Appendix C: About Poe (Power Over Ethernet); Overview; Powered Device Classifications; C-1 Powered Device Classifications - Enterasys Platinum Distributed Forwarding Engine 7G4205-72 Hardware Installation Manual

This appendix provides an overview of Power over Ethernet Technology and how it is
implemented in relation to the 7G4285‐49 and 7G4205‐72 DFE modules.

Overview

Power over Ethernet (PoE) refers to the ability to provide operational power through the
same Ethernet cabling to a PD (powered device) connected to a data network. Modern
Ethernet implementations employ differential signals over twisted pair cables. This
requires a minimum of two twisted pairs for a single physical link. Both ends of the cable
are isolated with transformers blocking any DC or common mode voltage on the signal
pair. PoE exploits this fact by using two twisted pairs as the two conductors to supply a
direct current. One pair carries the power supply current and the other pair provides a
path for the return current. While several proprietary legacy implementations of PoE
have been deployed by LAN equipment vendors, in 2003 the IEEE published the IEEE
802.3af‐2003 specification, which is part of the 802.3 suite of standards.
The 7G4285‐49 and 7G4205‐72 are fully compliant with the IEEE 802.3af standard. They
support the standard resistor based detection method, as well as AC disconnect capability.
The 7G4285‐49 and 7G4205‐72 are also capable of supplying the maximum specified
current to all ports simultaneously.
Each PD has a PDC (Powered Device Classification) that is transmitted to the DFE module
for power management purposes. Table
power ranges.
Table C-1 Powered Device Classifications
About PoE (Power over Ethernet)
Class
0
1
2
3
4
C‐1 lists the classifications and the associated
Usage
Default
Optional
Optional
Optional
Not Allowed
DFE-Platinum Series Hardware Installation Guide C-1
PD Maximum Power Range Usage
0.44 to 12.95 Watts
0.44 to 3.84 Watts
3.84 to 6.49 Watts
6.49 to 12.95 Watts
Reserved for Future Use
C