Advance computer networks

Msc I.T Part I Advanced Computer Networks

Theory And Terminology

What Is a Socket? Normally, a server runs on a specific computer and has a socket that is

bound to a specific port number. The server just waits, listening to the socket for a client to make a connection request.

On the client-side: The client knows the hostname of the machine on which the server is running and the port number to which the server is connected. To make a connection request, the client tries to rendezvous with the server on the server's machine and port.

If everything goes well, the server accepts the connection. Upon acceptance, the server gets a new socket bound to a different port. It needs a new socket (and consequently a different port number) so that it can continue to listen to the original socket for connection requests while tending to the needs of the connected client.

On the client side, if the connection is accepted, a socket is successfully created and the client can use the socket to communicate with the server. Note that the socket on the client side is not bound to the port number used to rendezvous with the server. Rather, the client is assigned a port number local to the machine on which the client is running.

The client and server can now communicate by writing to or reading from their sockets.

Definition: A socket is one endpoint of a two-way communication link between two programs running on the network. A socket is bound to a port number so that the TCP layer can identify the application that data is destined to be sent.

The java.net package in the Java platform provides a class, Socket, that implements one side of a two-way connection between your Java program and another program on the network. The Socket class sits on top of a platform-dependent implementation, hiding the details of any particular system from your Java program. By using the java.net.Socket class instead of relying on native code, your Java programs can communicate over the network in a platform-independent fashion.

Additionally, java.net includes the ServerSocket class, which implements a socket that servers can use to listen for and accept connections to clients. This lesson shows you how to use the Socket and ServerSocket classes.

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Making TCP Connections

These classes are related to making normal TCP connections: ServerSocket Socket

For simple connections between a client and a server, ServerSocket and Socket are all that you will probably need.ServerSocket represents the socket on a server that waits and listens for requests for service from a client. Socket represents the endpoints for communication between a server and a client. When a server gets a request for service, it creates a Socket for communication with the client and continues to listen for other requests on the ServerSocket. The client also creates a Socket for communication with the server. The sequence is shown below how client and a server normally make a TCP connection with ServerSocket and Socket classes:

Once the connection is established, getInputStream() and getOutputSteam() may be used in communication between the sockets

Syntax:To open a socket Socket:

Socket MyClient;Myclient = new Socket(“Machine name”, PortNumber);

When Implementing server you also need to create a socket object from the ServerSocket in order to listen for and accept connections from clients. Socket clientSocket = null;

try {serviceSocket = Myservice.accpt();

}catch(IOException e){ System.out.println(e); }

(In the above program we have used exception handling.)User Datagram Protocol (UDP)

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Definition: A datagram is an independent, self-contained message sent over the network whose arrival, arrival time, and content are not guaranteed.

UDP provides an unreliable packet delivery system built on top of the IP protocol. As with IP, each packet is an individual, and is handled separately.

Because of this, the amount of data that can be sent in a UDP packet is limited to the amount that can be contained in a single IP packet. Thus, a UDP packet can contain at most 65507 bytes (this is the 65535-byte IP packet size minus the minimum IP header of 20 bytes and minus the 8-byte UDP header). UDP packets can arrive out of order or not at all. No packet has any knowledge of the preceding or following packet. The recipient does not acknowledge packets, so the sender does not know that the transmission was successful. UDP has no provisions for flow control--packets can be received faster than they can be used.

We call this type of communication connectionless because the packets have no relationship to each other and because there is no state maintained. The destination IP address and port number is encapsulated in each UDP packet. These two numbers together uniquely identify the recipient and are used by the underlying operating system to deliver the packet to a specific process (application). One way to think of UDP is by analogy to communications via a letter. You write the letter (this is the data you are sending); put the letter inside an envelope (the UDP packet); address the envelope (using an IP address and a port number); put your return address on the envelope (your local IP address and port number); and then you send the letter. Like a real letter, you have no way of knowing whether a UDP packet was received. If you send a second letter one day after the first, the second one may be received before the first. Or, the second one may never be received.

