Exactly as described, applicable to generator test instances, this indicates whether testing is currently in progress, and setting this to true is what actually initiates the test. This is distinct from, and comes after, the instance's own admin state being enabled -- admin state reserves the hardware resources while this flag is the separate trigger that actually starts traffic flowing, meaning an instance can sit enabled-but-not-started indefinitely while an operator prepares the far-end reflector. For example, an operator would first enable admin state on both the generator and reflector instances to reserve resources, confirm the reflector is ready, and only then set this Started flag true to actually kick off the test traffic.