The required readings for this homework are lectures 3 and 4 and the following papers:

a) “MACAW: A Media Access Protocol for Wireless LAN’s”

,b) 802.11 standard, which are available at the courseweb. You are encouraged to look formore sources online, which you need to cite.

Multiple-choice questions (choose one answer) (30pt)

1. The DCF mode in the IEEE 802.11 standard solves the following issues for thewireless channel access:

a. Hidden sender problems

b. Both hidden sender and exposed sender problems

c. Both hidden receiver and exposed receiver problems

d. All 4 problems: hidden/exposed, senders/receiverse. None of the above

2. The DS frame discussed in MACAW paper tries to address:

a. Exposed sender

b. Hidden sender

c. Exposed sender and hidden receiver

d. Hidden receiver

e. None of the above

3. Which of the following statements regarding fair channel access is true forMACAW and IEEE 802.11?

a. MILD is able to achieve absolute fairness

b. MACAW always provides best fairness

c. IEEE 802.11 DCF mode always provides best fairness

d. IEEE 802.11 PCF mode always provides best fairnesse. BEB favors stations that successfully contend for the channel mostrecently

Discussion questions (70pt)

1. MACAW always provides the best fairness? If not, what are the cases that it maybe unfair. Provide an example. (20pt)

2. Although RTS/CTS may prevent hidden terminal collisions, it is often disabled in802.11 commercial devices. What can be the reason for that? (10pt)

3. If you are asked to support time-critical applications in the IEEE 802.11 standard,which mode would you choose, the PCF or the DCF mode? Briefly justify youranswer. (10pt)

4. MACA introduces the idea of RTS/CTS to address hidden terminals. In whatscenario RTS/CTS cannot prevent collisions? (10pt)

5. 802.11 devices transmit an acknowledgment frame ACK after the reception of aDATA frame. What is the goal of the ACK frame? How does this design choiceconflict with the end-to-end argument discussed in the paper "End-To-EndArguments in System Design"? (20pt)

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