This illustration depicts a series of interactions between a router network and an SDN controller in order to illustrate a link state change. The interactions are numbered to correspond with the numbered list on page 417.

The interaction begins with the network of routers, which appears at the bottom of the illustration. There are four routers arranged in a diamond shape: the left point of the diamond is r1, the top of the diamond is r2, the bottom of the diamond is r3, and the right point of the diamond is r4. An arrow, labeled 1 and indicating step one of the interaction, points from r1 to the box labeled "OpenFLow" in the lowest layer of the SDN controller. The arrow, now labeled 2, continues from OpenFlow to a box labeled "Link state info" in the middle layer of the SDN controller-this is step two. The arrow, now labeled 3, goes past a box labeled "statistics" in the middle layer and into a box labeled "Dijkstra's link-state routing" in the top layer of the SDN controller. A second arrow, labeled 4, points back and forth from link-state info to Dijkstra's link-state routing. The arrow, now labeled 5, points downward from Dijkstra's link-state routing and into a box labeled "flow tables" in the middle layer of the SDN controller. The arrow travels through the bottom layer and through the OpenFlow, and emerges-now labeled 6. The arrow splits into three arrows, pointing to r1, r2, and r4.