TCPTuner

TCPTuner is TCP congestion control kernel module and GUI packaged together. By loading this kernel module and running the GUI, users can adjust several parameters of the CUBIC congestion control algorithm.

Two variations of CUBIC congestion control algorithm are implemented here:

• Conventional CUBIC (reference paper)
• Multipath CUBIC (reference paper)

Project report

How to Build and Load the Kernel Modules

This version of the project was developed and tested on an Ubuntu 20.04 machine running version 5.11 of the Linux kernel

To build the tcptuner kernel module:

cd module/tcptuner
make
sudo rmmod tcp_tuner.ko
sudo insmod tcp_tuner.ko
sudo sysctl -w net.ipv4.tcp_congestion_control=tuner # make 'tuner' the default choice for the system

Follow similar steps to build other kernel modules in modules directory.

The Graphical User Interface

Dependencies

First install the following packages:

sudo apt-get install qt5-qmake qt5-default

To Build and Run

To build and run the TCPTuner GUI:

cd gui/TCPTuner
qmake
make
sudo ./TCPTuner

Follow similar steps to build and run the mpCUBIC GUI.

GUI Parameters

TCPTuner exposes the parameters of TCP CUBIC to the user via the TCPTuner GUI. The parameters present in TCP CUBIC, along with their descriptions and default values are in the table below.

Parameter	Description	Default
alpha	Scales W_max, which adjusts the rate at which cwnd grows after a loss event	512
beta	beta for multiplicative decrease	717
fast_convergence	turn on/off fast convergence	1
tcp_friendliness	turn on/off tcp friendliness	1

Additonal Parameters from ip-route

The TCPTuner GUI also provides access to the following ip route parameters. The GUI will apply these ip route parameters to all of the routes in the routing table.

Parameter	Description	Default
rto_min	the minimum TCP retransmission timeout to use when communicating with this destination.	None
initcwnd	the initial congestion window size for connections to this destination. Actual window size is this value multiplied by MSS.	0

MahiMahi Simulation Environment

This repository also contains a MahiMahi simulation environment so that users can see the impact of TCP congestion control parameters.

Dependencies

First, you must install the mahimahi package:

sudo apt-get install mahimahi

Before you can run MahiMahi, you must:

sudo sysctl -w net.ipv4.ip_forward=1

Single TCP Flow with tail-drop Buffer

The first simulation shows throughput and delay of a single TCP flow on a 12Mbps uplink.

cd mahimahi
./start_all 0 # default cubic client
./start_all 1 # tuner cubic client
./start_all 2 # mpcubic client

Multiple TCP Flows Sharing a Bottleneck Link

The second simulation shows throughput graphs of each flow sharing a bottleneck link. This can be used to compare default cubic to tcptuner/mpcubic.

cd mahimahi
./start_shell

Now that the bottleneck link is created, we can run multiple clients within that shell:

./start_client 5050 0 & # creates a default cubic client as a new background process
./start_client 5050 1 & # creates a tcptuner client as a new background process
./start_client 5050 2 & # creates a mpcubic client as a new background process

To close these:

fg # to bring one of the background process to the foreground
Ctrl+C # repeat for each client
exit # to close the bottleneck link

pid=$(x=`sudo lsof -i :5050 -Fp` && echo ${x##p} | cut -d ' ' -f 1)
sudo kill $pid # kill any ghost process occupying port 5050

Plotting congestion window size graphs

Dependencies

First install the following packages:

sudo apt-get install iperf gnuplot texlive-font-utils

Build and Load the tcp_probe Kernel Module

cd modules/tcpprobe
make
sudo insmod tcp_tuner.ko

Capture Realtime Data

Use the tcp_probe kernel module to capture realtime data of:

• cwnd - congestion window size
• ssthresh - slow start threshold

# https://wiki.linuxfoundation.org/networking/tcp_testing
cd plot/data
sudo modprobe tcp_probe port=5051 full=1

iperf -p 5051 -s & # start iperf server on receiver's end
IPERFSERVER=$!

# record the captured data using one of the below techniques
sudo sysctl -w net.ipv4.tcp_congestion_control=tuner # if using CUBIC
sudo cat /proc/net/tcpprobe > cubic.dat &

sudo sysctl -w net.ipv4.tcp_congestion_control=mpcubic # if using mpCUBIC
sudo cat /proc/net/tcpprobe > mpcubic.dat &

TCPCAPTURE=$!
iperf -i 10 -t 300 -p 5051 -c 0.0.0.0 # start iperf client on sender's end

sudo kill $IPERFSERVER
sudo kill $TCPCAPTURE

Plot Graphs

Plot the captured data using gnuplot and epstopdf:

cd plot
./generate_plot.sh # generates a pdf containing graphs