Go Back N - Sender & Receiver

1. Go Back N Sender:

import java.io.*; import java.net.*; import java.lang.*; public class gbnsend { public static void main(String args[]) { int serverport=3333; String address="127.0.0.2"; try { InetAddress ipaddress=InetAddress.getByName(address); Socket socket=new Socket(ipaddress,serverport); InputStream sin=socket.getInputStream(); OutputStream sout=socket.getOutputStream(); DataInputStream in=new DataInputStream(sin); DataOutputStream out=new DataOutputStream(sout); BufferedReader keyboard=new BufferedReader(new InputStreamReader(System.in)); String line=null; String word []=new String [8]; int i; System.out.println("plz input the no of frames to b sent"); int n=Integer.parseInt(keyboard.readLine()); for(i=0;i<n;i++) { word[i]=keyboard.readLine(); } i=0; while(i<n) { System.out.println("sending frame "+word[i]); out.writeUTF(word[i]); out.flush(); i++; } try { Thread.sleep(1000); } catch(InterruptedException e) { e.printStackTrace(); } line=in.readUTF(); System.out.println("nack received for frame "+line); i=Integer.parseInt(line); out.writeUTF(word[i]); System.out.println("retransmitting all frames after "+word[i]); i++; while(i<n) { System.out.println("sending frame "+word[i]); out.writeUTF(word[i]); out.flush(); i++; } } catch(Exception e) { e.printStackTrace(); } } }

2. Go Back N Receiver:

import java.net.*; import java.io.*; public class gbnreceive { public static void main(String args[]) { int port=3333; try { ServerSocket ss=new ServerSocket(port); System.out.println("waiting for user2"); Socket socket=ss.accept(); System.out.println("user detected"); System.out.println(); InputStream sin=socket.getInputStream(); OutputStream sout=socket.getOutputStream(); DataInputStream in=new DataInputStream(sin); DataOutputStream out=new DataOutputStream(sout); BufferedReader keyboard=new BufferedReader(new InputStreamReader(System.in)); String line=null; String word []=new String [8]; int i=0; while(i<4) { line=in.readUTF(); word[i]=line; System.out.println("frame "+word[i]+" received successfully"); i++; } while(i<8) { if(i==4) { System.out.println("frame "+i+" not received"); i++; } else { System.out.println("frame "+i+" discarded"); i++; } } System.out.println("requesting for retransmaission"); line=keyboard.readLine(); out.writeUTF(line); out.flush(); i=4; while(i<8) { line=in.readUTF(); word[i]=line; i++; } System.out.println("received all retransmitted frames successfully"); } catch(Exception e) { e.printStackTrace(); } /*finally { sin.close(); sout.close(); in.close(); out.close(); }*/ } }

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