Time4: Time for SDN

TL;DR

Time4 leverages precise timing to coordinate network updates in SDN, reducing packet loss during path reconfigurations and enabling scenarios that are otherwise infeasible, with a formal foundation and open-source implementation.

Contribution

Introduction of Time4, a time-coordinated network update approach for SDN, including protocol extension, formal analysis, and an open-source prototype now part of OpenFlow 1.5.

Findings

Time4 reduces packet loss during network updates.

Time4 enables complex update scenarios infeasible with existing methods.

Prototype implementation demonstrates practical advantages of Time4.

Abstract

With the rise of Software Defined Networks (SDN), there is 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, so as to minimize disruptions that may occur during network updates. 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. 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. 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. Our work includes an extension to the OpenFlow protocol that has been adopted by the Open Networking Foundation (ONF), 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.