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Introduction to NS
Information
• Main website http://www.isi.edu/nsnam/
• Documentation, mailing list archive, tutorial
• Location of Source codes– C++ files
• $NS-HOME/ns-allinone-2.28/ns-2.28
– Tcl files• $NS-HOME/ns-allinone-2.28/ns-2.28/tcl/lib
NS2 – Network Simulator
• Event-Driven simulator– Maintain a sorted event queue – Dequeue head event
• Packet arrival
– Assign event to its handler • At TCP agent
– Handler processes event• Update Window
– Enqueue more events in the event queue• Schedule delivery of ACK
Basic Model
• Back-end C++– Protocols & Framework
• Front-end Otcl (Object-Oriented Tcl)– Scenarios
• Split Object– Object created in otcl has a corresponding object in
C++
• This tutorial only deals with otcl
Tcl/OTcl Basics• Variables
– set v1 10 – set v2 $v1
• Array (String indexed)– a($i) ≠ a( $i )
• Printing– puts $filename “string” (default filename is stdout)
• Arithmetic Expressions– set value [expr $v1+($v2 * 5.2)]
• Control Structures– if {condition} then {…….}– for {set i 0} {$i < 10} {incr i 2} {……}
• Procedures– proc proc_name {arg1 arg2…} { ……}
OTcl Basics (contd.) • Creating a class
– Class class_name– Class class_name –superclass Base_class
• Defining instance procedures– class_name instproc proc_name {args} {…..}
• Defining instance variables– $self instvar variable_name (inside a class method)
• Creating an instance– set new_inst [new class_name]
• Using value of an instance variable– $new_inst set v1 10 or set v2 [$new_inst set v1]
NS Communication Model
• Nodes– Hosts, Routers
• Links– Queue Management
– Queue Monitoring
• Agents– Protocol
1 2
3
4 5
TCP
TCP Sink
Node
n0
Addr Classifier
Port Classifier
classifier_
dmux_
entry_
Node entry
Unicast Node
Link 1
Link 2
Slide taken from Hung-Yun Hsieh’s
tutorial
Link
n0 n1
enqT_ queue_ deqT_
drophead_ drpT_
link_ ttl_
n1 entry_
head_
tracing simplex link
duplex link
Slide taken from Hung-Yun Hsieh’s
tutorial
Routing
n0 n1
Addr Classifier
Port Classifier
classifier_
dmux_
entry_
Node entry 0
1 enqT_ queue_ deqT_
drophead_ drpT_
link_ ttl_
n1 entry_
head_
Slide taken from Hung-Yun Hsieh’s
tutorial
Routing
n0 n1
Port Classifier
entry_
Addr Classifier
classifier_
dmux_1
0
Addr Classifier
Port Classifier
classifier_
dmux_
entry_
0
1 Link n0-n1
Link n1-n0
Slide taken from Hung-Yun Hsieh’s
tutorial
Transport
0
1
n0 n1
Addr Classifier
Port Classifier
classifier_
dmux_
entry_
0 Agent/TCP
agents_
Addr Classifier
Port Classifier
classifier_
dmux_
entry_
1
0Link n0-n1
Link n1-n0
0 Agent/TCPSink
agents_
dst_= 1.0 dst_= 0.0
Slide taken from Hung-Yun Hsieh’s
tutorial
Application
0
1
n0 n1
Addr Classifier
Port Classifier
classifier_
dmux_
entry_
0 Agent/TCP
agents_
Addr Classifier
Port Classifier
classifier_
dmux_
entry_
1
0Link n0-n1
Link n1-n0
0 Agent/TCPSink
agents_
dst_=1.0 dst_=0.0
Application/FTP
Slide taken from Hung-Yun Hsieh’s
tutorial
Packet Flow
0
1
n0 n1
Addr Classifier
Port Classifier
entry_
0 Agent/TCP Addr Classifier
Port Classifier
entry_
1
0Link n0-n1
Link n1-n0
0 Agent/TCPSink
dst_=1.0 dst_=0.0
Application/FTP
Slide taken from Hung-Yun Hsieh’s
tutorial
Starting off…
