1. Internet Computing Laboratory @ KUT Youn-Hee Han
NS2 Tutorial – Part I
Internet Computing KUT
Youn-Hee Han

2. VINT and NS (Network Simulator)
Virtual InterNet Testbed
a collaborative project between USC/ISI, LBL/UC Berkeley, and Xerox PARC
Goal
to extend the ns simulator so that network researchers can study the complex interactions between network protocols (e.g., unicast routing, multicast routing, TCP, reliable multicast, integrated services, etc.) in complex topologies and with a rich set of traffic generators.
ISI/USC: University of Southern California/Information Sciences Institute
LBL/UC Berkeley: Lawrence Berkeley National Laboratory/University of California, Berkeley
Data Structure

3. What is NS? http://www.isi.edu/nsnam
NS version2 is a discrete-event driven and object-oriented network simulator
Events  Packet and Timer
Characteristics
Freely distributed and open source
Discrete event simulator
Packet-level Event
Wired and wireless
Network Stacks from Layer 1 to Layer 7
Node mobility
Data Structure

4. What is NS? History Columbia NEST UCB REAL ns-1 ns-2 100K lines of C++
Modified from REAL network simulator
ns-2
100K lines of C++
70K lines of OTcl
30K lines of test suite
20K lines of documentation
Data Structure

5. Functionality of NS Wired world Wireless
Point-to-point link, LAN
Unicast/multicast routing
QoS
Intserve, Diffserv
Transport
TCP, UDP
Congestion control
Application layer
Web Caching
Mulimedia
Wireless
Mobile IP
Ad hoc routing
Tracing, visualization, various utilities
Data Structure

6. NS Flatform Most UNIX and UNIX-like systems Window 95/98/NT
Linux
It is preferred
Remote access with Xmanager
FreeBSD or NetBSD
Sun Solaris
Window 95/98/NT
with Cygwin
Some of features are not supported
Emulation only for FreeBSD for now
VMWare
Window host
Linux guest
Data Structure

7. NS Components ns-2 nam NS – Simulator NAM – Network AniMator
visual demonstration of NS output
Preprocessing
Handwritten TCL or
Topology generator
Post analysis
Trace analysis using Perl/TCL/AWK/GnuProt/MATLAB
We just saw this…
Now I will show you this…
tcl script
(specification
of experiment)
ns-2
trace file
(output)
nam
Data Structure

8. Current Status Users from approximately Releases 600 institutes
50 countries
Releases
Periodic releases (currently 2.29_3)
NS3 project just started (July 1, 2006)
Available from: USC (University of Southern California)/ISI (Information Sciences Institute), UC Berkeley, UK mirror
Data Structure

9. NS2 Language NS2 is written in C++ and OTcl
OTcl = Tcl + OO
C++ implements the code that executed frequently
It implements the system behavior of NS2 (e.g., routing)
OTcl configures the system (e.g., topology).
Object-oriented (C++, OTcl)
Fine-grained object composition
Modular approach
Data Structure

10. C++ and OTcl Separation
C++ for “data/behavior”
NS2 Core & packet processing
Fast Execution
Good for…
Frequent Access & Less Compilation
OTcl for “control”
Periodic or triggered action
Simulation Scenario setup
Less Access & Frequent Configuration
Pros.
Compromise between composibility and speed
Cons.
Learning and debugging
Data Structure

11. OTcl and C++: The Duality
Pure C++
objects
Pure OTcl
objects
C++/OTcl split objects
C++
OTcl ns
Data Structure

12. OTcl and C++: The Duality
Simulation Scenario 1 2
set ns_ [new Simulator]
set node_(0) [$ns_ node]
set node_(1) [$ns_ node]
Tcl Script
class MobileNode : public Node {
friend class PositionHandler;
public:
MobileNode(); • }
C++ Implementation
Data Structure

13. Object Correspondence
Agent/DSDV
Constructor
Agent
Constructor
Invoke parent
TclObject
Constructor
Invoke parent
AgentDSDV()
Constructor
Create C++
init complete
init complete
OTcl shadow
TCL
C++
TclObject()
Constructor
Invoke parent
Do nothing,
return
Agent()
Constructor
Invoke parent
bind and return
bind and return
Data Structure

14. User’s Perspective
From the user’s perspective, NS−2 is an OTcl interpreter that takes an OTcl script as input and produces a trace file as output
Data Structure

15. Extending Tcl Interpreter
Otcl
object-oriented Tcl
TclCL (Tcl with classes)
C++ and OTcl linkage
Discrete event scheduler
Data network components
Link layer and up
Emulation support
Event
Scheduler
Network
Components
TclCL
OTcl
Tcl
C/C++
ns-2
Data Structure

16. Discrete event simulator
ns-2 is an discrete event driven simulation
Physical activities are translated to events
Events are queued and processed in the order of their scheduled occurrences
Time progresses as the events are processed
Time: 1.5 sec
Time: 1.7 sec 1 2
Time: 2.0 sec
Time: 1.8 sec
Data Structure

