8. Configuration of POE
8.1. Overview
Power over Ethernet
，
Referred to as PoE
，
Is a technology that it can through in the Ethernet
twisted-pair cable to transmit power and data to the device. With the technology including network
telephone, WIFI AP, network camera, hubs, computer and other devices can get power directly from
the twisted-pair cable.
8.1.1.
Basic concepts
In the use of PoE switches build PoE system, PoE switches play PoE power supply and the
combination of PSE. Users of electrical equipment, such as WLAN wireless AP, VoIP phone, etc., can
be called the PD. PoE switch power supply in accordance with the standards for the longest distance
of 100 m. Support PoE switches can statistical each port and the whole equipment power supply, and
is displayed by a query command.
PoE system consists of three parts:
PoE power supply
PoE power for the whole of PoE power supply system ,the PoE system is divided into two types, that is,
external power supply and Internal power supply. In our products, Cassette PoE switches generally
have internal power supply, some products also supports external power supply, external power
supply is called the RPS.
PSE
PSE
（
Power Sourcing Equipment
）。
PSE on PoE interface circuit to find and detect PD, PD for grading,
and to the power supply.When detected PD uproot, PSE stop power supply.
PD
PD is accept PSE power supply equipment. Divided into standard PD and non-standard PD, Standard
PD refers to comply with the IEEE 802.3 af and 802.3 at standard of PD equipment. PD equipment in
PoE power supply at the same time, allowed to connect other power supply, power supply redundancy
backup.
8.1.2.
The related protocol specification
At present there are IEEE 802.3 af and IEEE 802.3 at PoE tandard, the main features and the
difference between these two standard shown in the table below:
Parameters
802.3af
802.3at
PD Available power
12.95W
25.50W
PSE provide maximum power
15.4W
30W
PSE Voltage range
44.0-57.0V
50.0-57.0V
PD Voltage range
37.0-57.0V
42.5-57.0V
The largest cable impedance
20 Ω
12.5 Ω
Power management ways
To divide the power
level when the line is
initialized
When line initialization is divided into
four levels or using 0.1W as a unit to
Dynamic adjustment.
Support Cable
CAT3 or CAT5
CAT5