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$ll_ set delay_ $delay$ll_ set bandwidth_ $bw$ll_ sendtarget $mac$ll_ recvtarget $iif. . .# per LAN# link-level overhead# bandwidth# interface queue at the sender side# input interface of the receiver14.7 LanRouterclassBy default, there is just one LanRouter object per LAN, which is created when a new LanNode is initialized. For everynode on the LAN, the link layer object (LL) has a pointer to the LanRouter, so it is able to find the next hop for the packetthat is sent on the LAN:Packet* LL::sendto(Packet* p, Handler* h){int nh = (lanrouter_) ? lanrouter_->next_hop(p) : -1;. . .}LanRouter is able to find the next hop by querying the current RouteLogic:int LanRouter::next_hop(Packet *p) {int next_hopIP;if (enableHrouting_) {routelogic_->lookup_hier(lanaddr_, adst, next_hopIP);} else {routelogic_->lookup_flat(lanaddr_, adst, next_hopIP);}One limitation of this is that RouteLogic may not be aware of dynamic changes to the routing. But it is always possible toderive a new class from LanRouter so that to re–define its next_hop method to handle dynamic changes appopriately.14.8 Other ComponentsIn addition to the C++ components described above, simulating local area networks also requires a number of existing componentsin ns such as Classifier, Queue, and Trace, networkinterface, etc. Configuring these objects requiresknowledge of what the user wants to simulate. The default configuration is implemented in the two Tcl files mentioned at thebeginning of this chapter. To obtain more realistic simulations of wireless networks, one can use the ErrorModel describedin Chapter 13.14.9 LANs and ns routingWhen a LAN is created using either make-lan or newLan, a “virtual LAN node” LanNode is created. LanNode keepstogether all shared objects on the LAN: Channel, Classifier/Mac, and LanRouter. Then for each node on the LAN,138