Description
In this lab, we will do some practice questions on link layer
Review Questions
Question 1) Suppose two nodes start to transmit at the same time a packet of length L over a broadcast channel of rate R. Denote the propagation delay between the two nodes as dprop. Will there be a collision if dprop<L/R? Why or Why not?
Question 2) Why would the token ring protocol be inefficient if a LAN had a very large perimeter? (
Question 3) Consider the 5-bit generator, G = 10011, and suppose that D has the value 1010101010. What is the value of R?
Question 4) In this problem, we explore some of the properties of the CRC. For the generator G = 1001 given is Section 6.2.3 of your textbook, answer the following questions. (10 marks)
- a) Why can it detect any single bit error in data D?
b)Can the above G detect any odd number of bit errors? Why?
Question 5) Graph the efficiency of slotted ALOHA and pure ALOHA as a function of p for the following values of N:
- a) N=15.
b)N=25.
Question 6) Suppose nodes A and B are on the same 10 Mbps broadcast channel, and the propagation delay between the two nodes is 245 bit times. Suppose A and B send Ethernet frames at the same time, the frames collide, and then A and B choose different values of K in the CSMA/CD algorithm. Assuming no other nodes are active, can the retransmissions from A and B collide? For our purposes, it suffices to work out the following example. Suppose A and B begin transmission at t = 0 bit times. They both detect collisions at t = 245 bit times. Suppose KA = 0 and KB = 1. At what time does B schedule its
retransmission? At what time does A begin transmission? (Note: The nodes must wait for an idle channel after returning to Step 2—see protocol.) At what time does A’s signal reach B? Does B refrain from transmitting at its scheduled time?
