A Fault-Tolerant Multistage Combining Network

multistage interconnection network. Various traffic control schemes have been proposed to handle hot-spot traffic [4–7, 17, 19, 24]. Among these schemes, the combining network [5, 6, 17], which can combine requests within a switching element accessing the same memory location, is an effective scheme for handling hot-spot traffic. It not only reduces network traffic, but also provides a fast synchronization rate if some synchronization primitives, such as Fetch&Add [6], are supported. However, a combining network is still a unique-path MIN; it lacks fault tolerance capability. To provide this capability, we use a chaining scheme [23] to enhance the combining network. Hence we propose a chained combining network. This paper is organized as follows: Section 2 gives an overview of fault tolerance and hot-spot contention problems in MINs. To cope with possible faults in the MIN, in Section 3, we present our fault tolerance scheme— chaining, which provides alternate routing paths by connecting intrastage switching elements. In Section 4, through simulations, we examine the behavior of chained networks with various congestion control schemes under hot-spot contention. In Section 5, we propose a fault-tolerant combining network that is augmented via chaining, and derive routing procedures for this network. In Section 6, we examine the overhead of the chained combining network and consider the other fault tolerance schemes for combining networks. In Section 7, we summarize the results of this research.