[ns] How to schedule an event in a proc

[haicheng flammy]

Hi there,
 
I want to schedule the UDP to send data at specified time.  but all of the event [$src send 1000] happened at time 0.   Why?  How can I do it?

 
set ns [new Simulator]
set tf [open out.tr w]
$ns trace-all $tf

set n1 [$ns node]
set n2 [$ns node]
set link [$ns simplex-link $n1 $n2 100kb 0ms DropTail]
set src [new Agent/UDP]
$ns attach-agent $n1 $src

proc finish {} {
 global ns tf
 $ns flush-trace
 close $tf
 exit 0
}
proc sendpacket {} {
 global ns src 
 $ns at 1.0 [$src send 1000]
 $ns at 2.0 [$src send 1000]
 $ns at 3.0 [$src send 1000]
 $ns at 4.0 [$src send 1000]
 $ns at 5.0 [$src send 1000]
 
}
set sink [new Agent/Null]
$ns attach-agent $n2 $sink
$ns connect $src $sink
$ns at 0 "sendpacket"
$ns at 10.0 "finish"
$ns run


		
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