Network switch including bandwidth allocation controller

A network switch includes a plurality of receive ports for receiving addressed data packets and a plurality of transmit ports for forwarding the addressed data packets and structure responsive to data in said the packets for directing received packets to the transmit ports. In respect of at least one of the transmit ports the switch includes an output buffer for storing data packets before they are forwarded from the port and an allocation controller. The allocation controller allocates each packet destined for the buffer and each packet leaving the buffer for the port into at least one of a plurality of categories, which may be based on priority or protocol data and may define traffic types such as video or audio. For each of the categories there is an allocation register for defining a respective selected proportion of the memory space of the output buffer and structure for accumulating a running total of packet sizes, the total being reduced by the size of each packet in the respective category and leaving the buffer for the port. A packet is discarded when the running total of packet sizes for packets of the same category exceeds the respective proportion of the memory space defined in the respective allocation register. The organization of the switch allows the allocation of a minimum bandwidth for each of the categories.