Load Detection; How The G250/G350 Detects A Powered Device - Avaya G250 Administration

Configuring PoE

Load detection

The MM314 PoE media module and the G250 periodically check all ports, powered and
non-powered, to check their status and the power status of connected devices. Power is
supplied to a port only after it has detected that a suitable Powered Device (PD) is connected to
the port. The MM314 PoE media module and the G250 look for an IEEE 802.3af-compliant
signature from the device that indicates that the device requires power.

How the G250/G350 detects a powered device

The following figure shows the process of applying PoE power to a PD.
Figure 23: Powered Device Detection
The MM314 PoE media module and the G250 apply a low voltage to the power feed pairs and
measure the current. A resistance of 19kΩ to 26.5kΩ is considered valid. If a valid signature is
detected, and the device has not exceeded its PoE allocated power, then power is supplied to
the port.
Once power is provided to a port, it is checked periodically to see if a PD is still connected. If a
PD is disconnected from a powered port, then power is denied to the port.
194 Administration for the Avaya G250 and Avaya G350 Media Gateways
Start Check
Valid Resistance
Signature?
Sufficient power?
No
No
No
Yes
Yes
Apply Power
Yes
PD still
connected?