2025-03-31

TCP

TCP chatroom

This is the first assignment of “Computer Network: a top- down approach” course. It’s a simple TCP chatroom. The server can accept multiple clients and exchange messages and files with them. The server and client are implemented by python.

Socket Programming Lab Report

Name: Bao
Student ID: xxxxxxxxxx
Date: 29/03

1.Experiment Objectives

To understand the basics of socket programming
To implement server-client architecture using TCP protocol.
To implement multi-thread server using TCP protocol.

2.Experimental Environment

Programming Language: Python 3.12.4
Libraries: socket and threading module in python
Tool: Wireshake for packet capture

Usage

For single thread TCP part,

Server

1 2	cd ./TCP/ python server.py 18080 input

Options:

18080: Server listening port (default:18080)
input: Server response type (default:upper), including “input” and “upper”

Client

1 2	cd ./TCP python client.py 127.0.0.1 18080

Options:

127.0.0.1 server IP to connect to (default:127.0.0.1)
18080 server port to connect to (default:18080)

For multiple thread TCP server part

Server

1 2	cd ./Threading/ python server.py 18080 upper 10

Options:

18080: Server listening port (default:18080)
10: the maximum number of clients the server can accept (default:10)
upper: Server response mode (default:upper), including “input” and “upper”

Client

1 2	cd ./Threading/ python client.py client0 127.0.0.1 18080

And for a new client

1 2	cd ./Threading/ python client.py client1 127.0.0.1 18080

And so on…
Options:

127.0.0.1 server IP to connect to (default:127.0.0.1)
18080 server port to connect to (default:18080)
client1 client name (default:client0), necessary for more than 1 clients, to separately manage the files different clients own.

Note:

All above commands are executed in the root directory of the project, and you can run without any arguments to use the default values.
Server is set a time out limit of 120, which is not necessary. It’s just to easily quit the server when it’s not being used.
Client is set a time out limit of 30.

After connection is set up, the client and server go in a circle of “receive - send”. User repeatedly give commands through client.
There are 3 types of input commands:

ask for file:someFile :require server sending someFile to the folder client manages
send file:someFile :send local file someFile to folder “server” that server manages
exit :quit connction with server
else: send the input message encoded by ‘UTF-8’ to server, and receive reponse from server. The argument responseType in class TCP_Server/Multithread_Server determines how server response. responseType = upper automatically return the total uppercase of client massage, responseType = input require server input response by hand.

3.Experimental Procedure

Using Wireshake, we can capture the packets sent between client and server.
Because multi-thread version totally inludes functions of single thread version, I will only show the result of multi thread version here.
The following figures shows the example:
cmd
During the connection, the WireShark capture the packets sent between client and server.
When the connections are setup:
capture
When client0 exits and client1 is receiving shore.jpg from server:
result
I didn’t show the whole process because shore.jpg takes too many packets to be sent.

For more test, the ./server/ has 出师表.txt, the ./client has keep.jpg.

4.Experiment Analysis

It can be easily found that “3-way” hand shake happens. Looking at the wireshark captures, before the first request of port 9461 and the connection of port 9465, there are 3 packets sent between client and server:No.109,110,111. In 109, client0 sends a SYN packet to server, and in 110, server sends a SYN-ACK packet to client0, and in 111, client0 sends a ACK packet to server. After that, the connection is established. Of course, the same thing happens for client1, which is demonstrated in No.144,145,146.