Each model of network dynamics is implemented as a separate class, derived from the base rtModel../ns-2/dynamics.tcl. We begin by describing the base class rtModel and the derived classesSectionsec:rtmodel. The network dynamics models use an internal queuing structure to ensure that simultaneous events are correctly handled, the rtQueue../ns-2/dynamics.tcl. The next subsectionSectionsec:rtqueue describes the internals of this structure. Finally, we describe the extensions to the existing classesSectionsec:nd-extensions: the Node, Link, and others.