Enterasys K6 - Appendix B: About PoE (Power over Ethernet); Overview; Powered Device Classifications

Enterasys K-Series K6 Chassis Hardware Installation Guide B-1
B
About PoE (Power over Ethernet)
ThisappendixprovidesanoverviewofPoweroverEthernettechnologyandhowitis
implementedinrelationtotheK‐Seriesdevices.
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K‐SerieschassisarefullycompliantwiththeIEEE802.3afand802.3at
standards.They
supportthestandardresistor‐baseddetectionmethod,aswellasACdisconnectcapability.
EachPDhasaPDC(PoweredDeviceClassification)thatistransmittedtotheK‐Serieschassisfor
powermanagementpurposes.Table B‐1liststheclassificationsandtheassociatedpowerranges.
Proprietary PD Detection
K‐SeriesdevicessupportasubsetofthecurrentlydeployedproprietaryPoEmethods.This
includessupportforCiscoPDs,includingaproprietarycapacitorbaseddetectionscheme.
Table B-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 Reserved 12.95 to 25.50 watts