gbn.java

本程序用java编写的模拟的go-to-back网络传送

import java.applet.Applet; 
import java.awt.*; 
import java.awt.event.ActionListener; 
import java.awt.event.ActionEvent; 
  
class packet 
 { 
 boolean on_way, reached_dest, acknowledged, packet_ack, selected; 
 int packet_pos; 
  
 packet() 
  { 
  on_way = false; 
  selected = false; 
  reached_dest = false; 
  acknowledged = false; 
  packet_ack = true; 
  packet_pos = 0; 
  } 
  
 packet(boolean onway, int packetpos) 
  { 
  on_way = onway; 
  selected = false; 
  reached_dest = false; 
  acknowledged = false; 
  packet_ack = true; 
  packet_pos = packetpos; 
  } 
 } 
 

public class gbn extends Applet  implements ActionListener, Runnable 
 {

 final int window_len_def = 5;    // Default values of parameters 
 final int pack_width_def = 10; 
 final int pack_height_def = 30; 
 final int h_offset_def = 100; 
 final int v_offset_def = 50; 
 final int v_clearance_def = 300; 
 final int total_packet_def = 20; 
 final int time_out_sec_def = 30; 
  
 final Color unack_color = Color.red;  //  Default colors of different packets 
 final Color ack_color = Color.yellow; 
 final Color sel_color = Color.green; 
 final Color roam_pack_color = Color.red; 
 final Color roam_ack_color = Color.yellow; 
 final Color dest_color = Color.blue; 
  
 int base, nextseq, fps, selected=-1; 
 boolean timerFlag, timerSleep; 
 Button send, stop, fast, slow, kill, reset; 
 Thread gbnThread, timerThread; 
  
 Dimension offDimension;    // flashing eliminator: double buffering 
    Image offImage; 
    Graphics offGraphics; 
  
 String statusMsg, strCurrentValues; 
  
 packet sender[]; 
  
 // Declaring properties 
  
 int window_len, pack_width, pack_height, h_offset, v_offset, v_clearance, total_packet, time_out_sec; 
//}

 public void init() 
  { 
  String strWinLen, strPackWd, strPackHt, strHrOff, strVtOff, strVtClr, strTotPack, strTimeout; 
  
        strWinLen = getParameter("window_length");  // Start collecting parameters 
        strPackWd = getParameter("packet_width"); 
        strPackHt = getParameter("packet_height"); 
        strHrOff = getParameter("horizontal_offset"); 
        strVtOff = getParameter("vertical_offset"); 
        strVtClr = getParameter("vertical_clearance"); 
        strTotPack = getParameter("total_packets"); 
        strTimeout = getParameter("timer_time_out"); 
  
        // Get the values of the parameters into properties. 
  
        try { 
            if (strWinLen != null) window_len = Integer.parseInt(strWinLen); 
            if (strPackWd != null) pack_width = Integer.parseInt(strPackWd); 
            if (strPackHt != null) pack_height = Integer.parseInt(strPackHt); 
            if (strHrOff != null) h_offset = Integer.parseInt(strHrOff); 
            if (strVtOff != null) v_offset = Integer.parseInt(strVtOff); 
            if (strVtClr != null) v_clearance = Integer.parseInt(strVtClr); 
            if (strTotPack != null) total_packet = Integer.parseInt(strTotPack); 
            if (strTimeout != null) time_out_sec = Integer.parseInt(strTimeout); 
            } catch (Exception e) {} 
  
        // If parameter is not found, use default values. 
  
        window_len = (window_len > 0) ? window_len : window_len_def; 
  pack_width = (pack_width > 0) ? pack_width : pack_width_def; 
  pack_height = (pack_height > 0) ? pack_height : pack_height_def; 
  h_offset = (h_offset > 0) ? h_offset : h_offset_def; 
  v_offset = (v_offset > 0) ? v_offset : v_offset_def; 
  v_clearance = (v_clearance > 0) ? v_clearance : v_clearance_def; 
  total_packet = (total_packet > 0) ? total_packet : total_packet_def; 
   time_out_sec = (time_out_sec > 0) ? time_out_sec : time_out_sec_def; 
  
  base = 0;    // Defining base 
  nextseq = 0;   // Defining Next sequence number. 
  fps = 5;    // Defining default Frame per Second. 
  
  sender = new packet[total_packet]; 
  statusMsg = "Ready to run. Press 'Send New' button to start."; 
  strCurrentValues = "Window Base = "+ base +".   Next Sequence No. = "+ nextseq; 
  
