25.2.1 The class rtModel

To use a new route model, the routine []rtmodel creates an instance of the appropriate type, defines the node or link that the model will operate upon, configures the model, and possibly enables tracing; The individual instance procedures that accomplish this in pieces are:

• The constructor for the base class../ns-2/dynamics.tclrtModel::init stores a reference to the Simulator in its instance variable, ns_. It also initializes the startTime_ and finishTime_ from the class variables of the same name.
• The instance procedure set-elements../ns-2/dynamics.tclrtModel::set-elements identifies the node or link that the model will operate upon. The command stores two arrays: links_, of the links that the model will act upon; nodes_, of the incident nodes that will be affected by the link failure or recovery caused by the model.
• The default procedure in the base class to set the model configuration parameters is set-parms../ns-2/dynamics.tclrtModel::set-parms. It assumes a well defined start time, up interval, down interval, and a finish time, and sets up configuration parameters for some class of models. It stores these values in the instance variables: startTime_, upInterval_, downInterval_, finishTime_. The exponential and deterministic models use this default routine, the trace based and manual models define their own procedures.
• The instance procedure []trace../ns-2/dynamics.tclrtModel::trace enables []trace-dynamics on each of the links that it affects. Additional details on []trace-dynamics is discussed in the section on extensions to the class LinkSectionsec:nd-extensions.

The next sequence of configuration steps are taken just prior to the start of the simulator. invokes []rtmodel-configure../ns-2/dynamics.tclSimulator::rtmodel-configure just before starting the simulation. This instance procedure first acquires an instance of the class rtQueue, and then invokes []configure for each route model in its list, rtModel_.

• The instance procedure []configure../ns-2/dynamics.tclrtModel::configure makes each link that is is applied to dynamic; this is the set of links stored in its instance variable array, links_. Then the procedure schedules its first event.
• The default instance procedure []set-first-event../ns-w/dynamics.tclrtModel::set-first-event schedules the first event to take all the links ``down'' at
  $startTime_ + upInterval_. Individual types of route models derived from this base class should redefine tihs function.
• Two instance procedures in the base class , []set-event../ns-2/dynamics.tclrtModel::set-event and []set-event-exact../ns-2/dynamics.tclrtModel::set-event-exact, can be used to schedule events in the route queue.

  [interval, operation]set-event schedules operation after interval seconds from the current time; it uses the procedure []set-event-exact below.

  [fireTime, operation]set-event-exact schedules operation to execute at fireTime.

  If the time for execution is greater than the finishTime_, then the only possible action is to take a failed link ``up''.

• Finally, the base class provides the methods to take the links []up../ns-2/dynamics.tclrtModel::up or []down../ns-2/dynamics.tclrtModel::down. Each method invokes the appropriate procedure on each of the links in the instance variable, links_.