Flow Setup Latency in SDN Networks

In software-defined networking, the typical switch-controller cycle, from generating a network event notification at the controller until the flow rules are installed at the switches, is not an instantaneous activity. Our measurement results show that this has serious implications on the performance of flow setup procedure, specifically for larger networks: we observe that, even with software switches, the flow setup latency for networks of around 500 switches is in the order of 50 ms, with 99th percentile exhibiting $10\times $ higher latencies. To reduce both the latency and the variance of the flow setup, we propose path aggregation strategies, which turn the network into a set of pre-configured pipes that connect any pair of nodes. Our approach radically simplifies the flow setup procedure by minimizing the set of switches to be updated for new user-initiated flows to a constant number. We implement our solution in our testbed and study its performance through measurements. The results show that in similar settings, it reduces the median and 99-percentile latencies to 5.9 and 7 ms, respectively, significantly improving the performance, especially in the tail.