Combining Efficiency and Scalability on Congestion Management for Interconnection Networks

Congestion has been an open issue in lossless interconnection networks for the last twenty years. In this environment, as packets can not be dropped, congestion may lead to a dramatic degradation of network performance. Although congestion was traditionally avoided by overdimensioning the network, this solution is no longer valid due to cost and power consumption concerns, that tend to reduce the size of the network in current systems. The restriction on network size makes the system working closer to the network saturation point, thus increasing congestion probability. Therefore, an effective congestion management mechanism is essential in order to avoid network performance degradation. However, except the recently proposed RECN mechanism, none of the congestion management strategies proposed in the literature had been able to achieve, at the same time, the required efficiency and scalability levels demanded by emerging systems. In this paper we analyze the difficulties in handling congestion on lossless interconnection networks, identifying the key points for the design of an efficient and scalable congestion management technique. We also describe how these ideas have been implemented in the RECN design. Moreover, we also show that RECN is fully compatible with the Advanced Switching standard, allowing efficient and scalable congestion management in real systems.