NErwork Lab Simulation Introduction.pptx

Computer Networks [BCS502]
Department of Computer Science Engineering – ( Data Science)

Introduction to Network Simulation
Network simulation is an important tool in developing, testing and evaluating network protocols.
Simulation can be used without the target physical hardware, making it economical and practical
for almost any scale of network topology and setup.
It is possible to simulate a link of any bandwidth and delay, even if such a link is currently
impossible in the real world.
With simulation, it is possible to set each simulated node to use any desired software.
Results are also easier to obtain and analyse, because extracting information from important points
in the simulated network is done by simply parsing the generated trace files.

Types of Simulators
 MIT's NETSIM
 NIST
 CPSIM
 INSANE
 NEST
 REAL
 NS
 OPNET
 NCTUns

Major Features of NS2:
Supports Unix like systems and Windows
It is written in C++ and TCL scripting language
OTCL in NS2 adds object oriented concept to TCL.
Open source simulator, which is object oriented in nature
Protocol Support in NS2:
Network Layer [Routing agent]
Transport layer[Traffic agent-TCP and UDP]
Logic link Control layer[IEEE 802.2, AR]
Interface Queue[Priority queue, FIFO queue, Drop tail queue]

Major Components:
NAM[Network Animator]:
Used to view the Network simulation traces
Supports packet transmission, topology, data inspection etc
During the execution of simulation, it supports animation
Trace File:
Used to store the coverage information or overall network information
To generate a trace file, we have to first create a trace file using OTCL Script.
X-Graph:
Used to visualize the resulting graph
AWK Script:


Tool Command Language (Tcl):
Scripting language used to create configuration files in NS2.
Used to build the network topology and structure
It is easy to code and integrate with other languages like OTCL and C++
Overall Script format contains[Simulator object, trace file, finish procedure, network setup(node, link, agent,
parameter), event scheduling(run and stop simulation)]
Steps in writing a Script in NS2:
Create an event scheduler
Turn on tracing
Create the network and setup routing
Insert Error and create transport connection
Create traffic
Transmit application level data

NS 2 programming
Basically NS 2 programming contains the following steps
1. Create the event scheduler
2.Turn on tracing
Two types of trace
i. generic trace - for use with xgraph, and other things
ii. nam trace - for use with visualization
3. Creating network
i. Computing setup routing
ii. Creating transport connection- Agents
iii. Creating traffic- Applications
4. Monitoring
i. Visualization using nam

Tcl scripting
 Tcl is a general purpose scripting language. [Interpreter]
 Tcl runs on most of the platforms such as Unix, Windows, and Mac.
 The strength of Tcl is its simplicity.
 It is not necessary to declare a data type for variable prior to the usage.
 In order to have output files with data on the simulation (trace files) or files used for visualization (nam files),
we need to create the files using “open” command
#Open the Trace file #Open the NAM trace file
set tracefile1 [open out.tr w]
$ns trace-all $tracefile1
set namfile [open out.nam w]
$ns namtrace-all $namfile

Structure of Trace Files
The trace is organized in 12 fields as follows in fig shown below:
Event Time From Node To Node PKT Type PKT Size Flags Fid Src Addr Dest Addr SeqNum Pkt id
 The first field is the event type. It is given by one of four possible symbols
r  receive (at the output of the link),
+  enqueued
-  dequeued
d  dropped.
 The second field gives the time at which the event occurs.
 Gives the input node of the link at which the event occurs.
 Gives the output node of the link at which the event occurs.
 Gives the packet type (eg CBR or TCP)

 Gives the packet size
 Some flags
This is the flow id (fid) of IPv6 that a user can set for each flow at the input,it is also used when
specifying stream color for the NAM display.
This is the source address given in the form of “node.port”.
This is the destination address, given in the same form.
This is the network layer protocol’s packet sequence number. Even though UDP implementations in a
real network do not use sequence number, ns keeps track of UDP packet sequence number for analysis
purposes
The last field shows the Unique id of the packet.

