Chapter 16.

Question 1

What is a good answer when you are asked to define a wireless survey to a client?

Answer 1

Determination of coverage, holes within coverage, looking for locations of interference, proper placement of APs, installation, and configuration of 802.11 hardware and related components.

Question 2

What are key components to a proper wireless survey today?

Answer 2

Capacity performance and application testing.

Question 3

What can Wi-Fi based protocol analyzers do?

Answer 3

1. Identify interference.
2. Examine 802.11 frames and identify SSID and BSSID information.
3. Packet and security information.
4. Signal Strength measurements
5. Channel information.

Question 4

How do Wi-Fi cards see the world?

Answer 4

Through frames and modulated bits.

Question 5

What is a spectrum analyzer?

Answer 5

Frequency domain measurement devices that can measure the amplitude and frequency space of electromagnetic signals.

Question 6

At what dBm level does background noise begin to have a severe effect on WLAN?

Answer 6

-85 dBm on both bands.

Question 7

At what rate of retransmissions can be handled without affecting performance too much on the DATA network?

Answer 7

10% retransmission rate.

Question 8

How do interfering devices prevent an 802.11 radio from transmitting?

Answer 8

If another RF source is transmitting with strong amplitude, an 802.11 radio can sense the energy during the clear channel assessment (CCA) and defer transmission. If the source of the interference is a constant signal, an 802.11 radio will continuously defer transmissions until the medium is clear. In other words, a strong source of RF interference could actually prevent your 802.11 client stations and access point radios from transmitting at all.

Question 9

What are some potential sources of interference in the 2.4 GHz ISM band?

Answer 9

1. Microwave ovens.
2. 2.4 GHz cordless phones, DSSS and FHSS
3. Fluorescent bulb.
4. 2.4 GHz video cameras.
5. Elevator motors
6. High heat output devices.
7. Bluetooth radios.
8. Nearby AP

Question 10

What frequency of cordless phones on the 5GHz band can cause interference?

Answer 10

5.8 GHz cordless phones operate in the 5.8 GHz ISM band, which overlaps with the upper U-NII band (5.725 GHz to 5.850 GHz). Indoor use of 5.8 GHz phones will cause interference with 5 GHz radios transmitting in the upper U-NII band.

Question 11

What is the FIRST test that you perform during a site survey?

Answer 11

A spectrum analysis site survey/layer 1 sweep.

Question 12

Why can an AP at 2.4 GHz transmitting at max power, actually cause you to have significantly worse signal strength?

Answer 12

Because at max power, the RF cell size will be very large. A massive RF cell size will pick up all kinds of interference. Will even cause the hidden node problem.

Question 13

What is one of the hardest parts of performing a site survey?

Answer 13

The hardest part of physically performing a coverage analysis site survey is often finding where to place the first access point and determining the boundaries of the first RF cell.

Question 14

Why don’t you want APs too close together?

Answer 14

Because you may confuse the clients with too strong of an RF signal from too many APs. This will cause roaming issues because the clients won’t know who to connect to and it can cause frequent roaming and performance degradation.

Question 15

What is a good number or percentage for cell overlap?

Answer 15

10-20%

15% - 30% for roaming, according to CWNA

Question 16

What is the recommended SNR for a data network and a voice network?

Answer 16

15 dB for data
(18 dB for Data according to CWNA)
25 for Voice.

Question 17

The radius of each cell should provide a signal greater than…..

Answer 17

-65 dBm

-67 dBm according to CWNA

Question 18

Cells on the same channel should be separated by a distance that provides a signal difference of at least…..

Answer 18

19 to 20 dB.

Question 19

What are semi directional patch antennas often used for?

Answer 19

With 802.11n and 802.11ac technology, semidirectional MIMO patch antennas are often pointed down from the ceiling to provide for sectors of coverage in areas where there is a high density of users and devices.

Question 20

Calculations necessary when deploying outdoor bridge links?

Answer 20

Fresnel zone, earth bulge, free space path loss, link budget, and fade margin.

Question 21

What does EIRP stand for?

Answer 21

Equivalent Isotropically Radiated Power or Effective Isotropic Radiated Power

Question 22

What type of data is collected during a passive manual survey?

Answer 22

The radio collects RF measurements, including
received signal strength (dBm), noise level (dBm), and signal-to-noise ratio (dB). Although the client adapter is not associated to the access point during the survey, information is received from radio signals that exist at layer 1 and layer 2.

Question 23

What information can you gather during an active survey that you can’t gather during a passive survey?

Answer 23

1. Layer 3 connectivity is established allowing for pings to be sent to the gateway testing response times.
2. Frame retransmissions can be detected.
3. Roaming can also be tested.
4. Packet loss.

Question 24

Why should you hold the phone you are taking RSSI readings with in a vertical position?

Answer 24

Because the phone’s antenna is usually vertically polarized.

Question 25

What does RMM (Radio Resource Management) do?

Answer 25

When implemented, RRM provides automatic cell
sizing, automatic monitoring, troubleshooting, and optimization of the RF environment, which can best be described as a self-organizing wireless LAN.

Question 26

What is a post install validation survey?

Answer 26

to audit or validate the installation. This validation allows you to verify the RF coverage and data
rates that are being provided by the installed network; you can then compare the actual values with expected values from your network design plans.