Hi this is the lab assignment everything is mentioned in attached document but for this assignment you will need to access my university website and login to portal as mentioned in instructions so here is my username and password.username: an688password: Zamanbhai1@
Microsoft Word - Lab 4 Laboratory 3 ‐ The Effect of Link Errors on Network Performance In class you will be investigating error detection and error correction protocols. This laboratory will show these protocols in operation, and will show how link errors affect network performance. A network simulator package, called “ns”, will be used. ns is widely used by researchers and engineers to test new networking concepts. Please note: This experiment will require you to run script files (.tcl) using the ns program in LINUX. These files can be obtained from the subject website for CSIT127. IMPORTANT: We use Ubuntu (not Windows) Step 1: Cold start your machine. If it is running shut it down. Use the computer’s power switch to bring it back to life. (This is not normal – we are experiencing network problems) Step 2: Select Ubuntu (not Windows). You will need to wait about 30-60 seconds for your machine to establish a network connection. Watch the network icon top right corner of your screen – you will notice when your machine establishes a network connection. Step 3: Enter your SOLS user name and password. Step 4: Start the Firefox web browser, open up UOW home page and login into SOLS then Moodle. Go to ISIT127’s web site, and download lab_3.zip. Drag/Copy/Move the zip file from the Download folder to the Desktop. For the next steps you will to need to use LINUX command line. (If this is new to you, you will need to follow the following instructions carefully or seek the help of your lab demonstrator.) Step 5: In the search window of Ubuntu One type terminal. Open terminal program to reveal command line window Step 5: Type ls You should be able to see the Desktop folder listed with other folders. You now need to move into the Desktop folder Step 6: Type cd Desktop (Remember this not Windows - lower case and upper case must be maintained) Step 7: Type ls (You should see the lab_3 zip file in the Desktop folder) Step 8 Unzip lab_3.zip into this folder. Type unzip lab_3.zip Step 9 Type ls. You should now see a folder called lab_3. You should know enough to shift into this folder (Hint type cd lab_3) You are ready to start! 4.1. Error Free Performance The lab_3 folder contains the .tcl scripts required for this experiment. Enter the following command: ns part_1.tcl This runs ns using the input file “part_l.tcl”. You should see a new window, which shows a simple network. At the top of this window is a series of play buttons, similar to those on a tape recorder. Press the start button (i.e. the forward arrow). Tip: click the “re-layout” to re-orient the network. You will see a simple network topology, comprising a single link, and a graph showing the throughput obtained over the link. Sketch this graph, and be sure to label all axes. For your information, sequence numbers refers to packets (will be covered in lectures in coming weeks). From your graph, calculate the throughput during the simulated time interval. (Note: if you resize the window of the graph you will observe two traces. This is not correct so do not re-size the window of the graph!) Note: you may need to slow the simulation down. You can do this by moving the slider in the top right hand corner of the window (to the left) – around 1ms works well for this experiment. In order to be able to answer the quiz questions you will need to use the correct terms. When talking about data transfer you need to make reference to “bits”. When referring to a description of packets we normally use “bytes”. We assume 8 bits to 1 byte. Sequence number and Packet size for Part 1 and Part 2 is 1000 bytes/packet 4.2. Link Errors Now we will investigate how the network performance changes when link errors appear. Close your previous ns windows, and enter the following command: ns part_2.tcl Press the start button on the window that appears, and record the graph as before. This network is the same as the previous one, except that the average bit error rate on the link has changed from 0 to 1/1000. The trace represents transmitted data over the time period. Note that there is a disruption in the trace. Take note of the time at which this disruption occurs on the trace and closely observe the simulation around this time. What do you see? In order to calculate the total amount of data transmitted you will need to add the data that was lost (and re-transmitted) due to link error. This information is recorded in the trace – you just need to work out how this can be achieved! Now measure the total amount of useful data transferred. This is the level reached at the end of the trace. You have now measured two quantities of data, one being the total amount transferred, the other being the total useful data transferred. You should realize by now that the difference between the two is due to packet retransmissions, caused by errors on the link. Calculate the amount of data retransmitted, and the efficiency. Also calculate the throughput, and compare your answer with the one obtained previously. How do you account for the differences you see? 4.3. Changing the packet size In this part, you will investigate the effect of increasing the packet size, for a constant average bit error rate. Repeat part 2, with the following two ns networks: ns part_3.tcl ns part_4.tcl Sketch the graph in each case. Similar to part 2, calculate the total data transmitted, the total useful data transmitted, the amount retransmitted and the throughput. The network in part 2 had a packet size of 1000 (8000 bits) bytes. The networks in ns part_3.tcl and ns part_4.tcl have packet sizes of 1250 bytes (10,000 bits) and 6250 bytes (50,000 bits) respectively. In all three cases, the average bit error rate is l/l000. Comment on any differences you see in your measurements for these three cases.