Hi All, Thanks for the reply. I read the comment about minimum sample code to be presented. But I am posting all here. (I am not able to edit). The comments will be useful in understanding the code.

#!/usr/bin/perl
#
#Program to calculate end to end delay.
#
#1. Program reads the trace file, finds for combination of 's' source 
+event and 'AGT' packet type. 
#2. For this combination, the program takes the packet id and timestam
+p.
#3. Within the same file, the program searches for a combination of 'r
+' receive event and 'AGT' packet type.
#4. For this combination, the program takes the packet id and compares
+ with previous packet id. If they are same, timestamp is noted.
#5. Difference between step 4 timestamp and step 3 timestamp gives the
+ end to end delay for that packet.
#6. Delays are aggregated and average delay is found.
#

#use strict;
use warnings;

$SIG{INT} = sub {
    my (@stack, $level);
    while(1)
    {
        my ($pkg, $fn, $ln, $sub) = caller($level++);
        if (!($pkg or $fn or $ln or $sub)) {
            for (my $i = 0; $i < @stack; $i++) {
                print " " x $i, $stack[$i], "\n";
            }
            exit;
        }
        unshift @stack, "-> $pkg: $fn (line $ln) sub $sub";
    }
};

#Input trace file
my($infile) =$ARGV[0]; 

#Keep track of variables
my($enqueue_time) = 0;
my($receive_time) = 0;
my($packet_id) = 0;
my($delay) = 0;
my($total_receive_count) = 0;
my($sum_of_delay) = 0;
my($average_delay) = 0;
my($simulation_time) = 0;
my($file_position) = 0;
my (@x);

open(DATA,"<","$infile" ) || die "could't open $infile$!";

while(<DATA>)
{
    @x=split(' ');
    if(($x[0] eq 's') && ($x[3] eq 'AGT'))
    {
        $file_position = tell(DATA);
        $enqueue_time = $x[1];
        $packet_id = $x[5];
        while(<DATA>)
        {
===LINE 58:             @x=split(' ');
            if(($x[0] eq 'r') && ($x[3] eq 'AGT'))
            {
                if(($x[5] == $packet_id))
                {
                    $receive_time = $x[1];
                    $total_receive_count++;
                    $delay = $receive_time - $enqueue_time;
                    $sum_of_delay = $sum_of_delay + $delay;

                    #Following is for debug.
                    $delay = $delay * 1000;
                    print("\nDelay:$delay");

                    last;
                }
            }
        }
        #Continue to search for next 's' event from where the previous
+ 's' was found.
        #So move to the same line where previous 's' event was found.
====LINE 78:        seek(DATA,$file_position,SEEK_SET);
    }
    #While(<DATA>) takes care of moving to the next line.
}

$simulation_time = $x[1];

print("\n Simulation Time = $simulation_time seconds");
print("\n Total Receive Count = $total_receive_count");

if($total_receive_count != 0 )
{
    $average_delay = $sum_of_delay / $total_receive_count;
    $average_delay = $average_delay * 1000;
    print("\n Average End to End Delay = $average_delay milliseconds")
+;
}
else
{
    print("\n No packet received.");
}

print("\n");
print("\n");
close DATA;
exit(0);
[download]

About the statements like "very quickly" "for some more time"...:
1. When I use a trace file with 800 lines, the script successfully completes without any problem.
2. When I use 80 MB trace file, it hangs. It stops within 12.456 seconds after invoking the script. stops at line 58. main: e2edelay.pl (line 58) sub main::__ANON__
3. When I use 100MB trace file, it hangs. It stops within 1.982 seconds after invoking the script. Stops at line 58. Same stack message.
4. When I use 107 MB trace file, it hangs. It stops within 0.4 seconds after invoking the script. Stops at line 58. Same stack message.

One comment: If the program works for small trace file, why it does not work for larger file?
Using "use strict" command throws error "Bareword "SEEK_SET" not allowed while "strict subs" in use at e2edelay.pl line 78."

I have marked line number in the code: LINE <num>

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