# First NS2 Program
#Create a simulator object
set ns [new Simulator]
#Define different colors for data flows (for NAM)
$ns color 1 Blue
$ns color 2 Red
#Open the NAM trace file
set nf [open out.nam w]
$ns namtrace-all $nf
set tf [open out.tr w]
$ns trace-all $tf
#Define a 'finish' procedure
proc finish {} {
global ns nf
$ns flush-trace
#Close the NAM trace file
close $nf
#Execute NAM on the trace file
exec nam out.nam &
#it is used to execute nam file on trace file ,no need to execute trace file explicitely ,all results of nam file will be transfered to trace file
exit 0
}
#Create four nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
#Create links between the nodes
$ns duplex-link $n0 $n2 5Mb 10ms DropTail
$ns duplex-link $n1 $n2 5Mb 10ms DropTail
$ns duplex-link $n2 $n3 1.7Mb 20ms DropTail
#Set Queue Size of link (n2-n3) to 10
$ns queue-limit $n2 $n3 2
#Give node position (for NAM)
$ns duplex-link-op $n0 $n2 orient right-down
$ns duplex-link-op $n1 $n2 orient right-up
$ns duplex-link-op $n2 $n3 orient right
#Monitor the queue for link (n2-n3). (for NAM)
$ns duplex-link-op $n2 $n3 queuePos 0.5
#Setup a TCP connection
#using these we are pointing to tcp agent which is object in ns
set tcp [new Agent/TCP]
#class_2 means traffic will be of vbr(variable bit rate) type
$tcp set class_ 2
#$tcp will be source node
$ns attach-agent $n0 $tcp
set sink [new Agent/TCPSink]
#$sink that will be destination node
$ns attach-agent $n3 $sink
$ns connect $tcp $sink
#fid means color id
$tcp set fid_ 1
#Setup a FTP over TCP connection
#by default ftp will be using tcp connection
set ftp [new Application/FTP]
$ftp attach-agent $tcp
#it is important to define explicitly set type using type_ftp
$ftp set type_ FTP
#Setup a UDP connection
set udp [new Agent/UDP]
$ns attach-agent $n1 $udp
#ending node wll be always null for udp as there is no destination for 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
#1000 bits/second
$cbr set packet_size_ 1000
#rate of transfer or bandwidth
$cbr set rate_ 1mb
#to send packets in random order
$cbr set random_ false
#Schedule events for the CBR and FTP agents
#at 0.1 second start cbr appllication
#$ns at <time> <event>
$ns at 0.1 "$cbr start"
$ns at 1.0 "$ftp start"
$ns at 4.0 "$ftp stop"
$ns at 4.5 "$cbr stop"
#scheduler is started when we will run ns i.e. through $ns run
#Detach tcp and sink agents (not really necessary)
#after 4.5 second detach agent from tcp
$ns at 4.5 "$ns detach-agent $n0 $tcp ; $ns detach-agent $n3 $sink"
#Call the finish procedure after 5 seconds of simulation time
$ns at 5.0 "finish"
#Print CBR packet size and interval
#puts is command for showing something on console view
puts "CBR packet size = [$cbr set packet_size_]"
puts "CBR interval = [$cbr set interval_]"
#Run the simulation
$ns run
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Tool Command Language(TCL) is a general purpose scripting language which is commonly used for GUIs and for testing. Everything is by default string in TCL. It was created by John Osterhout in 1989.
Variable is a identifier which is used to hold the value. set is used to create variables.
set name onecompiler
When ever you want to perform a set of operations based on a condition IF-ELSE is used.
if(conditional-expression) {
#code
} else {
#code
}
You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.
Switch is an alternative to If-Else-If ladder.
switch(conditional-expression) {
value1 {
# code
}
value1 {
# code
}
...
default {
# code
}
For loop is used to iterate a set of statements based on a condition.
for{start}{test}{next}{
# code
}
While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while(condition) {
# code
}
Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.
set ArrayName(Index) value
Procedure is a sub-routine which contains set of statements. Uusually procedures are required when multiple calls are made to same set of statements. Procedures increases re-usuability and modularity.
proc procedureName {arguments} {
# code
}