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Bridge.java
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Bridge.java
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// A stateless bridge between a client and a server simulating UDP packet loss and error.
// Author: Dr. Mohammad Rezaeian
import java.net.*;
class Bridge {
public static void main(String args[]) throws Exception {
boolean perfectNetwork = false;
boolean noLoss = true; //Packet loss is not possible (only error)
boolean noAckLoss = false;//Packets from client to server impossible to be lost
boolean s2c = false;
int N = 4;//statisticaly a loss or error event happens in every N packets
byte[] dataBuffer = new byte[128];
int bridgePort = 4000;
int serverPort = 5000;
InetAddress IPAddress = InetAddress.getByName("localhost");
DatagramPacket sendPacket = new DatagramPacket(dataBuffer, dataBuffer.length, IPAddress, serverPort);
DatagramPacket receivePacket = new DatagramPacket(dataBuffer, dataBuffer.length);
do {
try { //for avoiding rare binding exceptions
DatagramSocket routerSocket = new DatagramSocket(bridgePort);
routerSocket.receive(receivePacket);
int clientPort = receivePacket.getPort();
int downlink = 0, uplink = 1;
boolean lost = false;
while (true) {
if (!lost || noLoss) {
routerSocket.send(sendPacket);
}
lost = false;
dataBuffer = new byte[128];
receivePacket.setData(dataBuffer);
sendPacket.setData(dataBuffer);
System.out.println("Uplink=" + uplink + " Downlink=" + downlink);
routerSocket.receive(receivePacket);
if (receivePacket.getPort() == clientPort) {
sendPacket.setPort(serverPort);
uplink++;
s2c = false;
} else {
//String text = new String (receivePacket.getData());
//System.out.println(text);
sendPacket.setPort(clientPort);
downlink++;
s2c = true;
}
if (!perfectNetwork) {
if (!noAckLoss || (noAckLoss && s2c)) {
if ((int) (Math.random() * N) == 1) {
lost = true;
}
}
if ((int) (Math.random() * N) == 1) {
dataBuffer[2] = '*';
}
}
}
} catch (SocketException e) {
bridgePort++;
System.out.println("Note to client: Bridge port is " + bridgePort);
}
} while (true);
}
}