Go Back N ARQ using Java

Server.java

package com.t4b.demo.gobackn; import java.net.*; import java.io.*; import java.util.*; public class Server { public static void main(String args[]) throws Exception { ServerSocket server = new ServerSocket(6262); System.out.println("Server established."); Socket client = server.accept(); ObjectOutputStream oos = new ObjectOutputStream(client.getOutputStream()); ObjectInputStream ois = new ObjectInputStream(client.getInputStream()); System.out.println("Client is now connected."); int x = (Integer) ois.readObject(); int k = (Integer) ois.readObject(); int j = 0; int i = (Integer) ois.readObject(); boolean flag = true; Random r = new Random(6); int mod = r.nextInt(6); while (mod == 1 || mod == 0) mod = r.nextInt(6); while (true) { int c = k; for (int h = 0; h <= x; h++) { System.out.print("|" + c + "|"); c = (c + 1) % x; } System.out.println(); System.out.println(); if (k == j) { System.out.println("Frame " + k + " recieved" + "\n" + "Data:" + j); j++; System.out.println(); } else System.out.println("Frames recieved not in correct order" + "\n" + " Expected farme:" + j + "\n" + " Recieved frame no :" + k); System.out.println(); if (j % mod == 0 && flag) { System.out.println("Error found. Acknowledgement not sent. "); flag = !flag; j--; // it was like j-; } else if (k == j - 1) { oos.writeObject(k); System.out.println("Acknowledgement sent"); } System.out.println(); if (j % mod == 0) flag = !flag; k = (Integer) ois.readObject(); if (k == -1) break; i = (Integer) ois.readObject(); } System.out.println("Client finished sending data. Exiting"); oos.writeObject(-1); } }

Client.java

package com.t4b.demo.gobackn; import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.net.Socket; public class Client { public static void main(String args[]) throws Exception { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); System.out.print("Enter the value of m : "); int m = Integer.parseInt(br.readLine()); int x = (int) ((Math.pow(2, m)) - 1); System.out.print("Enter no. of frames to be sent:"); int count = Integer.parseInt(br.readLine()); int data[] = new int[count]; int h = 0; for (int i = 0; i < count; i++) { System.out.print("Enter data for frame no " + h + " => "); data[i] = Integer.parseInt(br.readLine()); h = (h + 1) % x; } Socket client = new Socket("localhost", 6262); ObjectInputStream ois = new ObjectInputStream(client.getInputStream()); ObjectOutputStream oos = new ObjectOutputStream(client.getOutputStream()); System.out.println("Connected with server."); boolean flag = false; GoBackNListener listener = new GoBackNListener(ois, x); listener = new GoBackNListener(ois, x); listener.t.start(); int strt = 0; h = 0; oos.writeObject(x); do { int c = h; for (int i = h; i < count; i++) { System.out.print("|" + c + "|"); c = (c + 1) % x; } System.out.println(); System.out.println(); h = strt; for (int i = strt; i < x; i++) { System.out.println("Sending frame:" + h); h = (h + 1) % x; System.out.println(); oos.writeObject(i); oos.writeObject(data[i]); Thread.sleep(100); } listener.t.join(3500); if (listener.reply != x - 1) { System.out.println( "No reply from server in 3.5 seconds. Resending data from frame no " + (listener.reply + 1)); System.out.println(); strt = listener.reply + 1; flag = false; } else { System.out.println("All elements sent successfully. Exiting"); flag = true; } } while (!flag); oos.writeObject(-1); } } class GoBackNListener implements Runnable { Thread t; ObjectInputStream ois; int reply, x; GoBackNListener(ObjectInputStream o, int i) { t = new Thread(this); ois = o; reply = -2; x = i; } @Override public void run() { try { int temp = 0; while (reply != -1) { reply = (Integer) ois.readObject(); if (reply != -1 && reply != temp + 1) reply = temp; if (reply != -1) { temp = reply; System.out.println("Acknowledgement of frame no " + (reply % x) + " recieved."); System.out.println(); } } reply = temp; } catch (Exception e) { System.out.println("Exception => " + e); } } }

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