Network Function Virtualization (NFV) represents a key shift in nowadays network service provisioning by entailing higher flexibility, elasticity, and programmability of network services. Dependability is one of the main aspects that need to be investigated and tackled in order to profitably use NFV in the future. The main objective of this paper is to propose a comprehensive approach to estimate the end-to-end NFV-deployed service availability and present a quantitative assessment of the network factors that affect the availability of the service provided by an NFV architecture. To achieve this goal, we adopted a two-level availability model where i) the low level considers the network topology structure and NFV connectivity requirements through the definition of the system structure function based on minimal-cut sets and ii) the higher level examines dynamics and failure modes of network and NFV elements through stochastic activity networks. By using the proposed model, we have carried out an extensive sensitivity analysis to identify the impact on the service availability of the different service elements involved in the delivery, and their deployment across the network. The results highlight the significant impact that network nodes have on the end-to-end network service. Less robust network nodes may reduce the availability of an NFV-enabled service by more than one order of magnitude even though NFV elements like VNFs or MANO are provided with redundancy. Moreover, the results show that adopting an SDN-integrated network degrades the service availability and increases the vulnerability of the network service to SDN controllers unless adequately protected.

中文翻译：

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支持 NFV 的端到端服务的网络感知可用性建模

网络功能虚拟化 (NFV) 代表了当今网络服务供应的关键转变，它要求网络服务具有更高的灵活性、弹性和可编程性。可靠性是需要调查和解决的主要方面之一，以便在未来有利可图地使用 NFV。本文的主要目的是提出一种综合方法来估计端到端 NFV 部署的服务可用性，并对影响 NFV 架构提供的服务可用性的网络因素进行定量评估。为了实现这一目标，我们采用了两级可用性模型，其中 i) 低级通过基于最小割集的系统结构函数定义来考虑网络拓扑结构和 NFV 连接要求 ii) 更高级别检查网络的动态和故障模式和 NFV 元素通过随机活动网络。通过使用所提出的模型，我们进行了广泛的敏感性分析，以确定交付中涉及的不同服务元素及其在整个网络中的部署对服务可用性的影响。结果突出了网络节点对端到端网络服务的重大影响。即使为 VNF 或 MANO 等 NFV 元素提供了冗余，但不太稳健的网络节点可能会将支持 NFV 的服务的可用性降低一个数量级以上。此外，结果表明，除非得到充分保护，否则采用 SDN 集成网络会降低服务可用性并增加网络服务对 SDN 控制器的脆弱性。