300-110 Sample Questions & Answers

Cisco's voice WLAN design targets at the cell edge are an RSSI of -67 dBm or better (with about 20% cell overlap so that at least two APs are heard at -67 dBm), a noise floor no higher than -92 dBm for an SNR of 25 dB, and packet loss of 1% or less (plus channel utilization under 40% and 802.11 retries under 20%). End to end, Cisco QoS design guidance targets one-way latency of 150 ms or less and average jitter under 30 ms for voice.

Predictive surveys are only as good as the data entered into them. Attenuation depends on metal content, moisture, thickness and conductivity: Cisco lists drywall at about 3 dB, brick about 10 dB and concrete about 12 dB, and rates metal as very high attenuation, so lead-lined walls and dense metal medical equipment block far more signal than the 3 dB drywall assumed in the model. The remediation is to correct the model with measured wall losses, add APs to close the gaps (for example inside the shielded rooms rather than relying on penetration from the corridor), and validate with a post-deployment survey against the voice targets (-67 dBm with enough overlap that two APs are heard). Raising AP power is not a remedy, because the battery-powered badges cannot transmit back through the same walls.

A 100% duty cycle means the transmitter is sending RF energy constantly without pausing. Analog devices such as wireless video cameras have a constant, always-on signal (Cisco shows video-camera duty cycles of 90-100%), so Wi-Fi devices that hear it above the Clear Channel Assessment (CCA) threshold defer indefinitely; in a study cited by Cisco, an analog video camera 25 feet from the AP or client degraded Wi-Fi throughput by 100 percent (no ability to connect). A microwave oven, by contrast, cycles on and off with the AC power (about a 50% duty cycle) and is used in short bursts, and a BLE beacon sends brief, narrow, low-duty-cycle bursts. Design response: locate and remove or relocate the camera, or keep the affected APs and clients on channels or a band it does not occupy; CleanAir ED-RRM can move an AP off a channel hit by such a high-duty-cycle interferer.

For location analytics and tracking (like Cisco Spaces), it is critical to deploy APs along the perimeter (corners and outer edges) of the coverage area. This ensures that a tracked client is inside the convex hull of the APs, allowing algorithms to accurately triangulate the location rather than guessing if the client is outside the array.

Every AP model has specific RF characteristics (antenna gain, radiation pattern, Rx sensitivity). Surveying with an older or different model will yield inaccurate heatmaps that will not reflect how the production APs will actually perform in the environment.

In high-density deployments, providing RF signal (coverage) is easy, but providing enough airtime for hundreds of clients is difficult. The design must focus on capacity by creating smaller, isolated RF cells (using directional antennas or lower Tx power) to allow channels to be reused without interference.