Solutions_for_CHAPTER_1_2011_
嵌入式。
Computer networks [2011 SPRING]
ASSIGNMENTS FOR CHAPTER 1
Review Question:
R13. At time t0 the sending host begins to transmit. At time t1 = L/R1, the
sending host completes transmission and the entire packet is received at the router (no propagation delay). Because the router has the entire packet at time t1, it can begin to transmit the packet to the receiving host at time t1. At time t2 = t1 + L/R2, the router completes transmission and the entire packet is received at the receiving host (again, no propagation delay). Thus,
R14. a) 2 users can be supported because each user requires half of the
link bandwidth.
b) Since each user requires 1Mbps when transmitting, if two or fewer users transmit simultaneously, a maximum of 2Mbps will be required. Since the available bandwidth of the shared link is 2Mbps, there will be no queuing delay before the link. Whereas, if three users transmit simultaneously, the bandwidth required will be 3Mbps which is more than the available bandwidth of the shared link. In this case, there will be queuing delay before the link.
c) Probability that a given user is transmitting = 0.2
d) Probability that all three users are transmitting simultaneously =
3 33 3 p1 p= (0.2)3 = 0.008. Since the queue grows when all the users are 3
transmitting, the fraction of time during which the queue grows (which is equal to the probability that all three users are transmitting simultaneously) is 0.008.
