Network softwarization is one of the major paradigm shifts in the next generation of networks. It enables programmable and flexible management and deployment of the network. Network function virtualization (NFV) is referred to the deployment of software functions running on commodity servers instead of traditional hardware-based middle-boxes. It is an example of network softwarization. In NFV, a service is defined as a chain of software functions named service chain function (SFC). The process of allocating the resources of servers to the services, called service placement, is the most challenging mission in NFV. Dynamic nature of the service arrivals and departures as well as meeting the service level agreement make the service placement problem even more challenging. In this paper, we propose a model for dynamic reliability-aware service placement based on the simultaneous allocation of the main and backup servers. Then, we formulate the dynamic reliability-aware service placement as an infinite horizon Markov decision process (MDP), which aims to minimize the placement cost and maximize the number of admitted services. In the proposed MDP, the number of active services in the network is considered to be the state of the system, and the state of the idle resources is estimated based on it. Also, the number of possible admitted services is considered as the action of the presented MDP. To evaluate each possible action in the proposed MDP, we use a sub-optimal method based on the Viterbi algorithm named Viterbi-based Reliable Static Service Placement (VRSSP) algorithm. We determine the optimal policy based on value iteration method using an algorithm named VRSSP-based Value Iteration (VVI) algorithm. Eventually, through the extensive simulations, the superiority of the proposed model for dynamic reliability-aware service placement compared to the static solutions is inferred.

中文翻译：

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用于网络功能虚拟化 (NFV) 的动态可靠性感知服务部署

网络软件化是下一代网络的主要范式转变之一。它支持可编程且灵活的网络管理和部署。网络功能虚拟化（NFV）是指部署运行在商品服务器上的软件功能，而不是传统的基于硬件的中间盒。这是网络软件化的一个例子。在 NFV 中，服务被定义为名为服务链功能 (SFC) 的软件功能链。将服务器资源分配给服务的过程称为服务放置，是 NFV 中最具挑战性的任务。服务到达和离开的动态特性以及满足服务水平协议使得服务安置问题更具挑战性。在本文中，我们提出了一种基于主服务器和备用服务器同时分配的动态可靠性感知服务放置模型。然后，我们将动态可靠性感知服务放置制定为无限范围马尔可夫决策过程（MDP），旨在最小化放置成本并最大化接纳服务的数量。在提出的MDP中，网络中活跃服务的数量被认为是系统的状态，并在此基础上估计空闲资源的状态。此外，可能被接纳的服务的数量被视为所呈现的 MDP 的动作。为了评估所提出的 MDP 中每个可能的操作，我们使用了一种基于维特比算法的次优方法，称为基于维特比的可靠静态服务放置 (VRSSP) 算法。我们使用名为 VRSSP-based Value Iteration (VVI) 算法的算法基于值迭代方法确定最优策略。最终，通过广泛的模拟，推断出所提出的动态可靠性感知服务放置模型与静态解决方案相比的优越性。