groups at the beginning of the series of groups comprising only packets of the second packet type, and transmitting a packet. A packet of the second packet type is available for transmission if but only if the group counter is indicative that the number of groups at the beginning of the series of groups comprising only packets of the second packet type is greater than zero.