Chapter 6 - Wireless LANs ( WLANs )

3b. Why does the access point connect to the corporate Ethernet LAN?

Answer: (1) to reach the corporate Servers or (2) to reach the Internet Access Router

8e. What two propagation problems become worse as frequency increases?

Answer: (1) Attenuation ( loss of signal strength ) (2) Dead zones

6a. Distinguish between omnidirectional and dish antennas in terms of operation.

Answer: (1) Omnidirectional antennas transmit in all directions but shorter distances (2) Dish antennas concentrate signals in a particular direction, which allows signals to travel longer distances .

9a. Distinguish among the frequency spectrum, service bands, and channels.

Answer: (1) The frequency spectrum is the range of all possible frequencies from 0 Hz to infinity. (2) A service band is a contiguous range of the frequency spectrum dedicated to a specific purpose, such as FM radio, emergency response, GPS, etc. (3) Service bands are subdivided further into channels. .

17d. Distinguish between a BSS, and ESS, and an SSID.

Answer: (1). Basic service set (BSS) is an access point and its wireless hosts. (2) Service set ID (SSID) identifies an access point. (3).Extended service set (ESS) is a group of BSSs with the same SSID that connect via a distribution system.

22b. Compare the market status of 802.11n and 802.11ac.

Answer: 802.11n still dominates the installed base today, but 802.11ac dominates sales and will supplant 802.11n as the dominant Wi-Fi technology.

2a. Distinguish between 802.3 standards and 802.11 standards.

Answer: 802.3 = Ethernet Standards 802.11 = Wireless LAN Standards

12. In Figure 6-12, there are question marks between several pairs of routers. For each of these pairs, list their channels of operation and whether they will interfere.

Answer: Access Point D-E - both on channel 6 = interference ( this is the only one ) Access Point E ( chan 6 ) -> B ( chan 1 ) - NO interference Access Point B ( chan 1 ) -> C ( chan 6 ) - NO interference Access Point C ( chan 6 ) -> F ( chan 11 ) - NO interference Access Point F ( chan 11 )- -> E ( chan 6 ) - NO interference

25c. Distinguish between MIMO and multiuser MIMO (MU-MIMO).

Answer: MIMO allows only a pair of wireless devices to simultaneously send or receive multiple data streams. Multi-user MIMO allows multiple wireless devices to simultaneously receive the multiple data streams.

8a. Contrast inverse square law attenuation and absorptive attenuation.

Answer: (1) Inverse square law attenuation is due to the signal spreading (2) Absorptive attenuation is signal loss due to energy absorption

2b. What is the actual difference between 802.11 and Wi-Fi?

Answer: 802.11 = wireless standards created by IEEE 802.11 Working Group Wi-Fi = certification system used by the Wi-Fi Alliance

10f. What other types of system do we call broadband?

Answer: "Fast" systems are also called broadband

10b. If the lowest frequency in a channel is 1.22 MHz and the highest frequency is 1.25 MHz, what is the channel bandwidth?

Answer: 0.03 MHz

7a. If you quadruple propagation distance, how much will signal intensity change at the receiver?

Answer: 1/16

9c. How many channels are there in the FM band?

Answer: 101 channels (each 0.2 MHz wide)

13a. In what two service bands does 802.11 operate?

Answer: 2.4 Ghz and 5= GHz

10c. If you want to transmit seven times as fast, how much wider must the channel be?

Answer: 7 times

22a. Compare the rated speeds of 802.11n and 802.11ac.

Answer: 802.11n products deliver speeds of 100 to 600 Mbps. The newer 802.11ac standard delivers far higher rated speeds of 433 Mbps to 6.9 Gbps.

8b. What causes dead zones?

Answer: A block/interference in the path of the wireless signal between the sender and the receiver.

5c. What is a hertz?

Answer: A measure of frequency ( one cycle per second )

25b. What are the benefits of Beamforming?

Answer: A stronger signal with longer range

11b. What is the advantage of using unlicensed service bands?

Answer: Avoiding the Cost and Burden of Licensing

16a. Why must an access point remove an arriving packet from the frame and place the packet in a different frame when it sends the packet back out?

Answer: Because an 802.11 frame cannot travel over the 802.3 LAN ( so it needs to covert it )

15b. Why does Spread Spectrum Transmission divide the channel into subcarriers?

Answer: Because it is easier to send many slow signals in many small subcarriers.

5d. At what range of frequencies do most wireless systems operate?

Answer: Between 500 megahertz (MHz) and 10 gigahertz (GHz).

18c. Does media access control (MAC) apply to wireless hosts, access points, or both?

Answer: Both.

10e. What do we call a system whose channels are wide?

Answer: Broadband channels

18b. How does media access control (MAC) address the collision problem?

Answer: By controlling when devices may transmit so that only one device transmits at a time.

9e. An FM radio station is called Moldy Oldies 101.1. Is this a channel or a service band?

Answer: Channel

6c. Under what circumstances would you use a dish antenna?

Answer: Dish antennas are used for longer distances

25a. What is Beamforming?

Answer: Focusing a WiFi signal more directly to the receiving device ( in straightline or beam )

5b. Is wireless radio transmission usually described in terms of wavelength or frequency?