• Things common to all simulation scripts:• Create a new simulator object
set ns [new Simulator]
• Finish procedureproc finish { } { …….. exit 0}
• Last line $ns run
Basic Script
set ns [new Simulator]proc finish { } {
exit 0}
• Topologyset n1 [$ns node]set n2 [$ns node]$ns duplex-link $n1 $n2 1Mb
10ms DropTail
• Agentsset a1 [new Agent/TCP]set a2 [new Agent/TCPSink]
• Attach and Connect Agents
$ns attach-agent $n1 $a1
$ns attach-agent $n2 $a2
$ns connect $a1 $a2
• Start and Finish Time$ns at 0.5 “$a1 advance 10”
$ns at 1.5 “finish”
$ns run
A more useful scriptset ns [new Simulator]set nam_file [open out.nam w]$ns namtrace-all $nam_file
proc finish {} {global ns nam_file
$ns flush-trace close $nam_file
exec nam out.nam & exit 0}
set n1 [$ns node]set n2 [$ns node]$ns duplex-link $n1 $n2 1Mb
10ms DropTail
set a1 [new Agent/TCP]
set a2 [new Agent/TCPSink]
$ns attach-agent $n1 $a1
$ns attach-agent $n2 $a2
$ns connect $a1 $a2
$ns at 0.5 “$a1 advance 10”
$ns at 1.5 “finish”
$ns run
Recording Data
• Add a new procedure
proc record-data { duration } {global datafile a1 ns# data format -- time bytes-receivedputs $datafile “[$ns now] [$a1 set
ndatabytes_]”$ns after $duration “record-data $duration”
}
set datafile [open “datafile.dat” w]$ns at 0.5 “record-data 0.1”
More Complex Case
• Bottleneck Link
Topology
for {set i 0} {$i < 4} {incr i} {set border($i) [$ns node]
}
for {set i 0} {$i < 2} {incr i} {set core($i) [$ns node]
}
$ns duplex-link $border(0) $core(0) 10Mb 5ms DropTail$ns duplex-link $border(1) $core(0) 10Mb 5ms DropTail$ns duplex-link $border(2) $core(1) 10Mb 5ms DropTail$ns duplex-link $border(3) $core(1) 10Mb 5ms DropTail$ns duplex-link $core(0) $core(1) 1Mb 5ms DropTail$ns queue-limit $core(0) $core(1) 20set qmon [$ns monitor-queue $core(0) $core(1) “”]
Agentsset tcp [new Agent/TCP]
$ns attach-agent $border(0) $tcp
set tcpsink [new Agent/TCPSink]
$ns attach-agent $border(3) $tcpsink
set udp [new Agent/UDP]
$ns attach-agent $border(1) $udp
set lm [new Agent/LossMonitor]
$ns attach-agent $border(2) $lm
$tcp set fid_ 0
$udp set fid_ 1
$ns color 0 Red
$ns color 1 Blue
Sources
• Attach traffic source to agents and connect
set cbr [new Application/Traffic/CBR]
$cbr attach-agent $udp
$cbr set rate_ 2Mb
set ftp [$tcp attach-app FTP]
$tcp set packetSize_ 100
$ns connect $tcp $tcpsink
$ns connect $udp $lm
Data Collection
proc record-data { duration } {global ns tcp tcp_file lm udp_file queue_file qmon
puts $tcp_file “[$ns now] [expr [$tcp set ndatabytes_]/$duration]”$tcp set ndatabytes_ 0
puts $udp_file “[$ns now] [expr [$lm set bytes_]/$duration]”$lm set bytes_ 0
puts $queue_file “[$ns now] [$qmon set pkts_]”$ns after $duration “record-data $duration”
}
Other detailsset ns [new Simulator]
# Nam, TCP-data, UDP-data, Queue-data files# Finish method# Topology# Agents# Sources# Data Collection
$ns at 0.1 “$ftp start”$ns at 4.0 “$ftp stop”$ns at 1.0 “$cbr start”$ns at 2.0 “$cbr stop”$ns at 0.1 “record-data 0.1”$ns at 4.1 “finish”$ns run
Things to Remember
• Topology, agents, sources, start
• Connect the agents– Slot not found error
• Start/Stop the sources
• In procedures, declare global variables before use
• “$ns run” – last line
