Computer Network Laboratory
Computer Network Laboratory
INDEX
EXP NO
TITLE OF EXPERIMENT
PAGE NO
1
PART-A
Write a program for error detecting code using CRC-CCITT (16- bits).
2
2
Write a program for simple RSA algorithm to encrypt and decrypt the
data.
5
3
Using TCP/IP sockets, write a client – server program to make the
client send the file name and to make the server send back the contents
of the requested file if present.
8
4
Write a program for Congestion Control using Leaky Bucket
algorithm.
11
1
PART-B
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.
15
2
Implement a four node point-to-point network with duplex links
connected as follows: n0-n2,n1-n2 and n2-n3.Apply TCP agent
between n0-n3 and UDP between n1-n3.Apply relevant applications
over TCP and UDP agents changing the parameter and determine the
number of packets sent by TCP/UDP.
18
3
Implement transmission of ping messages/trace route over a network
topology consisting of 6 nodes and find the number of packets dropped
due to congestion.
21
4
Implement an Ethernet LAN using n-nodes and set multiple traffic
nodes and determine collision across different nodes.
23
5
Implement an Ethernet LAN using n-nodes and set multiple traffic
nodes and plot congestion window for different source / destination.
25
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 1
Computer Network Laboratory
1. Write a program for error detecting code using CRC-CCITT (16- bits).
import java.io.*;
import java.util.Scanner;
public class CRC {
public static void main(String args[]){
Scanner sc = new Scanner(System.in);
//Input Data Stream
System.out.println("Enter data stream:");
String datastream = sc.nextLine();
System.out.println("Enter generator: ");
String generator = sc.nextLine();
int l1 = datastream.length() ;
int l2 = generator.length() ;
int l3=l1+l2-1;
int data[] = new int[l3];
int divisor[] = new int[generator.length()];
for(int i=0;i<datastream.length();i++)
data[i] = Integer.parseInt(datastream.charAt(i)+"");
for(int i=0;i<generator.length();i++)
divisor[i] = Integer.parseInt(generator.charAt(i)+"");
//Calculation of CRC
for(int i=0;i<datastream.length();i++){
if(data[i]==1)
for(int j=0;j<divisor.length;j++)
data[i+j] ^= divisor[j];
}
//Display CRC
System.out.println("The CRC code is:" );
for(int i=0;i<datastream.length();i++)
data[i] = Integer.parseInt(datastream.charAt(i)+"");
for(int i=0;i<data.length;i++) System.out.print(data[i]);
System.out.println();
//Check for input CRC code
System.out.print("Enter CRC code: ");
datastream = sc.nextLine();
System.out.print("Enter generator: ");
generator = sc.nextLine();
int l4 = datastream.length() ;
int l5= generator.length();
int l6= l4 + l5 - 1;
data = new int[l6];
divisor = new int[generator.length()];
for(int i=0;i<datastream.length();i++)
data[i] = Integer.parseInt(datastream.charAt(i)+"");
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 2
Computer Network Laboratory
for(int i=0;i<generator.length();i++)
divisor[i] = Integer.parseInt(generator.charAt(i)+"");
//Calculation of remainder
for(int i=0;i<datastream.length();i++){
if(data[i]==1)
for(int j=0;j<divisor.length;j++)
data[i+j] ^= divisor[j];
}
//Display validity of data
boolean valid = true;
for(int i=0;i<data.length;i++)
if(data[i]==1){
valid = false;
break;
}
if(valid==true) System.out.println("Data stream is valid");
else
System.out.println("Data stream is invalid. CRC error occured.");
}
}
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 3
Computer Network Laboratory
Output:
