[ns] Changing TCP window (and sat parameter qlim) doesn't affect simulation results (?!)

[Giuseppe Tringali <gtringali@katamail.com>]

Hi all,

I have made  these changes to the script sat-repeater.tcl that comes with NS.

set opt(bw_up)          2Mb;  --->  set opt(bw_up)              10Mb;

set tcp1 [$ns create-connection TCP $n2 TCPSink $n3 0] ---> set tcp0 [$ns 
create-connection TCP/Newreno $n2 TCPSink $n3 0]

$ns at 7.0 "$ftp1 produce 100"  --->  $ns at 7.0 "$ftp1 start"

I have also written a simple script in AWK to calculate the throughput. 
According to this script the throughput is very low.
(few hundreds of kb/s) Is it correct or is the script wrong?
Probably the script is wrong but
I really don't understand why changing TCP window, $tcp1 set window_ .... 
all you want, I don't see any difference in the results. Please, help me.


I have also modified the parameter qlim. As reported in the manual, it's 
the length of the interface queue, in packet. If I have understood well the 
figure 17.3 of the manual, this queue is between Mac and LL, so these 
packets are in other words frames. However I haven't seen particular 
changes in the simulation results. Is it correct? I have made a mistake 
..., I haven't understood something ...
Please tell me something


And if the throughput is low, what can I do to increase it?

Below you can find the AWK script.

Any help is appreciated. Thank you in advance,

Giuseppe Tringali

OS: Linux Red Hat 6.2
NS: ns-allinone-2.1b6
AWK: GNU Awk 3.0.4


BEGIN {slot = 0.5; bytes_counter = 0; t_sampling = 0.5;}
{
    action = $1;
    time = $2;
    node_1 = $3;
    node_2 = $4;
    size = $6;
    type = $5;

    if ( (action == "r") && (node_2 == "2") && (type == "tcp") ) {

         if ( time <= t_sampling) bytes_counter = bytes_counter + size;

         if ( time > t_sampling) {
                                 th = ( (bytes_counter * 8) / (1000000 * 
slot) );
                                 printf("%f %f\n", t_sampling, th);
                                 bytes_counter = size;
                                 t_sampling = t_sampling + slot;
                                 }
         }
}
END { }