Networking

CSCD330 – Computer Networks

Final Exam v. 1.1, Fall 2020

Due: 09 DEC 2020, 11:59pm PST

Instructions: Write your answers to the following questions. A good idea would be to copy-and-

paste these questions to your document followed by your answer (not needed for binary blocks

in question 5). Add citations for anything you find not in the textbook or lecture notes. Also,

include your name on your answer sheet (5 points).

BE AWARE: NO LATE SUBMISSIONS WILL BE GRADED.

Question 1. (10 points)

A DHCP client sends out broadcast messages in two occasions before it hops on the Internet. What are these two and why are they broadcast?

Question 2. (10 points)

Given an IP address = 164.2.34.35 with subnet mask = 255.255.255.224, answer the following:

a. What is the subnet address?

b. What is the usable address range? (List the lowest and the highest addresses)

c. What is the broadcast address of the network containing the above IP address?

d. What is the base address of the network containing the above IP address? e. What is the Classless Inter-Domain Routing (CIDR) notation for the above IP

address/subnet mask?

Question 3. (10 points)

Describe how loops in paths can be detected in BGP.

Question 4. (10 points)

What is HOL blocking? Does it occur in input ports or output ports?

Question 5. (15 points)

On the attached sheet you will find 5 sets of 2-D error correction problems for sending 64 data bits and the associated parity bits. Each uses EVEN parity; the parity bits for each row and column are in bold. For each block, is it possible to determine if there has been some corruption of data? If corruption is detectable, give the position of the bits that are in error (e.g., zero-based index row and column).

Question 6. (12 points)

I have developed a new algorithm to solve the multiple access problem: Priority Slotted

ALOHA. Everything is the same as in Slotted ALOHA, but the probability can be different

between nodes depending on the assigned priority of the node: High, p = 0.75; Normal, p =

0.50; Low, p = 0.25.

a. Is this a good idea? How well does the above algorithm meet the ideal properties

that we want to achieve for solutions to the multiple access problem?

b. Are there any obvious problems with the above algorithm? Explain.

For the next 3 parts assume that there is one active node of each priority level attempting

to send data across the shared link.

c. What is the maximum efficiency of the node with High priority?

d. What is the maximum efficiency of the node with Normal priority?

e. What is the maximum efficiency of the node with Low priority?

Question 7. (10 points)

In class we discussed the routing protocols, RIP and OSPF. What are some of the reasons you would choose to use OSPF over RIP within your network? Are there circumstances where it is preferable to use RIP over OSPF? Explain.

Question 8. (10 points)

What conditions will cause a datagram to be fragmented? When a large datagram is fragmented into multiple smaller datagrams, where does this fragmentation occur? Where are these smaller datagrams reassembled into a single larger datagram?

Question 9. (18 points)

For the graph abstraction of a network with 6 nodes (Figure 1, shown below) with the cost of each link set near the link, compute the forwarding table (with associated cost) that would be generated for each of the six routers.

a. Router P b. Router Q c. Router R d. Router S e. Router T f. Router U

Figure 1. Question 9 Network

Question 10. (20 points)

Now, you get to be creative in designing your own secure, efficient, reliable protocol out

of carrier pigeons. For this problem, the Internet, phones and most other forms of

communication do not exist. Most people use carrier pigeon to communicate with each

other. Use your creativity and imagination. There are constraints on the protocol that

must be followed. All else is allowed.

