220-1101 Networking Practice Question
A technician is installing several wireless access points in a large office to provide Wi-Fi coverage. The access points are PoE-capable, but the existing network switches do not support Power over Ethernet. The access points are located too far from available power outlets. Which of the following devices should the technician use to provide both data connectivity and power to the access points?
⚠ Common exam trap
Watch out — candidates often choose PoE switch (Option B) because it seems like a direct solution, but the question specifies the existing switches do not support PoE and the goal is to work with them, not replace them.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
PoE injector
A PoE injector is the correct choice because it inserts power into the Ethernet cable between the non-PoE switch and the PoE-capable access point, providing both data and power over a single cable. This solves the problem of the access points being too far from power outlets without requiring replacement of the existing switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
PoE injector
Why this is correct
A PoE injector is a midspan device that inserts DC power (typically 48 V per 802.3af/at) into an Ethernet cable between a non-PoE switch and the access point. It uses either spare pairs (10/100BASE-T) or phantom powering on the data pairs (gigabit), letting the AP receive both data and power over one cable without changing the existing switch infrastructure. This is the correct choice because it adds PoE capability per-device, is inexpensive, and is commonly used when only a few APs need power.
- ✗
PoE switch
Why it's wrong here
A PoE switch is an endspan device with built-in power-sourcing equipment (PSE) on every port, meaning it can supply power directly over each Ethernet port. However, selecting a PoE switch would require replacing the existing non-PoE switches throughout the office, which is significantly more expensive and operationally disruptive than adding a small, per-device injector. While a PoE switch is a valid solution in a new deployment or a full refresh, it is overkill here because the question implies the existing switching infrastructure is adequate and only the APs need power.
- ✗
Network hub
Why it's wrong here
A network hub is a legacy physical-layer device that copies incoming signals to all ports without any addressing logic or power-supply circuitry. It is not a power-sourcing equipment (PSE) and cannot generate or inject DC voltage onto the cable; it only repeats electrical data signals, providing zero PoE capability. Even if one were to connect a hub, the access point would still remain unpowered, and the hub would actually increase collision domains and degrade performance—so it fails both on power delivery and on network design.
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Power supply unit
Why it's wrong here
A standard power supply unit (PSU) found in a desktop computer converts AC mains voltage to low-voltage DC and delivers it through a dedicated power connector; it is not designed to interface with an Ethernet cable's twisted-pair wiring. Unlike a PoE injector, a PSU lacks the magnetic coupling or diode-bridge circuitry needed to safely superimpose power onto the data pairs while preventing backflow and short circuits on the line. Attempting to connect a PSU to an Ethernet cable would be unsafe and technically incorrect, since it cannot provide power in the voltage/pin configuration that an 802.3af/at-compliant AP expects.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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