So why use UDP if it unreliable? Two reasons: speed and overhead. UDP packets have almost no overhead--you simply send them then forget about

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UDP client

Host A

UDP server

Host B internet


them. And they are fast, since there is no acknowledgement required for each packet. Keep in mind the degree of unreliability we are talking about. For all practical purposes, an Ethernet breaks down if more than about 2 percent of all packets are lost. So, when we say unreliable, the worst-case loss is very small. UDP is appropriate for the many network services that do not require guaranteed delivery. An example of this is a network time service. Consider a time daemon that issues a UDP packet every second so computers on the LAN can synchronize their clocks. If a packet is lost, it's no big deal--the next one will be by in another second and will contain all necessary information to accomplish the task. Another common use of UDP is in networked, multi-user games, where a player's position is sent periodically. Again, if one position update is lost, the next one will contain all the required information. A broad class of applications is built on top of UDP using streaming protocols.

With streaming protocols, receiving data in real-time is far more important than guaranteeing delivery. Examples of real-time streaming protocols are RealAudio and RealVideo which respectively deliver real-time streaming audio and video overthe Internet. The reason a streaming protocol is desired in these cases is because if an audio or video packet is lost, it is much better for the client to see this as noise or "drop-out" in the sound or picture rather than having a long pause while the client software stops the playback, requests the missing data from the server.

That would result in a very choppy, bursty playback which most people find unacceptable, and which would place a heavy demand on the server.

Practical 1

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Aim: Write a client server program that will display the IP address and the local host address.

Software Required: Java Development Kit 1.5

Description:java.net provides addressing-related class InetAddress for IP addressing.Class InetAddress represents an IP address, which is either a 32- or 128-bit unsigned number used by IP, the lower-level protocol on which protocols like TCP and UDP are built.

Server Program:import java.io.*;import java.net.*;public class inetServer{ public static void main(String a[]) {

System.out.println("Starting Server...WAIT...."); try { ServerSocket srv = new ServerSocket(5555);

System.out.println("Server Started : " + srv);Socket clt = srv.accept();InetAddress cltAddress = clt.getInetAddress();System.out.println("Client IP : "+ cltAddress.getHostAddress() + "\tPort no : "+ clt.getPort());PrintStream ios = new PrintStream(clt.getOutputStream());

ios.println("Server address is : " + srv); ios.close(); } catch(Exception e) { System.out.println("Error : " + e.toString()); } }}

Client Program:import java.net.*;import java.io.*;public class inetClient{ public static void main(String ss[])

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{ try { InetAddress inetaddr = InetAddress.getLocalHost();

Socket sock =new Socket (inetaddr,5555); System.out.println("Connection Established to Server");InputStreamReader input = new InputStreamReader (sock.getInputStream()); BufferedReader buffreader = new BufferedReader(input);System.out.println(buffreader.readLine());

} catch(Exception e) { System.out.println("Error : " + e.toString()); } }}

Output of Server Program:

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Output of Client Program:

Practical 2

Aim: Write a client server program to implement client server communication, create a server that will calculate the greater number

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for client using TCP.


Description: On the client side: Numbers is accepted from the user through “InputStreamReader(System.in)” which allows to read line of text and sent to server by opening socket client side and send the numbers to the server through “PrintWriter” and “OutputStreamWriter”. Output is sent from server and received by client using “PrintWriter”On the server side: First ServerSocket is created and waits client to open the socket that is “ss.accept()”. The result is sent from client and calculation is done by server.The output is sent to client side using “pw.println(Number " +n + " is greater than " +m);”

Server Program:import java.io.*;import java.net.*;class TCPServerGreater{

public static void main(String arg[]){

Socket s; int port=9999,n,m; try {

ServerSocket ss=new ServerSocket(port);System.out.println("Waiting for client");s=ss.accept();BufferedReader br=new BufferedReader(new InputStreamReader(s.getInputStream()));PrintWriter pw=new PrintWriter(new OutputStreamWriter(s.getOutputStream())) ;String str1=br.readLine();String str2=br.readLine();n=Integer.parseInt(str1);m=Integer.parseInt(str2);System.out.println("First Number recieve from client: " + n);System.out.println("Second Number receive from client: " + m);if (n > m)

pw.println("Number " +n + " is greater than " +m);else

pw.println("Number " +m + " is greater than " +n);pw.flush();pw.close(); br.close();s.close(); ss.close();

