-locally, or it can be configured to connect a given bridge to one or
-more external OpenFlow controllers, such as NOX.
+locally, or it can be configured to communicate with one or more
+external OpenFlow controllers. The switch is typically configured to
+connect to a primary controller that takes charge of the bridge's flow
+table to implement a network policy. In addition, the switch can be
+configured to listen to connections from service controllers. Service
+controllers are typically used for occasional support and maintenance,
+e.g. with \fBovs\-ofctl\fR.