Power over Ethernet, or POE in short, has become increasingly popular as a means of powering technology devices due to ease, convenience, and cost effectiveness in terms of both installation time and resources used.
With the increase in POE-capable devices such as access points, cameras, and phones in most business and enterprise applications, POE switches are becoming an indispensable element due to the way they reduce the complexity and cost of a network system’s installation, deployment, and implementation.
Office, business, and enterprise networks involving remote-powered devices can get increasingly complex as more devices are added. POE-powered devices can eliminate the headache of running parallel power cables or designing the network around power outlets since one cable supplies both a network connection and power.
A POE switch is designed to supply both power and network connection to a connected device via one network cable, unlike traditionally, where a device needed to be powered and connected to the network via two different power and network or signal cables.
While POE switches come in many different variations, there are two main categories of POE switches:
Active POE switches
Passive POE switches
What is the difference between the two? Which type of POE switch should be used, and why one over the other?
Active POE
What is the concept of active POE?
Also known as standard POE, active POE refers to a mode where there is negotiation between the power supply equipment (PSE), which would be the switch, and the powered device (PD), like a camera or phone.
When a cable is plugged into the device from the switch, the switch will first do a check to determine if the device is POE-compliant or capable before sending power down the link. If the device is incompatible with or incapable of accepting power over Ethernet, the switch will only deliver a network connection without sending power down the link.
On the other hand, if compatibility with the remote device is confirmed, both power and a network connection are delivered over the link.
The reason for this negotiation and verification is to ensure that a non-compliant or non-POE device is not erroneously sent power that might damage it. It’s thus a safety measure.
For instance, a POE switch can be connected to a Wi-Fi access point, a security camera, and a phone. All three devices require power and a network connection, and the POE switch will promptly send both data and power down the Ethernet cable.
Other devices, such as computers, might also need access to network resources, but they are not POE devices. This is a hybrid environment where some devices use POE and others are powered by alternative sources.
The POE switch will be able to determine that while the first three devices require both power and data, the fourth one is not a POE device and should therefore not be powered via POE but by an alternative source. So it only sends data down the cable link to avoid potentially damaging the computer’s non-POE Ethernet port.
Active POE switches are rated to be IEEE 802.3af, IEEE 802.3at or IEEE 802.3bt compliant. These are IEEE POE standards. (For details on POE standards). They can also be further divided into POE, POE+ and POE++ (More on this)
Passive POE
Also known as non-standard POE, it sends both data and power down the Ethernet link, but unlike active POE, there’s no negotiation or verification involved. This means that power is sent down the cable whether or not the remote device is POE-compatible.
It does not adhere to any IEEE POE standards whatsoever. In a passive POE network, the power is always on, and whatever device is plugged at the end of the cable will receive constant power, incompatibility notwithstanding.
Connecting non-POE devices on a passive POE network or switch is a risky endeavour as the Ethernet ports on the devices are not meant to accept any form of input power, and thus there’s a risk of permanent damage to the network port or to the device as a whole.
For instance, while access points and cameras will work fine with a passive POE switch, plugging in a computer to get a network connection is a risky undertaking. Additionally, passive POE sends a constant voltage down the Ethernet cable. If the device connected is not rated for that voltage despite being a POE device, the risk of damage is also very high.
Ethernet Speed Support
While passive POE switches typically support 10/100 Mbps Ethernet up to 100 meters, active POE switches can support up to 10/100/1000 gigabit speeds over Category 5e and Category cables or higher.
This means active POE switches can be applied both to traditional and modern POE networks without having to worry about compatibility issues, unlike passive POE.
Cost
Suffice it to say, active POE switches cost more than passive POE switches since they come with an “intelligent” power controller that aids in the “handshake” between the switch and device to determine compatibility, classification, and power requirements. This is a feature that passive POE switches do not have, thus the lower expected cost.
Summary
Power injection: Active POE injects power only after negotiation while Passive POE injects power immediately after a cable connection is made.
Ethernet Support: Active POE supports 10/100/1000 BASE-T, while Passive POE only supports 10/100 BASE-T
IEEE Standards: Active POE adheres to 802.3af/at/bt standards, while Passive POE does not
Safety: Due to negotiation and verification before power transmission, Active POE is safer than Passive POE.
While active POE switches would be the most recommended for POE deployments, passive POE switches can be used when budgets are tight or when there’s a clear identification between the powered device and the switch to ensure that there’s 100% compatibility.
Currently, when shopping for or purchasing a POE switch, one is likely to be offered an active POE switch as the default since it’s the standard, unless a passive POE switch is specifically requested. For consumers and inexperienced buyers, it’s imperative that the purchased switch be confirmed to be an active POE switch to avoid the risk of damaging devices that would be plugged into it.
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