}

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catch(Exception e) { }}

}

Client Program:import java.io.*;import java.net.*;class TCPClientGreater{


int port=9999;Socket s;String msg="";try{

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

InetAddress addr=InetAddress.getByName(null);s=new Socket(addr,port);OutputStreamWriter osw=new

OutputStreamWriter(s.getOutputStream());PrintWriter pw=new PrintWriter(osw);BufferedReader br1=new BufferedReader(new InputStreamReader(s.getInputStream()));System.out.print("Enter the First Number: ");String str1=br.readLine();System.out.print("Enter the Second Number: ");String str2=br.readLine();pw.println(str1);pw.println(str2);pw.flush();msg=br1.readLine();System.out.println("Answer from server : ");System.out.println(msg);

}catch(Exception e) { }

}}Output of Server Program:

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Practical 3

Aim: Write a client server program to implement client server communication, create a server that will calculate the factorial for client using UDP.

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Description: On the client side:A number is accepted from the user through ‘InputStreamReader(System.in)’ which allows to read line of text and sent to server using ‘ DatagramPacket outDgp = new DatagramPacket (numbers.getBytes(),numbers.length(),host,port)’ and ‘client.send(outDgp)’. Output is sent from server and received by client using ‘ DatagramPacket inDgp =new DatagramPacket (buffer,buffer.length)’ and ‘client.receive(inDgp)’On the server side: A number is sent from client and calculation is done by server. The output is sent to client side using ‘DatagramPacket outDgp=new DatagramPacket (rsp.getBytes() ,rsp.length() ,senderAddress ,senderPort)’ and ‘ss.send(outDgp)’

Server Program:import java.io.*;import java.net.*;public class UDPServerFactorial{ public static void main(String args[])

{int port =7896;try{

DatagramSocket ss=new DatagramSocket(port);byte[] buffer =new byte[256];DatagramPacket inDgp=new DatagramPacket(buffer,buffer.length);String req,rsp;System.out.println("Waiting for client");ss.receive(inDgp);InetAddress senderAddress =inDgp.getAddress();int senderPort =inDgp.getPort();req=new String(inDgp.getData(),0,inDgp.getLength());int fact=1;int num=Integer.parseInt(req);System.out.println("Number receive from client: "+num);for(int i=2;i<=num;i++)

fact=fact*i;rsp="Factorial of the number is "+ fact;DatagramPacket outDgp=new DatagramPacket(rsp.getBytes(),rsp.length(),senderAddress,senderPort);ss.send(outDgp); ss.close();

}

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catch(Exception e) {System.out.println("Exception "+ e);}}

}

Client Program:import java.io.*;import java.net.*;public class UDPClientFactorial{ public static void main(String args[])

{InetAddress host;int port=7896;try{

host = InetAddress.getLocalHost();DatagramSocket client=new DatagramSocket();BufferedReader br =new BufferedReader(new InputStreamReader(System.in));System.out.print("Enter a Number : ");String Numbers=br.readLine();DatagramPacket outDgp =new DatagramPacket (Numbers.getBytes() ,Numbers.length(),host,port);client.send(outDgp);byte buffer[]=new byte[256];DatagramPacket inDgp =new

DatagramPacket(buffer,buffer.length);client.receive(inDgp);String rsp=new

String(inDgp.getData(),0,inDgp.getLength());System.out.println("Answer from server:");System.out.println(rsp);client.close();

}catch(Exception e){

System.out.println(e);}

}//End of main}Output of Server Program:

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Practical 4

Aim: Create a TCP based echo server.


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Description: Basics in this program:

1. Open a socket. 2. Open an input stream and output stream to the socket. 3. Read from and write to the stream according to the server's protocol. 4. Close the streams. 5. Close the socket.

