ECGR-4187/5187 Data Communication and Networking-II Fall 2014

Homework Assignment 3: (LANs)

Due: Thursday, 10/23/14. The HW is due at the beginning of the lecture (5:00pm). Late submissions or submissions at the end of the lecture may not be accepted. 1) State the conditions under which each of the following three types of asynchronous

medium access control may achieve high efficiency: round robin, reservation, and contention based. Give brief explanations for each answer.

2) Give short answers to the following: a) State the functions of each of the following LAN components: repeater, hub, layer-

2 switch, bridge.

b) Explain the address learning mechanism in the IEEE 802.1 standard for routing in bridges.

3) State the difference between pure ALOHA and slotted-ALOHA medium access control method and explain the reason why slotted-ALOHA achieves higher average throughput in comparison to pure ALOHA.

4) A large number of stations (theoretically infinite) using slotted-ALOHA is generating messages according to a Poisson model at the rate of 50 frames/sec. Time is slotted in units of 40 msec.

a) What is the probability that a transmitted frame is not successful in the first attempt? b) What is the average throughput in the network in number of frames per second? [Hint: Pr. of success=Pr. of 0 frames generated in a slot]

5) Describe the p-persistent CSMA MAC protocol and explain how its performance will differ between p=0.1 and p=0.9 and why.

6) The IEEE 802.3 MAC (Ethernet) protocol uses 1-persistent CSMA, which is known to be unstable at high traffic loads. What features does Ethernet have that prevents this instability at heavy loads? Explain.

Homework Assignment 3: (LANs)