Networking

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ECE 436 – Computer Communication Networks II Take-Home Quiz 4

Q1. What does it mean for a wireless network to be operating in “ad-hoc mode?” If the network is not in ad-hoc mode, what mode of operation is it in, and what is the difference between that mode of operation and ad-hoc mode? Q2. What are the elements of a wireless network? Q3. What are the characteristics of wireless links which make them different from their wired counterparts? Q4. What is the hidden terminal problem in wireless networks? What is the solution for the hidden terminal problem in 802.11 (Wi-Fi)?

Q5. Consider the figure below. If the measured SNR level of a wireless host is 20dB and if its target is to

keep the BER below 10 -6

, what should be the transmission rate and what kind of modulation should be

used?

10 20 30 40

SNR (dB)

10 -1

10 -2

10 -3

10 -5

10 -6

10 -7

10 -4

QAM256 (8 Mbps)

QAM16 (4 Mbps)

BPSK (1 Mbps) B E R

Q6. Consider the figure below.

(a) Consider sender 2 in the above figure. What is the sender’s output to the channel (before it is added

to the signal from sender 1), Z2 i,m?

(b) How does the signal is reconstructed at receiver 2? Show the steps.

Q7. What are the techniques for sharing mobile-to-BS radio spectrum?

Q8. If a node has a wireless connection to the Internet, does that node have to be mobile? Explain. Suppose that a user with a laptop walks around her house with her laptop, and always accesses the Internet through the same access point. Is this user mobile from a network standpoint? Explain.

Q9. Consider a TCP connection going over Mobile IP. True or false: The TCP connection phase between the correspondent and the mobile host goes through the mobile’s home network, but the data transfer phase is directly between the correspondent and the mobile host, bypassing the home network.

Q10. In mobile IP, what effect will mobility have on end-to-end delays of datagrams between the source and destination?

Q11. What are the reasons of handoff in cellular networks?