Abstract: The rate-based flow control mechanism in asynchronous transfer mode (ATM) networks controls the transmission rate of available bit rate (ABR) traffic sources, based on feedback information contained in the resource management (RM) cells coming from the destination and/or the network switching nodes. While the source and destination end systems behavior are fully described in the ATM Forum Traffic Management Specification, the network switch mechanism is implementation dependent. Since there is a variety of algorithms an ATM switch vendor can choose from, different performance characteristics are expected. This paper investigates the interoperability issues in terms of network performance and fairness of bandwidth allocation when an ATM network consists of switches using different rate control mechanisms, namely, the explicit forward congestion indication (EFCI) mode and the explicit rate (ER) mechanism. Simulation results show that these algorithms will interoperate as long as the switch implementation conforms to the end system behavior for congestion notification and usage of RM cells. Moreover, the location of an ER switch in a given topology might be critical to solving the "beat-down" phenomenon, when traffic passing through a larger number of switches might get less bandwidth than single hop traffic.