Flow Control in Packet-Switched Networks by Gradual Restrictions of Virtual Calls

A network flow control method in virtual circuit-oriented packet-switched networks, such as international packet-switched networks based on the CCITT X.75 protocol, is proposed. Lengths of individual queues to outgoing routes are observed constantly in a switch (or node), and the virtual calls connected to a congested outgoing route are restricted gradually depending upon the queue length. Being proportional to the number of virtual calls restricted simultaneously, the amount of processing load to carry out flow control can be decreased by the introduction of gradual restrictions. Priorities of calls can also be considered in flow control. The proposed flow control method is analyzed theoretically by a simple queueing model and basic traffic characteristies are shown. Optimum restriction factors and threshold values are obtained. Through several numerical examples, the effectiveness of the method is demonstrated. The amount of processing load is also analyzed and evaluated quantitatively.