Congestion Control in ATM

Congestion control plays an important role in the effective traffic management of ATM networks. Congestion is a state of network elements in which the network can not assure the negotiated quality of service to already existing connections and to new connection requests. Congestion may happen because of unpredictable statistical fluctuations of traffic flows or a network failure.

Congestion control is a network means of reducing congestion effects and preventing congestion from spreading. It can assign CAC or UPC/NPC procedures to avoid overload situations. To mention an example, congestion control can minimize the peak bit rate available to a user and monitor this. Congestion control can also be done using explicit forward congestion notification(EFCN) as is done in Frame Relay protocol. A node in the network in a congested state may set an EFCN bit in the cell header. At the receiving end, the network element may use this indication bit to implement protocols which will lower the cell rate of an ATM connection during congestion.

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