SDN课程阅读作业（2）

1.过去20年中可编程网络的发展可以分为几个阶段？每个阶段的贡献是什么？

• We divide the history into three stages
• 1. active networks (from the mid-1990s to the early 2000s), which introduced programmable functions in the network to enable greater to innovation（引入了可编程功能）
• 2. control and data plane separation (from around 2001 to 2007), which developed open interfaces between the control and data planes（控制层数据层分离）
• 3. the OpenFlow API and network operating systems (from 2007 to around 2010), which represented the first instance of widespread adoption of an open interface and developed ways to make control-data plane separation scalable and practical.（开发了使控制数据平面分离可扩展且实用的方法）

2.网络虚拟化与SDN的关系？

• 1. SDN as an enabling technology for network virtualization. 多个客户共享同一网络基础设施和SDN一个控制器控制多个交换机的概念十分接近。
• 2. Network virtualization for evaluating and testing SDNs.为SDN在部署到实际网络之前提供实验平台。
• 3. Virtualizing (“slicing”) an SDN.虚拟化SDN交换机更简单。传统交换机的虚拟化要把各自的配置做也一起配置，而SDN交换机的虚拟化采用一个控制器和一片交换机的方式，简化了虚拟的过程。