1. Introduction to Power over Ethernet (PoE)
Power over Ethernet (PoE) is a networking technology that allows a single Ethernet cable to carry both data and electrical power.
Figure 1 – Power over Ethernet supplying a VoIP phone
It is mainly used to power VoIP phones, IP cameras, wireless access points, and IoT devices, all through the same cable that provides their network connection.
Benefits of PoE in Networking
Cost efficiency – no need to install electrical outlets next to each device.
Simplified cabling – one cable for both power and data.
Flexible placement – devices can be installed in areas without nearby power sources.
Centralized management – administrators can reboot or control power directly from the switch.
2. PoE Standards
IEEE 802.3af (PoE)
Introduced in 2003, this standard provides up to 15.4 watts of DC power per port from the Power Sourcing Equipment (PSE), with about 12.95 watts available at the Powered Device (PD) after cable loss. It is suitable for low-power equipment such as basic VoIP phones or small wireless access points.
IEEE 802.3at (PoE+)
Introduced in 2009, PoE+ increased the available power to 30 watts per port, with 25.5 watts reaching the PD. This improvement supports devices that require more energy, such as IP cameras with pan, tilt, and zoom (PTZ) functions.
IEEE 802.3bt (UPoE and UPoE+)
The most recent standard extends power delivery by using all four wire pairs of the Ethernet cable. In Type 3 (UPoE), it can supply up to 60 watts per port, which is suitable for video conferencing systems or larger wireless access points. In Type 4 (UPoE+), it delivers up to 100 watts per port, making it possible to power advanced devices such as interactive displays and high-consumption IoT systems.
Standard | Year Introduced | Power at PSE (per port) | Power at PD (usable) | Typical Devices |
|---|---|---|---|---|
IEEE 802.3af (PoE) | 2003 | 15.4W | 12.95W | Basic VoIP phones, small wireless APs |
IEEE 802.3at (PoE+) | 2009 | 30W | 25.5W | PTZ cameras, more demanding APs |
IEEE 802.3bt Type 3 (UPoE) | 2018 | 60W | ~51W | Video conferencing systems, large APs |
IEEE 802.3bt Type 4 (UPoE+) | 2018 | 100W | ~71–90W | Interactive displays, advanced IoT devices |
Table 1 – Comparison of PoE Standards
3. Components of PoE
Figure 2 – Components of Power over Ethernet (PoE)
Power Sourcing Equipment (PSE)
PSEs are the devices that supply power over Ethernet. These include PoE-enabled switches and PoE injectors. They automatically detect connected PDs and negotiate the required power level to ensure safe and efficient delivery.
Powered Devices (PD)
PDs are the endpoint devices that receive power. Examples include:
VoIP phones
IP cameras
Wireless access points
Access control panels
IoT sensors
These devices must support PoE standards to be properly powered by a PSE.
4. PoE Practical Example
When a VoIP phone is connected to a PoE-capable switch, the switch detects it using a PoE handshake protocol. It then delivers the correct amount of power through the Ethernet cable, eliminating the need for a separate power adapter.
Figure 3 – PoE practical example with a VoIP phone
Verifying Power Delivery
To confirm that the VoIP phone is receiving power, use the following CLI command on a Cisco switch:
Switch# show power inline
Available: 370.0(w) Used: 15.0(w) Remaining: 355.0(w)
Interface Admin Oper Power Device Class Max
(Watts)
--------- ------ ---------- ------- ------------------- ----- ----
Fa0/0 auto on 10.0 IP Phone 7960 3 15.4
Fa0/1 auto off 0.0 n/a n/a 15.4
Fa0/2 auto off 0.0 n/a n/a 15.4
Fa0/3 auto off 0.0 n/a n/a 15.4
Fa0/4 auto off 0.0 n/a n/a 15.4
Fa0/5 auto off 0.0 n/a n/a 15.4
Fa0/6 auto off 0.0 n/a n/a 15.4
Fa0/7 auto off 0.0 n/a n/a 15.4
Fa0/8 auto off 0.0 n/a n/a 15.4
Fa0/9 auto off 0.0 n/a n/a 15.45. Conclusion
If someone asks you : What is Power over Ethernet used for ?
The answer is simple:
It’s used to power and connect network devices like VoIP phones, IP cameras, wireless access points, and IoT systems all through a single Ethernet cable, without the need for separate power sources !!