Abstract
In Software-defined networks (SDNs), synchronization among network devices is an emergent phenomenon for enhancing the network scalability while preserving the centralized control. Owing to the fixed timeout values attributed to flow rules by the controller, flow table entries that are installed simultaneously are likely to timeout simultaneously and tend to trigger <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">packet_in</i> events at once during the upcoming sampling period. This phenomena in SDNs lead to serious performance and scalability issues when a large number of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">packet_in</i> events are invoked simultaneously. In the proposed model, the orchestrating agent and the controller duo modulate an ensemble of networking devices from their heterogeneous frequency and incoherent nature of querying the controller into a conciliatory and systematic manner. The orchestrating agent modulates the control flows by altering timeouts, especially for long-lived TCP connections so that the devices do not overwhelm the controller with bursty requests during the future events. In addition, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">flow_mods</i> to intermediate devices over a multi-hop path are scheduled based on the estimated flow setup latency to avoid redundant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">packet_ins</i> . The proposed orchestrating agent is implemented in conjunction with the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Floodlight</i> controller. The experimental results show that apart from the influence of external delays majority of the flows were well-synchronized and the results show significant improvement in scalability and in the overall performance of the network.
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