Abstract: The network architecture has been used for nearly 30 years. In order to make the whole network run smoothly, switches/routers have to run within more than 6000 protocols, which means if one network point increases a protocol the other points also have to make changes. SDN（Software Defined Network） makes the network programmable, so that it enables the network to be more flexible to fit needs of network users. In the SDN architecture, the control and data planes are decoupled, network intelligence and state are logically centralized, and the underlying network infrastructure is abstracted from the applications. As a result, enterprises and carriers gain unprecedented programmability, automation, and network control, enabling them to build highly scalable flexible networks that readily adapt to changing business needs. SDN controller plays a very important role in SDN because not only does it communicate with the underlying devices but also provides APIs for the application layer. This paper analyzes the background and principle of SDN as well as its development at first; then it does some researches on an open source project——Floodlight; at last this paper summarizes and analyses the features of SDN controller.

Key words: Software Defined Network（SDN）, SDN controller, network architecture

摘要： 目前正在使用的网络架构已有30年的历史。在此架构下，交换机/路由器需要在超过6 000个分布式协议中使整个网络正常运行。这意味着只要有一个网元增加一种新的协议，其他网元都必须在结构上做出变更。SDN（Software Defined Network，软件定义网络）则打破了这种桎梏，它使得网络可编程，从而让网络在满足用户需求方面更具灵活性。SDN架构将控制和转发解耦，将控制功能集中到逻辑独立的控制环境之中，同时为应用层提供底层网络的抽象视图。结果就是SDN可以为用户提供可编程性极强的网络、网络自动化管理以及网络控制等功能，从而满足日益变化与丰富的网络需求。SDN控制器在SDN架构中的作用至关重要，它既要与基础设施层交互也需要与应用层经由API交互。首先分析了SDN架构的产生背景、原理和其发展现状；随后研究并分析了一个SDN控制器的开源项目Floodlight；最后通过对当前7种控制器的实验以及SDN相关原理对SDN控制器的特性进行了总结与分析。

关键词: 软件定义网络, SDN控制器, 网络架构