Dynamically configurable message flow control 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 switching (WS), realize very good performance, but are prone to deadlock in the presence of faults. Conservative flow control mechanisms, such as pipelined circuit switching (PCS), ensure the existence of a path to the destination prior to message transmission, achieving reliable transmission at the expense of performance. This paper proposes a general class of flow control mechanisms that can be dynamically configured to trade-off reliability and performance. 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 WS like flow control to maximize performance. We refer to such protocols as two-phase protocols. 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 WS and PCS. The architecture of a network router supporting configurable flow control is also described.