usageGuide

Working with SUSS

Table of Contents

1. Introduction
2. Usage Example

Introduction

This tutorial provides an introduction to SUSS and demonstrates its application through a practical example. While SUSS can handle TCP data transfers across a big range of port numbers, we will focus on port 80 for this tutorial, utilizing the Apache2 web server. Please install Apache2 on the server where SUSS is already installed.

   sudo apt-get install -y apache2

Assuming you have a client capable of downloading files from the server, use the following command to download the file index.html. To avoid any optimizations made by web browsers, download the file using either either wget or curl from a command line interface. We recommend setting up a client-server connection with a round-trip time (RTT) exceeding 50ms and a bottleneck bandwidth greater than 50Mbps, as SUSS provides significant benefits in networks with large Bandwidth-Delay Products (BDP).

   wget http://IPaddress_of_the_server/index.html

SUSS records TCP measurements in /var/log/kern.log on the server, which allows for easy access to the measurements after downloading. To filter the logs after a successful download, execute the following command on the server:

   grep "SUSSmsg" /var/log/kern.log

Note: If no output appears, either the file has not been downloaded, or SUSS has not been installed correctly. Verify the installation of the new kernel by executing uname -a and ensure that the upgraded version is in use.

Given that index.html is a very small file, we recommend using a larger file, such as dummyfile.dat, to better explore the capabilities of SUSS. Create a dummy file and move it to the web root directory with these commands:

   dd if=/dev/zero of=dummyfile.dat bs=1M count=16
   sudo mv dummyfile.dat /var/www/html/.

Usage Example

1. By default, SUSS is disabled. To enable it, you must change the value of the suss module parameter from 0 to 1, and set the TCP congestion control algorithm to Cubic.

   cat  /sys/module/tcp_cubic/parameters/suss
   echo 1 | sudo tee /sys/module/tcp_cubic/parameters/suss
   sudo sysctl net.ipv4.tcp_congestion_control=cubic

2. To prevent previous logs from interfering with the current test, clear the contents of /var/log/kern.log:

   sudo sh -c '> /var/log/kern.log'

3. Using either wget or curl on the client, download the dummy file from the server. After a few minutes, copy the logs into a file on the server:

 
   cat /var/log/kern.log > raw.suss1

Use the name raw.suss1 if SUSS is enabled, and raw.suss0 if it is disabled. These filenames will be used in subsequent steps to extract useful information. Disable SUSS and repeat the previous two steps to gather logs for when SUSS is disabled.

Note: On newer operating systems, such as Ubuntu 24.04, you may use journalctl to read the kernel logs.

4. As shown in the example, you should now have two files, raw.suss0 and raw.suss1, representing the logs when SUSS is disabled and enabled, respectively. If the output of the following command for each raw file indicates a message like "SUSSmsg cubic starts sending data. Follow id=143 for Sport=20480", it suggests that each raw file documents a single download.

   grep "SUSSmsg cubic starts sending data" raw.suss?

5. Each download is identified by its id. Use the bash script extract.sh located here to prepare the files data.suss0 and data.suss1, which will be used for plotting:

   bash extract.sh raw.suss0
   bash extract.sh raw.suss1

6. At this stage, you should have two data files, data.suss0 and data.suss1, in your working directory. Using the provided Gnuplot script delivered.tr, located here, generate a plot that compares the total data delivered over time in both the enabled and disabled tested scenarios.

   gnuplot delivered.tr
   xdg-open delivered.eps

7. To also plot the improvement curve, execute the following commands:

   bash improvement.sh
   gnuplot improvement.tr
   xdg-open improvement.eps