stop and wait protocol using java programming language.

IMPLEMENTING STOP & WAIT PROTOCOL

AIM

            To implement the stop and wait protocol using java programming language.

PROCEDURE

Sender

Step1: sequence ß 0

Step2: Accept new packet and assign sequence to it.

Step3: Send packet sequence with sequence number sequence.

Step4: Set timer for recently sent packets.

Step5:   If error free acknowledgment from receiver and NextFrameExpected -> sequence                                           then sequenceß NextFrameExpected.

Step6:  If time out then go to step3.

Step7:  Stop.

Receiver

Step1:  Start.

Step2:  NextFrameExpectedß 0, repeat steps 3 forever.

Step3:  If error-free frame received and sequence= NextFrameExpected, then pass packet to higher layer and NextFrameExpectedß NextFrameExpected+1(modulo 2).

Step4:  Stop.

CODE

Sender.java

import java.io.*;

import java.net.*;

public class Sender{

Socket sender;

ObjectOutputStream out;

ObjectInputStream in;

String packet,ack,str, msg;

int n,i=0,sequence=0;

Sender(){}

public void run(){

 try{

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

System.out.println("Waiting for Connection....");

 sender = new Socket("localhost",2005);

sequence=0;

out=new ObjectOutputStream(sender.getOutputStream());

out.flush();

 in=new ObjectInputStream(sender.getInputStream());

 str=(String)in.readObject();

 System.out.println("reciver     > "+str);

System.out.println("Enter the data to send....");

packet=br.readLine();

n=packet.length();

do{

try{

if(i<n){

msg=String.valueOf(sequence);

msg=msg.concat(packet.substring(i,i+1));

}else if(i==n){

 msg="end";out.writeObject(msg);break;

}out.writeObject(msg);

sequence=(sequence==0)?1:0;

out.flush();

System.out.println("data sent>"+msg);

ack=(String)in.readObject();

System.out.println("waiting for ack.....\n\n");

if(ack.equals(String.valueOf(sequence))){

i++;

System.out.println("receiver   >  "+" packet recieved\n\n");

}else{    

System.out.println("Time out resending data....\n\n");

sequence=(sequence==0)?1:0;

}}catch(Exception e){}

}while(i<n+1);

System.out.println("All data sent. exiting.");

}catch(Exception e){}

finally{

try{

in.close();

out.close();

sender.close();

}

catch(Exception e){}

}}

public static void main(String args[]){

Sender s=new Sender();

s.run();

}}

Receiver.java

import java.io.*;

import java.net.*;

public class Receiver{

ServerSocket reciever;

Socket connection=null;

ObjectOutputStream out;

ObjectInputStream in;

String packet,ack,data="";

int i=0,sequence=0;

Receiver(){}

public void run(){

try{

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

reciever = new ServerSocket(2005,10);

System.out.println("waiting for connection...");

connection=reciever.accept();

sequence=0;

System.out.println("Connection established   :");

out=new ObjectOutputStream(connection.getOutputStream());

out.flush();

in=new ObjectInputStream(connection.getInputStream());

out.writeObject("connected    .");

do{

try{

packet=(String)in.readObject();

if(Integer.valueOf(packet.substring(0,1))==sequence){

data+=packet.substring(1);

sequence=(sequence==0)?1:0;

System.out.println("\n\nreceiver         >"+packet);

}

else

{

System.out.println("\n\nreceiver         >"+packet +"   duplicate data");

}if(i<3){

out.writeObject(String.valueOf(sequence));i++;

}else{

out.writeObject(String.valueOf((sequence+1)%2));

i=0;

}}

catch(Exception e){}

}while(!packet.equals("end"));

System.out.println("Data recived="+data);

out.writeObject("connection ended    .");

}catch(Exception e){}

finally{

try{in.close();

out.close();

reciever.close();

}

catch(Exception e){}

}}

public static void main(String args[]){

Receiver s=new Receiver();

while(true){

s.run();

}

}

}

RESULT:

Thus the program is executed successfully and the output is verified.