Ns-3-Network-Simulator/C3/Analyzing-TCP-Congestion-window/English

Visual Cue	Narration
Slide:1 Welcome	Welcome to the spoken tutorial on Analyzing TCP Congestion Window.
Show slide: Outline	In this tutorial, we will learn to Create a TCP socket with TCP Reno congestion control Track changes in congestion window size Plot the change in congestion window against time
Show slide: System Requirements	To record this tutorial, I am using Ubuntu Linux operating version 22.04 ns-3.38
Show slide: Prerequisite https://www.spoken-tutorial.org	To follow this tutorial: You must have basic knowledge of Linux and ns-3 software For pre-requisite Linux and ns-3 tutorials, please visit this website
Show slide: Code files	The files used in this tutorial are provided in the Code files link. Please download and extract the files. Make a copy and then use them while practicing.
Show diagram: Network topology with two nodes	The network topology consists of two nodes. They are connected using a point-to-point link.
Show slide: Classes and Methods	Let us have a look at the classes and methods. These would be needed to apply TCP New Reno congestion control. The RateErrorModel class object determines and flags lost or errored packets The CreateObject method of the Object base class creates an object by type
Show slide: Tutorial App	We shall be using a pre-coded application file, tutorial-app.cc in this tutorial. The application instance sends packets to the server node continuously.
Show slide: Trace sources	This program uses the CongestionWindow trace source. It tracks the changes in the congestion window size. Now we will go through the steps required to use the TutorialApp class in our program.
Open a terminal by pressing Ctrl, Alt and T keys simultaneously. Type cd ns-allinone-3.38/ns-3.38	Open a terminal by pressing Ctrl, Alt and T keys simultaneously. Navigate to the installation directory of ns-3. Go to ns-3.38 directory.
Type cp examples/tutorial/tutorial-app.cc src/applications/model	Now we will copy the required files. These folders and files are created by default when ns-3 is installed. First we copy the file tutorial-app.cc. Let us copy the file tutorial-app.cc which is available under examples/tutorial folder.
Only narration	The destination is the model directory under the src/applications directory. The src directory stores the header files and the associated source files. These files can be imported in our program.
Type cp examples/tutorial/tutorial-app.h src/applications/model	Now we copy the file tutorial-app.h. It is a header file. It contains the required definitions for the TutorialApp class.
Only narration	Once the files are copied, we need to edit the CMakeLists.txt file. The CMakeLists.txt file lists the files that will be compiled during the build process. We need to add the files we copied to the CMakeLists.txt file.
Type gedit src/applications/CMakeLists.txt	Using your favorite text editor, edit the CMakeLists.txt file. It is present under the applications directory, which is under the src directory. We are using the gedit text editor.
Under the SOURCE_FILES header, add the line: model/tutorial-app.cc after the last entry (usually model/udp-trace-client.cc)	In the text editor, find the SOURCE_FILES header. After the last line under the header, add the line model/tutorial-app.cc.
Under the HEADER_FILES header, add the line: model/tutorial-app.h after the last entry (usually model/tutorial-app.h)	Now find the HEADER_FILES header. After the last line under the header, add the line model/tutorial-app.h.
Save the file and close the text editor.	Save the file and close the text editor.
Switch to the terminal window. Type ./ns3 configure	In the terminal, type ./ns3 configure. This command scans for any changes in the build files.
Type ./ns3 build	Now type ./ns3 space build to start the build process. This command scans the CMakeLists.txt file for new changes and builds the ns-3 program again. Pause the video here and wait for the build process to finish. It could take several minutes.
Open the file tcp-congestion.cc in the text editor	Now we will take a look at the code for the program. I have created the source file tcp-congestion.cc for this program. The source code contains the required functions to implement a point-to-point network. Download this file from the Code files section and open it in a text editor.
Highlight #include “ns3/tutorial-app.h”	We have used this header file which we built earlier.
Highlight CwndChange	The CwndChange function is a callback function. It acts as a trace sink for the CongestionWindow trace source. The function prints the old and new sizes of the congestion window.
Highlight GetStream	It also writes these values to the output file using the GetStream function.
Only narration	For demonstration, we will be creating a point-to-point network.
Highlight csmaNodes.Create(2)	The network consists of 2 nodes.
Highlight DataRate and then Delay	We set the data rate to 5 Mbps and the delay to 2 milliseconds.
Highlight Ptr<RateErrorModel>	Next, we create a pointer to an object of the RateErrorModel class.
