[ns] RNG ( seed )

[maram al3asal]

hi all,could some one please explains to me why we need to use random variables RNG or seedI am confused . I read that some times we need them to generate random variables to use it in sending traffic but i dont how this is happeninghere is the example i have(partial):
	.	.set base_seed‭         [‬lindex‭ $‬argv 0‭];	.	.	.global defaultRNG‭$‬defaultRNG seed predef‭ $‬base_seed	.	.	.	.	.
‭#‬set up BE uplink flowsset be_ul_sink‭ [‬new Agent/LossMonitor‭]‬‭$‬ns‭_ ‬attach-agent‭ $‬W‭ $‬be_ul_sinkfor‭ {‬set j‭ $‬be_init‭} {$‬j‭ < $‬be_end‭} {‬incr j‭} {‬‭    ‬set be_tcp_ul‭_($‬j‭) [‬new Agent/TCP‭]‬‭    $‬ns‭_ ‬attach-agent‭ $‬node‭_($‬j‭) $‬be_tcp_ul‭_($‬j‭)‬‭    $‬ns‭_ ‬connect‭ $‬be_tcp_ul‭_($‬j‭) $‬be_ul_sink
‭    ‬set be_ftp_ul‭_($‬j‭) [‬new Application/FTP‭]‬‭    $‬be_ftp_ul‭_($‬j‭) ‬attach-agent‭ $‬be_tcp_ul‭_($‬j‭)‬‭ ‬‭}‬
‭# ‬random number generatorset gna_be_ul‭ [‬new RNG‭]‬‭$‬gna_be_ul seed predef‭ [‬expr‭ $‬base_seed‭ + ‬5‭]‬
for‭ {‬set j‭ $‬be_init‭} {$‬j‭ < $‬be_end‭} {‬incr j‭} {‬‭    ‬set stime‭ [‬expr 0.1‭ + [$‬gna_be_ul uniform 0‭ ‬1‭]]‬‭    $‬ns‭_ ‬at‭  $‬stime‭  "$‬be_ftp_ul‭_($‬j‭) ‬start‭"‬‭}‬	.	.
What is this  seed, RNG , uniform ant its parameters. and what is the result from using this.
Regards,Maram		
 		 	   		  
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