Course: CISC450/650 ELEG651 CPEG419 Computer Networks
Professor: Paul D. Amer
Title: Project/Program 1 - Simple File Transfer over TCP or UDP
Assignment last updated: 2/26/2015
Due Date:

Tasks

REQUIREMENT: For all parts, the client and server MUST run on different computers, not over a single machine's loopback interface. Afterall, this course is networking!

(10pts) Starting Easy

Read about TCP and UDP client-servers in Section 2.7. Note: the textbook's programs are named TCPClient, TCPServer, UDPClient, and UDPServer. More meaningful names would be: MakeUpperCaseClientUsingTCP, MakeUpperCaseServerUsingTCP, MakeUpperCaseClientUsingUDP, and MakeUpperCaseServerUsingUDP, respectively. It's important that you understand why these names are more meaningful. Do you?
Read about sockets in Python (e.g., http://docs.python.org/3.1/howto/sockets.html).
Install, change the names to the ones suggested, and execute Chapter 2's TCP and UDP client-servers. The client and server must be run on two DIFFERENT machines. Note: the textbook's Python programs can be cut and pasted from www.cis.udel.edu/~amer/650/Assignments/KuroseRoss-6ed-Section2.7-TCP-UDP-clients-servers.py
REQUIREMENT: Add appropriate, meaningful header comments to both the client and server. See Amer's coding standard.
REQUIREMENT: SUBMIT in class paper copies of your 4 scripts showing your source code and that it compiles, and then demonstrating that your client-servers work as described in the book. Your submitted output MUST provide evidence that your client and server are running on different machines. For example, here is a script for the MakeUpperCaseClientUsingTCP. You will need to submit analogous scripts for the other three modules.

start script for MakeUpperCaseClientUsingTCP

uname -a /* you MUST show name of machine that this module is executing on */

cat MakeUpperCaseClientUsingTCP.py /* show code */

execute MakeUpperCaseClientUsingTCP /* start the module */

... /* output feedback showing the module's actions */

end script

REQUIREMENT: Normally on assignments groups may not interact. As an exception, for this part only, after getting your client-servers working, groups MUST test their code with at least one other group. For example, Group A runs their server on a machine, and tells Group B the machine name and well-known port. Then Group B modifies their client to use Group A's server. Then Group A and B switch roles. SUBMIT: a brief description of which group you tested with, and the results of the test. Be honest, you are not graded on whether or not your code worked the first time.

(35pts) Simple File Transfer using TCP

Write an FTP client-server application where the client (1) prompts a user for two items: a destination file server machine name or IP address, and the name of a file supposedly stored on the destination file server, and (2) then uses TCP to ask the server to transfer the file back over TCP to the client. Your client-server should use 2 TCP connections; one for Control PDUs, and one for transferring the file.
Before the file is transferred, the client sends the filename to the server; the server checks if the file exists and returns a status (yes or no). If no, the client tells the user that the file is unavailable. If yes, the file is transferred. Be sure to clearly comment what the client and server do.

REQUIREMENT: Your client and server must be named: FTPClientUsingTCP.py and FTPServerUsingTCP.py, respectively.
The client/server textbook examples are designed for interactive input (the client reads input using "readline.") Ideally your FTP programs should be able to transfer any type of file: text or binary, and therefore should not use "readline" or any input method that assumes lines of text. (A binary file may have no newline characters in it.)
Your client/server may hard code a "well-known" port number on the file server.
You may assume the file to be transferred is no larger than 5,000 bytes.
REQUIREMENT: In FTPClientUsingTCP, if a connection fails, trap the exception, and output a meaningful message such as "FTPClientUsingTCP: Unable to open TCP connection to HOST X at PORT Y", and terminate gracefully. If the file to transfer does not exist at the server, the server should tell the client, and the client should print an appropriate message.

REQUIREMENT: Transfer a file of at least 2000 bytes.

