Adaptive Routing in Data Center Bridges

In an effort to drive down the cost of ownership of interconnection networks for data centers and high-performance computing systems, technologies enabling consolidation of existing networking infrastructure, which often comprises multiple, incompatible networks operating in parallel, are feverishly being developed. Such consolidation carries the promises of lower complexity, less maintenance overhead, and higher efficiency, which should translate into lower power consumption. 10-gigabit Ethernet is one of the contending technologies to fulfill the role of universal data-center interconnect. One of the key features missing from conventional Ethernet is congestion management; this void is being filled by the standardization work of the IEEE 802.1Qau working group. Here, we build on the congestion management scheme defined in 802.1Qau to exploit a crucial property of many data-center networks, namely, multi-pathing, i.e., the presence of multiple alternative paths between any pair of end nodes. We adopt a two-tier approach: in response to congestion detection, an attempt is made to reroute "hot'' flows (i.e., those detected as contributing to congestion) onto an alternative, uncongested path; only when no uncongested alternative exists are transmission rates of hot flows reduced at the sources. We demonstrate how this can lead to significant performance improvements by taking full advantage of path diversity. Moreover, we highlight the scheme's practical usefulness by showing how it improves the performance of parallel benchmark programs on a realistic network.