Hello I need help on how to complete to program.

Programming Assignment 3: UDP Pinger Lab

In this lab, you will study a simple Internet ping server written in the Java language, and

implement a corresponding client. The functionality provided by these programs are similar to

the standard ping programs available in modern operating systems, except that they use UDP

rather than Internet Control Message Protocol (ICMP) to communicate with each other. (Java

does not provide a straightforward means to interact with ICMP.)

The ping protocol allows a client machine to send a packet of data to a remote machine, and have

the remote machine return the data back to the client unchanged (an action referred to as

echoing). Among other uses, the ping protocol allows hosts to determine round-trip times to

other machines.

You are given the complete code for the Ping server below. Your job is to write the Ping client.

Server Code

The following code fully implements a ping server. You need to compile and run this code. You

should study this code carefully, as it will help you write your Ping client.

import java.io.*; import java.net.*; import java.util.*;

/* * Server to process ping requests over UDP. */

public class PingServer {

private static final double LOSS_RATE = 0.3; private static final int AVERAGE_DELAY =

100; // milliseconds

public static void main(String[] args) throws Exception {

// Get command line argument. if (args.length != 1) {

System.out.println("Required arguments: port");

return; }

int port = Integer.parseInt(args[0]);

// Create random number generator for use in simulating // packet loss and network

delay. Random random = new Random();

// Create a datagram socket for receiving and sending UDP packets // through the port specified

on the command line. DatagramSocket socket = new DatagramSocket(port);

// Processing loop. while (true) {

// Create a datagram packet to hold incomming UDP packet. DatagramPacket request = new

DatagramPacket(new byte[1024], 1024);

// Block until the host receives a UDP packet. socket.receive(request);

// Print the recieved data. printData(request);

// Decide whether to reply, or simulate packet loss. if (random.nextDouble() < LOSS_RATE) {

System.out.println(" Reply not sent.");

continue; }

// Simulate network delay. Thread.sleep((int) (random.nextDouble() * 2 *

AVERAGE_DELAY));

// Send reply. InetAddress clientHost = request.getAddress(); int clientPort =

request.getPort(); byte[] buf = request.getData(); DatagramPacket reply = new

DatagramPacket(buf, buf.length, clientHost, clientPort); socket.send(reply);

System.out.println(" Reply sent."); }

}

/* * Print ping data to the standard output stream. */

private static void printData(DatagramPacket request) throws Exception {

// Obtain references to the packet's array of bytes. byte[] buf = request.getData();

// Wrap the bytes in a byte array input stream, // so that you can read the data as a stream of

bytes. ByteArrayInputStream bais = new ByteArrayInputStream(buf);

// Wrap the byte array output stream in an input stream reader, // so you can read the data as a

stream of characters. InputStreamReader isr = new InputStreamReader(bais);

// Wrap the input stream reader in a bufferred reader, // so you can read the character data a line

at a time. // (A line is a sequence of chars terminated by any combination of and .)

BufferedReader br = new BufferedReader(isr);

// The message data is contained in a single line, so read this line. String line = br.readLine();

// Print host address and data received from it. System.out.println(

"Received from " + request.getAddress().getHostAddress() + ": " + new String(line) );

} }

The server sits in an infinite loop listening for incoming UDP packets. When a packet comes in,

the server simply sends the encapsulated data back to the client.

Packet Loss

UDP provides applications with an unreliable transport service, because messages may get lost in

the network due to router queue overflows or other reasons. In contrast, TCP provides

applications with a reliable transport service and takes care of any lost packets by retransmitting

them until they are successfully received. Applications using UDP for communication must

therefore implement any reliability they need separately in the application level (each application

can implement a different policy, according to its specific needs).

Because packet loss is rare or even non-existent in typical campus networks, the server in this lab

injects artificial loss to simulate the effects of network packet loss. The server has a parameter

LOSS_RATE that determines which percentage of packets should be lost.

The server also has another parameter AVERAGE_DELAY that is used to simulate transmission

delay from sending a packet across the Internet. You should set AVERAGE_DELAY to a

positive value when testing your client and server on the same machine, or when machines are

close by on the network. You can set AVERAGE_DELAY to 0 to find out the true round trip

times of your packets.

Compiling and Running Server

To compile the server, do the following:

javac PingServer.java

To run the server, do the following:

java PingServer port

where port is the port number the server listens on. Remember that you have to pick a port

number greater than 1024, because only processes running with root (administrator) privilege

can bind to ports less than 1024.

Note: if you get a class not found error when running the above command, then you may need to

tell Java to look in the current directory in order to resolve class references. In this case, the

commands will be as follows:

java -classpath . PingServer port

Your Job: The Client

You should write the client so that it sends 10 ping requests to the server, separated by

approximately one second. Each message contains a payload of data that includes the keyword

PING, a sequence number, and a timestamp. After sending each packet, the client waits up to one

second to receive a reply. If one seconds goes by without a reply from the server, then the client

assumes that its packet or the server's reply packet has been lost in the network.

Hint: Cut and paste PingServer, rename the code PingClient, and then modify the code.

You should write the client so that it starts with the following command:

java PingClient host port

where host is the name of the computer the server is running on and port is the port number it is

listening to. Note that you can run the client and server either on different machines or on the

same machine.

The client should send 10 pings to the server. Because UDP is an unreliable protocol, some of

the packets sent to the server may be lost, or some of the packets sent from server to client may

be lost. For this reason, the client cannot wait indefinitely for a reply to a ping message. You

should have the client wait up to one second for a reply; if no reply is received, then the client

should assume that the packet was lost during transmission across the network. You will need to

research the API for DatagramSocket to find out how to set the timeout value on a datagram

socket.

Your client will display the reply message from the server along with the RTT for each datagram

received or a message indicating lost packet for those not returned within the time limit.

When developing your code, you should run the ping server on your machine, and test your

client by sending packets to localhost (or, 127.0.0.1). After you have fully debugged your code,

you should see how your application communicates across the network with a ping server run by

another member of the class.

Message Format

The ping messages in this lab are formatted in a simple way. Each message contains a sequence

of characters terminated by a carriage return character (r) and a line feed character (n). The

message contains the following string:

PING sequence_number time CRLF

where sequence_number starts at 0 and progresses to 9 for each successive ping message sent by

the client, time is the time when the client sent the message, and CRLF represent the carriage

return and line feed characters that terminate the line.

When you are finished writing the client, complete the following exercise.

Currently the program calculates the round-trip time for each packet and prints them out

individually. Modify this to correspond to the way the standard ping program works. You