Chapter 3 - PoE Flashcards
What is a PSE device?
Power Sourcing Equipment.
- PoE Switches
- Routers with PoE Switch Module
- Power Injector
When it comes to PoE what is the term “mid-span” referring to?
Power injectors are sometimes called “mid-spans”.
What are the 3 PoE detection methods?
Cisco Inline Power (2000)
IEEE 802.3af standard (2003)
- Up to 15.4 W per port
IEEE 802.3at standard (2009)
- Up to 25.5 W per port; 50 W and more if using four pairs of wires
- Backward-compatible with 802.3af
How does Cisco Inline Power (legacy) detect power requirements of an end device?
The switch sends out a 340-kHz test tone on the Ethernet cable. A tone is transmitted instead of DC power because the switch must first detect the device before supplying it with power. With Cisco Inline Power, the most appropriate power level is determined by exchange of Cisco Discovery Protocol information.
How much power is supplied by IEEE Power Class 0 (zero)
15.4 Watts
This is the default class
How much power is supplied by IEEE Power Class 1
4 Watts
This is an optional class
How much power is supplied by IEEE Power Class 2
7 Watts
This is an optional class
How much power is supplied by IEEE Power Class 3
15.4 Watts
This is an optional class
How much power is supplied by IEEE Power Class 4
30 Watts
(up to 50 Watts)
Valid for 802.3at devices only
How does a 802.3af and 802.3at PoE device handshake with a PoE switch for power?
The switch tries to detect the powered device by supplying a small voltage across the Ethernet cable. The switch then measures the resistance. If the measured resistance is 25 kohm, a powered device is present. The powered device can provide the switch with power class information. Based on that information, the switch can allocate the powered device with the appropriate maximum power.
How do you disable PoE on a switchport?
(config-if)# power inline never
How do you enable PoE on a switchport?
(config-if)# power inline auto
