DFE-Platinum Series Hardware Installation Guide C-1
C
About PoE (Power over Ethernet)
ThisappendixprovidesanoverviewofPoweroverEthernetTechnologyandhowitis
implementedinrelationtothe7H4385‐49.
Overview
PoweroverEthernet(PoE)referstotheabilitytoprovideoperationalpowerthroughthe
sameEthernetcablingtoaPD(powereddevice)connectedtoadatanetwork.Modern
Ethernetimplementationsemploydifferentialsignalsovertwistedpaircables.This
requiresaminimumoftwotwistedpairsforasinglephysicallink.Both
endsofthecable
areisolatedwithtransformersblockinganyDCorcommonmodevoltageonthesignal
pair.PoEexploitsthisfactbyusingtwotwistedpairsasthetwoconductorstosupplya
directcurrent.Onepaircarriesthepowersupplycurrentandtheotherpairprovidesa
pathforthereturncurrent.WhileseveralproprietarylegacyimplementationsofPoE
havebeendeployedbyLANequipmentvendors,in2003theIEEEpublishedtheIEEE
802.3af‐2003specification,whichispartofthe802.3suiteofstandards.
The7H4385‐49isfullycompliantwiththeIEEE802.3afstandard.Itsupports
thestandard
resistorbaseddetectionmethod,aswellasACdisconnectcapability.The7H4385‐49is
alsocapableofsupplyingthemaximumspecifiedcurrenttoallportssimultaneously.
EachPDhasaPDC(PoweredDeviceClassification)thatistransmittedtothe DFEmodule
forpowermanagementpurposes.Table C‐1liststhe
classificationsandtheassociated
powerranges.
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
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