SDN allows network administrators to manage network services centrally (without need to configure network devices one by one) through abstraction of lower level functionality. This is done by decoupling the system that makes decisions about where traffic is sent (the control plane) from the underlying systems that forwards traffic to the selected destination (the data plane). The inventors and vendors of these systems claim that this simplifies networking.
It has been noted that this "overlay" approach raises a high likelihood of inefficiency and low performance by ignoring the characteristics of the underlying infrastructure.
Example is Google's Andromeda (codename of Google's nw virtualization)
