Simple ns2 script(Example)

Basically NS 2 programming contains the following steps.                                                                                    

1.Create the event scheduler

2.Turn on tracing

3.Creating network

            a) Computing setup routing - rtproto
            b) Creating transport connection-Agents
            c) Creating traffic-Applications

4. Monitoring

         a) Visualization using nam

Note: every tcl script must write in small letters only except protocol agents i.e. TCP, FTP,UDP

Example 

Every ns2 script starts with creating simulator object  
               
                    set ns [new Simulator] 

How to create node                                               
                      
                    set n0 [$ns node]
                    set n1 [$ns node]       
Creating link  
                 
                  $ns duplex-link $n0 $n1 1Mb 10ms DropTail

        This line tells the simulator object to connect the nodes n0 and n1 with a duplex link with the bandwidth.1Megabit,  a delay of 10ms and a DropTail queue.       

·  How to use Trace?

   We use simulator to see results. How is it achieved? Using trace

         Two types of trace

             1. generic trace
                       for use with xgraph, and other things

             2. nam trace
                        for use with visualization

                  # open trace file
                   set tracefile [open out.tr w]
                   $ns trace-all $tracefile

                  #Open the nam trace file
                  set nf [open out.nam w]
                  $ns namtrace-all $nf

       Since we have started tracing, we should end also. For this we use finish procedure.

   #Define a 'finish' procedure
            proc finish {}
            {
                   global ns tracefile nf
                   $ns flush-trace
                   close $nf
                   close $tracefile          # close tracefile
                   exec nam out.nam &   #Execute nam on the trace file
                   exit 0
            }

 Finish procedure is forced to be called at the end with the line
            $ns at 5.0 “finish”

 Every tcl script must contain following statement

              $ns run