1. A dual flow control method for available bit rate service in a distributed ingress queueing switch architecture using resource management cells carrying original congestion marking values, said switch including a plurality of egress buffer-pools each having at least one egress subport, at least one shared buffer-pool feeding into said egress buffer-pools, and a plurality of ingress buffer-pools feeding into said shared buffer-pool, wherein each ingress buffer-pool has a flow queue corresponding to each egress buffer-pool and each shared buffer-pool has at least one egress port, said method comprising the steps of: (a) periodically measuring utilization of the egress port of each shared buffer-pool; (b) performing a first queue-length based flow control algorithm for each resource management cell for its associated ingress flow queue to generate local-ingress congestion marking values for the resource management cell; (c) calculating a summation of all ingress flow queues contributing to each egress port of each shared buffer-pool; (d) performing a second queue-length based flow control algorithm for the resource management cell using the summation of all ingress flow queues contributing to the shared buffer-pool egress port associated with the resource management cell to generate global-ingress congestion marking values for the resource management cell; (e) determining whether congestion of the shared buffer-pool egress port associated with the resource management cell is global based on the measured utilization of the shared buffer-pool egress port and a current state of global-ingress control, wherein if the congestion is not global, merging the local-ingress congestion marking values and original congestion marking values carried by the resource management cell, marking the resource management cell based on the merged congestion marking values, and repeating the process beginning at step (a); and (f) merging the local-ingress congestion marking values, the global-ingress congestion marking values and the original congestion marking values carried by the resource management cell, marking the resource management cell based on the merged marking values, and repeating the process beginning at step (a).