NS2 - the network simulator which is proved useful in studying the dynamic nature of communication networks. Simulation of wired as well as wireless network functions and protocols( e.g. routing algorithms, TCP, UDP ) can be done using NS2

1. NETWORK SIMULATOR
(NS-2)
By
S.BHASEERUNNISHA
bhaseer21@gmail.com

2. TRANSPORT LAYER
 Flow Control and Error Control
 Two transport protocols.
* Transmission Control Protocol (TCP)
* User Datagram Protocol (UDP)

3. SYSTEM MODELLING APPROACH
 Analytical Approach - describe the system
mathematically, and apply numerical methods.
 Simulating Approach - recreates real-world
scenarios using computer programs and
simulation usually requires fewer simplification
assumptions.

4. PARTS OF GENERAL SIMULATION IN
COMPUTER NETWORKS
1. Planning
2. Implementing
a) Initialization
b) Result Generation
c) Post simulation Processing
3. Testing

5. SIMULATION PERFORMANCE
 Execution Speed
 Cost
 Fidelity
 Repeatability
 Scalability

6. EXAMPLES OF SIMULATION TOOL
The following are some of the widely used network
simulation tools:
• NS2
• GloMoSim
• QualNet
• Opnet
• MATLAB

7. SIMULATION TYPES
A. Time-Driven Simulation
B. Event-Driven Simulation

8. NS2
 NS2-Network Simulator (Version 2), widely known as
NS2, is simply an event-driven simulation tool that has
proved useful in studying the dynamic nature of
communication networks. Simulation of wired as well as
wireless network functions and protocols (e.g., routing
algorithms, TCP, UDP) can be done using NS2.

9. NS2 –TWO KEY LANGUAGES
 C++ - The internal mechanism (i.e., a backend) of the simulation
 Object-Oriented Tool Command Language (OTcL) - Sets up
simulation by assembling and configuring the objects as well as
scheduling discrete events (i.e., a frontend)
C++ and OTcL are linked together using TclCL

10. NS2 VISUALIZATION TOOL (NAM)

11. NS2 ANALYSIS TOOL (XGRAPH)

12. INSTALLATION OF NS2
 NS2 builds and runs under windows using Cygwin.
Cygwin provides Linux like environment under
windows.
 Download Cygwin from following link
http://www.cygwin.com/setup.exe

22. TERMINOLOGIES
1. The complied hierarchies
2. The Interpreted hierarchies
3. Upstream Object
4. Downstream Object

23. BASIC OF TCL

24. BASIC OPERATIONS
 Assignment: set <name> <value>
(e.g., set x 0)
 Deassignment: unset <name>
(e.g., unset x)
 Input: gets <channel> [<varname>]
(e.g., gets x)
 Output: puts [-nonewline] [<channel>] <str>
(e.g., puts $x)
 Error reporting: error <str>
(e.g., error "Fatal Error!!")

25. LOGICAL AND MATHEMATICAL OPERATIONS
Logical statement:
A <ops> B
operators <ops> is given below.
 < (less than) = (equal)
 <= (less than or equal) != (Not Equal)
 > (greater than) || (OR)
 >= (greater than or equal) && (AND)
 ! (negation)

26. Increment:
incr <varName> [<incrVal>]
Arithmetic operation:
expr A <ops> B
 Basic arithmetic operators <ops> are given below:
+ (addition) - (subtraction) * (multiplication)
/ (division) % (modulo)
 The advanced arithmetic operators <ops> are
shown below:
& (bitwise AND) | (bitwise OR)
<< (left shift) >> (right shift)
x?y:z (If x is nonzero, then y. Otherwise, z)

27. Mathematical function:
expr <fn>([<args>])
Mathematical functions <fn> are defined below:
abs(x) cosh(x) log(x) sqrt(x) acos(x) double(x)
log10(x) srand(x) asin(x) exp(x) pow(x,y)
tan(x) atan(x) floor(x) rand(x) tanh(x)
atan2(x) fmod(x) round(x) wide(x) ceil(x)
hypot(x,y) sin(x) cos(x) int(x) sinh(x)

28. CONTROL STRUCTURE
Selection Structure
if.. else, elseif ,and switch are the selection
structure.
Their syntaxes are shown below:
if {<condition1>} { <actionSet1> }
elseif {<condition2>} { <actionSet2> }
...
else { <actionSetN> }
switch <variable> {
<pattern_1> { <actionSet1> }
<pattern_2> { <actionSet2> }
...
default { <actionSetN> }
}

29. Repetition Structure
The commands “while,” “for,” and “foreach” are
used when actions need to be repeated for several
times.
 while {<condition>} { <actions> }
 for {<init>} {<condition>} {<mod>} { <actions> }
 foreach {<var>} {<list>} { <actions> }

30. Jumping Structure
The structure “break” and “continue” are used
to stop the iterative flow of the above “while,” “for,”
and “foreach” repetitive structures.

