[ns] Problem: very low throughput on a satellite link

[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;

$ns at 7.0 "$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)
I have tried to increase the TCP window size and to use TCP New Reno but 
the result is the same.
Is it correct or is the script wrong? 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 { }