TopTechnical Dictionary802.3af - data and power transmission standard

802.3af - data and power transmission standard

PoE (Power over Ethernet) defines a method of powering devices over a twisted pair cable with simultaneous data transmission. The devices powered with the PoE technology include IP cameras, VoIP communication devices, access points and wireless network adapters.

 

Unlike USB (Universal Serial Bus), that can also be used to transmit power and data over a single cable, PoE guarantees transmission at a distance of at least 100 m.

 

In 2003, IEEE has approved PoE 802.3af, a standard in which the maximum output power of the power supply was 15.4 W, and the power source voltage of 44–57 V. The voltage at the receiving side must be 37–57 V at the maximum power input of 350 mA for a single device.

 

Table 1. IEEE 802.3af parameters 

Power supply output power 15,4 W
Minimum power available to the receiver 12,95 W
Output voltage range of the power adapter 44,0 ... 57,0 V
Voltage range available at the receiver 37,0 ... 57,0 V
Maximum current 350 mA
Maximum twisted pair resistance 20 Ω (Cat. 3)
Compatible twisted pair categories Cat. 3 and higher
Guaranteed maximum distance 100 m

Among the companies using PoE technology, some have implement the standard using four pairs to transmit power, e.g. UPOE (Universal Power Over Ethernet) by Cisco. The maximum output power of the power supply is approx. 60 W and can be used to supply devices up to approx. 51 W.

 

PoE-based standards are implemented in accordance with IEEE 802.3af 2003 or IEEE 802.3at 2005 requirements.

 

The main PoE advantage is the reduced cabling costs, since one cable can be used both for data and power transmission. Low voltage guarantees safety and the minimum distance with suitable cable is at least 100 m. All PoE devices are backward compatible, easy to install and use.

 


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