5.1 Node Basics

The basic primitive for creating a node is

    set ns [new Simulator]
    $ns \fcnref{\textbf{node}}{../ns-2/ns-lib.tcl}{Simulator::node}

The instance procedure node constructs a node out of more simple classifier objectsSectionsec:node:classifiers. The Node itself is a standalone class in OTcl. However, most of the components of the node are themselves TclObjects. The typical structure of a (unicast) node is as shown in Figure 5.1. This simple structure consists of two TclObjects: an address classifer (classifer_) and a port classifier (dmux_). The function of these classifiers is to distribute incoming packets to the correct agent or outgoing link.

Figure 5.1: Structure of a Unicast Node. Notice that entry_ is simply a label variable instead of a real object, e.g., the classifier_.

All nodes contain at least the following components:

• an address or id_, monotonically increasing by 1 (from initial value 0) across the simulation namespace as nodes are created,
• a list of neighbors (neighbor_),
• a list of agents (agent_),
• a node type identifier (nodetype_), and
• a routing module (described in Section 5.5 below)

By default, nodes in ns are constructed for unicast simulations. In order to enable multicast simulation, the simulation should be created with an option ``-multicast on'', e.g.:

        set ns [new Simulator -multicast on]

The internal structure of a typical multicast node is shown in Figure 5.2.

Figure 5.2: Internal Structure of a Multicast Node.

When a simulation uses multicast routing, the highest bit of the address indicates whether the particular address is a multicast address or an unicast address. If the bit is 0, the address represents a unicast address, else the address represents a multicast address.