SP-EPRCA: an ATM Rate Based Congestion Control Scheme based on a Smith Predictor
Dirceu Cavendish, Saverio Mascolo, Mário Gerla · 2000
This report presents a feedback control algorithm for ATM congestion control in which ABR source rates are adjusted according to VC queue levels at intermediate nodes along the path. The goal is to fully and promptly utilize the available bandwidth left by QOS constrained traffic (CBR+VBR) for transmitting the less QOS stringent ABR traffic, without incurring in queue overflow and consequently cell loss. In order to obtain this, we propose a simple and classical proportional controller, plus a Smith Predictor to overcome instabilities due to large propagation delays. In the SP-EPRCA model, each queue ideally behaves as a simple first order dynamic system with a delay in cascade. The delay is out of the feedback loop, and therefore does not affect stabilitity. Moreover, since the system dynamic is a first order one, it is not only stable but it has no damped oscillations as well. The real SP-EPRCA implementation, however, may behave as a higher order system due to innacuracies in estima...