What are the two main purposes of a CTS frame?

What is the difference between passive scanning and active scanning?

Why are acknowledgments used in 802.11 but not in wired Ethernet?

Suppose an 802.11b station is configured to always reserve the channel with the RTS/CTS sequence. Suppose this station suddenly wants to transmit 1,000 bytes of data, and all other stations are idle at this time. Assume a transmission rate of 12 Mbps. As a function of SIFS and DIFS, and ignoring propagation delay and assuming no bit errors, calculate the time required to transmit the frame and receive the acknowledgment.

Suppose an 802.11b station is configured to always reserve the channel with the RTS/CTS sequence. Suppose this station suddenly wants to transmit 1,000 bytes of data, and all other stations are idle at this time. Assume a transmission rate of 12 Mbps. As a function of SIFS and DIFS, and ignoring propagation delay and assuming no bit errors, calculate the time required to transmit the frame and receive the acknowledgment.

In step 4 of the CSMA/CA protocol, a station that successfully transmits a frame begins the CSMA/CA protocol for a second frame at step 2, rather than at step 1. What rationale might the designers of CSMA/CA have had in mind by having such a station not transmit the second frame immediately (if the channel is sensed idle)?

Suppose there are two ISPs providing WiFi access in a particular café, with each ISP operating its own AP and having its own IP address block.

a. Further suppose that by accident, each ISP has configured its AP to operate over channel 11. Will the 802.11 protocol completely break down in this situation? Discuss what happens when two stations, each associated with a different ISP, attempt to transmit at the same time.

b. Now suppose that one AP operates over channel 1 and the other over channel 11. How do your answers change?

Describe the role of the beacon frames in 802.11.

Another pitfall cited is expecting to improve the overall performance of a computer by improving only one aspect of the computer. Consider a computer running a program that requires 250 s, with 70 s spent executing FP instructions, 85 s executed L/S instructions, and 40 s spent executing branch instructions. 1. By how much is the total time reduced if the time for FP operations is reduced by 20%? 2. By how much is the time for INT operations reduced if the total time is reduced by 20%? 3. Can the total time can be reduced by 20% by reducing only the time for branch instructions?

As a mobile node gets farther and farther away from a base station, what are two actions that a base station could take to ensure that the loss probability of a transmitted frame does not increase?

If two CDMA senders have codes (1, 1, 1, -1, 1, -1, -1, -1) and (1, -1, 1, 1, 1, 1, 1, 1), would the corresponding receivers be able to decode the data correctly? Justify.

The Pentium 4 Prescott processor, released in 2004, had a clock rate of 3.6 GHz and voltage of 1.25 V. Assume that, on average, it consumed 10 W of static power and 90 W of dynamic power. The Core i5 Ivy Bridge, released in 2012, had a clock rate of 3.4 GHz and voltage of 0.9 V. Assume that, on average, it consumed 30 W of static power and 40 W of dynamic power. 1. For each processor find the average capacitive loads. 2. Find the percentage of the total dissipated power comprised by static power and the ratio of static power to dynamic power for each technology. 3. If the total dissipated power is to be reduced by 10%, how much should the voltage be reduced to maintain the same leakage current? Note: power is defined as the product of voltage and current.

What are the differences between the following types of wireless channel impairments: path loss, multipath propagation, interference from other sources?

After selecting the AP with which to associate, a wireless host sends an association request frame to the AP, and the AP responds with an association response frame. Once associated with an AP, the host will want to join the subnet to which the AP belongs. What does the host do next?