Time4: Time for SDN

With the rise of software defined networks (SDNs), there is a growing interest in dynamic and centralized traffic engineering, where decisions about forwarding paths are taken dynamically from a network-wide perspective. Frequent path reconfiguration can significantly improve the network performance, but should be handled with care soas to minimize disruptions that may occur during network updates. Network updates are especially challenging when the network is heavily utilized; some of the existing approaches suggest that spare capacity should be reserved in the network in order to allow updates in such scenarios, or that the network load should be temporarily reduced prior to a network update. In this paper, we introduce Time4, an approach that uses accurate time to coordinate network updates. Time4 is a powerful tool in softwarized environments that can be used for various network update scenarios, including in heavily utilized networks. Specifically, we characterize a set of update scenarios called flow swaps, for which Time4 is the optimal update approach, yielding less packet loss than existing update approaches without requiring spare capacity, and without temporarily reducing the network's bandwidth. We define the lossless flow allocation problem, and formally show that in environments with frequent path allocation, scenarios that require simultaneous changes at multiple network devices are inevitable. We present the design, implementation, and evaluation of a Time4-enabled OpenFlow prototype. The prototype is publicly available as open source. This paper includes an extension to the OpenFlow protocol that has been adopted by the open networking foundation, and is now included in OpenFlow 1.5. Our experimental results show the significant advantages of Time4 compared to other network update approaches, and demonstrate an SDN use case that is infeasible without Time4. Our experimental results demonstrate the significant advantages of Time4 compared to other network update approaches.