A network system includes end nodes which are connected to a plurality of cascaded hubs. A two priority protocol is provided for selecting end nodes to send network packets over the network. When at least one end node in the network system has a high priority network packet to send, each end node with a high priority network packet is acknowledged in turn. Each end node, when acknowledged, sends its high priority network packet through the network. When no end nodes have a high priority network packet, and at least one end node in the network system has a normal priority network packet to send, each end node with a normal priority network packet is acknowledged in turn. This includes a root hub acknowledging in turn each second level hub which is connected to an end node which has a normal priority network packet to send. Each second level hub, when acknowledged, proceeds to acknowledge in turn each end node which is connected to the second level hub and which has a normal priority network packet. Each end node, when acknowledged, sends its normal priority network packet. However, when the root hub receives a request for an end node to send a high priority packet, the root hub signals to the second level hub that a high priority request has been received. The second level hub stops acknowledging the end nodes connected to the second level hub which have a normal priority network packet. Then each end node with a high priority network packet is acknowledged in turn. Each end node, when acknowledged, sends its high priority network packet.