CWDP CWDP Outdoor and Mesh Networking 1 — Questions and Answers
Question 1: What is the primary advantage of using a mesh WLAN architecture over a traditional wired infrastructure deployment in outdoor environments?
- Higher throughput than wired backhaul
- Elimination of cabling requirements by using wireless backhaul between nodes (Correct answer)
- Lower latency for all mesh hops
- Support for more clients per access point
Correct answer: Elimination of cabling requirements by using wireless backhaul between nodes
Mesh networks use wireless backhaul between nodes, avoiding the need to trench cables to every AP location.
Question 2: In an outdoor point-to-point wireless bridge, what is the first Fresnel zone and why must it be kept clear?
- The line-of-sight path that must be perfectly straight
- An elliptical region around the direct path where reflections constructively interfere; obstruction causes significant signal loss (Correct answer)
- The antenna beam pattern measured at 3 dB below peak
- The regulatory exclusion zone around outdoor APs
Correct answer: An elliptical region around the direct path where reflections constructively interfere; obstruction causes significant signal loss
The first Fresnel zone must be at least 60% clear of obstructions to avoid destructive interference that degrades link performance.
Question 3: What path loss model is most commonly used for outdoor WLAN link budget calculations in open terrain?
- Two-ray ground reflection model
- Free-Space Path Loss (Friis) model (Correct answer)
- ITU indoor model
- Log-distance indoor model
Correct answer: Free-Space Path Loss (Friis) model
The Friis free-space path loss model is used for outdoor line-of-sight links, calculating loss based on distance and frequency.
Question 4: Which regulatory domain restriction must a CWDP consider when deploying outdoor 5 GHz point-to-point bridges in the US?
- All 5 GHz channels are prohibited outdoors
- UNII-2 and UNII-2 Extended channels require DFS radar detection and avoidance (Correct answer)
- Outdoor 5 GHz use is limited to UNII-3 channels only
- Maximum EIRP for all outdoor 5 GHz links is 20 dBm
Correct answer: UNII-2 and UNII-2 Extended channels require DFS radar detection and avoidance
UNII-2 and UNII-2e channels in the 5 GHz band require Dynamic Frequency Selection (DFS) to detect and avoid radar interference.
Question 5: In a mesh network, what is 'backhaul efficiency' and how does the number of hops affect it?
- Backhaul efficiency increases with each additional hop
- Each additional mesh hop typically halves available client throughput due to half-duplex relay overhead (Correct answer)
- Backhaul efficiency is independent of hop count
- More hops increase redundancy without throughput penalty
Correct answer: Each additional mesh hop typically halves available client throughput due to half-duplex relay overhead
Each wireless mesh hop roughly halves throughput because the relay node must receive and retransmit on the same channel.
Question 6: What design technique allows a mesh AP to avoid throughput halving by separating backhaul and access traffic?
- Using the same channel for both backhaul and access
- Deploying dual-radio or tri-radio mesh nodes with dedicated backhaul radios (Correct answer)
- Increasing transmit power on the mesh node
- Using 2.4 GHz exclusively for backhaul
Correct answer: Deploying dual-radio or tri-radio mesh nodes with dedicated backhaul radios
Dedicated backhaul radios (on a separate channel or band) allow simultaneous backhaul and client access without sharing the medium.
CWDP CWDP Outdoor and Mesh Networking 1
What is the primary advantage of using a mesh WLAN architecture over a traditional wired infrastructure deployment in outdoor environments?