As one of the most popular south-bound protocol of software-defined networking(SDN), OpenFlow decouples the network control from forwarding devices. It offers flexible and scalable functionality for networks. These advantages may cause performance issues since there are performance penalties in terms of packet processing speed. It is important to understand the performance of OpenFlow switches and controllers for its deployments. In this paper we model the packet processing time of OpenFlow switches and controllers. We mainly analyze how the probability of packet-in messages impacts the performance of switches and controllers. Our results show that there is a performance penalty in OpenFlow networks. However, the penalty is not much when probability of packet-in messages is low. This model can be used for a network designer to approximate the performance of her deployments.
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