Clock synchronization within a distributed system is a problem that has been studied extensively in recent years. Of the many solutions proposed thus far, probabilistic synchronization algorithms provide arguably the best compromise between tightness of synchronization and overhead imposed on the system. The main drawbacks of probabilistic algorithms are the requirement of a master/slave organization of clocks, and the relatively high number of synchronization messages that must be sent. These two drawbacks can make them unsuitable for use in large distributed systems. In this paper, we propose a synchronization algorithm that does not use master/slave clocks and reduces the number of synchronization messages needed. The nodes of the system are divided into a number of overlapping groups. Within a group, each node uses one of two probabilistic techniques to estimate the values of other clocks in the group, and uses an interactive convergence algorithm on the resulting estimates to adjust its local clock. Groups are selected so that the maximum skew between any two group members is bounded.>

The cost of synchronizing a multicomputer increases with system size. For large multicomputers, the time and resources spent to enable each node to estimate the clock value of every other node in the system can be prohibitive. We show how to reduce the cost of synchronization by assigning each node to one or more groups, then having each node estimate the clock values of only those nodes with which it shares a group. Since each node estimates the clock value of only a subset of the nodes, the cost of synchronization can be significantly reduced. We also provide a method for computing the maximum skew between any two nodes in the multicomputer, and a method for computing the maximum time between synchronizations. We also show how the fault tolerance of the synchronization algorithm may be determined.>

It is important for a distributed computing system to be able to route messages around whatever faulty links or nodes may be present. We present a fault-tolerant routing algorithm that assures the delivery of every message as long as there is a path between its source and destination. The algorithm works on many common mesh architectures such as the torus and hexagonal mesh. The proposed scheme can also detect the nonexistence of a path between a pair of nodes in a finite amount of time. Moreover, the scheme requires each node in the system to know only the state (faulty or not) of each of its own links. The performance of the routing scheme is simulated for both square and hexagonal meshes while varying the physical distribution of faulty components. It is shown that a shortest path between the source and destination of each message is taken with a high probability, and, if a path exists, it is usually found very quickly.>

Synchronization algorithm is proposed which uses one of two probabilistic techniques to estimate remote clock values, and uses an interactive convergence algorithm on the resulting estimates to adjust the local clock. The algorithm does not require master/slave clocks and reduces the number of messages needed. As a result it is suitable for use in large distributed systems.>