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UserInheritPLMTopologyInstantiatePLMPLM/nsPLMLayerPLMLayerPLMLayer/nsPLMLayer/nsAgent/LossMonitor/PLMAgent/LossMonitor/PLMPLMLossTracePLMLossTraceNumber of layersFigure 37.1: Inheritance and instantiation when we create a receiver.create-layer and, by this way, creates as many instances of the class PLMLayer/ns (the ns interface to the PLMLayerclass) as there are layers. Each instance of PLMLayer/ns creates an instance of the class PLMLossTrace which is reponsiblefor monitoring the received and lost packets thanks to the fact that the class PLMLossTrace inherits from the classAgent/LossMonitor/PLM. Fig. 37.1 schematically describes the process of a PLM receiver instantiation. In the following wedescribe the behavior of a PLM receiver when it receives a packet and when it detects a loss.37.3.3 Reception of a PacketWe create a new c++ class PLMLossMonitor (~ns/plm/loss-monitor-plm.cc) that inherits from LossMonitor. The OTcl classname of the c++ PLMLossMonitor class is Agent/LossMonitor/PLM.class PLMLossMonitor : public LossMonitorpublic:PLMLossMonitor();virtual void recv(Packet* pkt, Handler*);protected:// PLM onlyint flag_PP_;double packet_time_PP_;int fid_PP_;;static class PLMLossMonitorClass : public TclClasspublic:PLMLossMonitorClass() : TclClass("Agent/LossMonitor/PLM")TclObject* create(int, const char*const*)return (new PLMLossMonitor());class_loss_mon_plm;327