ON DESIRABLE FAULT-TOLERANT TOPOLOGY FOR CLUSTER-BASED NETWORK

Management of control functions in large computer networks is a very difficult problem. One of the effective way to overcome the difficulty is to introduce hierarchical control structure (network cluster) in the management. When a fault occurred in the cluster, routing information at some nodes in the network must be updated in order to react the fault. However, the number of such nodes can be reduced by introducing ingenious topology into the cluster. This paper presents a fundamental discussion on network topology for a network cluster. First, L-FT is defined to represent a degree of fault-tolerance in a cluster with respect to link failures. Secondly, the minimum link problem M is defined to find the minimum number of links to make the cluster L-FT. The following results are obtained. (1) For a network cluster with the fault-tolerant topology 1-FT, at least 2n - 2 links have to exist in the cluster where n is the number of border nodes in the cluster. (2) As far as connectivity of the whole network is held, for multiple L link failures in a L-FT cluster, the update of routing information at each node is localized within only the cluster containing the failed links. (3) Several hierarchical networks with fault-tolerant conditions are presented as case studies for a LAN and a MAN.