4.1 Simulator Initialization

When a new simulation object is created in tcl, the initialization procedure../ns-2/ns-lib.hSimulator::init performs the following operations:

• initialize the packet format (calls create_packetformat)
• create a scheduler (defaults to a calendar scheduler)
• create a ``null agent'' (a discard sink used in various places)

The packet format initialization sets up field offsets within packets used by the entire simulation. It is described in more detail in the following chapter on packetsChapterchap:pformat. The scheduler runs the simulation in an event-driven manner and may be replaced by alternative schedulers which provide somewhat different semantics (see the following section for more detail). The null agent is created with the following call:

        set nullAgent_ [new Agent/Null]

This agent is generally useful as a sink for dropped packets or as a destination for packets that are not counted or recorded.