In recent years, Software Defined Networking (SDN) has emerged as a pivotal element not only in data-centers and wide-area networks, but also in next generation networking architectures such as Vehicular ad hoc network and 5G. SDN is characterized by decoupled data and control planes, and logically centralized control plane. The centralized control plane in SDN offers several opportunities as well as challenges. A key design choice of the SDN control plane is placement of the controller(s), which impacts a wide range of network issues ranging from latency to resiliency, from energy efficiency to load balancing, and so on. In this paper, we present a comprehensive survey on the controller placement problem (CPP) in SDN. We introduce the CPP in SDN and highlight its significance. We present the classical CPP formulation along with its supporting system model. We also discuss a wide range of the CPP modeling choices and associated metrics. We classify the CPP literature based on the objectives and methodologies. Apart from the primary use-cases of the CPP in data-center networks and wide area networks, we also examine the recent application of the CPP in several new domains such as mobile/cellular networks, 5G, named data networks, wireless mesh networks and VANETs. We conclude our survey with discussion on open issues and future scope of this topic.

中文翻译：

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SDN控制器布局调查

近年来，软件定义网络 (SDN) 不仅在数据中心和广域网中成为关键元素，而且在车载自组织网络和 5G 等下一代网络架构中也已成为关键元素。SDN的特点是数据平面和控制平面解耦，控制平面在逻辑上集中。SDN 中的集中控制平面提供了多种机遇和挑战。SDN 控制平面的一个关键设计选择是控制器的放置，这会影响从延迟到弹性、从能源效率到负载平衡等广泛的网络问题。在本文中，我们对 SDN 中的控制器放置问题 (CPP) 进行了全面调查。我们介绍了 SDN 中的 CPP 并强调了它的重要性。我们介绍了经典的 CPP 公式及其支持系统模型。我们还讨论了广泛的 CPP 建模选择和相关指标。我们根据目标和方法对 CPP 文献进行分类。除了 CPP 在数据中心网络和广域网中的主要用例外，我们还研究了 CPP 最近在几个新领域的应用，例如移动/蜂窝网络、5G、命名数据网络、无线网状网络和VANET。我们以对该主题的未决问题和未来范围的讨论来结束我们的调查。我们还研究了 CPP 最近在几个新领域的应用，例如移动/蜂窝网络、5G、命名数据网络、无线网状网络和 VANET。我们通过讨论未解决的问题和该主题的未来范围来结束我们的调查。我们还研究了 CPP 最近在几个新领域的应用，例如移动/蜂窝网络、5G、命名数据网络、无线网状网络和 VANET。我们以对该主题的未决问题和未来范围的讨论来结束我们的调查。