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PoE ( Power over Ethernet)

As the name suggests PoE also referred as Power over Ethernet is the device which provides direct current electrical power over twisted pair of ethernet cable. This makes it possible to carry both ethernet data as well as power over the same port.

The standard for Power over Ethernet is first introduced in the year 2003 later 802.3af is rectified. This is also referred as clause 33 in the 802.3 standard. PoE device as per 802.3af standard delivers 15.4watts of DC power. Power over Ethernet works with 10baseT,100baseT and 1000baseT.

Another version of the standard is developed in 2009 and is referred as 802.3at supplement. It provides power upto 34.2Watts. Standard version such as Universal PoE provides 60Watts and is developed by Cisco. Power over HDBASE-T delivers 100Watts over cat-5e and cat-6 cable over all the four pairs.

The Power over Ethernet standard defines two device types viz. power sourcing equipment(PSE) and Powered device(PD). PSE is the one which delivers power over twisted pair ethernet cable. Examples of PSE are ethernet switch ports, power injector and adapter.

PD is usually powered by PSE device. Examples of PD are wireless AP(Access Point),VOIP compliant phone, IP based video camera and so on. PD is also referred as DTE(Data Terminal Equipment) as per standard.

PoE

Fig.1 depicts typical power over ethernet device which takes AC power and Data as input and provides data and DC power on the same single port. Fig.2 describes the application of Power over Ethernet adapter used in typical wimax system.

The fig.2 describes the use of PoE adapter used in wimax system designed for high speed internet connectivity. Data-IN port is connected with the ethernet port of the laptop to access/browse the internet. The

Power over Ethernet

The second input port is connected with 3-pin AC port. The output port will have both the data as well as DC power on the same port which is interfaced with the SU-ORF in this application example. SU-ORF is the subscriber terminal typically installed in the user premises. The fig.2 is the lab set up. As shown further SU-ORF is interfaced with Base Station(AN-100U) from redline communication. BS is interfaced with LAN to provide backbone internet connectivity.

PoE Ethernet Switch

Another example application is as shown in the fig.3 where in PoE ethernet switch takes AC power and deliveres multiple POE ports. These multiple ports are interfaced with VOIP phone,IP enabled video camera and wireless access point. All these devices gets power as well as data from the switch.

The Power over Ethernet standard specifies two types of PoE systems viz. Type 1 and Type 2. The table mentions different parameters for both of these types. Type 1 PoE device is meant for low-power system while Type 2 designed for higher power applications.

Specifications PoE 802.3af Type1 PoE 802.3at Type2
Power at the PD 12.95W 25.5W
Maximum power using PSE 15.4W 34.2W
Voltage range(at PSE) 44 to 57 50 to 57
Voltage range(at PD) 37 to 57 42.5 to 57
Maximum Current 350 mA 600 mA
Maximum cable loop resistance 20 Ohm with cat.3/Cat.5 or better 12.5 Ohm with cat.5 or better

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