Highlight em->SetAttribute	Then set the error rate to 0.00001.
Highlight devices.Get(1)->SetAttribute("ReceiveErrorModel", PointerValue(em));	For this program, node 2, with index 1 is the receiver node. On the receiver node, set the ReceiveErrorModel attribute. The value of the attribute is the pointer we created earlier.
Highlight SetBase	The IP address of the network is set to 10.1.1.0 with subnet mask 255.255.255.0.
Highlight packetSinkHelper.Install	To receive packets, we create a packet sink on the receiver node. We shall have the first node, with index 0 as the sender node. It will then send the packets to the receiver node, node 2.
Highlight Socket::CreateSocket	Create a socket on node 1 using the CreateSocket method.
Highlight Config::Set	Then set the socket type using the set method.
Highlight Ptr<TutorialApp> app	Now let’s create an instance of the TutorialApp class.
Highlight Setup(ns3TcpSocket, sinkAddress, 1040, 1000, DataRate("1Mbps"))	The app uses the socket we created earlier.
Highlight nodes.Get(0)->AddApplication(app);	Further, let’s add the application to the first node of the CSMA network.
Highlight app->SetStartTime(Seconds(1.))	Then we will set the start and stop times for the application.
Highlight AsciiTraceHelper	The AsciiTraceHelper object creates an output file stream.
Highlight TraceConnectWithoutContext	Then we connect the stream to the CongestionWindow trace source.
Highlight GnuplotHelper plotHelper	Next, we create an object of the GnuplotHelper class.
Highlight plotHelper.ConfigurePlot	Configure the parameters for the plot. The first argument is the file name prefix. The second argument is the plot title. Here it is TCP Window Size vs Time’. The third and fourth arguments are the x-axis and y-axis labels respectively.
Highlight plotHelper.PlotProbe	Using the PlotProbe method, we set attributes for the probe. These include: probe name probe path output trace source and data series label The probeName and probeTrace values were set previously. The FileHelper class object writes packet byte count over time.
Highlight Simulator::Run()	Finally we use the Run and Destroy for running and stopping the simulation.
Open terminal and navigate to the ns-3.38 directory	Let’s run the simulation for the program. Navigate to the ns-3.38 directory.
Type ./ns3 run scratch/tcp-congestion.cc	Run the source script using the run command. Here the name of the source file is tcp-congestion.cc. The output shows the time at which the change occurs in the size of the window. Also available in the output are the old and new window sizes. Now we shall observe the plot of the congestion window change. On running the simulation, a file with cwnd extension is created.
Open ns-3.38 directory and highlight the tcp-congestion.cwnd file	You can find the file in the ns-3.38 directory. The name of the file is the one specified in the CreateFileStream function. Here the name of the file is tcp-congestion.cwnd. The cwnd file is used to provide the values for the plot.
Open the congestion.plt file. Show terminal	Using the commands displayed, we configure the plot. Let us first download the congestion.plt file from the Code files section. Make sure that the file is in the same directory as the cwnd file. The commands in this file will configure the plot.
Type sudo apt install gnuplot	To generate the gnuplot, we use the gnuplot command. To install it, type sudo apt install gnuplot in the terminal. If it is already installed, proceed to the next command.
Type gnuplot congestion.plt	Next, we generate the plot using the command gnuplot space congestion.plt.
Switch to the file manager window. Show the congestion.png file	An image file is generated in the same directory with the plot.
Open congestion.png file	The plot shows the change in the size of the congestion window over time.
Show slide: Summary	This brings us to the end of the tutorial. Let us summarize. In this tutorial, we have learnt to Create a TCP socket with TCP Reno congestion control Track changes in congestion window size Plot the change in the congestion window size against time
Show slide: Assignment	As an assignment, please do the following Write an ns-3 program The program should have a CSMA network with 6 nodes Send packets from node 2 to node 5 Trace the changes in the congestion window size Plot the changes using gnuplot
Show slide: Assignment - Observation	In the terminal, observe the change in congestion window size over time.
Show slide: Assignment - Observation	The image generated by gnuplot depicts the change in congestion window size.
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Show slide: Acknowledgement	Spoken Tutorial Project was established by the Ministry of Education, Government of India.
Show slide: Acknowledgement	We thank Dr.Moyukh Laha from IIT Kharagpur for his domain support. We would also like to thank Dr. R. Radha, Dr. X. Anita, and Dr. T. Subbulakshmi from VIT, Chennai for their support.
Show slide: Thank You	This is Josiga, a FOSSEE summer fellow 2023, IIT Bombay signing off. Thanks for joining.

Contributors and Content Editors

Madhurig, Nirmala Venkat