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A Practical Guide to Power over Ethernet (PoE)
Document Summary
This document contains basic, but practical information concerning Power over Ethernet. Powering devices
like Access Points (APs), IP Telephones, Web Cameras, etc. through the Ethernet cable is a natural
evolution in the networking industry. The Central Office in the PSTN historically powered analog phones for
many decades. The PBX has also powered digital phones through the wires. Appliances, like Access
Points and Web-based Cameras are positioned in hard to reach locations, like ceilings, and are therefore
prime candidates for power through the Ethernet cable that connects them. There are benefits in powering
IP telephones through the Ethernet cable. One is convenience and another is the ability to monitor devices.
This paper will discuss the highlights in the Power over Ethernet standard (IEEE 802.3af) and the earlier
pre-standard PoE implementations. Common implementation issues are also addressed to help you avoid
unpleasant surprises.
The first part of this paper describes the basics of the IEEE 802.3af standard that was ratified in June 2003.
The second part of this paper describes practical differences in Power over Ethernet (PoE) implementations
of Avaya and Cisco equipment compared to the standard and to each other. This paper is not intended to
point out shortcomings of any other vendor, but it is beneficial to reveal subtle issues in vendor specific
implementations of PoE that can cause issues during and after installation. Since many customers use a
Cisco data infrastructure, Cisco specific examples are cited and compared to Avaya's products. A PoE
checklist is included in Appendix A as a quick check to aid your implementations.
Table of Contents
A Practical Guide to Power over Ethernet (PoE) Document Summary .........................................3
A Practical Guide to Power over Ethernet (PoE) Paper .................................................................4
1
Introduction.............................................................................................................................4
2
Definitions...............................................................................................................................4
3
IEEE 802.3af - how it works ...............................................................................................5
4
Static vs. Dynamic Power Allocation..................................................................................7
PoE Implementation Details ................................................................................................9
5
6
Avaya Configuration ...........................................................................................................12
7
Cisco Configuration.............................................................................................................14
Future Directions .................................................................................................................22
8
MJK
Copyright ©
2006 Avaya Inc. All Rights Reserved.
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