Cisco Certified Support Technician (CCST) NetworkingNetwork AccessHard
A network administrator is configuring a new Cisco switch for a small business. The business requires that all network devices, including IP phones and computers, receive Power over Ethernet (PoE) from the switch. The administrator needs to ensure that the switch port can automatically detect and provide the necessary power level for connected devices up to 30W. Which IEEE standard should the administrator look for in the switch's specifications?
- AIEEE 802.3af
- BIEEE 802.1Q
- CIEEE 802.3at
- DIEEE 802.3bt
Show answer & explanationAnswer & explanation
Correct answer: C. IEEE 802.3at
IEEE 802.3at, also known as PoE+, supports up to 30W of power per port, which is suitable for powering IP phones, wireless access points, and networked cameras. IEEE 802.3af (PoE) only provides up to 15.4W, and 802.3bt (PoE++) supports even higher power levels (up to 90W) but would be overkill if 30W is the maximum needed.
Why the other options are wrong
- A. IEEE 802.3af (PoE) provides up to 15.4W per port, which might not be sufficient for some IP phones or newer access points.
- B. IEEE 802.1Q is the standard for VLAN tagging and is unrelated to Power over Ethernet.
- D. IEEE 802.3bt (PoE++) supports up to 60W or 90W per port, which is more than the specified 30W requirement and typically used for higher-power devices.
IEEE 802.3at (PoE+)
An IEEE standard for Power over Ethernet that delivers up to 30 watts of power per port over standard Ethernet cables, supporting devices like IP phones, wireless access points, and PTZ cameras.
- Provides up to 30W per port
- Backward compatible with 802.3af (PoE)
- Commonly used for IP phones and WAPs
- Requires Cat5 or higher cabling
Memory trick: af=phone, at=AP, bt=big devices.