Lantronix
SM24TBT2DPA Install Guide
33737 Rev. L
Page
28
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38
Troubleshooting PoE Problems
1.
Note that this product is to be connected only to UL listed PoE networks and without routing to the outside
plant.
2.
Note that PoE devices initially draw more power during their boot up sequence than during normal
operation.
3.
Determine what the requested power was at the time of failure.
4.
Identify how long the device was up and what events may have occurred at the time of the error to help find
the root cause (e.g., an IP phone that comes out of sleep and turns on fully may draw more power
momentarily).
5.
Determine if there is an issue with the PD drawing too much power; check the PD vendor documentation to
determine why it exceeds the power it has negotiated with the switch.
6.
Check the type and length of the cabling for any effect on the electrical characteristics and impact on the
amount of power drawn on a port.
7.
Investigate the power negotiation and confirm that the power requested by a device is also the amount of
power that gets allocated. For example, using LLDP requires additional power budget for cabling between the
PD and the PSE.
8.
Use power measuring and testing equipment to determine if the PD overdraws the amount of power it gets
allocated.
9.
Enable CDP awareness via the Web UI or the CLI. CDP (Cisco Discovery Protocol) is a Cisco-proprietary Layer 2
protocol that runs on most Cisco equipment and shares information about directly connected Cisco
equipment. PoE switches with CDP enabled can recognize Cisco powered devices such as IP phones and
WAPs. The actual power requirement can be advertised by the powered device, and the unused class power
is returned to the switch power budget.
