The Buffer Size Vs. Link Bandwidth Tradeoff In Lossless Networks

Data center networks demand high bandwidth switches. These networks also sustain common incast scenarios, which require large switch buffers. Therefore, network and switch designers encounter a buffer-bandwidth tradeoff as follows. Large switch buffers allow absorbing larger incast workload. However, higher switch bandwidth allows both faster buffer draining and more link pausing, which reduces buffering demand for incast. As the two features compete for silicon resources and device power budget, modeling their relative impact on the network is critical.In this work our aim is to evaluate this buffer-bandwidth tradeoff. We analyze the worst case incast scenario in the lossless network and find by how much the buffer size can be reduced, while the link bandwidth increased to stand in the same network performance. In addition, we analyze the multi- level incast cascade and support our findings by simulations. Our analysis shows that increasing bandwidth allows reducing the buffering demand by at least the same ratio, while preserving the same network performance. In particular, we show that the switch buffers can be omitted if the links bandwidth is doubled.