| With the rapid expansion of the scale of the network, there are a lot of problems in the expansion of the traditional Internet of management and control, flexibility, etc. In recent years, the rapid development of software defined networking(SDN) is quietly breaking this deadlock, and becoming one of the hot spots in the future Internet. Control layer and data layer separation, network centralized control are the core ideas of SDN. With the continuous increase of data flow and network size, only a single controller placement strategy has been unable to meet the needs of the actual network deployment, so multiple independent controller instead of centralized single controller is the effective strategy to solve the control layer expansion. For the given network topology, how to place the controller, and which switches should be controlled by each controller, that is, the controller placement problem, needs in-depth study. In this paper, we mainly study the controller placement problem based on time delay in the SDN, and the specific work includes the following aspects:Firstly, in view of the current SDN controller placement schemes only considering the link propagation delay, but ignoring the switchtransmission delay and the controller time delay effects on the performance of the network. In this paper, queuing theory and network calculus are respectively introduced to deal with the controller time delay.Secondly, a new minimum average time delay / maximum minimum time delay model is proposed. According to the existing time delay model, a new minimum average time delay / maximum minimum time delay model is proposed by considering the link propagation delay, the switch transmission delay and the controller time delay.Finally, according to the given example topology, analysis and obtain optimum controller position under the minimal average time delay model and maximum minimum time delay model. And contrasted with stochastic controller placed position by mininet simulation platform. |
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