220-1101 Question 135
Single answerPoE standardsA technician is installing several new ceiling-mounted wireless access points in an office. The access point documentation states that each unit requires up to 25.5W of power over Ethernet. The existing network switch supports only IEEE 802.3af on its PoE ports. The access points power on briefly during testing but then reboot repeatedly when users begin connecting. Which action should the technician take to provide the correct PoE support without replacing the access points?
- A
Replace the switch or use injectors that support IEEE 802.3at PoE+
- B
Use a passive PoE adapter because any higher voltage will stabilize the access points
- C
Disable SSID broadcasting so the access points draw less power from the switch
- D
Replace the Ethernet cabling with Cat 6a because 802.3af cannot deliver full power over older cable
Show answer and explanation
Correct answer: A
Explanation
This scenario tests practical understanding of PoE standards. IEEE 802.3af PoE is intended for lower-power devices and provides up to 15.4W at the power sourcing equipment (PSE). IEEE 802.3at PoE+ increases available power to 30W at the port, with up to 25.5W available to the powered device (PD), which matches the requirement in the scenario. Reboots under load are a realistic symptom of insufficient power delivery. Best practice is to verify the PD's wattage requirement, confirm the switch port's supported PoE standard, and check the switch's overall PoE power budget. Standards-based guidance comes from IEEE 802.3 PoE specifications, and vendor installation guides commonly state the required PoE class or minimum standard for access points.
- A. Correct.
Correct. IEEE 802.3af provides up to 15.4W at the port, with less power available to the powered device after cable loss. A device needing up to 25.5W typically requires IEEE 802.3at (PoE+), which can provide up to 30W at the port. If the switch only supports 802.3af, the technician should use 802.3at-capable switch ports or compliant PoE injectors.
- B. Incorrect.
Incorrect. Passive PoE is not the same as standards-based PoE and can damage equipment if voltage and pinout do not match the device requirements. It is not an appropriate fix for a device designed to negotiate power using IEEE PoE standards. The misconception is that 'more voltage' alone solves a power issue, but proper 802.3at negotiation and power budget are what matter.
- C. Incorrect.
Incorrect. Disabling SSID broadcasting does not meaningfully solve a PoE standards mismatch. The issue is insufficient available power from the 802.3af source, not a configurable wireless feature. Someone might choose this because reducing workload sounds logical, but the AP's required power class still exceeds what 802.3af is designed to provide.
- D. Incorrect.
Incorrect. While cable quality and length can affect PoE performance, 802.3af is limited by the standard's power delivery, not simply by cable category. Standard-compliant PoE can operate over suitable twisted-pair Ethernet cabling, commonly up to 100 meters, and changing to Cat 6a does not turn an 802.3af port into an 802.3at port.