2.1.8. Power over Ethernet (PoE)
š” First Principle: PoE delivers power and data over the same Ethernet cable. This sounds like a convenience feature, but it's actually transformativeāit means you can deploy access points, cameras, and phones anywhere you can run a cable, even if there's no power outlet.
Before PoE, deploying a security camera meant running Ethernet AND hiring an electrician. Now you just run one cable. That's why PoE has become standard on enterprise switches.
PoE Standards:
| Standard | IEEE | Power at Device | Typical Use |
|---|---|---|---|
| PoE | 802.3af | 12.95W | IP phones, basic APs |
| PoE+ | 802.3at | 25.5W | PTZ cameras, high-power APs |
| UPoE/PoE++ | 802.3bt | 60-90W | Video conferencing units, thin clients |
What happens when PoE fails: Powered devices go dark. If your PoE switch crashes, every IP phone, camera, and AP connected to it loses power instantly. That's why PoE switches in critical deployments have redundant power supplies.
ā ļø Exam Trap: The switch providing power is the PSE (Power Sourcing Equipment). The device receiving power is the PD (Powered Device). Know these terms.