中文摘要：

网络虚拟化提供一种灵活高效的方式实现了底层物理基础设施的共享，使得多个租户可以同时部署独立的网络应用。传统网络复杂且难于管理，软件定义网络作为一种新兴网络范例有助于解决当前网络障碍。本文针对SDN网络虚拟化技术进行全面的描述和总结，对现有实现方案进行分类，选取每类方案的典型代表，对比各自的系统架构和工作原理，总结其在网络抽象和流量隔离方面的优势和不足。

英文摘要：

Network Virtualization provides an efficient and flexible way to share the physical network infrastructure so that multiple ten- ants can run their own applications concurrently. Traditional networks are complex and hard to manage, Software Defined Networking has emerged as a promising paradigm to solve many of current barriers in communication networks. In this paper, we comprehensively survey hypervisors for SDN networks and categorize network virtualization approaches. Moreover, the system architectures and princi- ples of three typical SDN hypervisors are compared and analyzed, The network abstraction and isolation features are also discussed.