how events are scheduled

Hi,

In OTcl when you write any statement like
$ns at $stop "finish_proc"

then in scheduler.cc, it schedules the the 'finish_proc' (or anything u
want) to execute/run at time 'stop'.

In C++, you have to call the schedule method with the parameters (a handler,
a packet and delay), like here

Scheduler::instance().schedule(handler, packet, delay);

Basically, scheduler.cc is the main file that does all the scheduling
whenever called and then running one after other.

Hope it will help.

Shafiq


----- Original Message -----
From: "Savitri P. Pandharikar"
To:
Sent: Tuesday, December 05, 2006 10:30 PM
Subject: [ns] how events are scheduled


>
> Hi,
>
> I want to know more about NS-2 but I am still confused only about the
> event
> scheduler.I studied the NS manual also.But then also its not clear.Can
> please explain how events are scheduled one after another.
>
> Thanks
> Savitri P

tags : ns2 network simulator event schedule

Initialization of network simulator event

Things to remember when initialization of network simulator, Ns-2

When a new simulation object is created in tcl, the initialization procedure 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)

** Ns-2 is an event-driven simulator, therefore scheduler is a crucial component for simulation to determine all the events to be simulated accordingly.

There are 4 different types of scheduler that is created by using a different data structure:

1. a simple linked-list,
2. heap,
3. calendar queue (default)
4. and a special type called "real-time".

The actual definition of event is found is ~ns/scheduler.h

class Event {
public;
Event* next_; /* event list */
Handler* handler_; /* handler to call when event ready */
double time_; /* time at which event is ready */
int uid_; /* unique ID */
Event() : time_(0), uid_(0) {}
};
/*
* The base class for all event handlers. When an event’s scheduled
* time arrives, it is passed to handle which must consume it.
* i.e., if it needs to be freed it, it must be freed by the handler.
*/
class Handler {
public:
virtual void handle(Event* event);
};