SDN is a technology poised to reinvent the way the Internet is wired. It could do for the network what the idea of virtual machines did for computer hardware in data centers. So where exactly did the idea for SDN come from? This article by Tom Simonite discusses one genesis point:

[Martin Casado] presented one in his 2007 PhD thesis, which proposed a radical new way for computer networks to operate. Now he’s cofounded a company called Nicira, which is poised to use that idea to make the Internet more powerful than ever before. Nicira’s technology won’t just help intelligence agencies keep secrets. It should also improve the security, lower the price, and increase the power of any technology that uses the Internet, unlocking innovation that is too expensive or technically impossible to achieve today.

In the following quote, you can identify two of the key features of SDN:

To avoid having to install their special software on network hardware, they used a trick known in computer science as virtualization, which creates a software replica of a piece of hardware—but the software does the job more intelligently. In Nicira’s case, software running on server computers could simulate programmable routers and switches. The physical devices themselves could fade in importance entirely. After four years of quiet hard work, Nicira has just launched that software as its first product. It should trigger a new wave of Internet innovation in everything from mobile apps to online banking security.

The “special software” is software that allows easy centralized management of many pieces of Internet hardware, such as routers. Instead of configuring each router separately, groups of routers can be configured together to achieve particular goals. Then, instead of using custom hardware, normal server hardware runs software that turns it into a router. In this way, both the administration and hardware costs of running a network go down significantly.

Nicira has dozens of patents in the SDN arena, all of which are available here:

https://www.google.com/search?tbm=pts&hl=en&q=martin+casada#bav=on.2,or.r_qf.&fp=84b334388f228b16&hl=en&q=nicira&tbm=pts