Flashcards in Chapter 16. Deck (26):
What is a good answer when you are asked to define a wireless survey to a client?
Determination of coverage, holes within coverage, looking for locations of interference, proper placement of AP's, installation, and configuration of 802.11 hardware and related components.
What are key components to a proper wireless survey today?
Capacity performance and application testing.
What can Wi-Fi based protocol analyzers do?
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.
How do Wi-Fi cards see the world?
Through frames and modulated bits.
What is a spectrum analyzer?
Frequency domain measurement devices that can measure the amplitude and frequency space of electromagnetic signals.
At what dBm level does background noise begin to have a severe effect on WLAN?
-85 dBm on both bands.
At what rate of retransmissions can be handled without affecting performance to much on the DATA network?
10% retransmission rate.
How do interfering devices prevent an 802.11 radio from transmitting?
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.
What are some potential sources of interference in the 2.4 GHz ISM band?
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
What frequency of cordless phones on the 5GHz band can cause interference?
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.
What is the FIRST tests that you perform during a site survey?
A spectrum Analysis site Survey.
Why can an AP at 2.4 GHz transmitting at max power, actually cause you to have significantly worse signal strength?
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.
What is one of the hardest parts of performing a site survey?
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.
Why don't you want AP's too close together?
Because you may confuse the clients with too strong of an RF signal from to many AP's. This will cause roaming issues because the clients won't know who to connec too. it can cause frequent roaming and performance degradation.
What is a good number or percentage for cell overlap?
15% - 30% for roaming.
What is the recommended SNR for a data network and a voice network?
18 dB for Data
25 for Voice.
The radius of each cell should provide a signal greater than.....
Cells on the same channel should be separated by a distance that provides a signal difference of at least.....
What are semi directional patch antennas often used for?
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.
Calculations necessary when deploying outdoor bridge links? Name them.
Fresnel zone, earth bulge, free space path loss, link budget, and fade margin.
What does EIRP stand for?
Equivalent isotropically radiated power
What type of data is collected during a passive manual survey?
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.
What information can you gather during an active survey that you can't gather during a passive survey?
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.
Why should you hold the phone you are taking RSSI readings with in a vertical position?
Because the phone's antenna is usually vertically polarized.
What can RMM do? Radio Resource Management.
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.