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Switch support the PDs quantity for one/two power module Highlighted

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[Problem Description]

In November 2018, a customer in Kuwait reported that cameras from multiple vendors connected to a Huawei

S5720-52X-PWR-SI PoE switch occasionally went offline and then recovered automatically. The customer

also provided logs to Huawei.

[Problem Analysis]

On November 28, 2018, Huawei received and analyzed the logs.
The logs showed that interfaces 20 and 21 alternated between Up and Down.


According to the logs, PDs were powered on and off when interface 21 went Up and Down.


For interface 22, there was a "powered success" record. This indicated that the PD connected to interface

22 was not powered on earlier.


PDs connected to the switch were checked.


There were 22 interfaces connected to PDs, and the PD level is 4 (that is, 802.3at-compliant).

However, the switch supports only twelve 802.3at interfaces fully loaded. In addition, the switch

reserves 20% of the total PoE power for power bursts by default. In this situation, there is a high

risk that the required PoE power exceeds the system capacity. If the burst power on interfaces

exceeds the power capacity of the switch, PDs connected to the interfaces are powered off.


If the PD connected to an interface is not a standard PD, for example, the holding current does not

meet requirements of 802.3at, the PD will also be powered off.


The switch has only one power module and supports twelve 802.3at interfaces fully loaded. However,

on the live network, 22 PDs using the 802.3at power level (30 W) are connected to the switch.
According to current information which have provided from your side,
1. It is recommended that more power modules be added to improve reliability in power burst scenarios.
2. It is advised to check standards compliance of the connecting PDs.
3. Also you may check the connecting cable quality

  • x
  • convention:


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