Enter Data Stream
11011
Enter generator
100
The CRC Code is 1101100
Enter CRC Code 1101100
Enter Generator
100
Data Stream is valid
Output: 2
Enter Data Stream
11011
Enter generator
100
The CRC Code is 1101100
Enter CRC Code 11011001
Enter Generator
101
Data Stream is invalid
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 4
Computer Network Laboratory
2. Write a program for simple RSA algorithm to encrypt and decrypt the data.
import java.io.DataInputStream;
import java.io.IOException;
import java.math.BigInteger;
import java.util.Random;
public class RSA
{
private BigInteger p;
private BigInteger q;
private BigInteger N;
private BigInteger phi;
private BigInteger e;
private BigInteger d;
private int
bitlength = 1024;
private Random r;
public RSA()
{
r = new Random();
p = BigInteger.probablePrime(bitlength, r);
q = BigInteger.probablePrime(bitlength, r);
N = p.multiply(q);
phi = p.subtract(BigInteger.ONE).multiply(q.subtract(BigInteger.ONE));
e = BigInteger.probablePrime(bitlength / 2, r);
while (phi.gcd(e).compareTo(BigInteger.ONE) > 0 && e.compareTo(phi) < 0)
{
e.add(BigInteger.ONE);
}
d = e.modInverse(phi);
}
public RSA(BigInteger e, BigInteger d, BigInteger N)
{
this.e = e;
this.d = d;
this.N = N;
}
@SuppressWarnings("deprecation")
public static void main(String[] args) throws IOException
{
RSA rsa = new RSA();
DataInputStream in = new DataInputStream(System.in);
String teststring;
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 5
Computer Network Laboratory
System.out.println("Enter the plain text:");
teststring = in.readLine();
System.out.println("Encrypting String: " + teststring);
System.out.println("String in Bytes: "
+ bytesToString(teststring.getBytes()));
// encrypt
byte[] encrypted = rsa.encrypt(teststring.getBytes());
// decrypt
byte[] decrypted = rsa.decrypt(encrypted);
System.out.println("Decrypting Bytes: " + bytesToString(decrypted));
System.out.println("Decrypted String: " + new String(decrypted));
}
private static String bytesToString(byte[] encrypted)
{
String test = "";
for (byte b : encrypted)
{
test += Byte.toString(b);
}
return test;
}
// Encrypt message
public byte[] encrypt(byte[] message)
{
return (new BigInteger(message)).modPow(e, N).toByteArray();
}
// Decrypt message
public byte[] decrypt(byte[] message)
{
return (new BigInteger(message)).modPow(d, N).toByteArray();
}
}
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 6
Computer Network Laboratory
Output:
Enter Plain text: HELLO WORLD
Encrypting String: HELLO WORLD
String in bytes: 10410 110810811132119111114108100
Decrypting bytes: 10410 110810811132119111114108100
Decrypting String: HELLO WORLD
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 7
Computer Network Laboratory
3. Using TCP/IP sockets, write a client – server program to make the client send the file
name and to make the server send back the contents of the requested file if present.
import java.io.*;
import java.net.*;
public class Client
{
public static void main(String[] args) throws Exception
{
Socket sock = new Socket("127.0.0.1", 3000);
// reading from keyboard (keyRead object)
BufferedReader keyRead = new BufferedReader(new InputStreamReader(System.in));
// sending to client (pwrite object)
OutputStream ostream = sock.getOutputStream();
PrintWriter pwrite = new PrintWriter(ostream, true);
// receiving from server ( receiveRead object)
InputStream istream = sock.getInputStream();
BufferedReader receiveRead = new BufferedReader(new InputStreamReader(istream));
System.out.println("Start the chitchat, type and press Enter key");
String receiveMessage, sendMessage;
while(true)
{
sendMessage = keyRead.readLine(); // keyboard reading
pwrite.println(sendMessage);
// sending to server
pwrite.flush();
// flush the data
if((receiveMessage = receiveRead.readLine()) != null) //receive from server
{
System.out.println(receiveMessage); // displaying at DOS prompt
}
}
}
}
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 8
Computer Network Laboratory
import java.io.*;
import java.net.*;
public class Server
{
public static void main(String[] args) throws Exception
{
ServerSocket sersock = new ServerSocket(3000);
System.out.println("Server ready for chatting");
Socket sock = sersock.accept( );
// reading from keyboard (keyRead object)
BufferedReader keyRead = new BufferedReader(new InputStreamReader(System.in));
// sending to client (pwrite object)
OutputStream ostream = sock.getOutputStream();
PrintWriter pwrite = new PrintWriter(ostream, true);
// receiving from server ( receiveRead object)
InputStream istream = sock.getInputStream();
BufferedReader receiveRead = new BufferedReader(new InputStreamReader(istream));
String receiveMessage, sendMessage;
while(true)
{
if((receiveMessage = receiveRead.readLine()) != null)
{
System.out.println(receiveMessage);
}
sendMessage = keyRead.readLine();
pwrite.println(sendMessage);
pwrite.flush();
}
}
}
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 9
Computer Network Laboratory
Output:
Client
C:\Documents and settings\cnlab>cd\
C:\cd program files
C:\Program Files>cd java
C:\Program Files\java>cd pgm3
C:\Program Files\java\pgm3>javac
C:\Program Files\java\pgm3>javac Client.java
C:\Program Files\java\pgm3>java Client
WELCOME TO NETWORKS LAB
Server
C:\Documents and settings\cnlab>cd\
C:\cd program files
C:\Program Files>cd java
C:\Program Files\java>cd pgm3
C:\Program Files\java\pgm3>javac
C:\Program Files\java\pgm3>javac Server.java
C:\Program Files\java\pgm3>java Server
Ready to type now
WELCOME TO NETWORKS LAB
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 10
Computer Network Laboratory
4. Write a program for congestion control using leaky bucket algorithm.
Leaky Bucket Implementation
import java.util.*;
public class leaky
{
public static void main(String[] args)
{
Scanner my = new Scanner(System.in);
int no_groups,bucket_size;
System.out.print("\n Enter the bucket size : \t");
bucket_size = my.nextInt();
System.out.print("\n Enter the no of groups : \t");
no_groups = my.nextInt();
int no_packets[] = new int[no_groups];
int in_bw[] = new int[no_groups];
int out_bw,reqd_bw=0,tot_packets=0;
for(int i=0;i<no_groups;i++)
{
System.out.print("\n Enter the no of packets for group " + (i+1) + "\t");
no_packets[i] = my.nextInt();
System.out.print("\n Enter the input bandwidth for the group " + (i+1) + "\t");
in_bw[i] = my.nextInt();
if((tot_packets+no_packets[i])<=bucket_size)
{
tot_packets += no_packets[i];
}
else
{
do
{
System.out.println(" Bucket Overflow ");
System.out.println(" Enter value less than " + (bucket_size-tot_packets));
no_packets[i] = my.nextInt();
}while((tot_packets+no_packets[i])>bucket_size);
tot_packets += no_packets[i];
}
reqd_bw += (no_packets[i]*in_bw[i]);
}
System.out.println("\nThe total required bandwidth is " + reqd_bw);
System.out.println("Enter the output bandwidth ");
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 11
Computer Network Laboratory
out_bw = my.nextInt();
int temp=reqd_bw;
int rem_pkts = tot_packets;
while((out_bw<=temp)&&(rem_pkts>0))
{
System.out.println("Data Sent \n" + (--rem_pkts) + " packets remaining");
System.out.println("Remaining Bandwidth " + (temp -= out_bw));
if((out_bw>temp)&&(rem_pkts>0))
System.out.println(rem_pkts + " packet(s) discarded due to insufficient bandwidth");
}
}
}
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 12
Computer Network Laboratory
Output:
Enter the bucket size
3
Enter the Number of groups
2
Enter the number of packets for group1
1
Enter the input bandwidth for group1
2
Enter the number of packets for groups2
3
Enter the input bandwidth for group2
1
Bucket overflow
Enter the value less than 2
1
The total required bandwidth is 3
Enter the output bandwidth
2
Data sent
1 packet remaining
Remaining bandwidth 2
Data sent
0 packets remaining
Remaining bandwidth2
BUILD SUCCESSFULL
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 13
Computer Network Laboratory
PART-B
Boot your machine from NCTUNS.
1- Right click on your mouse and open terminal and type.
/usr/local/nctuns/bin/dispatcher
2- Right click on your mouse and open another terminal and type.
/usr/local/nctuns/bin/coordinator
3- Right click on your mouse and open terminal and type.
/usr/local/nctuns/bin/nctunsclient.
After opening third terminal a working window will be shown. Select the draw topology.
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 14
Computer Network Laboratory
1. Implement three node point to point network with duplex links between them. Set the queue
size,vary the bandwidth and find the number of packets dropped.
STEPS:
Steps to draw the topology.
Step1:Select the switch icon on the toolbar and drag it on the working window.
Step2:Select the host icon on the toolbar and drag it on the working window.
Repeat this for the number of host required.
Step3:Select the link icon on the toolbar and drag it on the screen from host1 to switch and again
from host2 to switch. Here the switch acts as node3 in the point to point network.This leads to
the creation of 3 node point to point network topology.Save this topology by .tpl extension by
going to the edit mode on the toolbar.Move the mouse near the host icon to see the IP address, in
the same manner check the IP address of the remaining host and note down.p.Click on the
command box and type the command
Step4:Double click on host1.Click on the node editor and different layer interface will be shown
like ARP,FIFO,MAC,TCP_DUMP.From these select full duplex for switch and hald duplex for
hubs and in log statistics select number of drop packets.Then click on ADD.By this another
dialog box pops up.Click on the command box and type the command according to the
following syntax.