Server Program:import java.io.*;import java.net.*;class TCPServerEcho{


Socket s;int port=9999,count=0;try{

ServerSocket ss=new ServerSocket(port);System.out.println("Echo Server Started... \n Waiting for Client");s=ss.accept();BufferedReader br=new BufferedReader(new InputStreamReader (s.getInputStream()));PrintWriter pw=new PrintWriter(new OutputStreamWriter (s.getOutputStream())) ;while(true)

{ String str=br.readLine();

if (str.equals("bye")) System.out.println("Client Terminated");

System.out.println("Message from the Client: "+str);pw.println(str.toUpperCase()); pw.flush();

}pw.close();br.close();s.close();ss.close();


}}Client Program:import java.io.*;import java.net.*;

class TCPClientEcho

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{public static void main(String arg[]){

int port=9999;Socket s;String msg="";try{

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

InetAddress addr=InetAddress.getByName(null);s=new Socket(addr,port);OutputStreamWriter osw=new

OutputStreamWriter(s.getOutputStream());PrintWriter pw=new PrintWriter(osw);BufferedReader br1=new BufferedReader(new InputStreamReader(s.getInputStream()));while(true){

System.out.print("Message: ");String str=br.readLine();pw.println(str);pw.flush();if(str.equals("bye")) System.exit(0);msg=br1.readLine();System.out.println("Echo: " + msg);

}br1.close();pw.close();osw.close();s.close();ss.close();


}}


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Practical 5

Aim: Create a UDP based echo server.


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Server Program:import java.io.*;import java.net.*;public class UDPServerEcho{ public static void main(String args[])


DatagramSocket ss=new DatagramSocket(port);byte[] buffer =new byte[256];DatagramPacket inDgp=new DatagramPacket(buffer,buffer.length);String req,rsp;System.out.println("Waiting for client");while(true){

ss.receive(inDgp);InetAddress senderAddress =inDgp.getAddress();int senderPort =inDgp.getPort();req=new String(inDgp.getData(),0,inDgp.getLength());

if(req.equals("bye")) System.out.println("Client Terminated");

ss.close();System.exit(0);System.out.println("Message from Client: " + req);rsp=req.toUpperCase();DatagramPacket outDgp=new DatagramPacket (rsp.getBytes() ,rsp.length(), senderAddress ,senderPort);ss.send(outDgp);

}}catch(Exception e) {

System.out.println("Exception "+e); }

}} Client Program:import java.io.*;import java.net.*;

public class UDPClientEcho{ public static void main(String args[])

{InetAddress host;int port=7896;

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try{

host = InetAddress.getLocalHost();DatagramSocket client=new DatagramSocket();BufferedReader br =new BufferedReader(new

InputStreamReader(System.in));while(true){

System.out.print("Message: ");String str1=br.readLine();DatagramPacket outDgp =new DatagramPacket (str1.getBytes(), str1.length(), host,port);client.send(outDgp);if(str1.equals("bye"))

System.out.println("Client Terminated"); break;byte buffer[]=new byte[256];DatagramPacket inDgp =new

DatagramPacket(buffer,buffer.length);client.receive(inDgp);String rsp=new String(inDgp.getData(),0,inDgp.getLength());System.out.println("Echo: " + rsp);

}client.close();



}//End of main}


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Practical 6Aim: Create an iterative connection-oriented server.


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Server Program:import java.io.*;import java.net.*;

class TCPServerFactorial{


Socket s;int id;

int port=9999,count=0;try{

ServerSocket ss=new ServerSocket(port); System.out.println("Waiting for client");

s=ss.accept();BufferedReader br=new BufferedReader(new InputStreamReader(s.getInputStream()));PrintWriter pw=new PrintWriter(new OutputStreamWriter (s.getOutputStream())) ;while(true)

{ String str=br.readLine();

if (str.equals("bye")) System.out.println("Client Terminated");

int n=Integer.parseInt(str);int i,f=1;System.out.println("Number receive from client: " + n);for(i = 2; i <= n; i++)

f = f * i;pw.println("Factorial is : "+f); pw.flush();

}}catch(Exception e) { }


class TCPClientFactorial{


int port=9999;Socket s;String msg="";try

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{BufferedReader br=new BufferedReader(new

InputStreamReader(System.in));InetAddress addr=InetAddress.getByName(null);s=new Socket(addr,port);OutputStreamWriter osw=new

OutputStreamWriter(s.getOutputStream());PrintWriter pw=new PrintWriter(osw);BufferedReader br1=new BufferedReader(new InputStreamReader(s.getInputStream()));while(true){

System.out.print("Enter a Number (bye to EXIT): ");String str=br.readLine();pw.println(str);pw.flush();if(str.equals("bye"))

System.exit(0);msg=br1.readLine();System.out.println("Answer from server : ");System.out.println(msg);

}br1.close();pw.close();osw.close();s.close();ss.close();

}catch (Exception e) { }

}}


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Practical 7

Aim: Create an iterative connection-less server.


