Assignment #3 CS 3357a


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We have seen how to send data over a TCP connection and now we want to explore data transfer using
UDP. As you recall from the lectures, UDP is a non­reliable protocol so we are going to need to create a
reliable transfer protocol in the application layer.
We will once again have two applications ( and but this time we will be
using the UDP protocol, not TCP to communicate across the network. This means we have to create the
reliable data transfer protocol (rdt) we saw in our textbook, specifically, we will create rdt2.2 for this
Just to refresh your memory, below are the FSMs for both the client and server we need to create:
We will be using the following format for our Pseudo UDP packet:
ACK – Indicates if packet is ACK or not. Valid values (1 or 0)
SEQ – Sequence number of packet. Valid values (1 or 0)
DATA – Application Data (8 bytes)
CHKSUM – MD5 Checksum of packet (32 Bytes)
You will need to create the packet, load it with the necessary values and then send it to the server. The
server will receive the packet, check to see if it is corrupted and then take appropriate action. This
process will exactly mirror rdt2.2 as shown in the textbook, so please make sure you follow it
You must create two files, and The details of each are shown below.
UDP_Client –
This app must connect to the UDP_Server app via UDP (you can use the local loopback address of along with any port number you wish) then send three separate packets containing the
following information:
Remember, in order to accomplish this, the client application must also be able to receive data in the
form of acknowledgements from the server because we will be using the rdt2.2 process for creating a
reliable transfer over UDP.
UDP_Server –
This app will establish a UDP socket and listen for incoming connections from the client. When a
connection is made the server will consume the data and follow the rdt2.2 process as shown in chapter 3
of the course textbook.
Remember, in order to accomplish this, the server application must also be able to send
acknowledgements because we will be using the rdt2.2 process for creating a reliable transfer over UDP.
Other Information
The output from the UDP_Server and UDP_Client should display a line of text for each of the following
Received Packet (with all packet values shown)
Packet Checksum Compare Result (ie. Corrupt or not corrupt)
Sent Packet (with all packet values shown)
I have included sample files for both UDP_Client and UDP_Server to get you started. The sample files
show you how to do the following:
Create a UDP connection
Create a ‘pseudo UDP packet’
Calculate the checksum
Fill the packet and send it to the server
Receive the packet and unpack it
Compare checksums to ensure the packet is not corrupted
You will need to do the rest. (The files are tested for Python v3)
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What to Submit
You will be submitting the following via OWL :
Files and with documentation for any command line
arguments/variables to be set, and Python Version. (We need to know how to run your app!)
Two screen captures showing
1. output messages during the session
2. output messages during the session
100 points Total
100 points Function and design of your client and server apps
You will be graded on the following:
Design and function of your applications
Documentation within your applications (Yes, it is important. No one wants to work on
undocumented apps)
Assignment Text
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