Behavior of TCP
Welcome back to the Lab Programme!
In this lab, we’ll investigate the behavior of TCP in detail. We’ll do so by analyzing a trace of the TCP segments sent and received in transferring a 150KB file (containing the text of Lewis Carrol’ s Alice’s Adventures in Wonderland) from your computer to a remote server. We’ll study TCP’s use of sequence and acknowledgement numbers for providing reliable data transfer; we’ll see TCP’s congestion control algorithm – slow start and congestion avoidance – in action; and we’ll look at TCP’s receiver-advertised flow control mechanism. We’ll also briefly consider TCP connection setup and we’ll investigate the performance (throughput and round-trip time) of the TCP connection between your computer and the server.
Before beginning this lab, you’ll probably want to review sections 3.5 and 3.7 in the text. 1
1. Capturing a bulk TCP transfer from your computer to a remote server
Before beginning our exploration of TCP, we’ll need to use Wireshark to obtain a packet trace of the TCP transfer of a file from your computer to a remote server. You’ll do so by accessing a Web page that will allow you to enter the name of a file stored on your computer (which contains the ASCII text of Alice in Wonderland), and then transfer the file to a Web server using the HTTP POST method. We’re using the POST method rather than the GET method as we’d like to transfer a large amount of data from your computer to another computer. Of course, we’ll be running Wireshark during this time to obtain the trace of the TCP segments sent and received from your computer. Do the following:
• Start up your web browser. Go the http://gaia.cs.umass.edu/wireshark-labs/alice.txt and retrieve an ASCII copy of Alice in Wonderland. Store this file somewhere on your computer.
• Next go to http://gaia.cs.umass.edu/wireshark-labs/TCP-wireshark-file1.html
• You should see a screen that looks like: • Use the Browse button in this form to enter the name of the file
In this lab, we’ll investigate the behavior of TCP in detail. We’ll do so by analyzing a trace of the TCP segments sent and received in transferring a 150KB file (containing the text of Lewis Carrol’ s Alice’s Adventures in Wonderland) from your computer to a remote server. We’ll study TCP’s use of sequence and acknowledgement numbers for providing reliable data transfer; we’ll see TCP’s congestion control algorithm – slow start and congestion avoidance – in action; and we’ll look at TCP’s receiver-advertised flow control mechanism. We’ll also briefly consider TCP connection setup and we’ll investigate the performance (throughput and round-trip time) of the TCP connection between your computer and the server.
Before beginning this lab, you’ll probably want to review sections 3.5 and 3.7 in the text. 1
1. Capturing a bulk TCP transfer from your computer to a remote server
Before beginning our exploration of TCP, we’ll need to use Wireshark to obtain a packet trace of the TCP transfer of a file from your computer to a remote server. You’ll do so by accessing a Web page that will allow you to enter the name of a file stored on your computer (which contains the ASCII text of Alice in Wonderland), and then transfer the file to a Web server using the HTTP POST method. We’re using the POST method rather than the GET method as we’d like to transfer a large amount of data from your computer to another computer. Of course, we’ll be running Wireshark during this time to obtain the trace of the TCP segments sent and received from your computer. Do the following:
• Start up your web browser. Go the http://gaia.cs.umass.edu/wireshark-labs/alice.txt and retrieve an ASCII copy of Alice in Wonderland. Store this file somewhere on your computer.
• Next go to http://gaia.cs.umass.edu/wireshark-labs/TCP-wireshark-file1.html
• You should see a screen that looks like: • Use the Browse button in this form to enter the name of the file