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Two instance procedures in the base class , set-event{} and set-event-exact{}, can be used to scheduleevents in the route queue.set-event{interval, operation} schedules operation after interval seconds from the current time; it uses theprocedure set-event-exact{} below.set-event-exact{fireTime, operation} 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{} or down{}. Each method invokes the appropriateprocedure on each of the links in the instance variable, links_.ExponentialThe model schedules its first event to take the links down at startTime_ + E(upInterval_);It also defines the procedures, up{} and down{}; each procedure invokes the base class procedure to perform the actualoperation. This routine then reschedules the next event at E(upInterval) or E(downInterval_) respectively.Deterministic The model defines the procedures, up{} and down{}; each procedure invokes the base class procedure toperform the actual operation. This routine then reschedules the next event at upInterval or downInterval_ respectively.TraceThe model redefines the instance procedure set-parms{} to operan a trace file, and set events based on that input.The instance procedure get-next-event{} returns the next valid event from the trace file. A valid event is an event thatis applicable to one of the links in this object’s links_ variable.The instance procedure set-trace-events{} uses get-next-event{} to schedule the next valid event.The model redefines set-first-event{}, up{}, and down{} to use set-trace-events{}.Manual The model is designed to fire exactly once. The instance procedure set-parms{} takes an operation and thetime to execute that operation as arguments. set-first-event{} will schedule the event at the appropriate moment.This routine also redefines notify{} to delete the object instance when the operation is completed. This notion of the objectdeleting itself is fragile code.Since the object only fires once and does nto have to be rescheduled, it does not overload the procedures up{} or down{}.31.2.2 class rtQueueThe simulator needs to co-ordinate multiple simultaneous network dynamics events, especially to ensure the right coherentbehaviour. Hence, the network dynamics models use their own internal route queue to schedule dynamics events. There isone instance of this object in the simulator, in the class Simulator instance variable rtq_.The queue object stores an array of queued operations in its instance variable, rtq_. The index is the time at which the eventwill execute. Each element is the list of operations that will execute at that time.The instance procedures insq{} and insq-i{} can insert an element into the queue.277