Assignment 2 (UDP Ping)

In this lab, you will learn the basics of socket programming for UDP in Python. You will learn how
to send and receive datagram packets using UDP sockets and also, how to handle UDP packet
retransmissions. Throughout the lab, you will gain familiarity with a Ping application and its
usefulness in computing statistics such as packet loss rate.
You need to be familiar with the standard ping protocol Internet Control Message Protocol
ICMP available in modern operating systems first. 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.
Then you are required to implement these functionalities using a simpler protocol, UDP, rather
than the standard ICMP to communicate between a client and a server. You are given a
skeleton code for the Ping server pingserver.py . Your task is to complete the Ping server
code first and then design and implement your Ping client ( pingclient.py ).
You are provided a skeleton code for the Ping server. You are required to complete the skeleton
code pingserver.py first. The places where you need to fill in code are marked with
??????????? . Each place may require one or more lines of code. (Note: You may modify
pingserver.py any way you like, as long as it meets the following requirements. You may
even ignore this sample code and start all over from scratch.)
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
Programming assignment 2 (UDP Ping)
Problem Statement
Server Code
Server sample code
Functionalities of your server
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.
In the sample code, 30% of the client’s packets are simulated to be lost. You should study this
sample code carefully, as it will help you write your Ping client. 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 capitalizes the encapsulated data and sends it
back to the client; if the randomized integer is smaller than 3, the server needs to inform to
the client which packet has been dropped and then client needs to retransmit the dropped
packet.
You need to develop your client code from scratch.
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 <ping_index time_stamp
where ping_index starts at 1 and progresses to 100 for each successive ping message
sent by the client, and time_stamp is the time when the client sends the message.
You client program should support the following:
The client should send 100 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. Therefore, your client
should support retransmitting the dropped packets. (Note that you client is not allowed to
use socket timeout)
Specifically, your client program should
1. send the ping message using UDP to the Ping server ;
2. print the ping response message from the Ping server if the ping message has not been
dropped ;
Client Code
Ping Message Format
Functionalities of your client
3. retransmit the same ping message if the previous ping message(s) have been dropped by
the Ping server ; print which ping message needs to be retransmitted ;
4. calculate and print the round trip time (RTT) in seconds of each ping message/response
pair. (Note that for the retransmitted ping request/response pairs, the starting time-stamp
can be either the time-stamp of the initial ping request message or the most recent ping
request message)
1. Start CSC361-VM , open a terminal, and type sudo mn -x to generate a simple
network topology ;
2. Flush all arp caches (more details can be found in the provided
WiresharkEthernetARP.pdf) ;
3. Run your Ping server over one of the hosts created (e.g., h1)
python pingserver.py <IP addr of Ping server <Port number of Ping server
4. Run your Ping client over one of the hosts created (e.g. h2)
python pingclient.py <IP addr of Ping server <Port number of Ping server
You must demonstrate your working code inside the CSC361-VM using Wireshark. Using
CSC361-VM , the server and the client must use different IP addresses and port numbers.
Your Wireshark demo must capture all related packets, including ARP and UDP .
You are required to create one single document before your demo that has
The screen shot of all your ARP packets and at least 20 UDP packets
The screen shot of your client
You are also required to answer a few questions about your programming assignment during
the demo in ECS 360.
The evaluation scheme is:
(50%) Correctness of Python code
(20%) The created document before your demo. You should clearly write up how to handle
Run the code
Evaluation
the retransmissions at both server and client sides and how to calculate the RTT for the
retransmitted ping request/response pairs
(30%) Questions and Answers during the demo (at least 5 questions)
You will hand in the complete client/server code along with the single document created to
Connex 
What to Hand in