Each network node of the simulation stands in truth not only for a single WAN router but also for a LAN connected to the WAN router. The router ``asks'' the hosts in his LAN if they are interested in the multicast data (IGMP)[Fen97]. If no host is interested the Router sends a prune message to the preceeding node in the multicast tree. Afterwards the data is no longer send to this router. After a certain time the pruning becomes invalid and the multicast data is flooded again into the network.
The prune button simulates the pruning process described in the DVMRP standard. Click on the button and select a router you would like to send a prune message. This means that at this node no receiver has joined the session and therefore does not need the data packets any longer. The timout of the pruning is set to 5 multicast packages.
The pruning process is described in more detail in section [Den97, , ].
According to the lates version of DVMRP a node can actively ask for a multicast group which is currently pruned. The graft button allows to graft a node to the transmission tree. This means that this node was pruned before and now wants to join the session again.
The grafting process is described in more detail in section [Den97, , ].
After this short introduction you should start playing with the applet to understand the complex protocol. In the following section you will find a complete description of each AWT-element of the applet to help.