Biamp Tesira - Network Cabling; Poe Class Support on the Ports; Poe Budget Limitation; Poe Port Priority and Management Tools

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the PoE device does not power on, reboots repeatedly, or is not responding as expected, there may be a PoE

negotiation problem. Consider the following when troubleshooting:

Network cabling

Standard Ethernet data limitations apply to the network cabling: maximum cable length is 100m from switch to the PoE

endpoint device even if a PoE injector is between the switch and endpoint. A PoE injector does not work as a repeater

unless a manufacturer explicitly specifies this feature. Cable performance is impacted by cable type, the number of

interconnects, integrity of field termination and even ambient temperature. Varying cable resistance connecting a

802.3at Class 4 device may require up to 34.20W from the switch instead of the 30W defined by the standard.

Best practice is to verify capabilities of the switch and observe actual PoE loads and performance when a system is

commissioned. Document this information for future reference.

PoE class support on the ports

Verify the PoE switch/injector ports support the PoE class of the connected endpoint device and can provide "Max

Power From Switch" defined by the IEEE standard for this class.

PoE budget limitation

For PoE switches and multi-port PoE injectors, confirm the total PoE budget is enough to supply "Max Power From

Switch" to all connected endpoint devices simultaneously. If the PoE budget is exceeded when all endpoint devices

draw maximum power at the same time, some design changes will be required. Consider a PoE switch with a larger PoE

budget or move the PoE endpoints to other PoE switches on the network.

PoE Port Priority and management tools

PoE Budget is a shared resource in a network switch and users can prioritize PoE on each port as Critical, High or Low.

If the switch is presented with PoE loads totaling more than the available budget, it will provide power according to the

assigned prioritization. The PoE switch often has management tools available via CLI or web interface for PoE

management and diagnostics.

PoE negotiation

When the 802.3at Class 4 endpoint and switch/injector are initially connected, they use the following methods to classify

power needs:

• Hardware-based 2-event classification

• Software-based LLDP classification

If a switch supports 802.3at but does not support hardware-based 2-event classification, LLDP will need to be enabled.

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