ATM flow control based on rate prediction with extrapolation under WAN environment

The adaptive rate control technique AREX (Adaptive Remote rate control based on Extrapolation) is proposed, which realizes an access to a high-speed bandwidth and a high utilization rate without increase of required buffer amount and degradation of the transfer characteristics, even in an ATM (Asynchronous Transfer Mode) network with a long delay, by carrying out prediction of congestion based on periodically reported information on the utilization rate. In the AREX method, the downstream node (Obsv node) without a rate modification capability observes the utilization rate of the output link and informs the upstream node (Cntl node) with a rate control capability. Based on the information, the Cntl node controls the output rate dynamically. In the conventional feedback rate control, only past information can be obtained due to propagation delay, and the information is given only at an appropriate notification interval. Therefore, as the network size is increased, the necessary amount of buffers is increased, or the response speed for the bandwidth modification request from users needs to be reduced. However, since the worst traffic is estimated from the notification information in the AREX method, a safe rate control can be realized even if the notification is delayed and is given intermittently. Also, by regulating the rate enhancement ratio as an appropriate increasing function, quick access to a large bandwidth can be realized at low load, and a high congestion control effect is achieved at high load.