EL6383 High-speed Networks: Labs Instructor: Yang Xu Lab 3: Bufferbloat Name: ________________________ ID: ___________________ Date: ______________________ 1. Objectives – Understand the bufferbloat problem – Observe the bufferbloat problem on mininet 2. Lab Tutorial 2.1 Reference to go through 1) BufferBloat: https://github.com/mininet/mininet/wiki/Bufferbloat 2) Iperf: https://iperf.fr/ 3) Google: A universal reference 2.2 Home Network Emulation Setup Figure 1 Typical home network environment In this exercise we will study the dynamics of TCP in home networks. Take a look at Figure 1 which shows a “typical” home network with a Home Router connected to an end host. The Home Router is connected via Cable or DSL to a Headend router at the Internet access provider’s office. We are going to study what happens when we download data from a remote server to the End Host in this home network. In a real network it’s hard to measure cwnd (because it’s private to the Server) and the buffer occupancy (because it’s private to the router). To make our measurement job easier, we are going to emulate the network in Mininet. EL6383 High-speed Networks: Labs Instructor: Yang Xu 2.3 BufferBloat Environment Setup Figure 2. BufferBloat Environment Setup In this lab, the environment is already provided as git repository. Get the repository by cloning it using the following command, > git clone https://github.com/bovenyan/bufferbloat Run the emulator, > cd bufferbloat/ > sudo ./run.sh After Mininet is running, you can measure the delay from H1 to H2 with the command: > mininet> h1 ping –c 10 h2 2.4 Exercise 1: Sketch the CWND of Web page downloads and “Streaming Videos” Measure how long it takes to download a web page from H1, mininet> h2 wget 1. Answer: _________________ seconds. 2. Sketch how you think cwnd evolves over time at H1. Mark multiples of RTT on the x-axis: EL6383 High-speed Networks: Labs Instructor: Yang Xu To see how the dynamics of a long flow (which enters the AIMD phase) differs from a short flow (which never leaves slow-start), we are going to repeat Part 2 for a “streaming video flow”. Instead of actually watching videos on your machine, we are going to set up a long-lived high speed TCP connection instead, to emulate a long-lived video flow. You can generate long flows using the iperf command, and we have wrapped it in a script which you can run as follows: mininet> h1 ./iperf.sh You can see the throughput of TCP flow from H1 to H2 by running: mininet> h2 tail -f ./iperf-recv.txt You can quit viewing throughput by pressing CTRL-C. 3. Sketch how you think cwnd evolves over time at H1. You might find it useful to use ping to measure how the delay evolves over time, after the iperf has started: mininet> h1 ping -c 100 h2 EL6383 High-speed Networks: Labs Instructor: Yang Xu To see how our long-lived iperf flow affects our web page download, download the webpage again – while iperf is running. Write down how long it takes. mininet> h2 wget 4. Answer: _________________ seconds 5. Why does the web page take so much longer to download? Please write your explanation below. Answer: 2.5 Measuring the real cwnd and buffer occupancy values. Stop and restart Mininet and the monitor script, then re-run the above experiment as follows. mininet> exit bash# sudo ./run.sh Monitor TCP CWND and Buffer Occupancy in Mininet. In another bash terminal, go to bufferbloat directory and type the following giving a name for your experiment. bash# ./monitor.sh Don’t worry if you see “ERROR: Module tcp_probe does not exist in /proc/modules”, it just means this module is not previously loaded. mininet> h1 ./iperf.sh (wait for 70 seconds …) mininet> h2 wget Wait for the wget to complete, then stop the python monitor script followed by the instructions on the screen. The cwnd values are saved in: _tcpprobe.txt and the buffer occupancy in _sw0-qlen.txt Plot the TCP cwnd and queue occupancy …

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