220-1101 Question 132
Single answerPower over Ethernet (PoE)A technician is installing several new ceiling-mounted wireless access points in an office. Each access point is designed to receive both network connectivity and electrical power through a single Ethernet cable. After mounting the first unit, the technician connects it with a Cat 6 patch cable to an older unmanaged switch, but the access point does not power on. The same access point powers on immediately when connected to a newer switch in another room. Which of the following is the MOST likely reason?
- A
The older switch does not support PoE on its Ethernet ports
- B
The Cat 6 cable cannot carry electrical power to network devices
- C
The access point requires a crossover cable to receive PoE
- D
PoE only works over fiber uplink ports, not standard RJ-45 ports
Show answer and explanation
Correct answer: A
Explanation
The key clue is that the access point works on a newer switch but not on the older unmanaged switch. That strongly indicates the older switch is not PoE-capable. In real deployments, devices that rely on PoE must be connected either to a PoE-enabled switch port or to a PoE injector placed between the switch and the powered device. According to IEEE PoE standards such as 802.3af and 802.3at, power is delivered over standard twisted-pair Ethernet cabling, typically with RJ-45 connections. A+ candidates should recognize that when a PoE-powered device fails to turn on, an early troubleshooting step is to verify PoE support and power budget on the switch port before suspecting the cable type or Ethernet pinout.
- A. Correct.
This is correct. Power over Ethernet (PoE) allows compatible switches or injectors to deliver DC power over standard twisted-pair Ethernet cabling to devices such as access points, IP phones, and cameras. If the access point powers on when connected to a newer switch but not to the older unmanaged switch, the most likely cause is that the older switch lacks PoE capability on its ports.
- B. Incorrect.
This is incorrect. Standard Ethernet cabling such as Cat 5e and Cat 6 can carry PoE when used with compatible equipment and within Ethernet distance limits. A common misconception is that a special category of copper cable is required just for PoE, but PoE is specifically designed to operate over standard twisted-pair copper Ethernet cabling.
- C. Incorrect.
This is incorrect. PoE does not require a crossover cable. Modern Ethernet devices commonly support auto-MDI/MDIX, and PoE delivery is negotiated by compatible equipment independently of using a straight-through or crossover cable in normal installations. Choosing a crossover cable would not explain why the same access point powers on from a different switch.
- D. Incorrect.
This is incorrect. PoE is delivered over copper Ethernet connections using RJ-45 ports, not fiber. Fiber uplinks carry data using light and do not provide electrical power in the way PoE does. This option reflects a misunderstanding of how PoE is physically delivered.