Mixed Deck — All CWDP Topics Flashcards

Which IEEE amendment defines fast BSS transition (FT), reducing roaming latency for real-time applications?

Answer: IEEE 802.11r

IEEE 802.11r defines Fast BSS Transition, enabling pre-authentication with target APs to reduce handoff time below 50 ms.

A CWDP designer is planning for 20 simultaneous VoIP calls per AP. What minimum data rate should be supported per call (G.711 codec)?

Answer: 87.2 kbps with headers

G.711 at 64 kbps payload plus RTP/UDP/IP/802.11 headers totals approximately 87.2 kbps per call.

What information should be gathered during a pre-survey site visit?

Answer: Building materials, ceiling heights, existing infrastructure, RF interference sources, and client requirements

A thorough pre-survey visit documents construction materials (wall composition, glass types), ceiling types and heights, existing cabling and mounting points, potential RF interference sources, aesthetic requirements, and client needs.

What factor most significantly increases free-space path loss between two outdoor wireless nodes?

Answer: Doubling the operating frequency or distance

Free-space path loss increases by 6 dB when distance or frequency doubles, as defined by the Friis transmission equation.

What is the key benefit of using 802.11ax (Wi-Fi 6) APs in an outdoor high-density deployment such as a sports venue parking area?

Answer: OFDMA allows simultaneous transmission to multiple clients, improving efficiency in dense environments

OFDMA in Wi-Fi 6 subdivides channels into resource units, enabling parallel transmissions to multiple clients and improving dense-environment efficiency.

What is the primary advantage of MU-MIMO over SU-MIMO in wireless network design?

Answer: It allows the AP to communicate with multiple clients simultaneously

Multi-User MIMO allows an access point to transmit to or receive from multiple clients at the same time using spatial multiplexing, significantly improving network capacity in dense environments.

Which strategy improves wireless network performance in high-density environments?

Answer: Deploying multiple access points with smaller coverage areas.

In high-density environments, deploying multiple access points with smaller coverage areas is crucial for improving network performance. This strategy distributes the client load across more radios and allows for more efficient channel reuse, minimizing co-channel interference and maximizing overall network capacity and throughput for a large number of users.

A CWDP is designing a hospital WLAN for VoIP over Wi-Fi phones. Which frequency band should be preferred and why?

Answer: 5 GHz for more non-overlapping channels and less interference

5 GHz provides more non-overlapping channels (up to 25 in the US), reducing co-channel interference in dense deployments.

What is jitter in the context of VoIP over WLAN, and what is the typical acceptable maximum?

Answer: Variation in packet arrival times; under 50 ms

Jitter is the variance in packet inter-arrival delay; values above 50 ms cause audible distortion in VoIP calls.

What is the primary difference between a wireless bridge and a wireless mesh node?

Answer: A bridge connects two fixed points; a mesh node dynamically routes through multiple paths

Wireless bridges create fixed point-to-point or point-to-multipoint links, while mesh nodes dynamically discover and route through multiple paths.

How should channel planning be approached in a multi-floor building to minimize co-channel interference?

Answer: Use a 3D channel reuse pattern ensuring the same channel is not used on adjacent APs vertically or horizontally

A 3D channel reuse plan considers both horizontal and vertical AP adjacencies, ensuring that co-channel APs are separated by enough distance and floor attenuation to prevent significant co-channel interference.

What IEEE amendment enables BSS Transition Management, allowing APs to suggest better APs to clients?

Answer: 802.11v

802.11v BSS Transition Management allows APs to send BTM Request frames suggesting clients move to a better AP.

What is the primary benefit of using a mesh network topology in wireless design?

Answer: Provides multiple redundant paths for data transmission.

A mesh network topology is characterized by multiple interconnected nodes, where each node can communicate with several others. This design creates numerous redundant pathways for data transmission, meaning if one path or node fails, data can automatically reroute through an alternative route, significantly enhancing network reliability and resilience.

Which type of site survey is performed before deploying a wireless network?

Answer: Predictive survey

A predictive site survey is performed before any access points are physically deployed. It utilizes software tools and floor plans to model the RF environment, estimate signal coverage, and determine optimal access point locations and configurations based on design requirements, thereby saving time and resources during the actual deployment phase.

How does transmit power mismatch between APs and clients affect network performance?

Answer: Clients may hear the AP but cannot transmit back reliably, creating asymmetric communication

When an AP transmits at much higher power than the client device, the client can receive the AP's signal from far away but its lower-power response may not reach the AP, creating an asymmetric link with poor performance.

Which factor most affects RF signal propagation?

Answer: Physical obstructions and interference.

RF signal propagation is most significantly affected by physical obstructions and interference. Walls, furniture, and other physical barriers can absorb or reflect radio waves, weakening the signal. Additionally, interference from other electronic devices operating on similar frequencies can disrupt the signal, leading to reduced range and slower speeds.

In a Layer 3 roaming scenario, what mechanism preserves a client's IP address when crossing subnet boundaries?

Answer: Mobility tunneling (e.g., GRE tunnel back to anchor AP)

Layer 3 roaming solutions use tunneling (GRE or proprietary) to forward client traffic back through the anchor AP, preserving the original IP.

What is the key advantage of 802.11r Over-the-DS (Distribution System) fast transition versus Over-the-Air?

Answer: It allows key exchange with the target AP before the client reassociates

Over-the-DS FT pre-stages authentication keys with the target AP via the wired network before the client completes the air-interface roam.

What is the maximum channel width supported by 802.11ac Wave 2?

Answer: 160 MHz

802.11ac Wave 2 supports channel widths up to 160 MHz (either contiguous or as 80+80 MHz non-contiguous), enabling higher throughput compared to Wave 1's maximum of 80 MHz.

Which frequency band is commonly used for Wi-Fi networks?

Answer: 2.4 GHz and 5 GHz

The 2.4 GHz and 5 GHz frequency bands are the most commonly used for Wi-Fi networks. The 2.4 GHz band offers wider coverage but is more susceptible to interference, while the 5 GHz band provides faster speeds and less interference but with a shorter range. Modern Wi-Fi devices and routers often support both bands to offer flexibility and optimize performance.