• The default switch configuration always power demotes all Class 4-8 SS PDs to Class 3 power and requires
successful LLDP dot3Tlv 29 octet power negotiation for Class 5-8 PDs or 12 octet power negotiation for Class
4 PDs before increasing the power delivery to above 16W.
• The default switch configuration always power demotes all Class 4 and above DS PDs to Class 3 power at
PLC. It requires successful LLDP dot3Tlv 29 octet power negotiation through DLC.
• The switch requires the PD to negotiate through LLDP for any power request above 13W. In this case, the
switch class demotes the PD to Class 3 power.
• The switch does not have enough available power in its reserve to supply the full power requested by the PD.
In this case, the switch offers a lower Class level of power to the PD. For example, the switch offers Class 4
power (25.4 W) or class 3 power (13 W) to a Class 5 PD or a Class 6 PD.
DLC disabled
When DLC is disabled, a PD can draw full power as requested at the PLC. This can go up to a maximum of Class
6 for Single Signature and Class 4 for Dual Signature PD.
Recommendations
• IEEE standards do not require Class 4/Type 2 PSE to interoperate with Class 5-8 PDs. However, the PLC
mutual identification in the beginning of power-up cycle will indicate to a class 5-8 PD that it is connected to
PSE capable of only 30W. If required, a class 5-8 PD can power up with 30W and operate in reduced
functionality modes.
• Some Class 5-8 PDs may require their full requested power. The PD can power up and shut down when
exceeding iCut ~33W in Class4/Type 2 switches.
• Ensure that the PSE port supports the same or higher Class than the connected PD Class for interoperability.
You can continue to use Cat5e cable deployments to deliver power. Operating at link speeds of 5Gbps or greater
may require you to limit the cable length to less than 100 meter. This limitation is imposed by the Ethernet
physical capabilities and not by the PoE standard.
Show commands
The show commands display the following:
• Dual Signature Indicator (#) which denotes the PD connected to the port is a Dual Signature PD.
• Power Delivery Indicator (*) which indicate loss of power to a port in the event of loss of a PSU powering the
port.
• Power Demotion Indicator (^) which appears when the switch is unable to supply the entire power requested
by the PD. The scenarios include:
Example of show pow br
switch(config)# show pow br
Status and Configuration Information
System Power Status : No redundancy
PoE Power Status : No redundancy
Operational Power Status : No redundancy
Available: 1440 W Used: 89 W Remaining: 1351 W
PoE Pwr Pwr Pre-std Alloc Alloc PSE Pwr PD Pwr PoE Port PLC PLC
Port Enab Priority Detect Cfg Actual Rsrvd Draw Status Cls Type
------ ---- -------- ------- ----- ------ ------- ------- ----------- --- ----
#1 Yes low off usage usage 57.3 W 49.1 W Delivering 4 3
Chapter 4 Power Over Ethernet (PoE/PoE+) Operation 125
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