Programming Assignment: UDP Ping Lab In this lab, you will learn the basics of socket programming for UDP in C.

Programming Assignment: UDP Ping Lab

In this lab, you will learn the basics of socket programming for UDP in C. You will learn how to

send and receive datagram packets using UDP sockets and also, how to set a proper socket

timeout. Throughout the lab, you will gain familiarity with a Ping application and its usefulness

in computing statistics such as packet loss rate.

You will first study a simple Internet ping server written in Python, and implement a

corresponding client in C. The functionality provided by these programs is similar to the

functionality provided by standard ping programs available in modern operating systems.

However, these programs use a simpler protocol, UDP, rather than the standard Internet Control

Message Protocol (ICMP) to communicate with each other. 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 task is to write the Ping client

in C. You must test your code in CSIL. That is where we will grade your program.

Server Code

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

running your client program. You do not need to modify this code.

In this server code, 30% of the client's packets are simulated to be lost. You should study this

code carefully, as it will help you write your ping client.

# UDPPingerServer.py

# We will need the following module to generate randomized lost

packets

import random

from socket import *

# Create a UDP socket

# Notice the use of SOCK_DGRAM for UDP packets

serverSocket = socket(AF_INET, SOCK_DGRAM)

# Assign IP address and port number to socket

serverSocket.bind(('', 12000))

while True:

# Generate random number in the range of 0 to 10

rand = random.randint(0, 10)

# Receive the client packet along with the address it is

coming from

message, address = serverSocket.recvfrom(1024)

# If rand is less is than 4, we consider the packet lost

and do not respond

if rand < 4:

continue

# Otherwise, the server responds

serverSocket.sendto(message, address)

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

and if a randomized integer is greater than or equal to 4, the server simply returns the

encapsulated data back to the client.

Packet Loss

UDP provides applications with an unreliable transport service. Messages may get lost in the

network due to router queue overflows, faulty hardware or some other reasons. 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 creates a variable randomized

integer which determines whether a particular incoming packet is lost or not.

Client Code

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.

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

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, a packet

sent from the client to the server may be lost in the network, or vice versa. For this reason, the

client cannot wait indefinitely for a reply to a ping message. You should get the client wait up to

one second for a reply; if no reply is received within one second, your client program should

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

the C documentation for DatagramSocket to find out how to set the timeout value on a datagram

socket.

During development, you should run the UDPPingerServer.py 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 the ping server and

ping client running on different machines in CSIL.

Message Format

The ping messages in this lab are formatted in a simple way. The client message is one line,

consisting of ASCII characters in the following format:

PING sequence_number time

where sequence_number starts at 1 and progresses to 10 for each successive ping message sent by

the client, and time is the time when the client sends the message.

Client Output

Your client should produce output modeled after the actual ping command. To see the ping command

output, type ping <hostname>. For example, ping www.google.com, or ping csil-01.

Similar to the output you see from this command, your output should be in the following format:

PING received from machine_name: seq#=X time=Y ms

where X is the sequence number of the received packet and Y is the RTT in milliseconds. As your

client terminates after it receives the tenth ping response (or timeout), it should print the following:

--- ping statistics --- X packets transmitted, Y received, Z% packet loss rtt min/avg/max = MIN AVG

MAX ms

where X is the number of packets transmitted, Y is the number of packets received, and Z is the

percent that were lost. To produce the last line of output you will need to calculate the minimum,

average, and maximum RTTs and fill in the appropriate values.

What to Hand in

You will hand in the complete client code (named PingClient.c) and a Makefile that compiles

your program.