Lab #9
CS1150 Introduction to Computer Science
Lab #9 – Networking, 40 points
Objective:
To study how networks route packets to various destination hosts. Learn how networks ensure reliable delivery.
Instructions:
Make sure to do the Activity as outlined in the LabCH19.pdf file. The activity is actually a tutorial that will help you to solve the problems in the exercises. It is expected that you will complete the Activity before you begin the exercises.
When you are finished, save and rename the completed document as “firstname_lastname_lab9.docx”. Then, submit the saved document to Pilot.
EXERCISE 1
1) Start the “TCP/IP” applet.
2) Copy and paste the following text into the “Your Message” box:
Computer networking is essential in our world today.
Note that this message is exactly 52 ASCII characters long, counting spaces and the period at the end.
It should look like this:
Then, press the button “Send a message” and watch.
3) Count how many DAT and ACK packets were sent. (Don’t rely on the “Status” box, actually count the packets yourself.)
Write your answers here:
DEFINE DAT AND GIVE NUMBER OF DAT PACKETS:
DEFINE ACK AND GIVE NUMBER OF ACK PACKETS:
4) Determine the steps for calculating how many characters were sent during the entire exchange.
Assuming that:
· Every DAT or ACK packet has a packet header (example: DAT 1 0 221)
· Besides the packet header, every DAT packet carries AT MOST 10 characters of data.
· The last packet carried less than 10 characters of data. (52 data characters in the message, remember? 52 doesn’t divide nicely into 10)
· ACK packets have no data, just a packet header.
· Every blank space, even in a packet header, counts as a character.
· Assume that every packet header is 9 characters long
We calculated that exactly 171 characters were sent back and forth in total during the entire process. How did we get that number?
Show the mathematical steps to calculate the number 171 here, below this line.:
5) Calculate the overhead, expressed as a percentage. Here is the process:
· There are 52 characters of actual data in the message, including blanks and punctuation.
· Subtract the number of characters of actual data (52 characters) from the total number of characters sent in both directions in all the packets (from earlier in the lab). This gives you the number of characters sent that were not actually data, just part of the cost/overhead of sending the actual data.
· Divide the number of overhead characters by the total number of characters to calculate the overhead expressed as a percentage of the total.
Write the overhead percentage here, below this line:
6) Imagine you have a million-character message to send. Calculate how many packets will be needed and how many characters will be sent in total for the entire process to move the message from node 0 to node 1:
Write your answers here:
HOW MANY PACKETS TOTAL:
HOW MANY CHARACTERS TOTAL:
7) What would be an obvious way to decrease the overhead percentage? Why might this solution backfire? Under what conditions would that occur?
Write your answers here:
OBVIOUS WAY TO DECREASE OVERHEAD PERCENTAGE:
HOW THAT COULD BACKFIRE:
UNDER WHAT CONDITIONS:
8) What is the purpose of IP address? What is the purpose of Routers?
Write your answers here:
EXERCISE 2
1) Start or restart the “TCP/IP” applet again. Once again, copy and paste the following text into the “Your Message” box:
Computer networking is essential in our world today.
2) This time, change the selection away from Leave packets undamaged to Delete packets that are touched.
3) Delete some data packets by clicking on them as they move along the wire, and watch the re-transmission after timeout.
4) What happens if you delete the re-transmitted packet? Does the TCP/IP applet need to take any special action?
Write what happens here, below this line:
Is special action needed if re-transmitted packet is deleted? Write your answer here, below this line:
5) What happens if you delete ACK or NAK packets?
Write your answer here, below this line:
EXERCISE 3
1) Start the “Network router” applet.
Select Example 3, the ring network.
2) Double-click on the node 37.61.25.46. List the nodes it is directly connected to (the nodes in its connection table).
Write your list of nodes here, below this line:
3) If 37.61.25.46 wants to send packets to a node that is not directly connected, to which node will it first send the packets? (Check the routing table by double clicking on the node.)
Write the address of the next node here, below this line:
4) Run the applet for a while, letting it generate packets continuously. Double-click on 37.61.25.46 again and look at its statistics. How many packets were sent? Received? Forwarded?
Write your answers here:
PACKETS SENT:
PACKETS RECEIVED:
PACKETS FORWARDED:
5) Which nodes are sending packets out, and to whom?
Write your answers here:
NODES THAT ARE SENDING PACKETS:
NODES THAT ARE RECEIVING PACKETS:
6) Click on 138.92.6.17. Write down its statistics.
PACKETS SENT:
PACKETS RECEIVED:
PACKETS FORWARDED:
EXERCISE 4
1) Start the “Network router” applet. Select Example 4, the star network.
2) Look at the routing and connection tables for the center node and several other nodes. Describe any pattern you can see in these tables.
Write your description here, below this line:
3) How is the connection table for the center node different from the other nodes?
Write your answer here, below this line:
4) Select Generate when I click on a node from the pull-down menu.
5) If you double-click on 159.121.2.13, you will see that its destination node is 126.14.5.46. Run the applet, click on 159.121.2.13, and watch the packets go. What color does the sending computer turn briefly? What color does the destination computer turn? What does it mean if a node flashes green?
Write your answers here:
WHAT COLOR (SENDING COMPUTER):
WHAT COLOR (DESTINATION COMPUTER):
WHAT DOES IT MEAN IF A NODE FLASHES GREEN:
Try it again with 8.10.20.25 to confirm.
6) Many early computer networks used a star topology like this example. What would happen if the center node in this type of network dies?
Write your answer here, below this line:
Exercise 5
Create a new topology using 4 nodes.
1) Create 4 nodes with following IP addresses
Node 1 = 130.108.7.11
Node 2 = 130.108.7.22
Node 3 = 130.108.7.33
Node 4 = 130.108.7.44
2) Make Node 3 as a forwarding node and connect it with all the other remaining nodes.
3) Let the sender receiver pair be as following:
| Sender | Receiver |
| Node 1 | Node 2 |
| Node 2 | Node 4 |
| Node 4 | Node 1 |
4) Your topology should look like as given below:
5) Paste your screenshot below this line:
Rubric (40 pts possible):
| Exercise | Points | |
| 1 | Question 1 | 0 |
| Question 2 | 0 | |
| Question 3 | 1 | |
| Question 4 | 1 | |
| Question 5 | 2 | |
| Question 6 | 1 | |
| Question 7 | 1 | |
| Question 8 | 2 | |
| 2 | Question 1 | 0 |
| Question 2 | 1 | |
| Question 3 | 1 | |
| Question 4 | 3 | |
| Question 5 | 3 | |
| 3 | Question 1 | 1 |
| Question 2 | 1 | |
| Question 3 | 1 | |
| Question 4 | 1 | |
| Question 5 | 2 | |
| Question 6 | 2 | |
| 4 | Question 1 | 1 |
| Question 2 | 1 | |
| Question 3 | 1 | |
| Question 4 | 1 | |
| Question 5 | 2 | |
| Question 6 | 2 | |
| 5 | Question 1 | 2 |
| Question 2 | 2 | |
| Question 3 | 2 | |
| Question 5 | 2 | |
| Total | 40 |
Do you need a similar assignment done for you from scratch? Order now!
Use Discount Code "Newclient" for a 15% Discount!
