45.1.1 Basic Configuration

The basic configuration consists of creating and configuring a multicast session. Each Session (, a multicast tree) must be configured strictly in this order: (1) create and configure the session source, (2) create the session helper and attach it to the session source, and finally, (3) have the session members join the session.

        set ns [new SessionSim]          # preamble initialization;
        set node [$ns node]    
        set group [$ns allocaddr]

        set udp [new Agent/UDP]         # create and configure the source;
        $udp set dst_ $group
	set src [new Application/Traffic/CBR]
	$src attach-agent $udp
        $ns attach-agent $node $udp

        $ns create-session $node $udp   # create attach session helper to src;

        set rcvr [new Agent/NULL]        # configure the receiver;
        $ns attach-agent $node $rcvr
        $ns at 0.0 "$node join-group $rcvr $group" # joining the session;

        $ns at 0.1 "$src start"

A session level simulation scales by translating the topology into a virtual mesh topology. The steps involved in doing this are:

1. All of the classifiers and replicators are eliminated. Each node only stores instance variables to track its node id, and port ids.
2. Links do not consist of multiple components. Each link only stores instance variables to track the bandwidth and delay attributes.
3. The topology, consisting of links is translated into a virtual mesh.

Figure 45.1: Comparison of Multicast Trees for Detailed vs. Session Routing

Figure 45.1 shows the difference between a multicast tree in a detailed simulation and one in a session level simulation. Notice that the translation process results in a session level simulation ignoring queuing delays. For most simulations, ns already ignores processing delays at all of the nodes.