Introduction to Programming

Definition

"A program is a precise sequence of steps to solve a particular problem.”It means that when we say that we have a program, it actually means that we know about a complete set activities to be performed in a particular order. The purpose of these activities is to solve a given problem. Alan Perlis, a professor at Yale University, says:"It goes against the grain of modern education to teach children to program. What fun is there in making plans, acquiring discipline in organizing thoughts, devoting attention to detail and learning to be self-critical? ". It is a sarcastic statement about modern education, and it means that the modern education is not developing critical skills like planning, organizing and paying attention to detail. Practically, in our day to day lives we are constantly planning, organizing and paying attention to fine details (if we want our plans to succeed). And it is also fun to do these activities. For example, for a picnic trip we plan where to go, what to wear, what to take for lunch, organize travel details and have a good time while doing so.

Xgraph in NS2

 

One part of the ns-allinone package is 'xgraph', a plotting program which can be used to create graphic representations of simulation results. In this section, I will show you a simple way how you can create output files in your Tcl scripts which can be used as data sets for xgraph. On the way there, I will also show you how to use traffic generators.
A note: The technique I present here is one of many possible ways to create output files suitable for xgraph. If you think there is a technique which is superior in terms of understandablity (which is what I aim for in this tutorial), please let me know.


First of all, we create the following topology:
 

 
The following piece of code should look familiar to you by now if you read the first sections of this tutorial.

set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set n4 [$ns node]

$ns duplex-link $n0 $n3 1Mb 100ms DropTail
$ns duplex-link $n1 $n3 1Mb 100ms DropTail
$ns duplex-link $n2 $n3 1Mb 100ms DropTail
$ns duplex-link $n3 $n4 1Mb 100ms DropTail

NS2 installation using Ubuntu Software Center

There is an absolute easy way to install ns2 (network simulator) by using the easiest technique available on ubuntu. 
Let us install ns2 in a very nice and easy way. Ubuntu Software Center provides with ease to install different softwares by wizard.

Here is how it is done.

Open “Ubuntu Software Center” as hightlighted in the below figure.

Now, in the search box on the top right corner. Write ns2 and press enter.

You will see the package. Hit install button and it will install ns2. Ofcourse, internet connectivity is must :)
Similarly, you can install nam(network animator) by following the same procedure. Just enter "nam" in the search box and hit enter.

Install the first package that you see. And there you go, you have installed ns2 and nam .  You can always install it using terminal simply by writing the following command.

sudo apt-get install ns2 nam xgraph


Remember, when you do the same in Ubuntu 13.04, it will not show you the desired ns2 package. And you will have to install it manually. I guess this is only available for 12.04 version. So, there is another way available if you want to install ns2 in that version.

This could be resolved by applying the following command.


sudo apt-get update


When the update is completed, go and run the command to install ns2 , nam and xgraph. If you want an easy way out to install Ubuntu using windows. Please click here.

 

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Dynamic Nodes generation and traffic flow in ns2

Here is the code for dynamically creating nodes and create traffic flow dynamically using protocol.


#Create a simulator object
set ns [new Simulator]

#Tell the simulator to use dynamic routing
$ns rtproto DV

#Open the nam trace file
set nf [open out.nam w]
$ns namtrace-all $nf


#Define a 'finish' procedure
proc finish {} {
        global ns nf
        $ns flush-trace
#Close the trace file
        close $nf
#Execute nam on the trace file
        exec nam out.nam &
        exit 0
}

#Create seven nodes
for {set i 0} {$i < 7} {incr i} {
        set n($i) [$ns node]
}


#Create links between the nodes
for {set i 0} {$i < 7} {incr i} {
        $ns duplex-link $n($i) $n([expr ($i+1)%7]) 1Mb 10ms DropTail
}

#Create a UDP agent and attach it to node n(0)
set udp0 [new Agent/UDP]
$ns attach-agent $n(0) $udp0

# Create a CBR traffic source and attach it to udp0
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 500
$cbr0 set interval_ 0.005
$cbr0 attach-agent $udp0

EVIL IS NOTHING BUT ABSENCE OF GOOD

Professor : You are a Muslim, aren’t you, son ?

Student : Yes, sir.

Professor: So, you believe in GOD ?

Student : Absolutely, sir.

