A COMPARATIVE STUDY OF SELF HEALING PROTOCOLS FOR ATM NETWORKS

Abstract

The standardization of ATM as the transfer mode for the implementation of BISDN services means that, the existing networks would be substituted by ATM networks with BISDN deployment. Since ATM networks are high speed networks, the volume of information carried by them at any instant of time would be enormous. Not only that, information is likely to be of high commercial value because of the high degree of economic activity that these networks would support. In the light of these facts, the effect of a transmission link or node failure would be catastrophic. Therefore, ATM networks need to be equipped with mechanisms by which the failure of a network entity can be detected and service restored by changing over to alternate entities. The restoration if achieved under 2 seconds would prevent any interruption of service to the users due to the failure. The focus therefore, is on the design of restoration mechanisms which can achieve this objective. Restoration mechanisms based on the Self Healing concept have been successful in achieving restoration times well below the 2 second limit. This concept adopts a distributed approach wherein the entities around the point of failure restore service by exchange of control messages. In the present dissertation, two Self Healing protocols, the Backup Virtual Path Self Healing protocol and Broadcast Self Healing protocol have been studied. Simulation studies were carried out to compare their restoration speeds, spare resource requirement and maximum restoration ratio. The effect of network size on the restoration speed and that of network load on the maximum restoration ratio was also studied. The merits and demerits of the two protocols were highlighted by the study. Findings suggest that the Backup Virtual Path protocol has an edge over the Broadcast protocol.