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HierNodeEntry0123401234Level 201234Level 3To HierNodePort DemuxLevel 13-Level classifiers for HierNode (hier-addr:0.2.1)Figure 32.1: Hierarchical classifiersNode instproc add-route dst target$self instvar rtnotif_# Notify every module that is interested about this# route installationif $rtnotif_ != ""$rtnotif_ add-route $dst $target$self incr-rtgtable-sizeFor an example of 3 level of hierarchy, the level 1 classifier demuxes for domains, level 2 for all clusters inside the node’sdomain and finally classifier 3 demuxes for all nodes in the particular cluster that the node itself resides. For such a topology,a HierNode with address of 0.1.2 looks like the figure below:Thus the size of the routing tables are considerably reduced from n 2 as seen for flat routing where each node had to storethe next_hop info of all other nodes in the topology. Instead, for hierarchical routing, a given node needs to know aboutits neighbours in its own cluster, about the all clusters in its domain and about all the domains. This saves on memoryconsumption as well as run-time for the simulations using several thousands of nodes in their topology.32.3 Creating large Hierarchical topologiesThe previous section describes methods to create hierarchical topologies by hand. However, there is a script availablein ns that converts Georgia-tech’s SGB-graphs into ns compatible hierarchical topologies. Please refer to http://wwwmash.CS.Berkeley.EDU/ns/ns-topogen.htmlfor downloading as well as instructions on using the hierarchical converter package.See hier-rtg-10.tcl and hier-rtg-100.tcl in ~ns/tcl/ex for example scripts of hier routing on small and large topologies respectively.283