摘要：
Various middleboxes have been deployed to enable diversified functionalities in enterprise networks.For example, Firewalls and Intrusion Detection Systems are used to enhance the security of the network, and Cache Proxies and WAN Optimizations are used to improve the performance of the enterprise networks.However, it is painful for enterprises to deploy, update, or maintain such physical devices in their enterprise networks.Moreover, because of the discrepancybetween network function devices of the different manufacturers, enterprises need to hire large management teams with extensive knowledge to manage the network functions devices.Because of the fixed location and network traffic process capacity of the hardware network function devices, the network traffic congestion always causes the failure of the network functions.The overhead of middlebox management, maintenance and update increase significantly as enterprise networks grow.Fortunately, the emerging Network Function Virtualization (NFV) technology can address these issues by decoupling the physical network equipment from the network functions that run on them.With the NFV technology, an enterprise can efficiently reduce complicated network function management and the cost of deploying network function equipment by deploying network functions in commercial servers.It can also enable flexible service deployment strategies for the enterprises, e.g., dynamically scale in/out.Although NFV can bring significant benefits to enterprises, there are still many challenges in developing practical and efficient NFV.In order to solve such problems, researchers in academia and industry have devoted to the study of the NFV technology.This paper presents the first systematic study of the literature of the NFV technology.Firstly, we review the standard architecture of NFV established by the European Telecom Standards Institute Industry Specification Group for NFV (ETSI ISG NFV).We classify and summarize the problems and challenges in the developing of NFV systems based on the standard architecture of NFV.The study can be classified into the following three categories:Network Function Virtualization, Network Function Virtualization Infrastructure (NFVI), and Management And Network Orchestration (MANO).Furthermore, Software Defined Network (SDN) is a new type of network architecture which are designed to achieve flexible and intelligent network traffic control by decoupling the control plane and data plane of network devices, NFV and SDN can complement each other in various aspects, we study the relationship between the NFV and SDN.Secondly, we systematically study building blocks of NFV, i.e., virtual network function (VNF) construction, and the running environment optimization in NFV, the design of NFV management system and its optimization, policy enforcement and verification, resource allocation and migration, load balance and state management technology, and NFV security.Thirdly, the NFV technology has been deployed in different kinds of industry fields, we show the practical deployment issues of NFV by discussing the application scenario cases of NFV, e.g.in cloud computing, mobile communication, and home network.Finally, we summarize the advantages and shortcomings of NFV by comparing the NFV technology and classical physical network function devices and present the future research directions of the NFV technology from six aspects based on the standard architecture of ETSI NFV.%企业通常部署各种网络功能设备来实现企业网络所需的网络功能.例如,防火墙和入侵检测系统可以加强企业网络的安全性;缓存代理和广域网优化器可以提升企业网络的性能.然而,企业部署、更新和维护网络功能设备需要大量开销.不同网络功能设备之间的差异使得企业需要庞大的专业团队来管理网络设备.物理设备固定的位置和处理能力使得企业网络无法有效解决网络拥塞带来的设备失效问题.随着企业网络规模的增长,网络功能设备管理、维护和更新产生的开销急剧上升.面对日益增长的网络功能设备运维开销和管理难度,网络功能虚拟化(Network Function Virtualization,NFV)技术提出将网络功能和物理硬件设备解耦,通过在通用商用服务器上部署和管理网络功能,为企业降低了网络设备管理难度,减少了网络功能设备开销,提供了灵活的网络服务部署策略,例如,动态回收/扩展.尽管NFV技术能为企业带来便捷和利益,但是实现一个实用而高效的NFV系统存在很多挑战.针对NFV系统实现中存在的问题和挑战,学术界和工业界已投入大量精力对NFV技术进行研究和尝试.该文首先介绍欧洲电信标准协会制定的NFV技术标准结构,并根据其分类总结NFV系统实现中存在的问题和挑战,将当前研究成果分为网络功能虚拟化、网络功能虚拟化设施和管理、网络编排三个部分.软件定义网络(Software Defined Network,SDN)和NFV技术可以相互弥补促进,该文对其之间的关系进行了研究.然后,该文着重从虚拟化网络功能(Virtual Network Function,VNF)构建及运行环境优化、NFV管理系统设计及优化、策略实施与验证、资源分配和迁移策略、NFV负载均衡和状态管理技术、NFV架构中的安全问题几个方面来深入分析NFV技术当前的学术研究成果.最后介绍了NFV技术在云计算、移动通讯以及家庭网络中的应用场景实例,同时对NFV技术进行总结并展望未来研究发展方向.
