Task 1: Simple client

In this assignment you will implement a TCP client that opens a TCP connection to the adnet-agent server assuming the simple_topo topology in our Mininet setup. After you send initial control message TASK-001 keyword to the server, it will respond by sending a large message consisting of alphanumeric characters to the same socket. Replace “keyword” with the word that is randomly given to you in MyCourses task description. You should read all data the server sends. After server has finished sending data, it closes the TCP connection. Your task is to repeat this assignment applying different properties on the bottleneck link, and report the results following the instructions given below.

Note that the course git repository contains Rust templates for this task that you may use if you want.

You should repeat the assignment applying the following four scenarios:

1. Long delay. The bottleneck link has one-way delay of 200 ms, no limits on the transmission speed: sudo aalto/simple_topo.py --delay=200ms

2. Slow transmitter The bottleneck link has one-way delay of 50 ms, but transmission speed is limited to 100 kbps: sudo aalto/simple_topo.py --delay=50ms --bw=0.1

3. Lossy link The bottleneck link has one-way delay of 200 ms. Packet loss rate is 10%: sudo aalto/simple_topo.py --delay=200ms --loss=10

4. Survival: In this case you can find the parameters yourself. What is the most challenging network scenario you can think of that can still complete the TCP connection, delivering the same amount of bytes as the previous scenarios? In addition to delay, bandwidth and loss rate, you can also limit the packet queue size at the bottleneck link (argument max_queue_size).

Write a report that describes the following details. The report, and answers to the following questions need to be submitted in MyCourses for grading. For all the four afore-mentioned scenarios, the answers to the following three questions should be the same:

• What was the keyword you used? (As randomly given in MyCourses task assignment)
• How many bytes did the server transmit before closing connection?
• What were the last 8 characters you received from server before connection was closed?

In addition, for each of the above four scenarios, report the following:

• How long does it take to complete the transfer? Give exact (millisecond granularity) answer, as measured by your program
• How many round-trip times did the transfer take? If you think there were TCP retransmission timeouts, tell also that.
• How many retransmissions did TCP do during the transmission?

Tell also what parameters you used in the “Survival” scenario.

For this task, you will need to use Wireshark to analyze the TCP traffic, to determine the number of round-trip times and retransmissions.

Here are the likely useful steps on the Mininet command line, after starting the simple_topo script in each of the four scenarios:

• lh1 xterm &: start a separate xterm window representing host “lh1” (IP: 10.0.0.1)
• rh1 xterm &: start another xterm window representing host “rh1” (IP: 10.0.0.3)
• On window representing “rh1”: start adnet-agent server. It will be listening to TCP connections at IP address 10.0.0.3, port 12345
• On window representing “rh1”, start Wireshark: wireshark &. Start capturing traffic on “rh1-eth0” interface. Because in this case server is doing the transmission of most data, analyzing e.g. round-trip times and retransmissions is easier when observing the server side of the connection.
• Start your client implementation on window representing “lh1”