Stop and Wait Protocol With Timeout

// Stop and Wait Protocol

// Using Timers to create delays and Timeout

// Sender

import java.io.*;

import java.net.*;

import java.util.*;

public class Sdr

{

     Socket sender;

   

     ObjectOutputStream out;

     ObjectInputStream in;

   

     String pkt, ack="", data="";

    

     int seq = 0;

    

     boolean Dup = false;

    

     Sdr()

     {

     }

   

     public void run() throws IOException

     {

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

           

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

          sender.setSoTimeout(5*1000);

          seq = 0;

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

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

                       

          while(true)

          {

                  

               try

              {

                   if(Dup)

                   {

                        out.writeObject(pkt);

                        Dup = false;

                   }

                   else

                   {

                        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();

                   try

                   {            

                        ack = (String)in.readObject();

                                                                       

                        if(data.equals("Terminate"))

                             break;

                       

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

                        {

                             System.out.println("ack received : " + ack);

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

                        }

                        else

                             Dup = true;

                       

                   }  

                   catch(SocketTimeoutException ste)

                   {

                        System.out.println("Ack timeout. resend data");

                        Dup = true;

                   }

              }            

              catch(Exception e)

              {

              }

                  

          }

         

          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.*;

import java.util.*;

public class Rcr

{

     ServerSocket reciever;

    

     Socket conc = null;

   

     ObjectOutputStream out;

     ObjectInputStream in;

   

     String ack, pkt, data="";

     int seq = 0, delay ;

  

     Random r = new Random();

     

     Rcr()

     {

     }

   

    

     public void run() throws IOException, InterruptedException

     {

       

          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)

          {

              try

              {

                   pkt = (String)in.readObject();

                   ack = pkt.substring(0,1);

                   data = pkt.substring(1);

                                     

                   if(data.equals("Terminate"))

                        break;

                       

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

                   {

                        delay = r.nextInt(10);

                        Thread.currentThread().sleep(delay*1000);

                       

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

                        System.out.println("sending ack " +ack);

                       

                        out.writeObject(ack);

                       

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

                   }

                   else

                        out.writeObject(ack);     

                       

                                 

                   out.flush();

                  

              }                 

         

              catch(Exception e)

              {  

              }

          }

          in.close();

          out.close();

          reciever.close();

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

     }

    

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

     {

          Rcr r = new Rcr();

          r.run();

     }

}