Server Program:import java.io.*;import java.net.*;import java.lang.*;public class UDPServerPalindrome{ public static void main(String args[])


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DatagramSocket ss=new DatagramSocket(port);byte[] buffer =new byte[256];DatagramPacket inDgp=new DatagramPacket(buffer,buffer.length);String req,rsp,rev;System.out.println("Waiting for client");while(true){

ss.receive(inDgp);InetAddress senderAddress =inDgp.getAddress();int senderPort =inDgp.getPort();req=new String(inDgp.getData(),0,inDgp.getLength());if(req.equals("quit"))

{System.out.println("Client Terminated");break;}System.out.println("String recieved from client: " + req);rev = new String((new StringBuffer(req)).reverse());if(rev.equals(req))

rsp="The given string " + req + " is a palindrome";else

rsp="The given string " + req + " is not a palindrome";DatagramPacket outDgp=new DatagramPacket (rsp.getBytes(), rsp.length(), senderAddress, senderPort);ss.send(outDgp);

}ss.close();

}catch(Exception e) { System.out.println("Exception "+e);}


public class UDPClientPalindrome{ public static void main(String args[])

{InetAddress host;int port=7896;try{

host = InetAddress.getLocalHost();DatagramSocket client=new DatagramSocket();BufferedReader br =new BufferedReader(new

InputStreamReader(System.in));while(true){

System.out.print("Enter a String : ");String str=br.readLine();

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DatagramPacket outDgp =new DatagramPacket (str.getBytes(), str.length(), host,port);client.send(outDgp);if(str.equals("quit"))

System.out.println("Client Terminated");break;byte buffer[]=new byte[256];DatagramPacket inDgp =new

DatagramPacket(buffer,buffer.length);client.receive(inDgp);String rsp=new String(inDgp.getData(),0,inDgp.getLength());System.out.println("The Answer from server:");System.out.println(rsp);

}client.close();



}//End of main}



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Practical 8

Aim: Create a concurrent connection-oriented server that will calculate string length for client request.


Description: This is a concurrent server program. Concurrent server is a server which can handle more than one client at a time. In this program, client will request to calculate length of string entered by user. As a response, server will send calculated string length.


class StringThread extends Thread{

Socket client; BufferedReader br; PrintWriter pw;

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public StringThread(Socket clt) { try {

this.client = clt;InetAddress cltAddress = clt.getInetAddress();System.out.println("Client IP : "+cltAddress.getHostAddress() + "\tPort : "+client.getPort());

br = new BufferedReader(new InputStreamReader(client.getInputStream())); pw = new PrintWriter(client.getOutputStream(),true); } catch(Exception e) { System.out.println("Error "); } }

public void run() {

String g="Exit";String str;

try { do { str = br.readLine();

str = str.trim();if ( str.indexOf("bye") == -1)

pw.println("Length of String '" + str +" ' is " +str.length());}while(str.indexOf("bye") == -1);

if(str.indexOf("bye") == 0) {

System.out.println("Client "+client.getLocalPort()+" Exited"); client.close(); } } catch(Exception e) {

System.out.println("Error : "+e.toString()); } }}class ThreadServer {

public static void main(String args[]) throws Exception {

ServerSocket srv = new ServerSocket(5555); System.out.println("Server Started :" +srv);

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for( ; ;){

Socket clt = srv.accept(); StringThread st = new StringThread(clt); st.start();

} }}

Client Program:import java.io.*;import java.net.*;

public class ThreadClient { public static void main(String args[]) { try {

InetAddress ia = InetAddress.getLocalHost(); Socket s = new Socket(ia,5555); BufferedReader br1 = new BufferedReader(new InputStreamReader(System.in));

