Power Over Ethernet
PSE — Power sourcing equipment
- A PoE Ethernet switch
PD — Powered Device
- A phone
PoE Splitter
- Use Ethernet as a power source for low power devices
PoE Extender
- Increases Ethernet’s data and power range beyond 100m
Passive PoE
- AKA Pre-standard PoE.
- Usually old installs
Endspan
- The switch is the PSE
Midspan
- The PSE is an injector and daisy chained into the Ethernet
Mode-A
- AKA Alt-A
- Deliver power on the data pairs of 10Base-T or 100Base-T. (pairs 2, 3)
Mode-B
- AKA Alt-B
- Deliver power on the spare pairs of 10Base-T or 100Base-T. (pairs 1, 4)
LLDP
- Link Layer Discovery Protocol
- The IEEE equivalent to CDP
- Used by IEEE PoE to request power
Important
Passive PoE
You must know and supply the correct voltage, there is no voltage or power negotiation.
As a Table
| Type | IEEE Standard | Maximum Power from PSE | Supported Modes | Notes |
|---|---|---|---|---|
| Passive PoE | - | No Negotiation | ||
| PoE | 802.3af | 15.4W | Mode A or Mode B (2-pair) | |
| PoE+ | 802.3at | 30W | Mode A or Mode B (2-pair) | |
| Cisco UPOE | Superset of 802.3at | 60W | Mode A, Mode B, or 4-pair | Works over CDP |
| PoE++, AKA 4PPPoE | 802.3bt aka 4PPoE | 90W | Mode A, Mode B, or 4-pair | |
| Cisco UPOE+ | Superset of 802.3bt | 90W | Mode A, Mode B, or 4-pair | Works over CDP |
As a Flowchart
graph TD;
Passive["Passive PoE"];
AF["802.3af — PoE \n (15.4W)"];
AT["802.3at — PoE+ \n (30W)"];
BT["802.3bt - PoE++ \n (90W)"];
UPOE["Cisco UPOE \n (60W)"];
UPOEP["Cisco UPOE+ \n (90W)"];
Passive --> AF;
AF --> AT;
AT --> |"Includes IEEE Standard \n adds 30W"| UPOE;
AT --> BT;
BT --> |"Includes IEEE Standard \n adds Cisco UPOE"| UPOEP;
Cisco’s Chart
Wire example - 4 Pairs
Power States
flowchart LR
A[Detection] --> B[Classification] --> C[Start to Power] --> D[Normal Power Supply]
References
Power over Ethernet - Wikipedia
Cisco - Industrial Power over Ethernet (PoE)
Cisco UPOE+- The Catalyst for Expanded IT-OT Convergence White Paper - Cisco