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.

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.

Abstract: A gas leakage detector comprising a solid state gas sensor having a sintered metallic oxide block which changes thermal conductivity by chemical adsorption thereto and a wire for transforming thermal conductivity charges into an electric signal. A suction pump draws gas through a gas intake path to the gas sensor. A voltage-frequency converter generates a pulse frequency that is a function of the gas sensor voltage. An alarm indicator including sound and/or light is controlled to pulse by the output pulse of the voltage frequency converter.