[ns] help needed

[Nikheel Kumar]

*hi friends,

following is the code for TCP connection that shares a noisy bottle link
with a UDP connection.*

set ns [new Simulator]
$ns color 1 Blue
$ns color 2 Red

#open the NAM trace file
set nf [open first_out.nam w]
$ns namtrace-all $nf

#open the trace file
set tf [open first_out.tr w]
set windowVsTime2 [open WindowVsTimeNReno w]
$ns trace-all $tf

#define a 'finish' procedure
proc finish {} {
    global ns nf tf
    $ns flush-trace
    close $nf
    close $tf
    exec nam first_out.nam &
    exit o
}

#creating four nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]

$ns at 0.1 "$n1 lable \"CBR\""
$ns at 1.0 "$n0 lable \"FTP\""

#create links between the nodes
$ns duplex-link $n0 $n2 2Mb 10ms DropTail
$ns duplex-link $n1 $n2 2Mb 10ms DropTail
$ns simplex-link $n2 $n3 0.07Mb 20ms DropTail
$ns simplex-link $n3 $n2 0.07Mb 20ms DropTail

#set queue size of link (n2-n3) to 10
$ns queue-limit $n2 $n3 10

#Monitor the queue for link (n2-n3) (for NAM)
$ns simplex-link-op $n2 $n3 queuePos 0.5

#set error model on link n3 to n2
set loss_module [new ErrorModel]
$loss_module set rate_ 0.2
$loss_module ranvar [new RandomVariable/Uniform]
$loss_module drop-target [new Agent/Null]
$ns lossmodel $loss_module $n2 $n3

#setup a tcp connection
set tcp [new Agent/TCP/Newreno]
$ns attach-agent $n0 $tcp
set sink [new Agent/TCPSink/DelAck]
$ns attach-agent $n3 $sink
$ns connect $tcp $sink
$tcp set fid_ 1

#set ftp over tcp connection
set ftp [new Application/FTP]
$ftp attach-agent $tcp
$ftp set type_ FTP

#setup a UDP connection
set udp [new Agent/UDP]
$ns attach-agent $n1 $udp
set null [new Agent/Null]
$ns attach-agent $n3 $null
$ns connect $udp $null
$udp set fid_ 2

#setup a CBR over UDP connection
set cbr [new Application/Traffic/CBR]
$cbr attach-agent $udp
$cbr set type_ CBR
$cbr set packet_size_ 1000
$cbr set rate_ 0.01mb
$cbr set random_ false

#schedule events for the CBR anf ftp agents
$ns at 0.1 "$cbr start"
$ns at 1.0 "$ftp start"
$ns at 624.0 "$ftp stop"
$ns at 624.5 "$cbr stop"

#printing the window size
proc plotWindow {tcpSource file} {
    global ns
    set time 0.01
    set now [$ now]
    set cwnd [$tcpSource set cwnd_]
    puts $file "$now $cwnd"
    $ns at [expr $now+$time] "plotWindow $tcpSource $file" }
$ns at 1.1 "plotWindow $tcp $windowVsTime2"

#sample the bottleneck queue every 0.1 sec. store the trace in qm.out
set qmon [$ns monitor-queue $n2 $n3 [open qm.out w] 0.1];
[$ns link $n2 $n3] queue-sample-timeout; # [$ns link $n2 $n3] start-tracing

#detach tcp and sink agent (not really necessary)
$ns at 624.5 "$ns detach-agent $n0 $tcp ; $ns detach-agent $n3 $sink"

$ns at 625.0 "finish"
$ns run

*during running the above tcl scrit it gives following error:
*
$ns first.tclp
ns: _o13 lable "CBR":
    (_o13 cmd line 1)
    invoked from within
"_o13 cmd lable CBR"
    invoked from within
"catch "$self cmd $args" ret"
    invoked from within
"if [catch "$self cmd $args" ret] {
set cls [$self info class]
global errorInfo
set savedInfo $errorInfo
error "error when calling class $cls: $args" $..."
    (procedure "_o13" line2)
    (SpliiObjest unknow line 2)
    invoked from within
"_o13 lable "CBR""

*what is this is this error*