多謝老大，看來隻能直說了

What is programmable network?
The techniques and protocols used by networks today were developed more than 20 years ago. Intermediate nodes (routers) between two end computers are “passive”. They just pass the information of packets to the next computer on the route and don’t have any ability to process the data transported in packets, i.e. routers only decide the route of packets and don’t change the content. Routing algorithms only work to IP level in OSI model, not application level. With the increase of network popularity, people hope more applications from network. But it is difficult and cost-inefficient to deploy new applications in the traditional network. Internet service providers (ISP) must wait service vendors to implement the whole application and produce the special hardware before the new application can be provided to normal users. Application users cannot change the service once the application is deployed and make new applications of their own. It is critical for ISPs to react to the market needs as quickly as possible. ISPs hope there is a kind of more flexible and simplified means to deploy new applications, and network users hope to make use of the distributed computing environment of network. Programmable networking model is formed to meet this requirement. In programmable network model, intermediate nodes (routers) are not “passive” any more, but “active”. They can change the data in transported packets or the processing environment of routers. As illustrated in Fig.1, routers work to application level in OSI model. ISPs deploy some components on network nodes and network users can assemble these components to achieve some application they want, i.e. program the network

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