For HUB: stg[-l duration(sec)][-u port number] HostIP address
Ex:stg –u 9800 HostIPadrr 1.0.1.2
For switch: stcp[-p port number][-l writesize] HostIPAddress
Ex:stcp –p 9800 –l 1024 1.0.1.2
And click ok.Here host1 acts as sender and HostIPAddr is the address of destination(host2).
Step5:Double click on host2 and follow the same steps as shown in step4 with a only change in
the command according to the following syntax.
For HUB:rtg[-i][-w log] [-p port number]
Ex:rtg –u –w log1
For switch:rtcp [–p port number][-l write size]
Ex:rtcp –p 9800 –l 1024
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 15
Computer Network Laboratory
And click on ok.
Step6:Double click on the link between node1 and switch to set the bandwidth to some initial
value.
Step7:Click on the E button to save the changes.Now click on the R button to Run the
simulation.
Step8:Then goto Menu→Simulation→Run.When the server is executing the user will see the
simulation playback time knot at the bottom of the screen moving.
Step9:To start the simulation playback mode “p” the user can left click the start icon of the time
bar.The animation is played out.During this process plot the graph for this goto
Menu→Tools→plot graph press enter.Here we will see the graph window in which open the file
name .results folder and select number of drop packets by File→open.
During animation three types of data lines are seen.
1.Red line indicates data is transmitted not received.
2. Blue line indicates the acknowledgement.
3. Yellow line shows the connection.
Step10:Run the simulation
Step11:To view the different results go to filename.results.
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 16
Computer Network Laboratory
Output:
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 17
Computer Network Laboratory
2. Implement a four node point-to-point network with duplex links connected as follows: n0-n2,
n1-n2 and n2-n3.Apply TCP agent between n0-n3 and UDP between n1-n3. Apply relevant
applications over TCP and UDP agents changing the parameter and determine the number of
packets sent by TCP/UDP.
STEPS:
Steps to draw the topology
Step 1. select the hub icon on the toolbar and drag it onto the working window.
Step 2. select the host icon on the toolbar and drag it onto the working window. Repeat this for
another 2 host icons.
Step 3. select the link icon on the toolbar and drag it on the screen from host1 to the hub, repeat
this for another 2 host icons.
Step 4. Go to edit mode "E" and save the topology.
Move the mouse near the host icon to see the IP address, in the same manner check the IP
addressess of the remaining host and note down.
Step 5. setup a TCP connection between node1 and node2 using the following commands.
1. double-click on host1. click on node editor and different layeras interface will be show like
ARP,FIFO,MAC,TCPDUMP,Physical layers .from those select MAC and then select full-duplex
for switches and roters and half-duplex for hubs,and in log statistics select the output and input
throughput log to determine the number of packets.press ok. then click on Add. by this another
dialogbox popsup.
click on the command box and type the command according to the following syntax
EX: stcp –p 9800 -1 1024 1.0.1.2 (IP addr of host2)
And click on ok
2. double-click on host 2.follow the same steps as shown in above step with a only changes in the
command.
EX: rtcp -p 9800 -l 1024
Step 6. setup a UDP connection between node2 and node3 using the hub and the following
commands.
1. Double-click on host 2. follow the same steps as shown in above steps with a only changes in
the command.
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 18
Computer Network Laboratory
EX: stg-u 9800 hostIP Addrr
2. double-click on host3 follow the same steps as shown in above steps with a only change in the
command.
EX: rtg-u-w log1
Step 7. click on the E button to save the changes. now click on the R button, to run the
simulation.
Step 8. Then go to menu -->simulation-->run when the sever is executing ,the user will see the
time.knot at the bottom of the screen moving .
Step 9. to start the simulation play back mode "P" the user can left -click the start icon()of the
time bar .The animation is played out.during this process plot the graphs for this go to menu ->tools-->polt graphs press enter . Here we will see a graph window in which open the filename .
results folder and select the output and input throughput log to determine the number of packets.
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 19
Computer Network Laboratory
Output:
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 20
Computer Network Laboratory
3.Implement transmission of ping messages/ trace route over a network topology consisting of 6
nodes and find the number of packets dropped due to congestion.