PrintWriter pw = new PrintWriter(s.getOutputStream(),true); BufferedReader br2 = new BufferedReader(new InputStreamReader(s.getInputStream()));

String str,st; System.out.println("'bye' to EXIT");

do{

System.out.println("Enter the string");str= br1.readLine();

pw.println(str); st =br2.readLine(); if(st !=null ) System.out.println(st);

}while(str.indexOf("bye") == -1); } catch(Exception e)

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{ System.out.println("Error"+ e.toString()); } }}


Output of Client Program (Port 1167):

Output of Client Program (Port 1168):

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Practical 9

Aim: Create a concurrent connection-less server that will calculate string length for client request.


Description: This is a concurrent server program. Concurrent server is a server which can handle more than one client at a time. In this program, client will request to calculate length of string entered by user. As a response, server will send calculated string length.

Server Program:import java.io.*;import java.net.*;import java.util.*;

class UDPPalindromeServer implements Runnable {

DatagramPacket rec_dp,send_dp,status_dp;DatagramSocket server;

public static void main(String args[])throws Exception{

UDPPalindromeServer udp_pal=new UDPPalindromeServer(); udp_pal.server=new DatagramSocket(22222);

try { Thread t=new Thread(udp_pal);

t.start();}catch(Exception e){

e.printStackTrace();}

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} public void run() { try { InetAddress add=InetAddress.getLocalHost(); byte send_buff[]=new byte[1024]; byte rec_buff[]=new byte[1024]; byte status_buff[]=new byte[256]; System.out.println("Welcome to UDP Server"); while (true) {

rec_dp=new DatagramPacket(rec_buff,rec_buff.length,add,22222);

server.receive(rec_dp);String in_val=new String(rec_dp.getData(),0,rec_dp.getLength());in_val=in_val.trim();String rev=new String((new StringBuffer(in_val)).reverse());String answer;if (in_val.equalsIgnoreCase(rev))

answer="The given String is a Palindrome";else

answer="The given String is Not a Palindrome";send_buff=answer.getBytes();

send_dp=new DatagramPacket (send_buff, send_buff.length, rec_dp. getAddress(), rec_dp.getPort());

server.send(send_dp); } } catch(Exception e) { e.printStackTrace(); } }} Client Program:import java.io.*;import java.net.*;

class UDPPalindromeClient{ public static void main(String args[])throws Exception { DatagramSocket server=new DatagramSocket(); BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); InetAddress add=InetAddress.getLocalHost(); byte send_buff[]=new byte[1024];

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byte rec_buff[]=new byte[1024]; byte status_buff[]=new byte[256];

System.out.println("\nCheck Palindrome or not"); while (true) { System.out.print("\nEnter String: "); String val=br.readLine();

send_buff=val.getBytes();DatagramPacket send_dp=new DatagramPacket(send_buff,send_buff.length,add,22222);

server.send(send_dp); DatagramPacket rec_dp=new DatagramPacket(rec_buff,rec_buff.length); server.receive(rec_dp); String result=new String(rec_dp.getData()); result=result.trim(); System.out.println("\n"+result+"\n"); System.out.print("\nTo Exit Enter x or X,press enter to continue: ");

String s=br.readLine();

if (s.equals("X") || s.equals("x") ){

br.close();server.close();System.exit(0);

}}

}}

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Practical 10

Aim: Write a program to implement file transfer protocol.


Description:

Server Program:import java.io.*;import java.net.*;class TCPFileServer implements Runnable{ public static void main(String args[])throws Exception { TCPFileServer fserver=new TCPFileServer(); Thread t=new Thread(fserver); t.start(); } public void run() { InputStream is=null;

OutputStream os=null; BufferedReader in_net=null, file_read=null; PrintWriter pw=null;

ServerSocket server=null;Socket client=null;

try {

System.out.println("Server Started\n"); server=new ServerSocket(30033);

client=server.accept(); System.out.println("Client Connected\n");

