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The routine send-periodic-update{} invokes send-updates{} to send the actual updates. It then reschedulessending the next periodic update after advertInterval jittered slightly to avoid possible synchronization effects.send-updates{} will send updates to a select set of peers. If any of the routes at that node have changed, or for periodicupdates, the procedure will send updates to all peers. Otherwise, if some incident links have just recovered, the procedurewill send updates to the adjacent peers on those incident links only.send-updates{} uses the procedure send-to-peer{} to send the actual updates. This procedure packages the update,taking the split-horizon and poison reverse mechanisms into account. It invokes the instproc-like, send-update{} (Notethe singular case) to send the actual update. The actual route update is stored in the class variable msg_ indexed by a nondecreasinginteger as index. The instproc-like only sends the index to msg_ to the remote peer. This eliminates the need toconvert from OTcl strings to alternate formats and back.When a peer receives a route update it first checks to determine if the update from differs from the previous ones. The agentwill compute new routes if the update contains new information.29.6 Unicast routing objectsRoutelogic and rtObject are two objects that are significant to unicast routing in ns. Routelogic, essentially, represents therouting table that is created and maintained centrally for every unicast simulation. rtObject is the object that every nodetaking part in dynamic unicast routing, has an instance of. Note that nodes will not have an instance of this object if Sessionrouting is done as a detailed routing protocol is not being simulated in this case. The methods for RouteLogic and rtObjectare described in the next section.29.7 Commands at a glanceFollowing is a list of unicast routing related commands used in simulation scripts:$ns_ rtproto where defines the type of routing protocol to be used, like Static, Manual, Session , DV etc. args may definethe list of nodes on which the protocol is to be run. The node list defaults to all nodes in the topology.Internal methods:$ns_ compute-routesThis command computes next_hop information for all nodes in the topology using the topology connectivity. Thisnext_hop info is then used to populate the node classifiers or the routing tables. compute-routes calls compute-flat-routesor compute-hier-routes depending on the type of addressing being used for the simulation.$ns_ get-routelogicThis returns a handle to the RouteLogic object (the routing table), if one has been created. Otherwise a new routing tableobject is created.$ns_ dump-routelogic-nh259