Enterasys Networks Enterasys Gold Distributed Forwarding Engine 4G4285-49 - Manual (Page 95)

Enterasys Matrix DFE-Gold Series PoE Module Hardware Installation Guide C-1
C
About PoE (Power over Ethernet)
This appendix provides an overview of Power over Ethernet Technology and how it is
implemented in relation to the 4G4285‐49 and 4G4205‐72 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 4G4285‐49 and 4G4205‐72 are fully compliant with the IEEE 802.3af standard. They
support the standard resistor based detection method, as well as AC disconnect capability.
The 4G4285‐49 and 4G4205‐72 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 C‐1 lists the classifications and the associated
power ranges.
Table C-1 Powered Device Classifications
Class Usage PD Maximum Power Range Usage
0 Default 0.44 to 12.95 Watts
1 Optional 0.44 to 3.84 Watts
2 Optional 3.84 to 6.49 Watts
3 Optional 6.49 to 12.95 Watts
4 Not Allowed Reserved for Future Use