Poe Details And Variations

Poe Details And Variations The 802.3af Poe Standard Allows Two Different Methods, Mode A Or B To Combine Data 

And Power Onto The Same Cable Supplying Power To The Remote Network Appliance Or PD.
To Comply With 802.3af, A PD Such As A Wireless AP, Downstream Switch Or IP Camera
Will Work On Both Mode A Or B. An 802.3af Compliant PSE Such As A Network Switch Will
Use Mode A Only. Some Legacy Switches From Major Network Equipment Suppliers Can
Work In 802.3af Compliant Mode A Or A Proprietary Form Of Mode B. A Product Called A Midspan Or Injector Is Used To Upgrade A Non-Poe Switch To Have PSE
Capability. A Midspan Or Injector Uses Mode B To Power The PD. See Diagram 1. Dia. 1

These Devices Can Be Fully Compliant With 802.3af Or Be “Passive” And Only Offer Power
Limiting. Passive Midspans Or Injectors Offer Lower Cost As Well As Higher Power
Capability And The Ability To Power Non 802.3af Compliant Network Appliances. In The
Wireless Industry, To Save Cost Or Draw More Power, It Is Common To Use Remote Client
Devices That Only Work With Passive Poe Injectors.
Mode A

802.3af Poe Mode A Combine’s Power Onto The Same Wires As The Data Signal Using A
Technique Called Phantom Powering. Phantom Powering Is A Common Technique Used In
The Telco Industry For Telephones And The Audio Industry For Microphones. For 10/100/1000baset, Data Pairs 1/2 And 3/6 Carry DC Power As Well As Data. Pairs 4/5
And 7/8 Are Used For Data Only. See Diagram 2.