Chapters 1 through 6 covered wireless communication with a focus on a single access point (AP) exchanging data with one or more clients. A single AP may be sufficient for home or small office use, but most wireless LANs involve a greater geographic area and require more APs. This chapter explains how wireless coverage can be adjusted to meet a need and how it can be grown to scale over a greater area and a greater number of clients. As you work through this chapter, remember that two things are important: the size of the BSA or AP cell and the location of cells in relation to each other.
“Do I Know This Already?” Quiz
The “Do I Know This Already?” quiz allows you to assess whether you should read this entire chapter thoroughly or jump to the “Exam Preparation Tasks” section. If you are in doubt about your answers to these questions or your own assessment of your knowledge of the topics, read the entire chapter. Table 7-1 lists the major headings in this chapter and their corresponding “Do I Know This Already?” quiz questions. You can find the answers in Appendix A, “Answers to the ‘Do I Know This Already?’ Quizzes.”
Table 7-1 “Do I Know This Already?” Section-to-Question Mapping
Foundation Topics Section
AP Cell Size
Adding APs to an ESS
Which of the following parameters can be adjusted on an AP to change the size of its cell or BSA? (Choose all that apply.)
- Channel number within a band
- Transmit power
- Supported modulation and coding schemes
- Supported data rates
An AP has been configured to use channel 1 with a transmit power of 20 dBm. With the AP located in the center of the lobby, you have determined that its signal will reach all locations in the lobby area. However, some users with small battery-operated devices report connectivity problems when they move toward the outer walls of the lobby. Which one of the following approaches will probably fix the problem?
- Increase the AP’s transmit power to increase its range
- Increase the client device’s transmit power
- Adjust the client device’s roaming algorithm
- Enable some lower data rates on the AP
Suppose that an AP is configured to offer the following data rates: 2-, 5.5-, 6-, 9-, 11-, 12-, 18-, 24-, 36-, and 48-Mbps data rates to its clients. Which one of the following strategies should be used to reduce the AP’s cell size?
- Enable the 1-Mbps data rate
- Enable the 54-Mbps data rate
- Disable the 36- and 48-Mbps data rates
- Disable the 2-Mbps data rate
All the APs on the second floor of a building are part of a single ESS. Each AP has been configured with a transmit power level of 14 dBm. In addition, each AP has been configured to use a non-overlapping channel that is different from its adjacent neighbors. All APs have been configured to offer only the 24-, 36-, 48-, and 54-Mbps data rates; all other rates are disabled. One day, one of the APs fails and someone replaces it. Afterward, users begin to call and complain about poor performance and roaming. You discover that the problems are not occurring in the area covered by the failed AP; instead, they are occurring about two APs away from it. Which one of the following could be causing the problem?
- The replacement AP has its radios disabled.
- The replacement AP is using a transmit level of 1 dBm.
- The replacement AP is using the 1- and 2-Mbps data rates.
- The replacement AP is new and cannot be causing the problem.
Which one of the following determines when a wireless client will roam from one AP to another?
- The current AP detects a weak signal coming from the client and forces the client to roam.
- The next AP overhears the client’s signal and asks it to roam.
- The client’s roaming algorithm reaches a threshold in signal quality.
- The client loses its IP address.
Which one of the following 802.11 frames is used to trigger a roam from one AP to another?
- Association request
- Disassociation request
- Reassociation request
Which one of the following statements is true about roaming?
- All wireless clients use the same algorithms to trigger a roaming condition.
- Wireless clients can scan available channels to look for a new AP when roaming.
- Wireless clients must roam from one AP to another on the same channel.
- The 802.11 standard defines a set of roaming algorithms for clients.
Which one of the following statements is true about a good wireless LAN design?
- Neighboring APs should use the same channel to promote good roaming.
- APs should be positioned so that their cells overlap.
- APs should be positioned so that their cells do not overlap at all.
- APs should use channels that overlap each other.
When you are designing the AP channel layout for an area, which one of the following is the most important consideration?
- The number of channels is conserved.
- APs in different areas use different channels.
- Adjacent APs use non-overlapping channels.
- Clients are grouped into common channels.
An AP is located in the main office on the third floor of a building. The AP is configured to use channel 6 in the 2.4-GHz band. Which of the following conditions might hinder clients as they move around on the third floor and need to roam? (Choose all that apply.)
- Two other APs in the third floor main office area use channel 6.
- None of the fourth floor APs directly above the main office use channel 6.
- One of the second floor APs directly below the main office use channel 6.
- All of these answers are correct.