Configurable flow control mechanisms for fault-tolerant routing

Fault-tolerant routing protocols in modern interconnection networks rely heavily on the network flow control mechanisms used. Optimistic flow control mechanisms such as wormhole routing (WR) realize very good performance, but are prone to deadlock in the presence of faults. Conservative flow control mechanisms such as pipelined circuit switching (PCS) insures existence of a path to the destination prior to message transmission, but incurs increased overhead. Existing fault-tolerant routing protocols are designed with one or the other, and must accommodate their associated constraints. This paper proposes the use of configurable flow control mechanisms. Routing protocols can then be designed such that in the vicinity of faults, protocols use a more conservative flow control mechanism, while the majority of messages that traverse fault-free portions of the network utilize a WR like flow control to maximize performance. Such protocols are referred to as two-phase protocols where routing decisions are provided some control over the operation of the virtual channels. This ability provides new avenues for optimizing message passing performance in the presence of faults. A fully adaptive two-phase protocol is proposed and compared via simulation to those based on WR and PCS. The architecture of a network router supporting configurable flow control is described, and the paper concludes with avenues for future research.