REQUIREMENT: SUBMIT in class paper copies of your two programs: FTPClientUsingTCP.py and FTPServerUsingTCP.py

REQUIREMENT: UPLOAD your two programs: FTPClientUsingTCP.py and FTPServerUsingTCP.py to the class Sakai site
REQUIREMENT: SUBMIT in class paper copies of 4 scripts, 2 for the case that the file to transfer is not on the server, and 2 when the file is on the server. For each case, show one script demonstrating FTPServerUsingTCP running on the server; and one script demonstrating FTPClientUsingTCP running on the client. For example:

start script for FTPServerUsingTCP
uname -a /* you MUST show name of machine that server is executing on */
ls -l /* show files that exist on the server */
execute FTPServerUsingTCP /* begin the server process */
... /* feedback indicating the failed file transfer */
end script

start script for FTPClientUsingTCP
uname -a /* you MUST show name of machine that client is executing on */
ls -l /* show files that exist at client (file to transfer should NOT appear on client) */
execute FTPClientUsingTCP /* begin the client process */
... /* feedback showing the failed file transfer */
ls -l /* show that no file has been transferred to client */
end script

File on server

start script for FTPServerUsingTCP
uname -a /* you MUST show name of machine that server is executing on */
ls -l /* show files that exist on the server */
execute FTPServerUsingTCP /* begin the server process */
... /* feedback indicating the file transfer */
end script

start script for FTPClientUsingTCP
uname -a /* you MUST show name of machine that client is executing on */
ls -l /* show files that exist at client (file to transfer should NOT appear on client */
execute FTPClientUsingTCP /* begin the client process */
... /* feedback showing when the file to transfer does exist*/
ls -l /* show file has been transferred to client */
end script

(35pts) Simple File Transfer using UDP

Analogous requirements as previous question, but using this time the client-server must use UDP to transfer the file.
REQUIREMENT: Your client and server must be named: FTPClientUsingUDP.py, FTPServerUsingUDP.py, respectively.
UDP provides unreliable transport service (i.e., no guarantee of delivery, no guarantee of ordered delivery, no guarantee that duplicate UDP-PDUs are not delivered to the receiving application). So your client-server application must implement a mechanism to provide reliablity. Your comments MUST clearly document whatever method you choose.
For example: Before the file is transferred, your client-server may open a TCP "control" connection, for exchanging control FTP-PDUs. Over this control connection, the client sends a filename to the server; the server checks if the file exists and returns a status (yes or no), and if yes, perhaps an MD5 hash of the file. The file itself is then transferred over UDP. After the file transfer, the client computes an MD5 hash on the received file and checks if the hash value matches what the server previously sent. If not, the file transfer fails and an appropriate message is output to the user. (A full application layer FTP over UDP would have to implement timers, and retransmissions. You do not have to do that.)

REQUIREMENT: SUBMIT in class paper copies of your two programs: FTPClientUsingUDP.py, FTPServerUsingUDP.py

REQUIREMENT: SUBMIT in class paper copies of 4 scripts analogous to above, showing FTPServerUsingUDP and for FTPClientUsingUDP in action.

REQUIREMENT: UPLOAD your two programs: FTPClientUsingUDP.py, FTPServerUsingUDP.py to the class Sakai web site.

Rules

For this assignment, students may work in groups of 2. If you do not know Python, now is the opportunity to learn. Find a partner who is Python proficient.
Groups should submit one answer clearly identifying both partners. In total, 8 well-labelled (e.g., "Part 1 MakeUpperCaseClientUsingTCP") scripts should be submitted in class, and 4 programs need to be uploaded to the class Sakai web site.
Students may get assistance with general Python language questions from anyone. Try your best to debug your own programs.
Clearly document your well known port numbers, and the handling of the control connection in Questions 2 and 3.

Programs are expected to be professionally prepared.

In the header of every module, comment your Name, Date, Course, Project, and Project Description.

REQUIREMENT: All code within the module must be commented.

REQUIREMENT: All variable names must be meaningful. The following varible names are not meaningful: x, data, value, number, count, input, infile, done.

REQUIREMENT: Readability of your ouput including consistency of indentation is vital. PRINTED SOURCE LISTINGS WITH LINES THAT WRAPAROUND TO THE NEXT LINE MAKE THE CODE UNREADABLE. They will be returned without being graded.

See Amer's coding standard.

Academic Honesty: A clear distinction exisits between getting general help from other students, and having someone else write your program. A student is responsible for understanding each and every line of code that s/he submits. You are all advanced computer science students, and by now should have a clear understanding of how much outside help one is permitted. When in doubt, ask the professor. Do NOT copy and edit another past or present student's program, and submit it as your own. It is better to not turn in an assignment, and accept the grade penalty than to be academically dishonest.

Grading

Submit your answers clearly labeled and IN ORDER (-2 points otherwise) - all papers dealing with Question 1, followed by all papers dealing with Question 2, followed by all papers for Question 3.
correctness (60%)

readability and documentation - comments, variable names, consistency of spacing and indentation (40%).