17. Using NS2 Problem Result Simulation Modify analysis model ns Setup/run
with ns
Data Structure

18. OTcl overview
programming language used for setting up simulation environment
object oriented
interpreted (slow)
Used for
Setting up topology
Placing agents
Injecting events
Configuring tracing
Examples:
variables
set x 10
puts “x is $x”
expressions
set y [pow x 2]
set y [expr x+x*3]
control
if ($x>0) { return $x } else { return [expr -$x] }
while ($x >0) { puts $x
set x [eval x+1] }
Data Structure

19. OTcl overview
programming language used for setting up simulation environment
object oriented
interpreted (slow)
Used for
Setting up topology
Placing agents
Injecting events
Configuring tracing
Examples:
variables
set x 10
puts “x is $x”
expressions
set y [pow x 2]
set y [expr x+x*3]
control
if ($x>0) { return $x } else { return [expr -$x] }
while ($x >0) { puts $x
set x [eval x+1] }
Data Structure

20. Basic ns-2 Create scheduler Create node Create link Schedule event
set ns [new Simulator]
Create node
set <var> [$ns node]
example: set n0 [$ns node]
Create link
$ns <link-type> <node1> <node2> <bandwidth> <delay> <queuetype>
example: $ns duplex-link $n0 $n1 10Mb 100ms DropTail
Schedule event
$ns at <time> <event>
example: $ns at 10.0 “$ftp start”
Start scheduler
$ns run
Data Structure

21. The 1st ns-2 script (two nodes, one link)
set ns [new Simulator]
set nf [open out.nam w]
$ns namtrace-all $nf
proc finish {} {
global ns nf
$ns flush-trace
close $nf
exec nam out.nam &
exit 0 }
$ns at 5.0 "finish"
$ns run
Create the simulator object
Open a file for nam trace data
“finish” procedure
Closes the trace file and starts nam
Execute the finish procedure after 5.0 seconds
Data Structure

22. The 1st ns-2 script (two nodes, one link)
set n0 [$ns node]
set n1 [$ns node]
$ns duplex-link $n0 $n1 1Mb 10ms DropTail
Creates two nodes and assigns them to the handle “n0” and “n1”
connect the nodes n0 and n1 with a duplex link with the bandwidth 1Megabit, a delay of 10ms and a DropTail queue
Data Structure

23. The 1st ns-2 script (two nodes, one link)
set udp0 [new Agent/UDP]
$ns attach-agent $n0 $udp0
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 500
$cbr0 set interval_ 0.005
$cbr0 attach-agent $udp0
set null0 [new Agent/Null]
$ns attach-agent $n1 $null0
$ns connect $udp0 $null0
Create a UDP agent and attach it to node n0
Create a CBR traffic source and attach it to udp0
Create a Null agent and attach it to node n1
Connect the two agents
Data Structure

24. The 1st ns-2 script (two nodes, one link)
$ns at 0.5 "$cbr0 start"
$ns at 4.5 "$cbr0 stop"
tell the CBR agent when to send data and when to stop sending
Data Structure

25. The 2nd ns-2 script (three nodes, two links)
set ns [new Simulator]
set nf [open out.nam w]
$ns namtrace-all $nf
proc finish {} {
global ns nf
$ns flush-trace
close $nf
exec nam out.nam &
exit 0 }
$ns at 10.0 "finish"
$ns run
Create the simulator object
Open a file for nam trace data
“finish” procedure
Closes the trace file and starts nam
Execute the finish procedure after 10.0 seconds
Data Structure

26. The 2nd ns-2 script (three nodes, two links)
Creates three nodes and assigns them to the handle “n0”, “n1”, and “n1”
#Create three nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
#Create link between the nodes
$ns duplex-link $n0 $n1 4Mb 10ms DropTail
$ns duplex-link $n2 $n1 1Mb 10ms DropTail
$ns queue-limit $n1 $n2 10
connect the nodes n0 and n1 with a duplex link with the bandwidth 4Megabit, a delay of 10ms and a DropTail queue
connect the nodes n0 and n2 with a duplex link with the bandwidth 1Megabit, a delay of 10ms and a DropTail queue
the maximum buffer size (#packets) of the queue in the link n0 n1 n2
Data Structure

27. The 2nd ns-2 script (three nodes, two links)
#Create a TCP agent and attach it to node n0
set tcp0 [new Agent/TCP]
$ns attach-agent $n0 $tcp0
#Create a TCP sink agent and attach it to node n2
set sink [new Agent/TCPSink]
$ns attach-agent $n2 $sink
#Connect both agents
$ns connect $tcp0 $sink
# create an FTP source
set ftp [new Application/FTP]
$ftp set maxpkts_ 1000
$ftp attach-agent $tcp0
#Inject starting events
$ns at 0.0 "$ftp start"
$ns at 10.0 "$ftp stop"
$ns at 10.1 "finish"
#Run the simulation
$ns run
Create a TCP agent and attach it to node n0
Create a TCP sink and attach it to node n2
Connect the two agents
Create a FTP application and attach it to agent tcp0
The maximum number of packets generated by the source.
ftp
tcp
tcp-sink n0 n1 n2
Data Structure