Constraints a. Your pigeons air space is regulated by the Federal Carrier Pigeon Regulatory

Commission (FPCRC). You can only fly your pigeons in your quadrant of Spokane. Spokane has been divided into 8 parts and you have purchased the right to operate in your partition. You could pay transit fees to other companies in other quadrants, but you will lose some of your profits. You should decide how you want to handle this as a company.

b. There is a limit to the pigeon air space. You will not be able to fly all your pigeons at once. They will crash into each other. And it is also regulated by the FPCRC. So, at least ½ of your pigeons need to be grounded at one time. You will need to schedule the pigeons to deliver messages.

c. Pigeons are also homing pigeons, so they return to their homes after delivering messages. Hence, they are their own ACK's. But they can meet with problems along the way while aloft. Eagles and hawks love to eat pigeons; hungry residents love to shoot pigeons as tasty treats.; pigeons do not see well and often fly into poles and electric wires dooming themselves and the messages they carry. You will need a strategy for resending messages if a pigeon should fail.

d. Your goal as any good American company is to maximize profit. How you do this comes down to your own nature. You can play fair or you can do some interesting things to outcompete your competitors. I leave this up to you!!

This question will be graded based on creativity and adherence to the constraints of the problem. You cannot create a protocol that violates all the constraints.

EXTRA CREDIT. (up to 10 points)

What are the bit values for the letters (A through I) if the below binary message is for an Extended (255, 247) Hamming Code with even parity?

A B C 1 D 1 0 1 E 1 1 0 1 1 1 1 F 1 0 0 0 0 1 1 0 0 0 0 0 0 0 1 G 1 0 0 0 0 0 0 1 0 0 1 0 1 0 1 0 0 0 1 0 0 0 1 0 0 1 1 1 1 1 1 H 0 1 0 1 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1 0 1 1 1 1 1 0 0 0 0 1 0 1 0 0 0 1 0 1 0 1 1 0 0 0 0 0 0 1 0 0 0 0 1 1 0 1 I 1 1 0 0 0 1 0 1 1 1 1 1 0 0 0 0 0 0 0 1 0 0 1 1 0 0 0 1 0 0 1 0 1 1 0 1 1 1 1 1 1 1 1 0 1 1 0 1 1 1 0 0 1 0 1 1 0 0 0 1 0 0 1 1 0 0 0 1 0 1 1 1 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 1 0 1 0 1 0 0 1 1 1 1 1 1 1 0 0 0 0 0 1 1 0 1 1 0 1 1 0 0 1 0 0 1 1 1 0 1 1 0 0

NEW SUPPLEMENTAL SHEET for Question 5

5a. 1 1 1 0 0 1 0 0 0 0 1 1 0 1 1 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 1 1 0 1 1 1 1 0 1 1 1 1 0 0 1 1 1 0 1 1 1 1 1 0 1 1 0 1 1 0 0 0 1 0 1 0 1 0 1 1 1 0 0 1 1 0 1 0 0 0 5c. 0 1 1 1 1 1 1 0 0 1 0 0 0 0 1 1 1 0 1 1 1 1 1 1 1 1 0 0 0 1 1 1 1 0 0 0 1 1 1 0 1 1 0 0 1 1 0 1 1 1 1 0 0 1 0 1 0 0 1 0 0 0 0 1 1 0 0 0 0 0 1 1 1 1 1 0 0 0 1 1 0 5e. 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 0 0 1 0 0 1 1 0 0 1 1 1 1 1 0 0 0 1 1 1 1 1 1 1 0 0 1 0 1 1 1 1 1 1 0 0 1 1 0 0 1 0 0 1 0 1 1 1 0 0 0 0 0 1 1 1 1 1 0 1 0 1 1 0

5b. 0 1 1 1 0 1 0 0 0 0 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 1 1 1 1 0 1 0 1 1 1 1 1 0 1 1 0 1 1 1 0 0 0 1 0 1 0 0 0 0 0 1 1 1 0 1 0 1 1 1 1 0 1 0 0 1 0 0 0 0 0 0 0 1 1 0 0 5d. 0 1 0 0 0 1 0 0 0 1 0 1 0 0 0 1 1 0 1 0 1 0 0 0 1 1 0 1 0 1 1 0 1 1 0 1 0 0 1 1 1 1 0 1 0 1 1 0 0 0 0 1 0 1 1 1 1 1 0 1 1 0 0 1 1 1 1 0 0 1 0 1 0 0 0 1 1 0 0 1 1