Power Over Ethernet PDF

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In the Power Over Ethernet PDF, the paper explores the fundamentals of Power Over Ethernet (PoE) technology. We review the two dominant PoE standards, IEEE 802.3af and Cisco ILP, and discuss many of the advantages of PoE as well as some of the challenges associated with its implementation.

Table of Contents

IEEE 802.3af – 2

Power Sourcing Equipment (PSE) – 3

Powered Device (PD) – 4

Powered device discovery process – 5

Power disconnect – 5

PoE Plus – 5

Cisco Inline Power – 6

Cisco Access Points Requirements – 6

Problems with PoE – 7

How to detect and test PoE – 8

Excerpts

“Within the definition of a PSE, there are two types described: endpoint PSE and midspan PSE. An endpoint PSE is a Power over Ethernet capable port on a switch that is directly connected to the cable supplying power to the PD. Power is delivered by the endpoint PSE using either the active data pairs (usually the orange and green pairs in Ethernet – Pins 1,2 and 3,6) or the spare pairs (usually the brown and blue pairs – 4,5 and 7,8).” – Page 3

“In November 2004, a study group was formed to create Power over Ethernet Plus. This group is researching the future of the PoE technology, with a goal of powering devices that need more than twice the wattage applied by 802.3af, such as a laptop.” – Page 5

“PoE is an evolving techology that will experience rapid growth over the next few years. Tools to test and monitor PoE will be necessary as switch vendors continue to implement it into their products. While the technology is still in its early stages, cross-vendor compatibility problems may occur, making PoE difficult to troubleshoot without tools.” – Page 6

“In a particular office floor, there may be 220 phones and 15 access points, all requiring Power over Ethernet. Using the standard power, with no Cisco intelligent power management, each device will be allocated 15.4W. This results in a total of 3619W to power all devices. The PSE itself is most likely a large switch that requires somewhere in the area of 1500W itself. This results in a total power requirement of almost 4200W to this one switch” – Page 7

“When the NetTool is first connected between a PSE and PD, it will attempt to establish a link on both sides. The PSE will detect this link signature and will begin sending PoE detection signals. At this point the NetTool will detect these signals and will stop sending link signals. After a few seconds, the NetTool will pass the PoE detection signals to the PD, enabling it to power up and establish link.” – Page 8