A testbed implementation of explicit rate based ABR service via a dual proportional-plus-derivative controller

An explicit rate (ER) based congestion control scheme to support a class of best effort service known as available bit rate service (ABR) has been proposed by the ATM Forum. In this scheme, the network informs the sources from time to time, the maximum rate at which they can transmit. We present an all software based implementation of one variant of this control scheme. We apply principles of control theory and implement the ER scheme via a dual proportional-plus-derivative controller (DPDC). We compare the performance of the DPDC scheme with the explicit forward congestion indication (EFCI) scheme, where a single bit is used to convey to the source the state of the network. We have studied the transient performance of the control in the presence of high priority cross traffic. The experimental results have been obtained from an ATM testbed which consists of two ATM LANs, one located in Princeton (USA) and the other in Berlin (Germany), that are connected by a T1 link. The results show that the DPDC scheme is very stable with good transient response, even under extreme loading conditions and very long propagation delays. The EFCI mechanism on the other hand is fundamentally oscillatory in nature and can lead to large cell loss