Professor : Is GOD good ?

Student : Sure.

Professor: Is GOD all powerful ?

Student : Yes.

OSPF on Packet Tracer

We are going to apply OSPF(open shortest path first) protocol on packet tracer. Let us take the following simple topology.



Now, let us apply the ospf on it. But before that, as usual :) , let us assign IP addresses and change the state of interfaces.

 

Similarly for the other router.

Lab Manual Of Computer Communication and Networks

1	Introduction to Networking Devices	https://cs-study.blogspot.com/2012/09/networking-devices.html
2	Introduction to Packet Tracer	https://cs-study.blogspot.com/2012/10/what-is-packet-tracer.html
3	Packet Tracer CLI commands	https://cs-study.blogspot.com/2012/10/packet-tracer-cli.html
4	Introduction to Cables	https://cs-study.blogspot.com/2012/10/networking-cables-and-connections.html
5	Communication in PT, getting started ..	https://cs-study.blogspot.com/2012/10/communication-between-pcs-in-packet.html
6	RIP on Packet Tracer	https://cs-study.blogspot.com/2012/10/rip-on-packet-tracer.html
7	RIP V2 on Packet Tracer	https://cs-study.blogspot.com/2012/10/rip-version-2-on-packet-tracer.html
8	EIGRP on Packet Tracer	https://cs-study.blogspot.com/2012/10/eigrp-on-packet-tracer.html
9	OSPF on Packet Tracer	https://cs-study.blogspot.com/2013/03/ospf-on-packet-tracer.html
10	DHCP on Router	https://cs-study.blogspot.com/2012/10/dhcp-on-packet-tracer.html
11	DHCP on PT through Server	https://cs-study.blogspot.com/2012/10/dhcp-on-packet-tracer-through-server.html
12	DNS on Packet Tracer	https://cs-study.blogspot.com/2012/10/dns-on-packet-tracer.html
13	VLANS on Packet Tracer	https://cs-study.blogspot.com/2012/11/vlan-on-packet-tracer.html
14	VTP on Packet Tracer	https://cs-study.blogspot.com/2012/11/vtp-on-packet-tracer.html
15	Spanning Tree Protocol on Packet Tracer	https://cs-study.blogspot.com/2012/11/spanning-tree-protocol-on-packet-tracer.html
16	Sticky MAC addresses	https://cs-study.blogspot.com/2012/12/sticky-mac-addresses.html
17	Inter VLAN Routing (Router on a Stick)	https://cs-study.blogspot.com/2012/11/inter-vlan-routing-router-on-stick.html
18	CDP on Packet Tracer	https://cs-study.blogspot.com/2012/12/cdp-cisco-discovery-protocol.html
19	Telnet and SSH	https://cs-study.blogspot.com/2012/12/telnet-and-ssh-on-packet-tracer.html
20	Password Authentication Protocol on PT	https://cs-study.blogspot.com/2012/12/password-authentication-protocol-on.html
21	Challenge Hand Shake Authentication Protocol on PT	https://cs-study.blogspot.com/2012/12/point-to-point-protocol-on-packet.html
22	Voice Over IP on PT (VOIP)	https://cs-study.blogspot.com/2012/12/voice-over-ip-voip-on-packet-tracer.html
23	Wireless Communication on Packet Tracer	https://cs-study.blogspot.com/2012/12/wireless-communication-in-packet-tracer.html
24	Access Control List on PT	https://cs-study.blogspot.com/2012/11/acl-on-packet-tracer.html
	NS2 (Network Simulator - 2) Tutorials
25	NS 2 and Ubuntu Installation	https://cs-study.blogspot.com/2012/12/ns2-installation-and-ubuntu.html
26	Nodes Creation in NS 2	https://cs-study.blogspot.com/2012/12/add-following-code-to-new-file-and.html
27	Traffic Flow in NS 2	https://cs-study.blogspot.com/2012/12/traffic-flow-on-nodes-in-ns2.html
28	Dynamic Nodes generation and traffic flow in ns2	https://cs-study.blogspot.com/2013/05/dynamic-nodes-generation-and-traffic.html
29	Xgraph in NS2	https://cs-study.blogspot.com/2013/05/xgraph-in-ns2.html

 30   Wireless Communication in NS2

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