Checkpoint 2: TCP Basics
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Late Policy
- You have free 4 late days in total.
- You can use late days for assignments. A late day extends the deadline 24 hours.
- Once you have used all 4 late days, the penalty is 20% for each additional late day (5 days later there will be no points).
- Remember that any questions should go to Piazza instead of emailing TAs or the professor.
Introduction
In this checkpoint, you need to implement a basic TCP with:
- Sequence number and acknowledgement number, and
- Sliding window.
The starter code is provided for you which is a stop-and-wait plementation built on UDP. You need to implement the seq/ack numbering and sliding window based on it.
Starter code
Compared to checkpoint 1, we provide more codes for you. You can use ```git pull`` to get the latest codes from our course Github repository.
git pull origin main
And switch to the main branch.
git checkout main
server.cc and client.cc
The two sample applications for server and client.
foggy_tcp.cc
The API exposed to application is defined in this file. There are four core functions whose signatures should not be changed :foggy_socket(), foggy_close(), foggy_read(), and foggy_write(). An application requests a new foggy-TCP socket by calling the foggy_socket function. The socket created in foggy_socket() is actuall a UDP socket and our job is to enhance it to TCP.
foggy_backend.cc
This file implements foggy-TCP’s core logic which runs in a separate backend thread. This is important as TCP must be able to work independently from the application (i.e., receiving, acknowledging and retransmitting packets).
foggy_function.cc
This file implements foggy-TCP’s function logics. Most of your implementations may be here.
foggy_packet.cc
This file implements helper functions to create and manipulate packets. Please do not modify this file.
Run the starter code
In this checkpoint and the following you need to use your own TCP (foggy-tcp) instead of system TCP. So use the following command to build foggy-tcp.
make foggy
In the server VM, at the /vagrant/foggytcp folder, run the server with the following command:
./server 10.0.1.1 3120 test.out
In the client VM, at the /vagrant/foggytcp folder, run the client with the following command:
./client 10.0.1.1 3120 src/client.cc
Now you have successfully transmitted the client.cc file from the client to the server, named as test.out.
How to debug
A bash script capture_packets.sh is provided for you to capture and analyze network packets.
Packet capture
Converting file capture_packets.sh to Unix format.
sudo apt-get install dos2unix
dos2unix capture_packets.sh
Start packet capture.
sudo ./capture_packets.sh start <name>.pcap
Stop packet capture
sudo ./capture_packets.sh stop <name>.pcap
Packet analyse
Packet analyse using the bash script
sudo apt-get install tshark
sudo ./capture_packets.sh analyze <name>.pcap
Then you should see something like this:
Packet analyse using Wireshark
Wireshark is a powerful network packet capture and analysis tool. Download here. After installation, copy the lua file tcp.lua to the directory for wireshark plugins, for example: E:\Applications\Wireshark\plugins. Then start wireshark and open the captured file <name>.pacp. Now you can analyze the packets with a beautiful user interface.
What to submit
Your implementation should be in the following files: foggy_function.cc, foggy_tcp.cc, foggy_function.h and foggy_tcp.h. You can run the submit.py at the root of the project which will generate a submit.zip file including these four files, then submit the submit.zip file to Gradescope. The autograder will copy those four files you submitted to the starter codes and do the testing.