SDN课程阅读作业（2）

Q:How many parts can be divided in the development of Software-Define-Network over last 20 years?And describe the contributions of each part.

active networks (from the mid-1990s to the early 2000s)

introduced programmable functions in the network to enable greater to innovation.

Intellectual contributions:

Programmable functions in the network to lower the barrier to innovation.

Network virtualization, and the ability to demultiplex to software programs based on packet headers.

The vision of a unified architecture for middlebox orchestration.

control and data plane separation (from around 2001 to 2007)

developed open interfaces between the control and data planes.

Intellectual contributions:

Logically centralized control using an open interface to the data plane.

Distributed state management.

the OpenFlow API and network operating systems (from 2007 to around 2010)

represented the first instance of widespread adoption of an open interface and developed ways to make control-data plane separation scalable and practical.

Intellectual contributions:

Generalizing network devices and functions.

Thevision ofanetwork operating system.

Distributed state management techniques.

Q:Relationship between Network virtualization and SDN.

Network virtualization played an important role throughout the historical evolution of SDN, substantially predating SDN yet taking root as one of the first significantusecasesforSDN.

SDN and network virtualization relate in three main ways:

SDN as an enabling technology for network virtualization.

NetworkvirtualizationforevaluatingandtestingSDNs.

Virtualizing (“slicing”) an SDN(Seems Network virtualization can suit SDN more properly).