An overview of congestion control techniques in ATM networks and some performance results

ATM is a high speed multiplexing and switching technique used for multimedia communication. Efficient congestion control and prevention schemes for packet switched networks need to be designed for their effective and stable operation. Their design becomes particularly critical in ATM networks due to the high link speed, diverse traffic characteristics and requirements of QOS. In this paper we have reviewed and compared the congestion control and prevention schemes for ATM networks on the basis of simulation results. There are basically two types of schemes namely, The Open Loop or Preventive Control and The Closed Loop or Reactive Control, The Open Loop or Preventive control schemes allow a call to be accepted only if enough network resources are available. In case an admitted call violates the negotiated parameters strict police action is taken. We have simulated all the proposed policing mechanisms and the results show that Open loop congestion control schemes are suitable for CBR and VBR traffic which are delay sensitive services, because their performance degrades rapidly for bursty traffic. No permanent bandwidth allocation is made in the closed loop or reactive control schemes prior to call setup. Rather the bandwidth made available to each call is varied dynamically depending on the degree of congestion, thus making these schemes unsuitable for delay sensitive services. The Closed loop or Reactive control schemes are more effective for ABR traffic, because it is delay insensitive.