Answer: Frequency

24c. What is its other benefit of MIMO?

Answer: Greater transmission range.

11c. What is the downside of using unlicensed service bands?

Answer: Interference from other networks.

13c. Why is the fact that the 2.4 GHz band only supports 3 non overlapping channels a problem?

Answer: It is difficult to put nearby access points on different channels

14b. What is the benefit of spread spectrum transmission for business communication?

Answer: It reduces signal propagation problems

Bonus 1: What is Latency?

Answer: Latency = delay. It's the amount of delay (or time) it takes to send information from one point to the next. usually measured in milliseconds

24b. What is the main benefit of MIMO?

Answer: MIMO increases speed without increasing bandwidth.

13d. Why are companies moving rapidly into the 5 GHz band?

Answer: More Bandwidth & Faster Speeds

8c. What is the most serious propagation problem in WLANs?

Answer: Multipath interference

14c. Is spread spectrum transmission done for security reasons in commercial WLANs?

Answer: No.

18d. Can a wireless access point and one of the wireless clients in its BSS transmit simultaneously?

Answer: No.

14d. Does spread spectrum transmission increase transmission speed thanks to its wider channels?

Answer: No. ( it does not transmit signals faster )

3a. In a Wi-Fi LAN, do two wireless hosts usually send frames directly to one another?

Answer: No. The source host transmits the frame to an access point. The access point then retransmits the frame to the destination host.

4b. In 802.11 Wi-Fi networks, can simple installation rules usually reduce propagation effects to nonissues?

Answer: No. This does not work in Wi-fi Networks.

15a. What spread spectrum transmission method dominates today?

Answer: OFDM ( Orthogonal Frequency Division Multiplexing )

1b. Do wireless LAN standards governed by OSI or TCP/IP standards?

Answer: OSI standards.

6d. What type of antenna normally is used in WLANs? Why?

Answer: Omnidirectional Antenna's

1a. At what layers do wireless LANs operate?

Answer: Physical and data link layer

5a. What is a transceiver?

Answer: Radios for data transmission ( that both transmit and receive )

9f. Wi-Fi operates in the 2.4 GHz and the 5 GHz.

Answer: Service Band

9d. Are the set of frequencies used for police communication in a city channels or a service band?

Answer: Service Bands

10a. Does a signal travel at a single frequency, or does it spread over a range of frequencies?

Answer: Signals spread over a range of frequencies.

10d. Why is large channel bandwidth desirable?

Answer: Speed. High bandwidth brings high radio transmission speed.

14a. In the 2.4 GHz and 5 GHz service bands, what type of transmission method is required by regulators?

Answer: Spread Spectrum Transmission

23b. What will happen to your speed as you move away from the access point? .

Answer: The Speed will be Lower ( The signal degrades with distance )

24a. How does MIMO ( Multiple-Input/Multiple Output ) use spatial streams to increase transmission speed?

Answer: The host or access point sends two or more spatial streams (radio signals) in the same channel between two or more different antennas

13e. If you triple channel bandwidth, what happens to the number of channels in a service

Answer: The number of channels go down ( i.e. - less channels )

16b. Describes the steps that occur when the server transmits a packet back to the wireless client.

Answer: The steps are: (1) wireless access point receives the 802.3 frame (2) removes the packet from the Ethernet frame (3) forwards the packet to the wireless host in a Wi-Fi frame.

18a. What problem does this cause? Scenario: All wireless hosts and the access point that serves them transmit on the same channel.

Answer: Their signals will interfere with each other.

17b. What characteristics do all access points in a corporate network share?

Answer: They all have the same SSID.

11a. Do WLANs today use licensed or unlicensed service bands?

Answer: Unlicensed

6b. Under what circumstances would you use an omnidirectional antenna?

Answer: Used to transmit in short distances ( such a wireless LAN or a cellular phone network).

9b. In radio, how can you send multiple signals without the signals interfering with one another?

Answer: Using different channels

17c. Over what transmission system do access points communicate with each other to accomplish roaming?

Answer: Wireless Distribution System

23a. You are using an access point with a rated speed of 4 Gbps. Why will you experience much less speed?

Answer: Yes actual speed is always lower than "rated" speed

2c. Do we use the two terms interchangeably?

Answer: Yes. It is common to call the 802.11 standards "Wi-Fi" standards. The terms have become almost interchangeable.

4a. In 802.3 Ethernet networks, can simple installation rules usually reduce propagation effects to nonissues?

Answer: Yes. This works in Ethernet networks.

8d. How is Multipath interference controlled?

Answer: by Spread Spectrum Transmission

13b. How many 20 MHz nonoverlapping channels does the 2.4 GHz band support?

Answer: only 3

22c. If you need an access point providing 3 Gbps service, what choice do you have?

Answer: only 802.11ac

21. If you triple channel bandwidth in a service band, what happens to the number of channels in a service band?

Answer: the channels in a service band decreases proportionately.

17a. What is a roaming in 802.11?

Answer: the process of moving from one Wi-fi access point to another Wi-Fi access point without losing connection