CompTIA Network+ (N10-009)Network TroubleshootingHard
A network technician is setting up a new point-to-point wireless bridge between two buildings. After configuring the access points (APs) and aligning the antennas, basic connectivity (ping) works, but observed throughput is significantly lower than expected, even with a strong signal. The wireless link is configured for 802.11ac using a 40 MHz channel width. Which of the following is the MOST likely cause of the poor throughput?
- AInsufficient power over Ethernet (PoE) budget.
- BHigh latency due to distance.
- CInterference from other 5 GHz devices.
- DIncorrect antenna polarization.
Show answer & explanationAnswer & explanation
Correct answer: D. Incorrect antenna polarization.
For point-to-point wireless bridges, especially with directional antennas, ensuring correct and matching antenna polarization (e.g., both vertical or both horizontal) is crucial for optimal signal transfer and throughput. If one antenna is vertically polarized and the other horizontally, the signal quality will be severely degraded, leading to poor throughput despite a strong overall signal indication.
Why the other options are wrong
- A. Insufficient PoE budget would likely cause the APs to not power on or function intermittently, not just poor throughput with a strong signal.
- B. While distance does add latency, it typically doesn't cause a significant drop in throughput with 802.11ac over a point-to-point link once basic connectivity is established, unless the distance is extreme and signal strength is marginal.
- C. Interference from other 5 GHz devices is possible, but incorrect polarization is a more specific and fundamental issue for a point-to-point link that would explain strong signal but poor throughput, especially after alignment.
Antenna Polarization Mismatch
Occurs when the polarization of transmitting and receiving antennas in a wireless link are not aligned, severely degrading signal strength and throughput.
- Antennas can be vertically, horizontally, or circularly polarized.
- For optimal performance, both ends of a link must have matching polarization.
- Results in significant signal loss and reduced data rates, even with strong line of sight.
Memory trick: Wireless slow? Check the 'angle' of your connection.