Description

Objectives

In this assignment, you will implement a client and server for file transfer. After completing this assignment, you should

• be able to construct application layer packets
• have a good understanding of communication protocol design.

 

The Unreliable Channel

We have implemented 3 simulators on the machine 172.28.176.63, to mimic unreliable channels. Your server and client have to connect to the simulators and transfer files.

• The simulator waits for both the client and server to connect the simulator via TCP connection before enabling the channel.
• The architecture can be found in fig:1
• Task
  • connect to the simulator with a handshake. The handshake is similar to Assignment 1, with an extra character C to signify client and S to signify server. The handshake details can be found in fig:2
  • The simulator will send you the current waiting list number; you need to wait till you receive 0_. We allow only 30 students to connect to a simulator at any given time.
  • Then you transfer file from the server to the client. The input_file_name will be provided as command line parameter to the server
  • Save the received file to the file name provided to client as command line parameter
• You earn 1 mark per correct file transfer in the case of Reliable Channel.
• You earn 2 mark per correct file transfer in the case of other channels.
• Forgot to mention; the simulator really hates making friends. It will timeout and terminate in 100 seconds.

Figure 1: Architecture.

Figure 2: Handshake FSM.

Let us understand the Simulator further:

• All the simulators have the following constraints
  • The packet size from the server is fixed to 1024 B.
  • The packet size from the client is fixed to 64 B.
  • Partial packets will not be delivered
  • No packets will be dropped
• The 3 Simulators are:
  • Reliable Channel (Mode 0): This channel introduces no error or reordering of packets. Fig 3
  • Error Channel (Mode 1): This channel introduces errors in packets. Fig 4
  • Reordering Channel (Mode 2): This channel reorders packets. Fig 5

Testing Your Program

To test your program, please use your SoC UNIX ID and password to log on to stu as instructed in Assignment_0.

Figure 3: Reliable channel FSM.

Figure 4: Error channel FSM. • Since you have 2 programs, you will be running them on 2 separate terminals

• Your program should receive five command-line argument as the following command shows:

python3 Sever-A0165432X.py <ip_address> <port_num> <input_file_name> <mode> <st key> python3 Client-A0165432X.py <ip_address> <port_num> <output_file_name> <mode> <s key>

• <ip_address>: The IP address of the machine on which the simulator is running.
• <port_num>: The port number of the TCP socket corresponding to the simulator.
• <input_file_name>: The file to be transferred
• <output_file_name>: The destination file name
• <mode>: Is the integer input corresponding to the simulator we are connecting to – <student_key>: The 6 digit key is the same as the one used in Assignment_1.

• During the evaluation, we will change the input files, the IP address and the port number; hence your code should accept all the above mentioned command line parameters.
• Note that your program should not read from stdin.
• Your program can print anything to stdout or stderr, and our test script will silently ignore them.
• We also release a set of grading scripts to you under the test
• To use the grading script, please upload your program along with the test folder given in the package, to stu. Ensure that your program and the test folder are

Figure 5: Reorder channel FSM.

in the same directory. You can run the following command for help: bash test/FileTransfer.sh -h

• To run the test script for the server, kindly use the -s option

“con

ges

All of you will be connected to a single simulator, hence start the assignment early to avoid tion” during the last few days.

Template

We have released the template of the code.

• The entire code structure is implemented.
• Handshake code is implemented.
• Few helper functions like Packet reception code are implemented.
• Kindly implement only the part of the code with #TODO

Enjoy!!!