31. Packet tracing- records the detail of packet flow during a
simulation.
Packet tracing can be classified based on
1. Text Based Packet Tracing
2. NAM Packet Tracing
Text Based Packet Tracing
Text-based packet tracing records the detail of packets
passing through network checkpoints (e.g., nodes and queues).
it is invoked by
>>$ns trace-all $file

32. Network AniMation (NAM) Packet Tracing
Many visualization features are available in
NAM. These features are for example animating
colored packet flows, dragging and dropping nodes
(positioning), labeling nodes at a specified instant,
shaping the nodes, coloring a specific link, and
monitoring a queue.
It is Invoked by
>>nam filename.nam

33. EXAMPLE
# myfirst_ns.tcl
# Create a Simulator
1 set ns [new Simulator]
# Create a trace file
2 set mytrace [open out.tr w]
3 $ns trace-all $mytrace
# Create a NAM trace file
4 set myNAM [open out.nam w]
5 $ns namtrace-all $myNAM

34. # Define a procedure finish
6 proc finish { } {
7 global ns mytrace myNAM
8 $ns flush-trace
9 close $mytrace
10 close $myNAM
11 exec nam out.nam &
12 exit 0
13 }

35. # Create Nodes
14 set n0 [$ns node]
15 set n1 [$ns node]
16 set n2 [$ns node]
17 set n3 [$ns node]
18 set n4 [$ns node]
# Connect Nodes with Links
19 $ns duplex-link $n0 $n2 100Mb 5ms DropTail
20 $ns duplex-link $n1 $n2 100Mb 5ms DropTail
21 $ns duplex-link $n2 $n4 54Mb 10ms DropTail
22 $ns duplex-link $n2 $n3 54Mb 10ms DropTail
23 $ns simplex-link $n3 $n4 10Mb 15ms DropTail
24 $ns queue-limit $n2 $n3 40

36. # Create a UDP agent
25 set udp [new Agent/UDP]
26 $ns attach-agent $n0 $udp
27 set null [new Agent/Null]
28 $ns attach-agent $n3 $null
29 $ns connect $udp $null
30 $udp set fid_ 1
# Create a CBR traffic source
31 set cbr [new Application/Traffic/CBR]
32 $cbr attach-agent $udp
33 $cbr set packetSize_ 1000
34 $cbr set rate_ 2Mb

37. # Create a TCP agent
35 set tcp [new Agent/TCP]
36 $ns attach-agent $n1 $tcp
37 set sink [new Agent/TCPSink]
38 $ns attach-agent $n4 $sink
39 $ns connect $tcp $sink
40 $tcp set fid_ 2
# Create an FTP session
41 set ftp [new Application/FTP]
42 $ftp attach-agent $tcp

38. # Schedule events
43 $ns at 0.05 "$ftp start"
44 $ns at 0.1 "$cbr start"
45 $ns at 60.0 "$ftp stop"
46 $ns at 60.5 "$cbr stop"
47 $ns at 61 "finish“
# Start the simulation
48 $ns run
We run the above simulation script by executing
>>ns myfirst_ns.tcl

39. The Text-Based Packet Tracing for the example
“myfirst_ns.tcl” is
...
+ 0.110419 1 2 tcp 1040 ------- 2 1.0 4.0 5 12
+ 0.110419 1 2 tcp 1040 ------- 2 1.0 4.0 6 13
r 0.115348 1 2 tcp 1040 ------- 2 1.0 4.0 3 10
+ 0.115348 2 4 tcp 1040 ------- 2 4.0 4.0 3 10
- 0.115348 2 4 tcp 1040 ------- 2 4.0 2.0 3 10
r 0.115376 2 3 cbr 1000 ------- 1 4.0 3.0 1 7
r 0.115431 1 2 tcp 1040 ------- 2 1.0 4.0 4 11
...
Format of each line in normal Trace line

41. SUMMARY
 Transport Layer
 Modeling Approach
 Parts of Simulation
 Simulation Performance
 Simulation Types
 NS2
 Installation of NS2
 Terminologies
 Basics of TcL
 Packet Tracing
 Example