Table of Contents
Advertisement
6.11 PoE (Power over Ethernet)
6.11.1
PoE
Power over Ethernet or PoE technology describes a system to pass electrical power safely,
along with data, on Ethernet cabling. PoE requires category 5 cable or higher for high power
levels, but can operate with category 3 cable for low power levels. Power can come from a power
supply within a PoE-enabled networking device such as an Ethernet switch or can be injected
into a cable run with a mid-span power supply.
The original IEEE 802.3af-2003 PoE standard provides up to 15.4 W of DC power (minimum
44 V DC and 350mA) to each device. Only 12.95 W is assured to be available at the powered
device as some power is dissipated in the cable.
The updated IEEE 802.3at-2009 PoE standard also known as PoE++ or PoE plus, provides up
to 25.5 W of power. Some vendors have announced products that claim to comply with the
802.3at standard and offer up to 51 W of power over a single cable by utilizing all four pairs in
the Cat.5 cable. Numerous non-standard schemes had been used prior to PoE standardization to
provide power over Ethernet cabling. Some are still in active use.
The new IEEE 802.3bt-2013 standard enables delivery of 90W over four pairs of Cat5e cables
and above. Such PoE level is expected to be the maximum level defined, as higher levels may
not be safe for the existing cabling and connectors deployed in today's infrastructures. The
standard will replace all existing pre-standard solutions that deliver 60W/75W/95W today, such
as U PoE or 4PPoE.
PSE: Power sourcing equipment (PSE) is a device such as a switch that provides ("sources")
power on the Ethernet cable.
PD: A powered device (PD) is a device such as an access point or a switch, that supports
PoE(Power over Ethernet) so that it can receive power from another device through a 10/100
Mbps Ethernet port.
Standard PoE parameters and comparison
802.3af (802.3at
Property
Type 1) "PoE"
Power available at
12.95 W
PD
Maximum power
15.40 W
delivered by PSE
Voltage range (at
44.0–57.0 V
PSE)
Voltage range (at
37.0–57.0 V
PD)
Maximum current
350 mA
Imax
802.3at Type
802.3bt Type
2 "PoE+"
3 "4PPoE"
25.50 W
51 W
30.0 W
60 W
50.0–57.0 V
50.0–57.0 V
42.5–57.0 V
42.5–57.0 V
600 mA
600 mA per pair
178
802.3bt Type
4
71 W
100 W
52.0–57.0 V
41.1–57.0 V
960 mA per
pair
Advertisement
Table of Contents