Ns2 Simulation:
Define the Simulation Object
Connect the object with each other through links
Start the Source applications.
Packets are created and transmitted through the network
Exit the simulation at fixed time

Create an Event Scheduler:
 Set ns [ new simulator ]//create a new simulator
$ns at < time > < event >//Schedules the event
$ns run// Start the scheduler
Tracing in NS2:
General syntax: $ns traceall[open filename.tr w]
$ns namtrace-all // open the nam file

To create Network topology:
• Link creation between two nodes:
• First create nodes using
• set n1 [ $ns node ]
• set n2 [ $ns node ]
• Now, create link using the command:
• $ns < link_type(Simplex/duplex)> $n1 $n2 <bandwidth> <delay> <queue-type>
To create transport connection and generate traffic:
• Traffic generation[FTP, telnet]
• set ftp new Application / FTP ]
• set telnet [new Application / Telnet ]

Steps to Run a TCL File:
Install NS2 and set your path
After NS2 Installation, go to $prompt and run ns filename[Ex. ns tcp.tcl]
After this, .nam and .tr files will be created automatically in the same folder [home folder]- here NAM-
Network animator and .tr-trace files have to be initialized in TCL files using commands.
To see the demo in GUI, run nam filename.nam [ex. Tcp.nam]
.tr files are used to check the actual performance of the Network [i.e throughput, packet drop etc]
Parse the .tr files into Xgraph [for graph generation]

Unix Commands
1) grep: The grep filter searches a file for a particular pattern of characters, and displays all lines that
contain that pattern.
Syntax:
grep [options] pattern [files]
Options Description
-c : This prints only a count of the lines that match a pattern
Matching the lines that start with a string :
The ^ regular expression pattern specifies the start of a line. This can be used in grep to match the lines
which start with the given string or pattern.
Example: $ grep "^unix" geekfile.txt

2) exec command in Linux is used to execute a command from the bash itself. This
command does not create a new process it just replaces the bash with the command to
be executed.
Example:$ exec ls

PART-A
Program 1: Implement three nodes point – to – point network with
duplex links between them. Set the queue size, vary the
bandwidth and find the number of packets dropped.

set ns [new Simulator]
set ntrace [open prog1.tr w]
$ns trace-all $ntrace
set namfile [open prog1.nam w]
$ns namtrace-all $namfile
proc Finish {} {
global ns ntrace namfile
$ns flush-trace
close $ntrace
close $namfile
exec nam prog1.nam &
puts "The number of packet drops is"
exec grep -c "^d" prog1.tr &
exit 0
}
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
$ns duplex-link $n0 $n1 10Mb 10ms DropTail
$ns duplex-link $n1 $n2 1Mb 10ms DropTail
$ns queue-limit $n0 $n1 10
$ns queue-limit $n1 $n2 05

set tcp0 [new Agent/TCP]
$ns attach-agent $n0 $tcp0
set sink0 [new Agent/TCPSink]
$ns attach-agent $n2 $sink0
$ns connect $tcp0 $sink0
set cbr0 [new Application/Traffic/CBR]
$cbr0 set type_ CBR
$cbr0 set packetSize_ 100
$cbr0 set rate_ 1Mb
$cbr0 set random_ false
$cbr0 attach-agent $tcp0
$tcp0 set class_ 1
$ns at 0.0 "$cbr0 start"
$ns at 5.0 "Finish"
$ns run

OUTPUT
n1
n0
n2
tcp0
cbr0
sink0
10Mb, 10ms
1
M
b
,
1
0
m
s

NErwork Lab Simulation Introduction.pptx

More Related Content

Similar to NErwork Lab Simulation Introduction.pptx (20)

More from AmbikaVenkatesh4 (18)

Recently uploaded (20)

NErwork Lab Simulation Introduction.pptx