CWNP CWDP-305 - Certified Wireless Design Professional

To determine the minimum RSSI required for a VoWLAN deployment with a specified SNR, use the formula:

Minimum RSSI = Noise Floor + Required SNR

Given:

Required SNR = 25 dB

Noise Floor = -88 dBm

Calculation:

Minimum RSSI = -88 dBm + 25 dB = -63 dBm

Thus, the minimum RSSI needed is -63 dBm.

Explanation with Extract:

Per the *CWDP-305 Study Guide*, Voice over WLAN (VoWLAN) deployments require robust signal quality. The SNR is critical for voice performance, and the guide specifies:

"For VoWLAN, an SNR of 25 dB is typically required to ensure clear voice quality and minimal latency."

"The minimum RSSI is derived by adding the required SNR value to the measured noise floor."

This aligns with RF fundamentals where SNR is the difference between the received signal strength (RSSI) and the ambient noise floor. A higher SNR (e.g., 25 dB for voice) demands a stronger signal relative to noise. Here, a noise floor of -88 dBm plus 25 dB SNR results in -63 dBm RSSI (Option D).

Why other options fail:

A. -70 dBm: Results in 18 dB SNR (−70 − (−88) = 18 dB), insufficient for VoWLAN.

B. -67 dBm: Yields 21 dB SNR (−67 − (−88) = 21 dB), below the 25 dB requirement.

C. -65 dBm: Provides 23 dB SNR (−65 − (−88) = 23 dB), still inadequate.

In the 2.4 GHz band, there are only three non-overlapping channels (1, 6, 11). Overuse of radios on the same or overlapping channels results in excessive co-channel interference (CCI), leading to contention and degraded throughput. The CWDP-305 Study Guide advises minimizing the number of active radios in the 2.4 GHz band in dense environments.

Turning off 2.4 GHz radios on some APs is the recommended action to reduce CCI without introducing adjacent-channel interference (ACI), which would occur if you used overlapping channels like 3, 4, or 8. This adjustment retains channel reuse efficiency and supports low-density legacy devices. It’s especially relevant in designs that primarily target 5 GHz or 6 GHz but include 2.4 GHz for backward compatibility.

When conducting a site survey, accurately determining ceiling heights is crucial for proper AP placement and coverage prediction.If ladder use is restricted, utilizing a laser distance meter provides a precise and cost-effective solution.Laser measures can quickly and safely determine vertical distances without the need for physical elevation.گروه آموزشی و پژوهشی سیب

The CWDP-305 Official Study and Reference Guide emphasizes:

"Laser distance meters are valuable tools during site surveys, allowing for accurate measurements of ceiling heights and other distances without the need for ladders or lifts."

In 802.1X/EAP authentication, the shared secret between the authenticator and the RADIUS server must match. If clients cannot associate and the RADIUS server is operational, the next step is to verify that the shared secret configured on both the authenticator and the RADIUS server is identical. A mismatch will prevent successful authentication.

Receive sensitivity indicates the minimum signal strength at which a device can successfully receive and demodulate a signal at a specified data rate.In this case, a receive sensitivity of −82 dBm @ 18 Mbps means that the device requires a signal stronger than −82 dBm to reliably demodulate data at 18 Mbps.Therefore, the device must receive a signal with a strength greater than −82 dBm (i.e., closer to 0 dBm) to maintain that data rate.