PoE Technology Reference and troubleshooting V1.0 [HoT]

What's the PoE？
PoE (Power over Ethernet) is the name of a number of methods that allow for powering network devices through UTP/FTP cables. This way it is possible to power devices such as cameras, phones, switches, access points, etc. In 2003, the IEEE established 802.3af PoE standard, upgraded to 802.3at in 2009. 802.3at distinguishes between the first type (prior 802.3af) and the second type with maxi mumtransmitted power of 30 W, nearly two times higher. The second type is suitable to power cameras with high-power IR illuminators, IP telephones, small network printers etc.
Comparison of 802.3af and 802.3at

Topology
Depending on the location in the transmission path where the power supply is combined with the data, the power-injection devices can be divided into 2 groups: PoE switches (endspam) and PoE adapters(midspam).
Depending on the transmitted power and data rates, the 802.3at standard encompasses 2 versions:
type 1 - for devices compliant with 802.3af and with power transmission employing 2 pairs of min. Cat.3 cable, with max output power of 12.95 W
type 2 - with max output power of 30 W, transmitted via min. Cat.5 cable
The standard also defines two types of PoE implementation:
Option A - power is sent together with the data on pairs 1/2 and 3/6
Option B - power is sent on pairs 4/5 and 7/8 (unused in Fast Ethernet networks, in the case of Gigabit Ethernet the pairs are used both for data and power transmission).
The power supply unit may implement both or just one of the PoE types, while remaining compliant with the standard. So, the powered device must therefore support both modes, however, as it turns out inpractice, not all end devices are fully compliant with the standard. This may be the reason for the lack of compatibility with some PoE power supplies

Wiring diagram for a PoE switch (endspan) and an 802.3af (802.3at type 1) powered device.
Option A - violet color, option B - yellow color

Wiring diagram for a PoE injector (midspan) and an 802.3af (802.3at type 1) powered device.
Option A - violet color, option B - yellow color

Wiring diagram for a PoE switch (endspan) and an 802.3at type 2 (PoE+) powered device.
Option A - violet color, option B - yellow color.

Wiring diagram for a PoE injector (midspan) and an 802.3at type 2 (PoE+) powered device.
Option A - violet color, option B - yellow color
Testing procedures and classes ofpowered devices (PD)
PoE standard has been optimized for safety. In addition to a safe voltage range, the devices must communicate according to established procedures. Before providing the supplying voltage, the PoE power supply unit tests the connection. The current is limited to milliamperes and is applied to determinethe actual type of the PoE implemented in the powered device (with the help of characteristic resistanceof about 25 kΩ used for this purpose in the device). In addition, this procedure allows for checking the continuity of the line.
Optional classification of equipment compliant with 802.3af standard provides useful information aboutits power requirements. It is based on the measurement of the current flowing when testing the connection.
The equipment is classified as follows:

Devices compliant with 802.3at also communicate with one another using Layer-2 power management protocol for enhanced power allocation, LLDP-MED (extended version of the protocol for auto-detectionof devices). With such communication it is possible to determine the actual power demand with accuracy to 1.11W. The power supply unit forwards the information on the demand for power at regular timeperiods.

What can we do if the AP cannot be powered to connect to the PoE switch?
Step1: If the switch does not have enough power then it won't actually overload itself, it's just that some ports will not get an power delivered to them.
The command CLi will help you to check whether the power is enough or not:
Ruijie#show poe powersupply

Step2: If the power is enough, try to enable the PoE  
compatible mode.

• Enable the energy-saving mode.
  

Ruijie(config)# poe mode energy-saving

• Enable the Poe legacy
  

Ruijie(config)#poe legacy
Ruijie(config-if)#poe legacy   -----some switches need enable under the interface.
Note:
When configuring the above commands, make sure the port is connected to the PD device.
Step3: Try to change another port or PoE switch to test, if it
can work normally, it should be the device hardware failure. Please contact RITA to confirm the issue or submit the case.
RITA: https://www.ruijienetworks.com/rita
Caseportal:
https://caseportal.ruijienetworks.com/

Good sharing

ruijiedemo@163. replied at 2022-4-25 09:56
Good sharing

Excellect

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