Networking

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ECE 436 – Computer Communication Networks II Take-Home Quiz 2

Q1. Briefly explain the channel partitioning MAC protocols.

Q2. What are the advantages and disadvantages of channel partitioning MAC protocols as compared to random access MAC protocols? Q3. There are four nodes in a wireless network; A, B, C, and D. They access the wireless channel using slotted ALOHA. Each node has an infinite number of packets to send. Each node attempts to transmit in each slot with probability p. (a) What is the probability that node A succeeds for the first time in slot 5?

(b) What is the probability that some node (either A, B, C, or D) succeeds in slot 3? (c) What is the efficiency of this four-node system?

Q4. Suppose nodes A and B are on the same 10Mbps broadcast channel, and the propagation delay between the two nodes is 325 bit times. Suppose CSMA/CD and Ethernet packets are used for this broadcast channel. Suppose node A begins transmitting a frame and, before it finishes, node B begins transmitting a frame. Can A finish transmitting before it detects that B has transmitted? Why or why not? (Note that the smallest packet size in the Ethernet is 64 bits.)

Q5. Why would the token-ring protocol be inefficient if a LAN had a very large perimeter?

Q6. Why is an ARP query sent within a broadcast frame? Why is an ARP response sent within a frame with a specific destination MAC address?

Q7. Consider the following figure.

(a) Suppose that all links are 100 Mbps. What is the maximum total aggregate throughput that can be achieved among the 6 hosts in this network?

A

A

’

B

B

’

C

C

’ 1 2

3 4 5

6

(b) Suppose the switch in the above figure is replaced by a hub. All links are 100 Mbps. What is the maximum total aggregate throughput that can be achieved among the 6 hosts in this network?

Q8. Consider the following network and assume that Bellman Ford algorithm is used as a routing protocol.

(a) What is the cost of the shortest path from A to H in one hop? After the next iteration (two hops)?

After the next iteration?

(b) What is the cost of the final shortest path from A to H? How many hops does it have?