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is=client.getInputStream();

os=client.getOutputStream(); in_net=new BufferedReader(new

InputStreamReader(client.getInputStream())); pw=new PrintWriter(os); String s,file_name; file_name=in_net.readLine(); file_name=file_name.trim(); File f=new File(file_name); if (f.exists()) { file_read=new BufferedReader(new FileReader(f)); while ((s=file_read.readLine()) != null) { pw.println(s); pw.flush(); } file_read.close(); } System.out.println("File Flushed"); in_net.close(); client.close();}

catch(Exception e) { e.printStackTrace(); }}

} Client Program:import java.io.*;import java.net.*;import java.lang.*;

public class TCPFileClient{

public static void main(String args[]) throws Exception { Socket echosocket = null; BufferedReader in = null, ins=null, d=null; PrintWriter pw=null,filename=null; try

{echosocket = new Socket(InetAddress.getLocalHost(),30033);d = new BufferedReader(new

InputStreamReader(echosocket.getInputStream()));ins = new BufferedReader(new InputStreamReader(System.in));

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pw=new PrintWriter(echosocket.getOutputStream());filename=new PrintWriter(echosocket.getOutputStream());


System.out.println("\nError in Connection\n :" +e );}

System.out.println("\nFile Transfer Protocol");

System.out.print("\nEnter File in Server with File Extension: - ");String line=ins.readLine();line=line.trim();filename.println(line);filename.flush();String file_ext=line.substring(line.indexOf("."));

String new_filename;System.out.print("\nEnter New File Name: - ");new_filename=ins.readLine();new_filename=new_filename.trim();

String new_file=new_filename+file_ext; String userinput; File f=new File(new_file); FileWriter sp=new FileWriter(f); while((userinput = d.readLine())!=null) { System.out.println(userinput); sp.write(userinput); sp.flush(); Thread.sleep(1000); } System.out.println("\nFile Transfer Done"); d.close(); echosocket.close(); }}

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Practical 11

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Aim: Write a program for chat server.



public class ChatServer {

Socket clientSocket; ServerSocket server; PrintWriter remoteOut; BufferedReader remoteIn,userIn; /** Creates a new instance of Chat */ public ChatServer()

{ try

{ server = new ServerSocket(2345); System.out.println("Starting Server"); clientSocket = server.accept();

System.out.println("Client Connected");remoteIn = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

remoteOut = new PrintWriter(clientSocket.getOutputStream(),true); userIn = new BufferedReader(new InputStreamReader(System.in));

System.out.println("Configured.Start chatting"); while(true)

{ String s = "";

System.out.println("RECEIVED: " + (s = remoteIn.readLine()));if(s.equals("bye"))

break; System.out.print("SEND: ");

remoteOut.println((s = userIn.readLine()));if(s.equals("bye"))

break;}

System.out.println("Shutting Server"); remoteIn.close(); remoteOut.close(); userIn.close(); clientSocket.close(); server.close(); } catch(Exception e)

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{ System.out.println(e); } }

public static void main(String[] args) {

try{

new ChatServer(); } catch(Exception e)

{ System.out.println(e); } }} Client Program:import java.io.*;import java.net.*;

public class ChatClient {

Socket clientSocket; PrintWriter remoteOut; BufferedReader remoteIn,userIn; public ChatClient ()

{ try

{ System.out.println("Client Started"); clientSocket = new Socket("localhost",2345); System.out.println("Connected to server.Configuring...");

remoteIn = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

remoteOut = new PrintWriter(clientSocket.getOutputStream(),true); userIn = new BufferedReader(new InputStreamReader(System.in)); System.out.println("Configured.\nStart Chatting"); while(true)

{String s = "";

System.out.print("SEND: "); remoteOut.println((s = userIn.readLine()));

if(s.equals("bye")) break;

System.out.println("RECEIVED: " + (s = remoteIn.readLine())); if(s.equals("bye"))

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break;}

System.out.println("Exiting..."); remoteIn.close(); remoteOut.close(); userIn.close(); clientSocket.close(); } catch (Exception e) { System.out.println(e); } } public static void main(String[] args)

{ try

{ new ChatClient();

} catch(Exception e)

{ System.out.println(e); } }}



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Advance computer networks

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Transcript of Advance computer networks