On the performance of submitting excess traffic to ATM networks

The author presents performance study results on forward congestion notification (FCN) in ATM (asynchronous transfer mode) networks; FCN is an element of an overall set of mechanisms that can be employed in ATM network traffic management. When a network element (e.g. a switch) becomes congested, it sets a notification indicator in chosen cell headers to inform destination terminals that there is congestion en-route. Terminal-to-terminal protocols may use this information to adapt their use of network resources to the prevailing conditions. The author investigates the efficacy of this scheme; in view of propagation delays that may affect the timeliness of the congestion information, it is not clear whether or not the mechanism would be useful in ATM networks. A simple terminal-to-terminal protocol that uses the FC indicator is described, and the behavior of network and terminal queues is investigated. It is found that FCN has significant value in helping terminal-to-terminal protocols adapt to the state of the network. Even when propagation delays are long, the use of the mechanism results in better behavior than if an open-loop mechanism is used