  // Defining the buttons 
  
  send = new Button("Send New"); 
  send.setActionCommand("rdt"); 
  send.addActionListener(this); 
  
  stop = new Button("Stop Animation"); 
  stop.setActionCommand("stopanim"); 
  stop.addActionListener(this); 
  
  fast = new Button("Faster"); 
  fast.setActionCommand("fast"); 
  fast.addActionListener(this); 
  
  slow = new Button("Slower"); 
  slow.setActionCommand("slow"); 
  slow.addActionListener(this); 
  
  kill = new Button("Kill Packet"); 
  kill.setActionCommand("kl"); 
  kill.addActionListener(this); 
  kill.setEnabled(false); 
  
  reset = new Button("Reset"); 
  reset.setActionCommand("rst"); 
  reset.addActionListener(this); 
  
  // Adding the buttons 
  
  add(send); 
  add(stop); 
  add(fast); 
  add(slow); 
  add(kill); 
  add(reset); 
  } 
  
  
 public void start() 
  { 
  if (gbnThread==null)     // Creating main thread and start it 
   gbnThread = new Thread(this); 
  gbnThread.start(); 
  } 
  
 public  void run() 
  { 
  Thread currenthread = Thread.currentThread(); 
  
  while (currenthread==gbnThread)   // While the animation is running 
   if (onTheWay(sender))    // Checks if any of the packets are travelling 
    { 
    for (int i=0; i<total_packet; i++) 
     if (sender[i]!= null) 
      if (sender[i].on_way)     // If packet is roaming 
       if (sender[i].packet_pos < (v_clearance-pack_height)) 
        sender[i].packet_pos+=5;  // Move packet 
       else if (sender[i].packet_ack)  // If it is moving to destination 
        { 
        sender[i].reached_dest = true; 
        if (check_upto_n(i))   // Send acknowledgement if all preceeding 
         {       // packets are received. 
         sender[i].packet_pos = pack_height+5; 
         sender[i].packet_ack = false; 
         statusMsg = "Packet "+i+" received. Acknowledge sent."; 
         } 
        else 
         { 
         sender[i].on_way = false; 
         statusMsg = "Packet "+i+" received. No acknowledge sent."; 
         if (i==selected) 
          { 
          selected = -1; 
          kill.setEnabled(false); 
          } 
         } 
        } 
       else if (!sender[i].packet_ack)   // acknowledgement 
        { 
        statusMsg = "Packet "+ i +" acknowledge received."; 
        sender[i].on_way = false; 
        for (int n=0; n<=i; n++) 
         sender[n].acknowledged = true; 
        if (i==selected) 
         { 
         selected = -1; 
         kill.setEnabled(false); 
         } 
  
        timerThread = null;    //resetting timer thread 
  
        if (i+window_len<total_packet) 
         base = i+1; 
        if (nextseq < base+window_len) send.setEnabled(true); 
  
        if (base != nextseq) 
         { 
         statusMsg += " Timer restarted."; 
         timerThread = new Thread(this); 
         timerSleep = true; 
         timerThread.start(); 
         } 
        else 
         statusMsg += " Timer stopped."; 
        } 
    strCurrentValues = "Window Base = "+ base +".   Next Sequence No. = "+ nextseq; 
    repaint(); 
  
    try { 
     Thread.sleep(1000/fps); 
     } catch (InterruptedException e) 
      { 
      System.out.println("Help"); 
      } 
    } 
   else 
    gbnThread = null; 
  
  
  while (currenthread == timerThread) 
   if (timerSleep) 
    { 
    timerSleep=false; 
    try { 
     Thread.sleep(time_out_sec*1000); 
     } catch (InterruptedException e) 
       { 
       System.out.println ("Timer interrupted."); 
       } 
    } 
   else 
    { 
    for (int n=base; n<base+window_len; n++) 
     if (sender[n] != null) 
      if (!sender[n].acknowledged) 
       { 
       sender[n].on_way = true; 
       sender[n].packet_ack = true; 
       sender[n].packet_pos = pack_height+5; 
       } 
    timerSleep = true; 
    if (gbnThread == null) 
     { 
     gbnThread = new Thread (this); 
     gbnThread.start(); 
     } 
  
    statusMsg = "Packets resent by timer. Timer restarted."; 
    } 
  } 
  
  
 public void actionPerformed(ActionEvent e) 
  { 
  String cmd = e.getActionCommand(); 
  
  if (cmd == "rdt" && nextseq < base+window_len) // Send button is pressed 
   { 
   sender[nextseq] = new packet(true,pack_height+5); 
  
   statusMsg = "Packet "+ nextseq +" sent."; 
  
   if (base == nextseq) 
    {    // i.e. the window is empty and a new data is getting in 
    statusMsg += " Timer set for packet "+ base +"."; 
    if (timerThread == null) 
     timerThread = new Thread(this); 
    timerSleep = true; 
    timerThread.start(); 
    }