Server.java

/**
 * A UDP Server
 * @author Kunal Kanade

 Go Back N ARQ(Automatic Repeat Request)
 */
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--;
			}
			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);
	}
}