1-11 PoE ConfigurationPoE OverviewPower over Ethernet (PoE) means that power sourcing equipment (PSE) supplies power to powereddevices (PDs) from Ethernet interfaces through twisted pair cables.Advantagesz Reliable: Power is supplied in a centralized way so that it is very convenient to provide a backuppower supply.z Easy to connect: A network terminal requires no external power supply but only an Ethernet cable.z Standard: In compliance with IEEE 802.3af, and a globally uniform power interface is adopted.z Promising: It can be applied to IP telephones, wireless LAN access points (APs), portable chargers,card readers, web cameras, and data collectors.CompositionAs shown in Figure 1-1, a PoE system consists of PoE power, PSE, power interface (PI), and PD.Figure 1-1 PoE system diagramPoE powerThe whole PoE system is powered by the PoE power.PSEA PSE is a device supplying power for PDs. A PSE can be built-in (Endpoint) or external (Midspan). Abuilt-in PSE is integrated in a switch or router, and an external PSE is independent from a switch orrouter.The PSEs of 3Com are built in, and can be classified into two types:z Device with a single PSE: Only one PSE is available on the device; so the whole device isconsidered as a PSE.z Device with multiple PSEs: For a device with multiple PSEs, an interface board with the PoE powersupply capability is a PSE. The system uses PSE IDs to identify different PSEs.
