Wireless Fundamentals 4

Here you will find answers to Wireless Fundamentals – Part 4

Question 1

True or false: A wireless PAN consumes little power from small handheld computer devices.

A. True
B. False

 

Answer: A

Explanation

An example of the Wireless PAN technology is Bluetooth. It is also known as IEEE 802.15.1, has the advantage of being very energy-efficient, which makes it particularly well-suited to use in small devices.

Question 2

Which IEEE standards group uses Bluetooth as the basis for the standard?

A. IEEE 802.15
B. IEEE 802.11
C. IEEE 802.13
D. IEEE 802.16

 

Answer: A

Question 3

In what frequency band does Bluetooth operate?

A. 2.2 GHz
B. 2.4 GHz
C. 2.6 GHz
D. 3.0 GHz

 

Answer: B

Question 4

A Bluetooth-enabled device is always transmitting. True or false?

A. True
B. False

 

Answer: B

Explanation

The Bluetooth device hops across all the channels. Although the energy emitted by the Bluetooth device may appear high, its duty cycle values are much lower (maximum is about 3.5%, which may not affect WiFi devices seriously). If a bluetooth-enabled device is always transmitting, its duty cycle should be 100%.

Question 5

What is the highest possible data rate of an IrDA device?

A. 2 Mbps
B. 4 Mbps
C. 6 Mbps
D. 8 Mbps

 

Answer: B

Explanation

IrDA is an acronym for the Infrared Data Association, an organization which sets communications standards for infrared over small distances. Some kinds of IrDA devices include printers, cameras, handheld portables, smart remotes with display screens, cell phones…

IrDA devices provide a point-to-point method of data transfer that is adaptable to a broad range of computing and communicating devices. The first version of the IrDA specification (version 1.0) provides communication at data rates up to 115.2 Kbps. Later versions (version 1.1) extended the data rate to 4 Mbps, while maintaining backward compatibility with version 1.0 interfaces.

Question 6

In what frequency band does 802.11a operate in?

A. 2.2 GHz
B. 2.4 GHz
C. 2.6 GHz
D. 5 GHz

 

Answer: D

Question 7

How many non-overlapping channels are available with 802.11b wireless LANs?

A. One
B. Two
C. Three
D. Four

 

Answer: C

Explanation

Fourteen channels are defined in the IEEE 802.11b channel set. Each channel is 22MHz wide but there is only 5MHz channel separation so, as can be seen in the illustration, the channels overlap.

There are only 3 non-overlapping channels available in the 802.11b standard, they are channels 1, 6 and 11. For WiFi access points that are located near each other it is recommended that they each use one of the above non-overlapping channels to minimize the effects of interference.

Question 8

True of false: 802.11g operates at up to 54 Mbps and interoperates with 802.11b.

A. True
B. False

 

Answer: A

Question 9

A learning bridge forwards all packets. True or false?

A. True
B. False

 

Answer: B

Explanation

A learning bridge monitors MAC  (OSI layer 2) addresses  on both positions of its connection and  attempts to learn which addresses are on which  side. When a packet arrives, it examines the destination address of the frame. If it does not find the destination address in its forwarding table so it floods it to all other ports. If the bridge already has that destination address in its forwarding table so it will forward that packet to the corresponding port.

In this question, maybe the author wants to mention about a “real” bridge (not switch, because these 2 terms are sometimes used interchangeable). A bridge, in some circumstances, must determine when it receives a packet whether it should let the packet cross the bridge or continue local (some packets may not want to cross the bridge because the source and  destination addresses are both on one side).

Question 10

True or false: FDMA requires users to take turns transmitting signals.

A. True
B. False

 

Answer: B

Explanation

When using Frequency Division Multiple Access (FDMA), the available bandwidth is subdivided into a number of narrower band channels. Each user is allocated a unique frequency band in which to transmit and receive on. During a call, no other user can use the same frequency band.

FDMA

“TDMA requires users to take turns transmitting signals” is a true statement. Time Division Multiple Access (TDMA) divides the available spectrum into multiple time slots, by giving each user a time slot in which they can transmit or receive.

TDMA

Question 11

A company has a wireless network. In this network, collisions occur when more than one device sends data at the same time. Which physical layer function can a network administrator perform to determine whether or not any device is sending data to the channel?

A. CSMA/CD
B. CCA
C. CSMA/CA
D. CCX

 

Answer: B

Explanation

Wireless devices cannot send and receive at the same time. It means that if more than one device were to send at the same time, a collision would result. If a collision occurs, the data from both senders would be unreadable and would need to be resent.

When a station is ready to send, it listens to the media to verify that nothing else is sending. If the media is free, the station sends its wave. This method is called Clear Channel Assessment (CCA).

CSMA/CCA copies the contention window (CW) size piggybacked in the MAC header of an overheard data frame within its basic service set (BSS) and updates its backoff counter according to the new CW size.

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is a layer 2 technique, not layer 1 (physical). In CSMA/CA, as soon as a device receives a packet that is to be sent, it checks to be sure the channel is clear (no other node is transmitting at the time). If the channel is clear, then the packet is sent. If the channel is not clear, the node waits for a randomly chosen period of time, and then checks again to see if the channel is clear. This period of time is called the backoff factor, and is counted down by a backoff counter. If the channel is clear when the backoff counter reaches zero, the node transmits the packet. If the channel is not clear when the backoff counter reaches zero, the backoff factor is set again, and the process is repeated.

Note:

CSMA/CD deals with transmissions after a collision has occurred, CSMA/CA acts to prevent collisions before they happen.

Question 11

A business customer uses Non-LOS WiMAX wireless network technology. Which of the following data rates is provided to the customer?

A. 30 Mbps
B. 70 Mbps
C. 40 Mbps
D. 15 Mbps

 

Answer: A

Explanation

The signal range of Non-LOS WiMAX is about 3 to 4 miles, and data rates are advertised at around 30 Mbps, but you can expect less, closer to 15 Mbps.

Question 12

A network administrator needs to determine what LAN devices to install on his network. What are two advantages of using Layer 2 Ethernet switches over hubs? (Choose two)

A. Allowing simultaneous frame transmissions
B. Increasing the size of broadcast domains
C. Increasing the maximum length of UTP cabling between devices
D. Filtering frames based on MAC addresses
E. Decreasing the number of collision domains

 

Answer: A D