In this assignment, you will build another custom topology and learn about TCP congestion control. You’ll also learn about the TCP sawtooth and see how TCP works to share bandwidth across multiple flows .
Over 80% of peak traffic on the Internet is transmitted via TCP . Therefore, its important to understand how TCP’s congestion control enables networks to function without congestion collapse. Collapse occurs when packets use bandwidth in one section of the network but are dropped at a downstream link, such that the flow is nonfunctional. TCP’s congestion control responds to packet drops, enabling a congested section of the network to recover.
To explore congestion control, you will create the following topology for N = 1, 2, 3, 4, 5 at a link speed of 10 Mbps per link and a delay of 1 ms (note the 10 Mbps speed differs from the lecture video to ensure the topology runs smoothly on a virtual machine). Then you will generate simultaneous TCP Reno flows using
iperf from each of the sender hosts to the lone receiver and measure the achieved throughput. A provided script will plot the time series of throughput vs time for each sender, for each experiment (N = 1, 2, 3, 4, 5).
assignment-4directory. Then install some additional packages for this assignment:
sudo apt-get -y install python-argparse
sudo easy_install termcolor
parkinglot.pyfile. You will need to complete two functions within the file to complete the assignment. Both functions are marked with
TODOcomments for your convenience.
__init__function of the
ParkingLotTopoclass. The class defines the topology used in the assignment. The framework code creates a parking lot topology for N=3. Your task is to generalize it for any N >= 1.
run_parkinglot_exptfunction. The function generates TCP flows between the senders and the receiver using
iperf, and monitors the throughput of each flow. Your task is to start and stop
iperffor the additional senders in the topology.
sudo python parkinglot.py --bw <link_bandwidth> --dir <output_dir> -t <expt_duration> -n <n>
parkinglot-sweep.shto generate a set of plots and the necessary log files:
python -m SimpleHTTPServer
bwm.txtfile, which contains the bandwidth measurements, for each of N = 2, 3, 4, and 5 on the assignment submission page.
 Based on CS 244 assignment.
 Sandvine Global Internet Phenomena Report, Fall 2011. TCP is largely video over HTTP (along with some web browsing and P2P.) BitTorrent over uTP and UDP accounts for the bulk of UDP traffic.