Stop and Wait Protocol without Timeout

// Stop and Wait Protocol

// Sender

import java.io.*;

import java.net.*;

public class Sdr

{

     Socket sender;

   

     ObjectOutputStream out;

    ObjectInputStream in;

   

     String pkt, ack, data;

    

    int n, i = 0, seq = 0;

    

     Sdr()

     {

     }

   

     public void run() throws IOException

     {

        try

          {

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

           

              sender = new Socket("localhost",1500);

            seq = 0;

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

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

                       

            while(true)

              {

                System.out.print("\nEnter the data to send : ");

              data = br.readLine().trim();

                       

                   pkt = String.valueOf(seq);

                   pkt = pkt.concat(data);

                   out.writeObject(pkt);

                   out.flush();

                  

                   if(data.equals("Terminate"))

                        break;                       

                       

                   ack = (String)in.readObject();

                       

                   if(ack.equals(String.valueOf(seq)))

                   {

                        System.out.println("ack recerived. ");    

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

                   }

                   else

                   {     

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

                   }            

            }

          }

          catch(Exception e){}

       

          finally

          {

              in.close();

              out.close();

              sender.close();

              System.out.println("\nConnection Terminated.");

          }

    }

    

    public static void main(String args[]) throws IOException

     {

        Sdr s = new Sdr();

            s.run();

    }

}

// Stop and Wait Protocol

// Reciever

import java.io.*;

import java.net.*;

public class Rcr

{

    ServerSocket reciever;

    

    Socket conc = null;

   

     ObjectOutputStream out;

    ObjectInputStream in;

   

     String ack, pkt, data="";

    int i = 0, seq = 0;

  

     Rcr()

     {

     }

   

    

     public void run() throws IOException

     {

        try

          {

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

           

              reciever = new ServerSocket(1500,10);

              conc = reciever.accept();

           

              if(conc!=null)

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

                            

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

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

             

              while(true)

              {

                   pkt = (String)in.readObject();

                   ack = pkt.substring(0,1);

                   data = pkt.substring(1);

                  

                   if(data.equals("Terminate"))

                        break;

                  

                   if(Integer.valueOf(ack) == seq)

                   {

                        System.out.println("\nMsg received : " + data);

                        out.writeObject(ack);

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

                   }

                   else

                   {

                        System.out.println("\nMsg : "+ data + "(-> Duplicate data)");

                   }

              }                 

          }

          catch(Exception e)

          {  

          }

          finally

          {

              System.out.println("\nConnection Terminated.");

              in.close();

              out.close();

              reciever.close();

          }

    }

    

    public static void main(String args[]) throws IOException

     {

        Rcr r = new Rcr();

          r.run();

     }

}

Output:

Sender Window

>javac Sdr.java

>java Sdr

Enter the data to send : asd

ack recerived.

Enter the data to send : qwe

ack recerived.

Enter the data to send : zxc

ack recerived.

Enter the data to send : Terminate

Connection Terminated.

> 

Receiver window

>javac Rcr.java

>java Rcr

Connection established :

Msg received : asd

Msg received : qwe

Msg received : zxc

Connection Terminated.

>