Lantronix
SMxTAT2SA Install Guide
33716 Rev. L
25
12. Pre-standard and post-standard VoIP phones may use different detection and connect / disconnect methods.
Note that PD detection occurs when an Ethernet device is first connected to a PoE port. If a non-PoE device
is connected to a PoE port, detection is deactivated. If the non-PoE device is later disconnected and replaced
by a PD, the switch may not detect it immediately.
13. Verify that the PD is not causing an overcurrent condition on the port. Specifically: does the VoIP phone
initially power on and then disconnect? If so, the problem may be an initial current surge that exceeds a
current-limit threshold for the switch port. Some PDs may have excessive “surge in” current when first
connected to a PoE port. The switch initially provides power to the port, and then quickly removes power due
to a momentary overcurrent condition. The PD starts to power up, but then quickly powers down.
14. Most PoE switches have voltage and current regulators that detect an overcurrent threshold and disconnect
power from the line. This prevents excessive current from being delivered by the PoE port, which could
possibly result in damage to port-level components.
15. A variety of disturbances on the AC power line (mains) can cause odd PoE problems. The power supplies in
various switches and PDs can react uniquely to AC input disturbances. AC disruption problems are usually
temporary or one-time occurrences. For example, a specific switch or PD may reboot due to an AC power
problem, while other switches or PDs may show a greater immunity to the problem. This is a typical
occurrence during lightning storms or AC power maintenance. In a worst-case scenario, a PoE power supply
may appear to shut down, with no PoE output voltage to any port. It’s possible the switch’s Ethernet functions
appear normal, and only the PoE functions are disrupted or degraded, or the switch may power down
completely due to the AC disturbance. PDs may exhibit unusual behavior. In such cases, power cycle the
switch (unplug the switch, wait at least three seconds, then plug it back in. This will ensure a total system
reset that should restore normal operation.
16. Check if related features (LLDP mode, CDP mode) are enabled.
