CS 571: Computer Networks Fall 2009
Homework 2
Assigned: Sept. 10, 2009 Due: Sept. 17, 2009
1. Suppose a non-standard 100Mbps Ethernet segment is 2500 meters long and the signal is propagated in the
Ethernet at 2∗108meters per second. Two stations (Aand B) attached to the Ethernet are located at the two
ends of the segment (you can assume that they are 2500 meters apart). What is the minimum frame size so that
A can always detect the collision with a frame sent by B? Show the calculation.
2. Peterson & Davie, Chapter 2, question 44 (a) (b) and (d)
Note: in (b), A3should be changed to A2, and A4should be changed to A3.
3. We discussed three MAC protocols – channel partitioning, CSMA/CD, token passing. For each of these pro-
tocols, give an application scenario in which it performs better than other two protocols. Be specific about
parameters of the application and explain why it performs better than others.
4. Peterson & Davie, Chapter 3, question 17
5. Peterson & Davie, Chapter 3, question 21
6. Consider five LANs connected by five bridges as shown in the following figure, assuming that B1< B 2<
B3< B4< B5< B 6.
a) Run the distributed spanning tree algorithms and give the messages that will be still forwarded in the steady
state.
b) Show what ports are logically disconnected. Why? (Explain the reason by showing what messages/comparisons
lead to the decision.)
B4
B1
B3 B2
B5 B6
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