STEPS:
Steps to draw the topology
Step1:Click on the subnet icon on the toolbar and then click on the screen of the working
window.
Step2:Select the number of host as 6 and bandwidth as 100.
Step3:In the edit mode get the IP address of one of the host say host1and then for other host say
host2.Set drop packets and number of collisions statistics.
Step4:Save topology and perform the same steps and Run the simulation.
Step5:Click on any one of the host and click on the command console and ty
Ng and destination IP address as
#ping 1.0.1.5 press enter
Step6:The number of packets are obtained only when the traffic is more on the network.
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 21
Computer Network Laboratory
Output:
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 22
Computer Network Laboratory
4.Implement an Ethernet LAN using n-nodes and set multiple traffic nodes and determine
collision across different nodes.
STEPS:
Steps to draw the topology
Step1:Select the Hub1 icon on the toolbar and drag it on the working window.
Step2:Select the host icon on the toolbar and drag it on the working window.Repeat this for
another 3 host icons.
Step3:Select the Hub2 icon on the toolbar and drag it on the working window.
Step4:Select the host icon on the toolbar and drag it on the working window.Repeat this for
another 3 host icons.Step3 and step4 creates second side LAN connect these two hubs with a
switch,this forms an Ethernet LAN
Step5:Save the topology by filename.tpl extension
Step6:Double click on host1 on hub1,click on ADD and type the command as
Stcp –p 9800 –l 1024 1.0.1.4 and click on ok.
Here don’t select MAC layer.
Step7:Double click on host2 on hub1,click on ADD and type the command as
Stcp –p 9800 –l 1024 1.0.1.5 and click on ok.
Here don’t select MAC layer.
Step8:Double click on host4 on hub2,Select only number of collision packets,click on ADD and
type the command as
rtcp –p 9800 –l 1024 and click on ok.
Step9:Double click on host5 on hub2,Select only number of collision packets,click on ADD and
type the command as
rtcp –p 9800 –l 1024 and click on ok.
Step10: Click on the E button to save the changes.Now click on the R button to Run the
simulation.
Step11:Then goto Menu→Simulation→Run.When the server is executing the user will see the
simulation playback time knot at the bottom of the screen moving.
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 23
Computer Network Laboratory
Step12:To start the simulation playback mode “p” the user can left click the start icon of the time
bar.The animation is played out.During this process plot the graph for this goto
Menu→Tools→plot graph press enter.Here we will see the graph window in which open the file
name .results folder and select number of drop packets by File→open.
Output:
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 24
Computer Network Laboratory
5.Implement an Ethernet LAN using n nodes and set multiple traffic nodes and plot congestion
window for different source /destination.
STEPS:
Steps to draw the topology
Step1:Select the Hub1 icon on the toolbar and drag it on the working window.
Step2:Select the host icon on the toolbar and drag it on the working window.Repeat this for
another 3 host icons.
Step3:Select the Hub2 icon on the toolbar and drag it on the working window.
Step4:Select the host icon on the toolbar and drag it on the working window.Repeat this for
another 3 host icons.Step3 and step4 creates second side LAN connect these two hubs with a
switch,this forms an Ethernet LAN
Step5:Save the topology by filename.tpl extension
Step6:Double click on host1 on hub1,click on ADD and type the command as
Stcp –p 9800 –l 1024 1.0.1.4 and click on ok.
Stcp –p 9800 –l 1024 1.0.1.5 and click on ok.
Here don’t select MAC layer.
Step8:Double click on host4 on hub2,Select only number of collision packets,click on ADD and
type the command as
rtcp –p 9800 –l 1024 and click on ok.
Step9:Double click on host5 on hub2,Select only number of collision packets,click on ADD and
type the command as
rtcp –p 9800 –l 1024 and click on ok.
Step10: Click on the E button to save the changes.Now click on the R button to Run the
simulation.
Step11:Then goto Menu→Simulation→Run.When the server is executing the user will see the
simulation playback time knot at the bottom of the screen moving.
Step12:To start the simulation playback mode “p” the user can left click the start icon of the time
bar.The animation is played out.During this process plot the graph for this goto
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 25
Computer Network Laboratory
Menu→Tools→plot graph press enter.Here we will see the graph window in which open the file
name .results folder and select number of drop packets by File→open.
Output:
Department of Computer science and Engineering
Faculty of Engineering and Technology
Page 26