The Industrial Internet of Things (IIoT) has been greatly impacted by Power over Ethernet (PoE). Since 2003, this simple yet transformative technology has made it possible to simultaneously supply DC power and transmit network data to a poe powered device via a single Ethernet cable, reducing the complexity and cost of network installation, deployment, and maintenance. The IEEE PoE standards adaptability have proven critical in deploying IIoT devices remotely as part of edge computing infrastructures where electrical power is not easily accessible.
Like all IIoT technology, standard PoE protocols are becoming smarter, more powerful, and benefiting from increasingly sophisticated management and control. In this blog we look at one of those advancements: Active PoE in Ethernet switches. It's predecessor, Passive PoE, is largely being phased out in favor of this safer, more standardized powered device technology. Here’s what you need to know.

What is Active PoE?

An Ethernet switch, midspan or other PSE (Power Sourcing Equipment) is said to be “active” if it is compliant with IEEE 802.3af (PoE), 802.3at (PoE+), 802.3bt (PoE++) or 802.3bt Type 4 (PoE++) standards, whereas a non-compliant PSE is using “passive" power or non-standard power.
All switches with active PoE are equipped with a built-in intelligent power controller. It will only inject power down the link to a device following a secure power negotiation known as a "handshake" that determines compatibility, classification, and power requirements. If the device is incompatible with or incapable of accepting standard PoE, the switch will only supply the network connection. Negotiation prevents power being sent to a non-compliant or non-PoE device which could damage its network port or burn out its electronics.
In contrast, a passive PoE switch doesn't engage in any form of power negotiation. Passive PoE is a straightforward approach to power transmission. Electricity at a fixed output voltage is always on, regardless of the rating of the endpoint device. As long as it is connected, it will receive constant power over the Ethernet cable that is injected immediately.
There is another important difference: Although both active PoE and passive PoE switches have a maximum cable distance of 100 meters, passive is limited to 10/100BASE-T Ethernet while active PoE switches support 10/100/1000BASE-T Ethernet for faster, more stable networks.

An Argument for Passive PoE

Passive POE switches are still deployed in older networks. Some users simply want power to be output at as low a cost as possible, i.e., WISP applications, while others have a simple legacy installation with fixed power requirements. An argument can be made that certain passive PoE switches also feature higher current limitations. However, the higher wattage benefit has been largely eliminated with the introduction of active PoE switches with 802.3bt and 802.3bt Type Four. As a result, passive PoE is largely being phased out however is found in select wireless products and low cost solutions.

How Active PoE Switches Operate

To illustrate how Active PoE works, we are going to assume an Antaira PoE managed Ethernet switch is connected to a PoE-enabled wireless access point. For simplicity, we will also assume IEEE 802.3af (PoE). The process goes as follows:
1. First, the Antaira switch will output minimum voltage to detect a characteristic signature of IEEE-compatible PDs (25kOhm resistance). Once this signature has been detected, the PSE knows that higher voltages can be safely applied. The switch now moves onto classification. If the signature is not recognized, the process stops here.
2. An Antaira switch now applies 15-20V to the WAP so it can classify the device. It does this by detecting resistance and measuring current. Every PoE-compatible device is classified from Class 0 to 8. Each Class signifies the proper input power, output power, PD type and matches to one of the corresponding IEEE PoE standards, as shown below.
3. Once PoE classification is complete, the Antaira switch begins to supply power to the WAP, starting from low voltage to full 48VDC. Once 48VDC reached, the Antaira switch continues stable output unless the WAP is removed or if power consumption is either overloaded, short-circuited, or is out of the switch’s power budget.

Configuring Antaira Active PoE

Depending on the switch model, Antaira software enables multiple ports on its active PoE switches to be configured as Disabled, PoE, PoE+ or PoE++ BT, along with giving the user the flexibility of setting the PoE-enabled port’s maximum power. Ports hosting non-PoE devices can be disabled or simply left alone due to the switch’s PoE auto-sensing function. In addition, each PoE port’s priority can be fixed as either Low, High or Critical. This is important when a remote device requires more power than the PoE power supply can deliver. In this event, the port with the lowest priority with be turned off so the higher priority port can tap into its voltage.
Other Antaira PoE innovations are:
• Antaira Ping Alive lets the user conduct failure checks of a specific PoE device connected to the switch at set intervals by enabling its port. Ping Alive gives network technicians more automated control over failed communication of edge devices. It checks the activity or inactivity of PDs and allows for automatic reboots when the PD becomes unresponsive, saving valuable time and labor.
• Antaira patented Power Remote Reset Technology (PRRT) lets the technician easily reset a PD at a remote site without physically visiting the location. This is done by reconnecting the nearby fiber cable that is connected to Antaira’s IEEE 802.3bt PoE device. Antaira’s PRRT technology helps save on travel costs and downtime.
• iPoE Budget Control is a patented technology that prevents devices from overrunning a PoE budget. iPoE Budget Control is implemented on the LNP-C501G-SFP-bt-24-T unmanaged PoE switch.
On a standard PoE switch, powered by the 48-55 VDC power, there is a single PoE power budget. If the PoE budget is overrun, the switch will turn off the port. Antaira's low power PoE switch can be powered by as low as 9 VDC up to 55 VDC, but keep in mind, the PoE budget will vary. The lower the input voltage, the smaller the PoE budget.
Antaira's IPoE Budget Control dynamically changes the set power budget of the switch based upon the input voltage being supplied.

• Antaira Safe PoE is a patented hot-swapping protection feature designed around the IEEE 802.3bt standard that allows up to 90 watts and at times up to 100 watts of power to be transmitted across an Ethernet cable. High-power being sent across the cable means the energy has a greater chance of arcing across a gap when a cable under full power is being disconnected. It allows an engineer to safely disable the power being sent across the Ethernet cable before disconnecting the cable at either end. This technology feature can be activated on a PoE switch by switching off the PoE port before pulling out the cable, deactivating the PoE power.
• Antaira Persistent PoE allows Antaira switches to reboot during a firmware update while still delivering continuous PoE power to PoE PDs which prevents the connected devices from rebooting.

Connect with an Antaira PoE Expert

Knowing the difference between an active and passive PoE switch may help prevent permanent damage to your network devices. If you have a legacy passive PoE switch, the smart move is to upgrade to an Antaira 802.3af/at/bt compliant managed or unmanaged Ethernet switch. Contact one of our PoE experts at sales@antaira.com.