POE Flashcards
With 10 Mbps and 100 Mbps Ethernet, how many pairs inside an Ethernet cord are used?
2 pairs only. The other 2 pairs are unused.
When was 802.3af created?
2003.
When was 802.3at created? What was it also known as?
The IEEE 802.3at amendment was ratified in 2009. It was also known as PoE+.
How much power in watts is 802.3at able to provide?
The IEEE 802.3at amendment is able to provide up to
30 watts of power using two pairs of wires in an Ethernet cable.
The 802.3at amendment defines PoE devices as either Type 1 or Type 2. Describe the difference.
Devices capable of supporting the higher power defined in the 802.3at amendment are defined as Type 2 devices, and devices not capable of supporting the higher power are defined as Type 1 devices.
What is a detection signature, used in PoE?
The PD must reply to the power-sourcing equipment with a detection signature and notify the power-sourcing equipment whether it is in a state in which it will accept power or will not accept power. The detection signature is also used to indicate that the PD is compliant with 802.3-2012, Clause 33.
What are the different power classes 1-4 and what Type 1 or 2 do they belong to?
Power classes 0 to 3 are for Type 1 devices that will work with 802.3af power sourcing equipment. Power class 4 is meant for Type 2 devices that work with 802.3at (PoE+) power sourcing equipment.
What is the max power draw for an af device and an at device? What is the max power distributed by
Power draw is 12.95 for af. 25 for at,
Supplied is 15.4 for af and 30 for at
What is alternative A and alternative B?
With Alternative A, the PSE (Power Sourcing Equipment) places power on the data pair. Originally, Alternative B was designed to provide power on the spare unused pair of wires in a 10BaseT/100BaseTX cable.
What is a midspan injector or a PSE?
The midspan PSE acts as an Ethernet repeater while adding power to the Ethernet cable.
What is the max length of a Ethernet?
100 meters or 328 feet.
What does auto MDIX do?
It auto senses the layout of the pairs in Ethernet.
How does PoE transmit power of data pairs?
When you power a device using Alternative A, the positive voltage is matched to the transmit pair of the PSE.
What is a class 0 device?
A device that needs to draw 3 watts and is not capable of providing a classification signature would be classified as Class 0 by default.
What is a class 1 device?
A device that was capable of providing a classification signature and was classified as a Class 1 device, only 4 watts would be subtracted from the power budget.
