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The IoC Metaphor in SDN

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You're probably familiar with the Inversion of Control pattern that became popular in the last decade.  It hands control of the application's flow of execution over to user events (i.e. event-driven applications).  Lori MacVittie sees some software-defined networking models taking a similar approach and giving control to the applications on the network, but many models of SDN still keep the network in the driver's seat with SDN controllers using an OpenFlow-based model.

The network (the SDN controller in an OpenFlow-based model) makes the decision where to reroute traffic upon encountering a problem. It is still in control and the application itself has absolutely no input in current SDN models. Even in proposed service chaining models, applications are not in control of the flow. The network remains the final arbiter of where and how traffic flows through the network…

… But as SDN controllers have no visibility above layer 4 (IP and port) it cannot recognize content types or that its decisions are inefficient and wasteful.

-- Lori MacVittie

Lori MacVittie's articles are always a good read, so check them out.