Which answer describes how a LAN switch dynamically chooses the initial power level to apply to a UTP cable with PoE?
- Autonegotiation
- CDP
- LLDP
- Preconfigured values
Explanation: First, the switch does not supply power based on a configured value to avoid the unfortunate case of supplying power over the cable to a device that does not support the circuitry to receive the power, because doing so will likely harm the electronics on the connected device.
If configured to use PoE, the switch begins with IEEE autonegotiation messages while sensing the load on the circuit, which indicates whether the device desires to receive power, and indicates the power class desired (which dictates the amount of power to initially deliver). Note that once the attached device (called the powered device, or PD) boots, the PD can request additional power using CDP and/or LLDP.
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