Apparatus and method for flow control

Abstract

In flow control apparatus formed of a network of switching hubs in a hierarchy configuration for performing data packet transfer within each of a plurality of respectively separate groups of terminals, based on use of group identifiers contained in the data packets, occurrence of congestion of the output section of a port of a switching hub is judged respectively separately for each of the terminal groups, and one or more congestion notification packets for effecting a pause in data packet transmission are generated and transmitted from that switching hub, directed only to one or more terminals of a group relating to the congestion. As a result, the effects of port congestion and of congestion control operations are limited to the terminal group concerned. Congestion can be judged for a terminal group based on a level of utilization of a port output buffer that is used only by that group, or based on a rate of flow of data from that group into a port output buffer which is used in common for all terminal groups, and congestion notification packets may be transmitted from a single port or from a plurality of ports of a switching hub, in accordance with the detected degree of congestion.