Fifth generation (5G) wireless networksare characterized by applying the software defined networking (SDN) and network function virtualization (NFV) concepts to provide higher reliability and scalability, and lower latency for advent data-hungry services. In the initial version of SDN based 5G, a centralized architecture for SDN controller has been proposed, which inherently cannot fulfill those requirements simultaneously. This observation has led us toward distributed architectures, where multiple SDN controllers across the network constitute the control layers. Furthermore, to fully achieve the network flexibility and agility offered by SDN, and also improve resource utilization and consequently to reduce network cost, we incorporate virtualized SDN (vSDN) controllers, enabled through the NFV technology. In vSDN with distributed architecture, controller placement is one of the main challenges, which is an NP-hard combinatorial optimization problem with conflicting objectives: 1) maximizing the reliability of network with low latency; 2) minimizing the total cost of implementation, which can be interpreted as reducing the number of vSDN controllers. In order to achieve such a compromise, in this work, we formulate the problem of vSDN controller placement and introduce some performance metrics to model the latency of communication between controller-switch pairs and also robustness against vSDN controller failures in a network. The introduced formulation is some sorts of submodular optimization, which is exploited to develop several algorithms. Simulations results demonstrate that, with a negligible performance loss, a significant reduction in the number of vSDN controllers is achievable. Finally, latency, cost, and robustness trade-offs are investigated.

中文翻译：

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5G 软件定义网络中近乎最优的稳健虚拟控制器布局

第五代 (5G) 无线网络的特点是应用软件定义网络 (SDN) 和网络功能虚拟化 (NFV) 概念，为大量数据的服务提供更高的可靠性和可扩展性以及更低的延迟。在基于 SDN 的 5G 的初始版本中，已经提出了 SDN 控制器的集中式架构，但它本质上无法同时满足这些要求。这一观察使我们转向分布式架构，其中跨网络的多个 SDN 控制器构成控制层。此外，为了充分实现 SDN 提供的网络灵活性和敏捷性，并提高资源利用率，从而降低网络成本，我们整合了通过 NFV 技术实现的虚拟化 SDN (vSDN) 控制器。在具有分布式架构的 vSDN 中，控制器放置是主要挑战之一，这是一个具有冲突目标的 NP-hard 组合优化问题：1）以低延迟最大化网络的可靠性；2）最小化实施的总成本，这可以解释为减少vSDN控制器的数量。为了实现这样的折衷，在这项工作中，我们制定了 vSDN 控制器放置的问题，并引入了一些性能指标来模拟控制器-交换机对之间的通信延迟以及对网络中 vSDN 控制器故障的鲁棒性。引入的公式是某种子模块优化，可用于开发多种算法。模拟结果表明，在性能损失可以忽略不计的情况下，可以实现 vSDN 控制器数量的显着减少。最后，研究了延迟、成本和稳健性的权衡。