Closed loop credit-based flow control with internal backpressure in input and output queued switches

A credit-based flow control scheme is very effective for handling cells of the ABR or controlled transfer service class in ATM networks. The properties of immediate ramp-up after congestion and the impossibility of buffer overflow by construction are what makes this method very attractive. For best results, many switches along the route must support flow control, acting as virtual source/destination node. To support closed loops along the route each of these switches must also provide an internal flow control to pass the backpressure from the destinations back to the sources and avoid internal buffer overflow. We treat the interaction of external and internal flow control and the alternatives of internal backpressure mechanisms, emphasizing virtual-output-queued switches. The properties are studied with Petri net models.