Understanding RRM

In Chapter 7, “Planning Coverage with Wireless APs,” you learned how to size access point (AP) cells appropriately by disabling data rates and changing the transmit power levels. You also learned how important a proper channel layout is to promote efficient roaming and minimize co-channel interference. You probably also realized how difficult these tasks are when you have to tune the radio frequency (RF) parameters manually across a large number of APs.

In this chapter, you learn about Cisco Radio Resource Management (RRM), a flexible and automatic mechanism that Cisco Wireless LAN controllers can use to make your life much easier.

“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 13-1 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 13-1 “Do I Know This Already?” Section-to-Question Mapping

1. Which one of the following correctly describes a mandatory data rate?

   1. A data rate that must be used by wireless clients all the time
   2. The highest data rate used by an AP and its clients
   3. A data rate that must be supported by a client before it can associate with an AP
   4. A data rate required by the IEEE 802.11 standards body

2. You can configure only one data rate as mandatory on an AP. True or false?

   1. True
   2. False

3. An AP sends 802.11 broadcast management frames at which one of the following data rates?

   1. The highest mandatory data rate
   2. The lowest mandatory data rate
   3. The lowest supported data rate
   4. All supported data rates

4. Which one of the following is the default state of 802.11n and 802.11ac support and the default channel width on a Cisco wireless LAN controller?

   1. Disabled; 20-MHz channels
   2. Enabled; 20-MHz channels
   3. Enabled; 40-MHz channels
   4. Disabled; 40-MHz channels
   5. Enabled; 80-MHz channels

5. Which one of the following correctly identifies the scope of the RRM algorithms?

   1. All APs joined to one controller
   2. All APs joined to all controllers
   3. All APs joined to controllers in an RF group
   4. All APs of a specific model

6. An RF group is automatically formed by which one of the following?

   1. All APs that share the same channel
   2. All clients that share the same SSID
   3. Any controllers that can overhear neighbor messages with identical RF group names sent between their APs
   4. All controllers that can overhear neighbor messages with identical mobility group names sent between their APs

7. The TPC algorithm is used for which one of the following purposes?

   1. To adjust the transmission control protocol rate
   2. To detect problems in transmission perimeter coverage
   3. To adjust the transmitting primary channel
   4. To adjust the transmit power level

8. If the DCA algorithm detects that an AP is experiencing interference or excessive noise, what might it do to mitigate the problem?

   1. Increase the AP’s transmit power level
   2. Decrease the AP’s transmit power level
   3. Change the AP’s channel number
   4. Direct the client to a different band

9. Which one of the following runs the DCA algorithm?

   1. RF group leader
   2. Master controller
   3. Each controller
   4. NCS or Cisco Prime Infrastructure

10. The 5-GHz radio in one of several APs in a building has failed. Which one of the following algorithms should be able to detect the failure?

    1. CCA
    2. DCA
    3. Dead radio detection
    4. Coverage hole detection