[ns] Question on Poisson Traffic

[wilson woon]

Hi all,

I'm doing a simulation on IEEE 802.15.4. I'm
simulating the MAC layer using poisson traffic. I'm
not sure of the purpose of the variable idle_time_ .
Can anyone tell me? Could it be delay time? Here's the
full declaration (from tcl script):

proc poissontraffic { src dst interval starttime } {
   global ns_ node_
   set udp($src) [new Agent/UDP]
   eval $ns_ attach-agent \$node_($src) \$udp($src)
   set null($dst) [new Agent/Null]
   eval $ns_ attach-agent \$node_($dst) \$null($dst)
   set expl($src) [new
Application/Traffic/Exponential]
   eval \$expl($src) set packetSize_ 70
   eval \$expl($src) set burst_time_ 0
   eval \$expl($src) set idle_time_ [expr
$interval*1000.0-70.0*8/250]ms	;# idle_time +
pkt_tx_time = interval
   eval \$expl($src) set rate_ 250k #250 kbps in 2.4
GHz ISM band
   eval \$expl($src) attach-agent \$udp($src)
   eval $ns_ connect \$udp($src) \$null($dst)
   $ns_ at $starttime "$expl($src) start"
}

I'm looking for the meaning of the line eval
\$expl($src) set idle_time_ [expr
$interval*1000.0-70.0*8/250]ms	;# idle_time +
pkt_tx_time = interval

THank you


		
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